the fastest growing electronics title in the uk …€¦ · 012 a02/ 00.2 p13 p14 a03/ p0.3 4 a 4,...

THE FASTEST GROWING ELECTRONICS TITLE IN THE UK

ELECTRONICSWORLD

INCORPORATING WIRELESS WORLD

February 1996 £2.10

Lockable videosync design

New poweramp concept

MathCad 6reviewed

Videocompressiontechniques

Notes onorgan tones

High powervalve audio

Fractional -nsynthesiser

Denmark DKr. 65.00Germany DM 15.00

Greece Dra.950Holland Dfl. 14

Italy L. 8000IR £3.30

Singapore SS12.60Spain Pts. 750

USA $4.94

A REED BUSINESS PUBLICATIONSOR DISTRIBUTION

0 2>

Radio -code clock modules - 25% exclusive EW 9 9 59 3301

At last! The completePC -Based PLDTraining System

THE PAL TRAINERUntil now, introducing students and engineers to the world of ProgrammableLogic Devices has been fraught with problems.Not only has the necessary hardware to be laboriously assembled in bits andpieces, but suitable software and - equally important - supporting documentationhas been, if anything, harder to source.

With the launch of THE PAL TRAINER system from Flight Electronics International,the entire problem has been neatly solved in one comprehensivehardware/software/documentation package...

...providing everything that the engineer and student needs for a thoroughintroduction to PLD's at a very realistic price.

COMPLETE &COMPREHENSIVEOne of the main advantages of THE PAL TRAINER is itscompleteness. The board and accessory kit consists of:

The MPLDT-10 main unit - a sturdy metal -cased PCBcontaining both a GAL programmer and a test unit.There is also a separate demo area for use with thedemonstration section of the manual.

A PCPET interface card, which plugs into a free PCexpansion slot, and connects to the main unit via asupplied API -37 cable. This allows rapid programmingof the PLO, and greater flexibility than a serial link candeliver.

III A 360kb system diskette containing the board driverfiles.

II An external power line for use with the experimentsection.

Various connection lines and block jumpers.

NI The comprehensive PAL TRAINER User's Manual. Thishas been written in precise, easy -to -understand English,

and takes the student right from unpacking and settingup the system, through a short demonstration programwhich runs without the need to do into PALASM andthen, in a gentle step-by-step sequence, through 23separate experiments.

The complete PALASM software package, whose separatemanual also contains a number of example programs.

SIMPLE, FAST, FRIENDLYThe design parameters of THE PAL TRAINER were that itshould:

run on IBM XT, AT or compatibles - with no need forANY other hardware.

provide a complete training course, from initial logicdesign, to PC simulation, device programming &testing.

be enjoyable, readily -understandable, but fullyapplicable to 'real -world' situations.

MI include a top programming language - in this caseAMD's PALASM Version 4, widely regarded as the PLDstandard. Version 4, incidentally, can be linked to otherschematic packages such as OrCad.

CIRCLE NO. 101 ON REPLY CARD

14 UNIQUEADVANTAGES!ti Superb Manual Everything in one box

i.Save time & money

lg Demo area provided

1E123 worked experiments

g Menu drive for fastlearning

g Includes PALASM

g 3 simultaneous PLD'sgJumper wire linkageg Supports GAL16V8

& GAL2OV8

Ei 3 input, 4 output areas

Li No tied up ports

ei 4 FREE GAL's

1E112 month guarantee

LIKE TO SEE THE PAL TRAINER IN ACTION?Nothing beats an actual hands-on experience of

the system's completeness, ease of use, and flexibility.Just call 01703 227721 and order today! -

We operate a 'no strings' 30 days'no risk' refund.

USING THE SYSTEMThe two main parts of the PAL TRAINER are theprogrammer and the applications sections.Using the programmer section, up to 3 GAL devices areplaced in ZIF sockets, and programmed from the PC usingthe supplied software. This lets you choose a particularPAL to emulate, loads a JEDEC file into memory (eithergenerated from the PAL TRAINER's own software or anyother appropriate software package), downloads theJEDEC file to the GAL, and even lets you 'view' the GALonce it has been programmed.

We accept:

Access

AftMasterCard

VISA

Flight House

Ascupart Street

Southampton

S014 1WP U.K.

Telephone:

01703 227721

Facsimile:

01703 330039

Email: Sales

©flight demon.co.uk

FlightINTERNATIONAL LIMITED

Flightalsomake

ELECTRONIC& MICROPROCESSOR TRAINING EQUIPMENT TEL: 01703 227721 TEST & MEASUREMENT EQUIPMENT 4 FREE COLOUR BROCHURES AVAILABLE - CALL TODAY! FAX: 01703 330039

Contents 102 VIDEO COMPRESSION

TECHNIQUESJohn Matthews outlines the techniques beingused to cram more image information intoless space and bandwidth, including MPEG,JPEG and H261.

110 HIGH POWER VALVEAUDIOA KT88-based push-pull power amplifierforms part of Morgan Jones' discussion ofhigh -power valve audio.

114 LOCKING ON TOVIDEO SYNCMichael Cox has been designing with ahighly integrated solution to sync pulsegeneration and video -signal genlocking,namely the SAAI 101.

119 MODELLING CABLEAnalysing loudspeaker cables using Spice,Ben Duncan discovered that cable formatcan have an affect on audio quality.

124 NOTES ON FREEPHASINGIan Hickman discusses his new solution onhow to achieve a simple, cheap and highlystable oscillator for free -phasing electronicorgan notes.

Special offer25% discount onPC interfacingRadio -Codereceivers

Read Radio -Codetime transmissions intoyour PC, and controlwith atomic timeprecision, page 129.

130 FRACTIONAL -NSYNTHESISCosmo Little reveals the benefits of a little-known frequency synthesis technique that ischeaper than direct synthesis - and requiresmuch less power.

136 DESIGNING CASCADE RCOSCILLATORSCascade RC oscillators are simple, stable, andoffer very fast start up. David Griffithsexplains how this configuration benefits frommodem op -amp technology.

140 AUDIO POWER WITH ANEW LOOPIn Marcel van de Gevel's high-performancepower amplifier, quiescent current isstabilised via feedback, using a non-linearcommon mode loop.

168 MATHCAD GETS A PLUSAllen Brown looks at the latest release ofMathcad and its DSP analysis option

Regulars 91 COMMENT

Sound reasons for digital tv?

94 NEWSInter -satellite communication, polysiliconshortage, Boat -Show, 400Gbit/s fibre, Braindrain

96 RESEARCH NOTES£32 million for holographic storage,Computing record that is rewriting atomicscience, Laser makes better steel, Laserstake on a chilling role, Chaos benefits.

146 CIRCUIT IDEASHf-to-vhf converter, Flasher for dogs,Frequency comparator with hysteresis,Control software flow through pc's serialport, Simple power flasher, Frequency -dependant negative conductance, Returninglocal -oscillator crystals, linear square andtriangle generator, Telephone line monitor,Edge detector/doubler, Low -batterymonitor shuts down gracefully.

156

159

164

LETTERSEMC, valve doubts, linear modulation,optical links, em fields and Foster -Seeley.

NEW PRODUCTSPick of the month - classified forconvenience.

APPLICATIONSLoad -dump testing, Surge protection andUncrackable electronic locks.

Cover - Hashim Akib

For the first time,satellites havecommunicated withoutthe intervention of aground station - Update,page 92.

New laser -based sensorpromises huge savings forsteel makers - ResearchNotes, page 96.

Morgan Jones discussesdesigning valve audiopower amplifiers capableof delivering more than theusual 10W - page 110.

MARCH ISSUE - ONSALE FEBRUARY 22

February 1996 ELECTRONICS WORLD 89

IL-.I TM

QUICKROUTE

Integrated PCB & SchematicDesign System for WindowsTM

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Quickroute 3.5 is a powerful,affordable and easy to use integrated schematic &PCB design system for Windows. With its multiple buttonbars, 'tool hints' and 'parts bin', Quickroute helps you todesign quickly and efficiently

There are four different versions of Quickroute giving you achoice of features & price. Quickroute is available with multi -sheet schematic capture, auto -routing, 'engineering change'(modification of a PCB from a schematic), copper fill, and a rangeof file import/export options. See the table for a selection of features.

Prices are Designer (£149), PRO (£249) and PRO+ (£399). ThePersonal edition is available for just £68, but has the manualprovided on disk as on-line help. Post & Packing is £5 (UK), £8(EC), £12 (World). VAT must be added to the total price.

'..of all the products included here, this is my personal favourite... Really,thats all I have to say about Quickroute - it certainly gets my vote!'

Review of QR 3.0 & other productsComputer Shopper Nov 95r

Lng-di allEUREMI

QUICKROUTESYSTEMS

VISAaims email [email protected] and specifications subject to change without notice. All trade marks are acknowledged & respected.

Tel/Fax 0161 449 7101Quickroute Systems Ltd., 14 Ley Lane, Marple Bridge,

Stockport, SK6 5DD, U.K.


0O

PCB & Schematic Design VVVS,Schematic Capture I/ V VAuto router $, VDesign Rule Checking V VExport WMF & Tango V VExport Gerber/NC-Drill V I/Extended Libraries

,V 5/

Tango -.. 6erber Import I/Update PCB from schematic VDXF & SPICE Export VCopper Fill V

ri-)111'rJ1FF(H11-1 r

CII:(111;1-'171/711/141r1,1

R

System Components from IS09001 SourceHalf Size ISA Single Board Computers

386SX40 to 486DX4-100 with PC/104, 2 Serial PortsIDE & FDD & Printer Port

and a variety of on -board functionality's:FLASH/ROM Disc. Cache. VGA CRT/Flat Panel Controller

PC/104 Modules:386 & 486 CPUs, Solid State Disc, Isolated RS232/485

VGA CRT/Flat Panel Display & SVGA ControllersPCMCIA types I, II & III

System Enclosures with Passive BackplanesColour & Mono Flat Panel LCD Displays

System Integration and Support

odd, LLBristol, 1,56oPFTel: 011 '/ L; U4'35

Fax: 0117 Y?3 7 L! b

ZOSZS

EMBEDDED C

ASDELYSIMULATION

8051G compiler, first released in 1991, now features:

Easy to use interrupt support with register bank switchingIEEE floating point arithmeticIEEE 695 source level debug outputIntegrated relocatable assembler

Simulator running under Microsoft Windows provides extensivesupport for the 8051 code development

eg000Our first G compiler/assembler package

now supports floating point arithmetic

has been widely adopted by many OEM's to support their68000 and 68307 hardware

CP(122

68020 C compiler/assembler, originally developed to accompanyMotorola's 68020 and 68EG020 evaluation models

Now supports the GPLJ3268881 co -processor supportIEEE 695 source level debug output

Further information from:CROSS WARE PRODUCTS

St John's Innovation Centre, Cowley Road, Cambridge, CB4 4WS , UKTel: +44 (0) 1223 421263, Fax: +44 (0) 1223 421006BBS: +44 (0) 1223 421207 (8-10-1), Internet: salesecrossware.com

CROMMARL

90

CIRCLE NO. 107 ON REPLY CARD (-NUE NO. 108 ON REPLY CARD

ELECTRONICS WORLD+WIRELESS WORLD February 1996

COMMENT

EDITORMartin Eccles0181 652 3128

EDITORIALASSISTANTRob Allcock0181 652 8638

CONSULTANTSJonathan CampbellPhilip DarringtonFrank Ogden

DESIGN &PRODUCTIONAlan Kerr

EDITORIALADMINISTRATIONJackie Lowe0181-652 3614

E-MAIL [email protected]

ADVERTISEMENTMANAGERRichard Napier0181-652 3620

DISPLAY SALESEXECUTIVEMalcolm Wells0181-652 3620

ADVERTISINGPRODUCTIONChristina Budd0181-652 8355

PUBLISHERMick Elliott

EDITORIAL FAX0181-652 8956

CLASSIFIED FAX0181-652 8956

SUBSCRIPTIONHOTLINE01622 721666Quote ref I NJ

SUBSCRIPTIONQUERIES01444 445566FAX

0144 4445447

NEWSTRADEDISTRIBUTIONDavid G. Sanders0181 652 8171

BACK ISSUESAvailable at £2.50

ISSN 0959-8332

#A, REED

*11", PUBLISHING

Sound reasons for digital tv?Unveiling the Government'sBroadcasting Bill at the end of

last year, Heritage Secretary VirginiaBottomley proudly proclaimed that"the rest of the world is watching,"because Britain "will be the firstmajor national market to go digital,"and "we must look forward to agolden future".

Will this perhaps be a future inwhich Ms Bottomley's Press Officelearns to use new fangled deviceslike the telephone and fax machine?My invitation to Ms B's briefingarrived by Christmas post -a dayafter the event. Others in thespecialist press never heard anything.

Perhaps it was intentional. Wemight have spoiled Ms B's day byasking whether the British public willpay money to install the equipmentthey will need to pay more money toview the new digital services?

When Britain's two satelliteservices launched around five yearsago, both Sky and BSB made themistake of assuming that peoplewould go out and buy a receiver, andthen pay for a dish to be installed.BSB also assumed that viewers wouldpay a premium of several hundredpounds for MAC instead of PAL.

Rupert Murdoch quickly woke upto reality, branded the brown goodstrade "unable to sell a toaster" andemployed hit squads to knock ondoors, and install Sky systems onfree trial. By the time BSB hadstopped snoring, and started toorganise one -stop installation, thestation was collapsing into merger.

For at least a year, David Elstein ofSky has been talking about Sky'splans to transmit more channels,using digital technology. But thereare clear signs that his station is nowgetting cold feet. Even if Sky couldafford to give every viewer a freedigital receiver - at a starting cost ofseveral hundred pounds - thecompany would also have to re-employ the hit squads. They wouldthen go up ladders and try to loosencorroded bolts to replace existingLNBs with Universal models thatcan receive Astra's new highfrequency digital transmissions.

The BBC wants to lead the UK -and Europe, and the world - intodigital terrestrial television, startingin 1997. At a recent briefmg DirectorGeneral John Bid compared thetransition from analogue to digital tv,with the switch from 405 line blackand white to 625 line colour. DTTVoffers wide screen pictures anddigital sound, he revealed to us.

Perhaps someone inside the BBCshould tell Boss Birt that his existinganalogue tv transmissions alreadycarry Nicam digital stereo sound to87% of the viewing population, andthe other 13% is hoping they will oneday get it too.

Birt also seems blissfully ignorantof the debate on wide screentelevision which has been runningsince long before the BSB fiasco, andChannel 4's recent decision to cutback on PAL Plus transmission. TheBritish public has been offered widescreen sets for many years andsteadfastly refuses to buy them.Indeed Birt admitted that although hehas seen a widescreen set, he doesnot actually own one.

The parallel with the 405/625 linetransition is fatuous. It took twentyyears, not the fifteen Birt claims, andoffered a completely new anddramatic upgrade - colour - at a timewhen there was very little electronicgadgetry in the shops. Today,consumers are sick to death of newdevelopments and need a goodreason to replace existing equipment.

Michael Grade of Channel 4recently reassured on radio thatviewers will not need a new tv set forDTTV, just a set -top digital adaptor.Perhaps one of Grade's staff couldask him how this will give thewidescreen pictures which John Birtthinks viewers will see as the reasonto go digital.

Presumably someone inside theBBC has a clearer vision than theboss. Hence the BBC's call for theGovernment to set a firm date for ananalogue switch off. This will bullyviewers into buying digitalequipment whenever they make anew purchase. Based on thefallacious fifteen year 405/625

I"...we must lookforward to agolden future"

change -over reference point, theBBC suggests a 15 year gate onanalogue services. An extraordinarypolicy paper, submitted to theHeritage Department by KeithBoyfield and Brian Sturgess,suggests switch -off by 2006, just tenyears away. As modern homes arefull of tv sets and VCRs that caneasily last ten years, this bright ideawould succeed mainly in killing salesof all existing analogue equipment.

Ms Bottomley has settled for areview when half of Britain'shouseholds can get digital tv. If thismeans 50% transmission coverageit is a daft idea. If it means 10million homes fully kitted out withdigital tvs and vcrs, it compareswith what happened over 405shutdown, and makes sense. It'sanother of those questions thespecialist press would have askedMs B if her staff had learned to usea phone or fax machine.

There is, of course, a hiddenagenda in all this. As broadcastersmove from analogue to digitaltransmission, they releasefrequencies which the governmentcan then sell. Anyone who can rushconsumers into buying digitalequipment will definitely be in therunning for a big thank -you from theTreasury - and probably a nice littleknighthood to go with it.Barry Fox

Electronics World + Wireless World is published monthly. By post, currentissue £2.25, back issues (if available) £2.50. Orders, payments and generalcorrespondence to L333, Electronics World + Wireless World, QuadrantHouse, The Quadrant, Sutton, Surrey SM2 5AS. Tlx:892984 REED BP G.Cheques should be made payable to Reed Business Publishing Group.Newstrade: Distributed by Markefforce (UK) Ltd,247 Tottenham Court Road London W1P OAU 0171 261-5108.Subscriptions: Quadrant Subscription Services, Oakfield House,Perrymount Road, Haywards Heath, Sussex RH16 3DH. Telephone 01444445566. Please notify change of address. Subscription rates 1 year £30 UK2 years £48.00 3 years £70.00. Surface mail 1 year £35.00 2 years £56.00 3years £80.00 Air mail Europe/Eu 1 year £43.00 2 years £68.00 ROW 1 year£52.00 2 years £83.00USA: $52.00 airmail. Reed Business Publishing (USA), Subscriptions office,205 E. 42nd Street, NY 10117.

Overseas advertising agents: France and Belgium: Pierre Mussard, 18-20Place de la Madeleine, Paris 75008. United States of America: Ray Barnes,Reed Business Publishing Ltd, 205 E. 42nd Street, NY 10117. Telephone(212) 867-2080.Tlx 23827.USA mailing agents: Mercury Airfreight International Ltd Inc, 10(b)Englehard Ave, Avenel NJ 07001. 2nd class postage paid at Rahway NJPostmaster. Send address changes to above.Printed by BPCC Magazines (Carlisle) Ltd, Newtown Trading Estate,Carlisle. Cumbria, CA2 7NRTypeset by Wace Publication Imaging 2-4 Powerscroft Road, Sidcup, KentDA14 5DT

©Reed Business Publishing Ltd 1995 ISSN 0959 8332


UPDATE

MEASUREREM1

Above: The four mainelements of this on -board

information system fornavigation at sea are

measurement, distribution,display and control.

Unlike traditionalalternatives, this system

keeps the four keyelements entirely separate.

The benefits: flexibleinformation displaysinstead of fixed -role

instruments, plus choice inthe way you put together

your boat informationsystem.

Right: General overview ofthe ST80 as installed on

the boat.

hulls are made of steel prevents arepeat of the digitally -compressed tvtransmissions which were tried duringthe last Whitbread. These usedInmarsat A, which needs a muchlarger antenna - too big to mountaway from the deck. This time thefleet will stay in touch via C -Sat,which provides e-mail and Internet,via a conical aerial no bigger than avacuum flask, and hf ssb radiothrough Portishead.

Leisure sailors meanwhile arebecoming increasingly reliant onelectronics. Arguably the mostsignificant launch product at thisyear's Boat Show was Admiraltycharts on CDrom. ARCS - theAdmiralty Raster Chart Service - as itis called, provides straightforwarddigital reproductions of the familiarpaper charts, for use with pc -basednavigating systems.

Two forms of display are possible:a 'life-size' close-up of a portion ofthe chart or a low -resolution overview

Brains forced overseasAlack of vision at the UK MedicalResearch Council has driven

overseas a multi -disciplinary groupdoing fundamental research on thebrain.

The MRC refused to renew theposition of the group's computerscientist jeopardising its future.

Late last year, the group moved tothe specially established Institute ofNeuro-informatics in Zurich, despiteit having secured long-term fundingand repeatedly expressing its wish toremain in the UK.

Group leader Kevan Martin says hefeels no bitterness towards the MRC

but questions its decision making."Its vision is to the floor rather than

the horizon," said Martin. "The MRCunit is directly supported bygovernment; its whole purpose is tosupport high risk, long term research,and that is exactly what we aredoing."

The MRC refused to comment.The group is developing a hybrid

digital -analogue vlsi architecture tomodel the neocortex - the bulk of thecircuitry that makes up the brain.

"The neocortex is a rather fantasticgeneral purpose processor, adaptableto many functions," said Martin.

"Understand its workings and youhave achieved somethingfundamental."

The unit's achievements to dateinclude collaborative work with theCalifornia Institute of Technology tocreate a silicon neuron that resemblesclosely the biological neuro cell.

And the unit has also constructedanalogue vlsi devices that incorporatemultiple neurons.

The MRC had wanted the group topursue a more biological slant for thework. This meant there would be nofunding for the analogue VLSI work.Roy Rubenstein, Electronics Weekly

Wired for Sea - electronics at the Boat ShowSailing - that simple, centuries -oldcommunion with wind and tide - is

now one of the most high-tech sportsin the world, and getting ever higher.

Nowhere is this more apparent thanin round -the -world yacht racing,which communications companiesseem to regard as an appropriatemetaphor for their activities, as wellas a proving -ground for theirtechnologies. BT, having providedrace communications for theWhitbread races, is now sponsoringone of its own, and took one of thelargest stands at this year's BoatShow to proclaim the fact.

The BT Global Challenge involves14 identical 67ft yachts racing the`wrong way' - i.e against prevailingwinds and currents - around theworld. Two of the boats aresponsored by other electronicscompanies, Motorola and Toshiba,and a third by a consortium of othertelecomms companies.

Unluckily for BT, the fact that the

/////////811.1 DTW10211 1002WD

\\\ \\\\\\\\

of the whole thing. As with the papercharts, different scales with differingamounts of detail are available.

Regular updating is available, alsoon CDroms, issued weekly, but withcumulative information so that justone set of data need be patched in,perhaps just prior to the summercruise. Charts cost £30 each; updateCDroms £10. One chart occupieesabout 1Mb of hard -disk space.

ARCS is already supported by PCMaritime's Navmaster Windows -based system, alongside its existingvector -based Livechart cartography.

Elsewhere at the show, integrationwas this year's great leap forward.Surprisingly, it is only 21 years sincethe first autopilot was launched. Sincethen GPS has arrived and windspeed/direction, compass bearing anddepth sounder have all been digitised.The result is - or can be -aproliferation of displays and complexharness of wires around the boat. Thesolution is an integrated system usinga single cable with multifunctiondisplays, which is what Autohelm hascome up with in in ST80, the latestdevelopment of its SeaTalk System.Navico meanwhile has enhanced itsown, similar Corns system with aninboard autopilot, Oceanpilot, capableof translating all this information intointelligent coursekeeping.

And if you should fall overboard,make sure you have your PLB7 withyou. This tiny device by Sea -Marshallis an electronic beacon, transmittingon the Search and Rescue frequency,which will help your own boat, or arescue aircraft to fmd you quickly.

92 ELECTRONICS WORLD February 1996

HART AUDIO KITS YOUR VALUE FORMONEY ROUTE TO ULTIMATE HI-FI

Hart Audio Kits and factory assembled units use the unique combina-tion of circuit designs by the renowned John Linsley Hood, the verybest audiophile components, and our own engineering expertise, togive you unbeatable performance and unbelievable value for money.We have always led the field for easy home construction to profes-sional standards, even in the sixties we were using easily assembledprinted circuits when Heathkit in America were still using tagboards!.Many years of experience and innovation, going back to the earlyDinsdale and Bailey classics gives us incomparable design back-ground in the needs of the home constructor. This simply means thatbuilding a Hart kit is a real pleasure, resulting in a piece of equipmentthat not only saves you money but you will be proud to own.Why not buy the reprints and construction manual for the kit you areinterested in to see how easy it is to build your own equipment theHART way. The FULL cost can be credited against your subsequentkit purchase.

K1100 AUDIO DESIGN 80 WATTPOWER AMPLIFIER.

This fantastic John Linsley Hood designed amplifier is the flagship ofour range, and the ideal powerhouse for your ultimate hifi system.This kit is your way to get 1K performance at bargain basementprices. Unique design features such as fully FET stabilised powersupplies give this amplifier World Class performance with startlingclarity and transparency of sound, allied to the famous HART qualityof components and ease of construction.Useful options are a stereo LED power meter and a versatile passivefront end giving switched inputs, with ALPS precision Blue Velvetlow -noise volume and balance controls. Construction is very simpleand enjoyable with all the difficult work done for you, even the wiringis preterminated, ready for instant use!. All versions are available withStandard components or specially selected Super Audiophile com-ponents at £29.60 extra per channel, plus 62.40 if you want to includeGold Plated speaker terminals.K11008 Complete STANDARD Amplifier Kit, £395.21A11008 Factory Assembled. £499.21K1100SC Complete SLAVE Amplifier Kit, £333.62A1100SC Factory Assembled £422.62K1100M Complete MONOBLOC Amplifier Kit, ..£261.20A1100M Factory Assembled. £329.20RLH11 Reprints of latest Amplifier articles £1.80K1100CM Construction Manual with full parts lists £5.50

"CHIARA" SINGLE ENDEDCLASS "A" HEADPHONE

AMPLIFIER.

This unit provides a high quality headphone output for 'stand alone'use or to supplement those many power amplifiers that do not havea headphone facility. Easily installed with special link -through featurethe unit draws its power from our new Andante Ultra High Quality lin-ear toroidal supply. Housed in the neat, black finished, Hart miniboxit features the wide frequency response, low -distortion and 'musical-ity' that one associates with designs from the renowned John LinsleyHood. Pre -terminated interconnecting leads and PCB mounted sock-ets prevent supply polarity reversal and on -board diagnostics providevisual indication of supply line integrity. Volume and balance controlsare Alps "Blue Velvet" components. Very easily built, even by begin-ners, since all components fit directly on the single printed circuitboard. The kit has very detailed instructions, and even comes with acomplementary roll of Hart audiograde silver solder. It can also besupplied factory assembled and tested. Selling for less than the totalcost of all the components, if they were bought separately, this unitrepresents incredible value for money and makes anattractive and harmonious addition to any hifi system.K2100 Complete Kit £109.50K2100SA Series Audiophile version with selected audiophilecomponents.. £112.48A2100SA Series Audiophile version, factory Assembled. £149.46K3565 "Andante" Power Supply Kit to suit "Chiara"... ....£85.42A3565 Power Supply, Factory Assembled £128.42CM2100 Construction Manual. £2.50SPECIAL OFFER. Both units together, Kit Form.... .....£184.92Factory Assembled and Tested. £267.88

QUALITYAUDIO KITS

"Andante" SERIES 20VAAUDIOPHILE POWER

SUPPLIESSpecially designed for exacting audio use requiring absolute mini-mum noise, low hum field and total freedom from mechanical noisethis unit is a logical development from our highly successful 1550series.Utilising linear technology throughout for smoothness and musicalitymakes it the perfect partner for any module requiring fully stabiliseds15v supplies.Two versions are available. K3550 has 2 *150 supplies and a single15v for relays etc. and can be used with our K1400 preamp and ourK1450 RIM pickup preamp, as well as other useful modules soon tobe introduced. The K3565 is identical in appearance but only has thet150 lighter current supply for use with the K1450 RIAA pickup preamplifier or "Chiara" headphone amplifier.K3550 Full Supply with all outputs £93.75K3565 Power Supply for K1450 & K2100. £85.42

ALPS "Blue Velvet"PRECISION AUDIO

CONTROLS.

Now you can throw out those noisy ill -matched carbon pots andreplace with the famous Hart exclusive ALPS 'Blue Velvet' rangecomponents only used selectively in the very top flight of World classamplifiers. The improvement in track accuracy and matching really isincredible giving better tonal balance between channels and rocksolid image stability. Motorised versions have 5v DC motor.MANUAL POTENTIOMETERS2 -Gang 100K Lin £15.672 -Gang 10K, 50K or 100K Log £16.402 -Gang 10K Special Balance, zero crosstalk and zerocentre loss £17.48MOTORISED POTENTIOMETERS2 -Gang 20K Log Volume Control £26.202 -Gang 10K RD Special Balance, zero crosstalk and less than 10%loss in centre position. £26.98

TECHNICAL BOOKSHELFNEW! Another Classic by John Linsley Hood. "AUDIO ELECTRON-ICS" Following the enormous ongoing success of his "Art of LinearElectronics" the latest offering is the all -new edition of "AudioElectronics", now entirely re -written by the master himself.Underlying audio techniques and equipment is a world of electronicsthat determines the quality of sound. For anyone involved in design-ing, adapting or using digital or analogue audio equipment under-standing electronics leads to far greater control over the reproducedsound. The subjects covered include tape recording, tuners, poweroutput stages, digital audio, test instruments and loudspeakercrossover systems. John's lifetime of experience and personal inno-vation in this field allow him to apply his gift of being so familiar withhis subject that he can write clearly about it and make it bothinteresting and comprehensible to the reader. Containing 240 pagesand over 250 line illustrations this new book represents great value formoney at only £18.99

"THE ART OF LINEARELECTRONICS."

The definitive linear electronics and audio book by John LinsleyHood. This 300+ page book will give you an unparalleled insight intothe workings of all types of audio circuits. Learn how to read circuitdiagrams and understand amplifiers and how they are designed togive the best sound. The virtues and vices of passive and activecomponents are examined and there are separate sections coveringpower supplies and the sources of noise and hum. As one wouldexpect from this writer the history and derivation of audio amplifiercircuitry have an entire chapter, as does test and measurement equip-ment. Copiously illustrated this book is incredible value for theamount of information it contains on the much neglected field of lin-ear, as opposed to digital, electronics. Indeed it must be destined tobecome the standard reference for all who work, or are interested in,this field. Latest reprinted edition with extended index. 1994 344Pages. 247 x 190. 1Kg. 0-7506-0868-4. £16 95"

"DIGITAL AUDIO AND COMPACT DISC TECHNOLOGY"0-7506-0614-2 £17.95*INTRODUCING DIGITAL AUDIO CD, DAT AND SAMPLING. ISBN1870775 22 8 . £7.95"THE ART OF SOLDERING" 0-85935-324-3. 0 £3 95"TOWERS' INTERNATIONAL TRANSISTOR SELECTOR"0-572-01062-1. £19.95""AUDIO" F.A.Wilson. BP111 £3 95"HOW TO USE OSCILLOSCOPES & OTHER TEST EQUIPMENT"R.A.Penfold. BP267 £3.50"THE LOUDSPEAKER DESIGN COOKBOOK" Vance Dickason.

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VALVE & EARLYCLASSIC BOOKS

THE VTL BOOK David Manley BKVT1 £17.95LOUDSPEAKERS; THE WHY AND HOW OF GOOD REPRODUC-TION. G.Briggs. 1949 0-9624-1913-3. £8.95MULLARD TUBE CIRCUITS FOR AUDIO AMPLIFIERS BICAA27

£13.95"THE WILLIAMSON AMPLIFIER." 0-9624-1918-4. £6.95AN APPROACH TO AUDIO FREQUENCY AMPLIFIER DESIGN.GEC 1957, 1-882580-05-2.... £18.95AUDIO ANTHOLOGIES, articles from Audio Engineering. Six voumescovering the days when audio wasyoung and valves were king!.BKAA3/1 to 6. All £13.95 each."A SIMPLE CLASS A AMPLIFIER" J.L.Linsley Hood M.I.E.E. 1969.RLH12 £2.50Postage on all books, unless starred, is only 01.50 per book, maxi-mum 04.50 for any number, any size!. Starred items are heavy bookscosting £2.50 to send.No waiting!. All listed books are normally in stock!SPECIAL OFFER. All book orders over £15 will receive a FREE JohnLinsley Hood monograph entitled "Digital versus Analogue, BlackDisks or Silver?"

SPECIAL OFFERPRECISION Triple PurposeTEST CASSETTE TC1D.

Are you sure your tape recorder is set up to give its best? Our latesttriple purpose test cassette checks thethree most important tapeparameters without test equipment. Ideal when fitting new heads.A professional quality, digitally mastered test tape at a price anyonecan afford. Test Cassette TC1D. Our price only £ff 99.

HC80 Replacement StereoCassette Head.

The excellent performance of modern cassette recorders dependstotally on the quality of the R/P head.Even the slightest amount ofwear can impair the frequency response and distortion levels. OurHC80 is atop quality head from one of the foremost manufacturers inJapan, easily fitted to most standard stereo recorders (except Sony)and will transform the performance over a worn head. Only the factthat we buy these in vast quantities enables us to offer them at theamazing price of only £11.70 each or 2 for £17.60.We also stock a range of other heads, including reel-to-reel stereoheads.

SOLDERINGThe size of modern components makes the right soldering equipmentessential for good results. Everything we offer we actually use in ourown workshops!. See our Lists for the full range. 845-820 XS240ANTEX 240v 25w Soldering Iron. This is the ideal Multi -purpose ironas the bit is designed to totally surround the element giving the bestheat transfer. This excellent design also means that although it issmall and handy enough for modem components its heating capaci-ty is better than larger irons of conventional construction. ExcellentValue. £9.93845-080 ST4 Lightweight Soldering Iron Stand. This has provision forthe classic damp sponge for bit wiping £3.95

HART SUPER AUDIOGRADESILVER SOLDER.

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845-007 3mtrs 22SWG in Hart Mini Tube £3.90845-008 100g. Reel Special Valve Grade, 20swg £12.90845-009 100g. Precision PCB Grade, 22swg £14.75845-110 100g Reel Superfine 24swg for ultra precise control andeasy working £21.45

9o14(35Y4

Aro::

UPDATE

CMOSgatesswitch in1 5psToshiba hasdeveloped a0.15pm gatec-mos structurebased on a singlegate that has adelay of only15.4ps. This isclaimed to becomparable tospeeds normallyachieved using a0.1 pm c-mosprocess. Use of asingle gatestructure wasintroduced byToshiba's ULSIResearchLaboratory totackle the costproblem of massproducing theconventionalc-mos dual gatestructure of N -typeand P -typepolysilicon for theNMOS andPMOS gateelectrodematerials.

Satellites communicate for the first timec or the first time, satellites have! communicated with each otherwithout the intervention of a groundstation. The inaugural message wastransmitted between Virginia andHawaii via two Milstar militarycommunication satellites.

Motorola's satellite mobile phonesystem Iridium is based on militarysatellite technology. Iridium satellitesare in such low orbits that they canonly 'see' a small part of the earth atany one time. To avoid the need for alarge number of ground stations,Iridium messages will be relayedbetween satellites to a satellite with aview of a ground station.

Japanese and American scientistshave used a laser to establish two waycommunication between a satelliteand Earth for the first time.

The US Jet Propulsion Laboratoryused a 10W argon laser based at itsTable Mountain telescope inCalifornia to communicate with theexperimental satellite ETV -VI, run byJapan's Communications ResearchLaboratory (CRL). Results from thetest will be used to upgrade the opticson CRL's OICETS satellite due to belaunched in 1998. The aim of theresearch is to let satellites in low earthand geostationary orbits communicatewith each other optically.

Semiconductor makers could face polysilicon shortageUS market research firmDataquest is predicting a

shortage of polysilicon assemiconductor demand continues togrow and production capacity lagsdemand.

The shortage is predicted to hitsemiconductor manufacturers in midto late 1996 and could last as long as10 months. But new polysiliconmarket capacity is reckoned to comeonline in 1997, which will let it catchup with demand.

"Silicon companies will have highmarket pricing power throughout therest of this decade, and particularly in1996 and 1997," said Clark Fuhs,

principal analyst for Dataquest. "Forthis reason we believe the siliconindustry, which has been ahistorically lower -margin industrialbusiness, will migrate to a businessmodel that more closely resemblesthe other segments of thesemiconductor ecosystem."

Dataquest also predicts a shortageof 200mm wafers as companiesprepare new fabs that use the largerformat size. The 200mm wafershortage will begin in 1996 and willcontinue for much of the rest of thedecade, peaking in 1997 and thenagain in 1999.

The firm estimates that 1995

demand for 200mm wafersworldwide is 1.280m wafers a month.This demand will almost double nextyear to reach 2.206m wafers and theindustry will require 5.213m wafers amonth by 2000. However, theindustry will only be able to supply1.956m wafers next year and 3.894mwafers a month by the end of thedecade. Dataquest points out thatthere is a mismatch of supply anddemand. This has created a shortageof 100 and 125mm wafer sizes, whichshould soon be solved.

And it predicts the most seriouslong term shortages will be in thesupply of 150mm wafers.

Researchers achieve 400Gbit/sdown a 100km fibrejapanese researchers have transmitted digital data at a400Gbit/s down 100km of optical fibre for the first

time. Telecoms developer Nippon Telegraph andTelephone (NTT) has achieved this data throughput bymultiplexing four light signals of different wavelengthseach carrying a 100Gbit/s data stream. As part of theexperiment NTT demonstrated in the laboratory aphase -locked loop timing extraction circuit capable ofworking at 6.3GHz and a 200Mbit/s optical timedivision demultiplexer.

The optical receiver must synchronise the incomingdata stream and a timing extraction circuit is used toderive the clock signal from the data. NTT used aprescaled PLL which relies on the nonlinearity of asemiconductor laser amplifier to extract a 6.3GHz clocksignal which is scaled up to the original 100Gbit/ssignal.

In the receiver the optical time divisiondemultiplexer splits the 100Gbit/s signal into 16separate 6.3Gbitls streams.

Pace could loose its set -top

lead to Pioneerjapanese consumer electronicscompany Pioneer, is poised to snatch

the title of 'leading digital set -topmaker in Europe' from under PaceMicro Technology's nose. Pioneerplans to mass produce boxes in Europein early 1997 and does not feel thatPace poses a threat on the Europeanmarket.

"Pace has been successful in theAsian area and Australia, but its successin Europe has been limited," said StuartLiddle, business development manager.

However, Pace is not phased byPioneer's claims, although its currentmarket share of 95 per cent may soonbe affected by it.

"We have seen Pioneer's announce-ments, but we can't comment," saidone Pace spokesman.

Pioneer plans to ramp up productionto up to 2 million units per year by1998, with prices close £400. Its

manufacturing of set -top boxes inEurope could involve the UK.

"It is very likely our manufacturingwill be in Belgium but as far as the UKis concerned, at the moment it is still upin the air," said Liddle.

BRT to cost Racal £30m paD acal is faced with spendingIN. hundreds of millions of pounds tomodernise British RailTelecommunications' (BRT) network.

Racal is to pay £132.75m acquiringBRT, which needs around £30m ayear for the next three years to keepits existing PDH network up toscratch.

"BRT requires £30m per annum forthe next three years, mainly forsupporting network resilience andserviceability," said Rupert Hunte,strategic business developmentdirector for Racal Network Services,which is to incorporate BRT.Sveltana Josifovska,Electronics Weekly


SMALL SELECTION ONLY LISTED - EXPORT TRADE AND QUANTITY DISCOUNTS - RING US FOR YOUR REQUIREMENTS WHICH MAY BE IN STOCKHP New Colour Spectrum AnalysersHP1417+855213 IF + 85538 RF- 1KHz-110Mcis -£700.HP1417+85528 IF + 85546 RF - 100KHz-1250Mds- £900.HP141T+ 855213 IF + 8556A RF -20Hz-300KHz - £700.Special Offer just in from MOD City 40 HP8555A RF Units 10Mc/s - 18GHzS.HP1417 +8552B IF + 8555A 10Mc/s-18GHzS 01200.HP ANZ Units Available separately - New Colours - TestedHP141T Mainframe - £350.HP8552B IF -£300.HP8553B RF 1KHz to 110Mds - 1200.HP85546 RF 100KHz to 1250Mc/s- £500.HP8555A RF 10Mc/s to 18GH2S - £800.HP8556A RF 20Hz to 300KHzS - £250.HP8443A Tracking Generator Counter 100KHz-110Mds- £300.HP84458 Tracking Preselector DC to 18GHz- E350.HP3580A 5Hz - 50KHz ANZ - £750 -£1000.HP3582A .02Hz to 25.6KHz - £2k.HP8568A 100Hz-1500Mds ANZ-HP8569B 10M c/s-22GHz ANZ- f6k.HP Mixers are available for the above ANZ's to 40GHzTEK 492 - 50KHz - 18GHz Opt 1+2 - £4k-E4.2k.TEK 492 -50KHz-18GHz Opt 1+2+3 - £4.5k.TEK 492P -50KHz- 21 GHz Opt 1+2+3 - £5k.TEK 494AP 1KC/S -21GHz- 07k.TEK 496P 1KHz-1.8GHz- £4k.TEK 5L4N 0-100KHz- £400.TEK 7L5 + L1 -20Hz-5Mc,/s -0700.TEK 7L5 + L3 - Opt 25 Tracking Gen -£900.TEK 7L12 -100KHz-1800Mds - £1000.TEK 7L18 - 1.5-60GHzs -£1500.TEK 491 10Mc/s-12.4GHzs-40GHzs- £750. 12.4Ghzs-40Ghzs with Mixers.Tektronix Mixers are available for above ANZ to 60GHzsSystron Donner 763 Spectrum ANZ + 4745B Preselector .01-18GHz + Two Mixers 18-40GHz in

Transit Case -£3k.HP8673D Signal Generator .05-26.5GHz- 020k.Systron Donner 16186 Microwave AM FM Synthesizer 50Mc/s 2-18GHzs

R&S SWP Sweep Generator Synthesizer AM FM 4-2500Mc/s - 03.5k.ADRET 3310A FX Synthesizer 300Hz-60Mc/s- £600.HP8640A Signal Generators -1024McIs - AM FM - £800.HP3717A 70Mc/s Modulator - Demodulator - £500.HP8651A RF Oscillator 22KC/S - 22Mds.HP5316B Universal Counter A+B.HP6002A Power Unit 0-5V 0-10A 200W.HP6825A Bipolar Power Supply Amplifier.HP461A-465A-467A Amplifiers.HP81519A Optical Receiver DC-400Mc/s.HP Plotters 7470A -7475A.HP3770A Amplitude Delay Distortion ANZ.HP3770B Telephone Line Analyser.HP8182A Data Analyser.HP59401A Bus System Analyser.HP6260B Power Unit 0-10V 0-100 Amps.HP3782A Error Detector.HP3781A Pattern Generator.HP3730A+ 3737A Down Convertor Oscillator 3.5-6.5GHz.HP Microwave Amps 491-492-493-494-495-1GHz-12.4GHz- £250.HP105B Quartz Oscillator - 0400.HP5087A Distribution Amplifier.HP6034A System Power Supply 0-60V 0 -10A -200W- £500.HP6131C Digital Voltage Source+ - 100V 1/2 Amp.HP4275A Multi Frequency L.C.R. Meter.HP3779A Primary Multiplex Analyser.HP3779C Primary Multiplex Analyser.HP8150A Optical Signal Source.HP1630G Logic Analyser.HP5316A Universal Counter A -I -B.HP5335A Universal Counter A+ B+C.HP595016 Isolated Power Supply Programmer.HP8901A Modulation Meter AM - FM - also 8901B.HP5370A Universal Time Interval Counter.Marconi TF2370 -30Hz-110Mc/s 750HM Output (2 BNC Sockets+ Resistor for 500HM MOD with

Marconi MOD Sheet supplied - 0650.Marconi TF2370 30Hz-110Mds 50 ohm Output - f750.Marconi TF2370 as above but late type- £850.Marconi TF2370 as above but late type Brown Case -CI 000.Marconi TF2374 Zero Loss Probe - £200.Marconi TF2440 Microwave Counter - 20GHz -£1500.Marconi TF2442 Microwave Counter -26.5GHz- £2k..Marconi TF2305 Modulation Meter- E2.3k.Racal/Dana 2101 Microwave Counter - 10Hz-20GHz -02k.Racal/Dana 1250-1261 Universal Switch Controller + 200Mds PI Cards.Racal/Dana 9303 True RMS Levelmeter+Head- £450. IFFE - 0500.TEKA6902A also A6902B Isolator - £300-0400.TEK 1240 Logic Analyser - £400.TEK FG5010 Programmable Function Generator 20Mc/s - 0600.TEK2465A 350Mc/s Oscilloscope - £2.5k + probes -0150 each.TEK CT -5 High Current Transformer Probe - 0250.TEK J16 Digital Photometer + J6523-2 Luminance Probe - £300.TEK J16 Digital PhotOmeter + J6503 Luminance Probe - £250.ROTEK 320 Calibrator + 350 High Current Adaptor AC -DC -0500.FLUKE 51026 AC -DC Calibrator - E4k.FLUKE 1120A IEEE -488 Translator - £250.Tinsley Standard Cell Battery 56446 - £500.Tinsley Transportable Voltage Reference - £500.FLUKE Y5020 Current Shunt -£150.HP745A + 746A AC Calibrator -0600.HP8080A MF + 8091A 1GHz Rate Generator + 8092A Delay Generator + Two 8093A 1GH, Amps

+ 15400A-0800.HP54200A Digitizing Oscilloscope.HP117296 Carrier Noise Test Set .01-18GHz- LEF- £2000.HP3311A Function Generator- £300.Marconi TF2008 - AM -FM signal generator - also sweeper - lOKc/s - 510Mc/s - from £250 -

tested to £400 as new with manual - probe kit in wooden carrying box.HP Frequency comb generator type 8406 - £400.HP Vector Voltmeter type 8405A- £400 new colour.HP Sweep Oscillators type 8690 A & B + plug -ins from 10Mc/s to 18GHz also 18-40GHz. P.O.R..HP Network Analyzer type 8407A + 8412A + 8501A -100Kc/s-110Mc/s- 0500- 01000.HP Amplifier type 8447A -1-400Mc/s £200 - HP8447A Dual - 0300.HP Frequency Counter type 5340A - 18GHz £1000 - rear output £800.HP 8410 -A -B -C Network Analyzer 110Mds to 12GHz or 18GHz - plus most other units and

displays used in this set-up- 8411a 8412 8413 8414 8418 8740 8741 -8742- 8743-8746 - 8650. From £1000.

Racal/Dana 9301A-9302 RF Millivoltmeter - 1.5-2GHz - £250-0400.Racal/Dana Modulation Meter type 9009 - 8Mc/s - 1.5GHz - £250.Marconi RCL Bridge type TF2700 -£150.Marconi/Saunders Signal Sources type - 60588 - 6070A - 6055A - 8059A - 6057A - 6056 -

0250-0350. 400Mc/s to 18GHz.Marconi TF1245 Circuit Magnification meter + 1246 & 1247 Oscillators -0100-0300.Marconi microwave 6600A sweep osc., mainframe with 6650 PI - 18-26.5GHz or 6651 PI - 26.5-

40GHz - £1000 or PI only 0600. MF only £250.Marconi distortion meter type TF2331- £150. TF2331A- £200.

Tektronix Plug -Ins 7A13 - 7A14 - 7A18 - 7A24 - 7A26 -7A11 -7M11 -7S11 - 7D10 -7S12 - S1- S2 - S6 - S52 - PG506 - SC504 - SG502 - SG503 - SG504 - DC503 -00508 - DD501 -WR501 -DM501A- FG501A-TG501 - PG502- DC505A - FG504 - 7880 + 85-7B92A

Gould J3B test oscillator + manual -0150.Tektronix Mainframes -7603 -7623A-7613 -7704A-7844-7904 - TM501 -TM503 -TM506 -

7904A -7834- 7623 - 7633.Marconi 6155A Signal Source -1 to 2GHz - LED readout -0400.Barr & Stroud Variable filter EF3 0.1Hz- 100kds + high pass + low pass -£150.Marconi TF2163S attenuator - 1GHz. £200.Ferns!l power unit H60/50 - £400 tested. H60/25 - 0250.Racal/Dana 9300 RMS voltmeter - 0250.HP 8750A storage normalizer - £400 with lead + S.A or N,A Interface.Marconi TF2330 - or TF2330A wave analysers- 0100-0150.Tektronix- 7S14 -7T11 -7511 -7S12 -S1- 52- 539 -S47- 551- 652 -S53- 7M11.Marconi mod meters type TF2304- £250.HP 5065A rubidrum vapour FX standard -f1.5k.Systron Donner counter type 60548 - 20Mc/s- 24GHz - LED readout -Elk.Racal/Dana 9083 signal source -two tone -£250.Systron Donner - signal generator 1702 -synthesized to 1GHz -AM/FM - BOO.Tektronix TM515 mainframe + TM5006 mainframe - £450 -0850.Farnall electronic load type RB1030-35- 0350.Racal/Dana counters - 9904 - 9905 - 9906 -9915 - 9916 - 9917 - 9921 - 50Mc/s - 3GHz - 0100-

£450 - all fitted with FX standards.HP4815A RF vector impedance meter dw probe -0500-0600.Marconi TF2092 noise receiver. A, B or C plus filters - £1 00-0350.Marconi TF2091 noise generator. A, B or C plus filters - 0100-0350.Marconi 2017 S/G 10Khz- 1024MHz.HP180TR, HP182T mainframes 0300-0500.Philips panoramic receiver type PM7900 -1 to 20GHz - 0400.Marconi 6700A sweep oscillator + 18GHz Pl's available.HP8505A network ANZ + 8503A S parameter test set + 8501A normalizer - 04k.HP8505 network ANZ 8505 + 8501A + 8503A.Racal/Dana VLF frequency standard equipment. Tracer receiver type 900A + difference meter

type 527E + rubidium standard type 9475- 02750.HP signal generators type 626 -628 -frequency lOGHz -21GHz.HP 432A - 435A or B - 436A - power meters + powerheads - Mds-40GHz- 0200-01000.Bradley oscilloscope calibrator type 192 - £600.HP8614A signal generator 800Mc/s -2.4GHz, new colour £400.HP8616A signal gen 1.8GHz -4.5GHz, new colour £400.HP 3325A syn function gen 20Mds -01500.HP 3336A or B syn level generator - £500-0600.HP 3586B or C selective level meter - 0750-01000.HP 3575A gain phase meter 1Hz - 13Mc/s- £400.HP 8683D S/G microwave 2.3 - 13GHz - opt 001 -003 - 04.5k.HP 8660 A -B -C syn S/G. AM + FM + 10Kc/s to 110Mc/s PI - 1Mc/s to 1300Mds - 1Mc/s to

2600Mc/s - £500-02000.HP 864013 S/G AM -FM 512Mds or 1024Mc/s. Opt 001 or 002 or 003- 0800-01250.HP 86222BX Sweep PI - 01 - 2.4GHz + ATT- 01750.HP 8629A Sweep P1- 2 -18GHz- £1000.HP 862908 Sweep PI -2 - 18GHz -01250.HP 86 Series Pi's in stock - splitband from 10A4c/s - 18.6GHz -0250-01k.HP 8620C Mainframe- £250. IEEE - 0500.HP 8615A Programmable signal source - 1MHz - 50Mcis - opt 002- 01k.HP 8601A Sweep generator .1- 110Mds- £300.HP 3488A HP -113 switch control unit - £500 + control modules various - 0175 each.HP 8160A 50Mc/s programmable pulse generator - 01000.HP 853A MF ANZ- £1.5k.HP 8349A Microwave Amp 2 - 20GHz Solid state -01500HP 3585A Analyser 20Hz -40Mds- 04k.HP 85698 Analyser .01 -22GHz- f5k.HP 3580A Analyser 5Hz - 50kHz - El k.HP 1980B Oscilloscope measurement system -0600.HP 3455A Digital voltmeter - 0500.HP 3437A System voltmeter - £300.HP 3581C Selective voltmeter - £250.HP 5370A Universal time interval counter -£450.HP 5335A Universal counter -200Mds- 0500.HP 5328A Universal counter - 500Mds - 0250.HP 6034A System power supply -0 -60V-0- 10 amps - £500.HP 5150A Thermal printer - £250.HP 1645A Data error analyser -0150.HP 4437A Attenuator- £150.HP 3717A 70Mc/s modulator - 0400.HP 3710A - 3715A - 3716A - 370213 - 370313 - 3705A - 3711A - 37918 - 3712A - 3793B

microwave link analyser- P.O.R.HP 3730A+B RF down converter - P.O.R.HP 3552A Transmission test set - £400.HP 3763A Error detector -£500.HP 3764A Digital transmission analyser - 0600.HP 3770A Amp delay distortion analyser- 0400.HP 3780A Pattern generator detector - £400.HP 3781A Pattern generator - 0400.HP 3781B Pattern generator (bell) - £300.HP 3782A Error detector - 0400.HP 3782B Error detector (bell) -0300.HP 3785A Jitter generator + receiver - 0750 -Elk.HP 8006A Word generator- 0100-0150.HP 8016A Word generator- £250.HP 8170A Logic pattern generator - £500.HP 59401A Bus system analyser - £350.HP 59500A Multi programmer HP- 18 -0300.Philips PM5390 RF syn -0.1 - 1GHz -AM + FM - 01000.S.A. Spectral Dynamics SD345 spectrascope 111 - LF ANZ- 01500.Tektronix R7912 Transient waveform digitizer - programmable -E400.Tektronix TR503 + TM503 tracking generator 0.1 - 1.8GHz -01k- or TR502.Tektronix 576 Curve tracer + adaptors - 0900.Tektronix 577 Curve tracer + adaptors - £900.Tektronix 1502/1503 TDR cable test set -01000.Tektronix AM503 Current probe + TM501 mtframe -01000.Tektronix SC501 - SC502 - SC503 - SC504 oscilloscopes -075-0350.Tektronix 465 -46513-475 -2213A 2215 2225 2235 2245 2246 0250-01000.Kikusui 100Mc/s Oscilloscope COS6100M -£350.Nicolet 3091 LF oscilloscope -0400.Racal 1991 - 1992 -1988 - 1300Mc/s counters - 0500-0900.Fluke 80K-40 High voltage probe in case- BN -0100.Racal Recorders -Store 4- 4D- 7 -14 channels in stock- 0250 -0500.Racal Store Horse Recorder & control - 0400-0750 Tested.EIP 545 microwavel 8GHz counter -01200.Fluke 510A AC ref standard -400Hz- 0200.Fluke 355A DC voltage standard - £300.Wiltron 610D Sweep Generator + 6124C PI -4 -8GHz- 0400.Wiltron 610D Sweep Generator + 61084D PI - 1Mc/s- 1500Mds - 0500.Time Electronics 9814 Voltage calibrator - 0750.Time Electronics 9811 Programmable resistance - 0600.Time Electronics 2004 D.C. voltage standard -01000.HP 8699B Sweep PI YIG oscillator .01 -4GHz -£300.86908 MF - 0250. Both 0500.Schlumberger 1250 Frequency response ANZ-£1500.Dummy Loads & power att up to 2.5 kilowatts FX up to 18GHz - microwave parts new and ex

equipt -relays- attenuators- switches -waveguides- Yigs -SMA-APC7 plugs -adaptors.MK Items in stock - ask for list.W&G Items in stock -ask for list.Power Supplies Heavy duty + bench in stock-Farnell - HP -Wei r-Thurl by -Racal etc. Ask for list.

ITEMS BOUGHT FROM HM GOVERNMENT BEING SURPLUS. PRICE IS EX WORKS. SAE FOR ENQUIRIES. PHONE FOR APPOINTMENT OR FOR DEMONSTRATION OF ANY ITEMS, AVAILABILITY ORPRICE CHANGE. VAT AND CARRIAGE EXTRA

ITEMS MARKED TESTED HAVE 30 DAY WARRANTY. WANTED: TEST EQUIPMENT -VALVES -PLUGS AND SOCKETS-SYNCROS-TRANSMITTING AND RECEIVING EQUIPMENT ETC.

Johns Radio, Whitehall Works, 84 Whitehall Road East, Birkenshaw, Bradford BD11 2ER, Tel. No: (012141 684001. Fax: 651160


February 1996 ELECTRONICS WORLD+WIRELESS WORLD 95

RESEARCH \OTESJonathan Campbell

Holographic storage gets £32 million fillipT he next generation of data storage

systems are likely to beholography -based if a $32Millionprogramme and some of the biggestnames in US electronics succeed intheir aims.

Holography, where data storageuses lasers to store information as"pages" of electronic patterns withinthe volume of special opticalmaterials, has looked like anattractive technology for some years.A million or more data bits can beplaced on each page and thousands ofpages can be stored in material nolarger than a small coin. In this wayholographic systems offer thepossibility of compact devices

holding many trillions of bytes ofinformation. Many commercialapplications are envisaged, thoughone of the first users could be themilitary, looking for a system to helpprovide its soldiers and commandcentres with rapid access to the largeamounts of information and visualimages they expect to need to besuccessful in the next decade.

However, only recently have someof the essential components andtechnologies - such as those used inmass -market camcorders and portablecomputer displays - become availableand affordable.

Now a joint university, industry andgovernment consortium has begun to

Computing record thatis rewriting atomic science

What do you suppose would be the resultof setting a computer running

continuously for two years to chew over asingle problem, using 448 processors, each ofwhich has about the same power as today'sfastest PCs.

The answer is a glueball, and despite itsrather unattractive name, scientists aredelighted.

The point of the research was to calculate theproperties of this elusive elementary particlealready predicted by theory. In fact theproperties were found to match those of apreviously unidentified particle detected inseveral experiments carried out over the last 12years. So two problems were solved at once -and it only took four hundred million billionarithmetic operations.

The arithmetic was carried out on GF11 -amassively parallel computer designed and builtspecifically for these type of calculations at theIBM Watson Research Center by Weingartenin collaboration.

The IBM result resolves a long standingpuzzle in particle physics. Although glueballsare predicted to exist by quantum chromodynamics (qcd) - the fundamental theory of

nuclear interactions - none had ever beforebeen positively identified in an experiment. Itis now clear that glueballs are frequentlycreated in particle accelerators, but have goneunrecognised, because the properties predictedfor glueballs by qcd had not been found withsufficient accuracy.

The new qcd calculation provides the firstaccurate numerical values for the mass of thelightest glueball and for the rate at which itdecays into several different combinations ofmore stable particles. Close agreementbetween these numbers and the observedproperties of a particle named f(1710) make itsidentification as a glueball practically certain.

So the glueball is now with us for ever.Over the years we have been used to ever-

more exotic labels emanating from the mindsof atomic scientists to identify their variousbuilding blocks. What a pity that this massivecalculation - the largest single numerical featin the history of computing - and the firstinstance of a particle's "discovery" by meansof a computer, will also be responsible formarking the existence of a particle that soundsmore like it has been dissolved out of anatomic scientist's ear.

develop the five-year, holographicdata -storage system (hdss)programme.

The aim is to develop keycomponents and integrate them intoseparate write -once and rewritablesystems, with a capacity of a trillionbits or more and a data -throughputrate of at least a billion bits a second.

At the same time, a secondprogramme - photo -refractiveinformation storage materials (Prism),with many of the same participants,will work to develop optically -sensitive materials optimised forstoring holograms.

The initial goals of the hdss projectare to develop several keycomponents for the system, includinga high -capacity, high -bandwidthspatial light modulator used for datainput; optimised sensor arrays fordata output; and a high -power red-light, semiconductor laser. The hdssresearchers will also investigateoptical systems architecture, such asmultiplexing schemes and accessmodes, data encoding/decodingmethods, signal processingtechniques, and the requirements oftarget applications.

Organisations involved in theprogrammes include, StanfordUniversity, Carnegie-Mellon, IBM,Rockwell and GTE and severalothers.

The programme's ultimate goal is tointegrate all the components intoseparately optimised systems that willdemonstrate write -once andrewritable holographic data storage.

Potential applications forholographic data storage systemsinclude satellite communications,airborne reconnaissance, high-speeddigital libraries, rugged storage fortactical vehicles, and imageprocessing for medical, video andmilitary purposes.

Professor Lamertus Hesselink, ElectricalEngineering, Stanford University,Stanford, California 94305-2245, USA.

96 ELECTRONICS WORLD January 1996

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9-1

RESEARCH NOTES

Newly developedhigh -temperature

sensing equipment,based on lasers,

significantly cuts thecost of steel making.

lasers make better steel...Successful testing of a laser -basedsensor, used to track the chemicalconversion of iron and carbon intosteel, has demonstrated the massivepotential of a commercial device,promising huge savings forsteelmakers.

The sensor package, developed atSandia National Laboratories, inAlbuquerque, contains two miniaturevideo cameras, filters for controllingboth the wavelength and the intensityof the light reaching the cameras,

laser diodes, coherent fibre optics forguiding images, single fibre opticsfor guiding laser light, and circuitryfor controlling the filters. All thecomponents are inserted into acompact package near the tip of anoxygen lance that is lowered into thefurnace to control the steelmaking.

Sensors monitor temperature at thecombustion zone and the bathsurface where a blast of oxygenpushes aside thick, foamy slag. Thelance instrument package also

...and take on chilling roleTwo per cent efficiency for a processused to cool a solid might not seemanything to get steamed up about. Butwhen that figure is shown to be10,000 times better than that so farachieved for the much easier problemof cooling a gas, then the extent of thebreakthrough made in optical

Cooled device

Metalmirror

Tranparent thermal link

Dielectricmirrors

Coo:0o* veil

Pony laser

Input laser light is shown as the solid lines and fluorescence as thedashed ones. Violet -coloured areas indicate the regions where thefluorescent radiation is most intense. White areas are in theshadow of the dielectric mirrors. These shadowed regions are notcompletely free of fluorescent radiation, however, due to theband pass of the dielectric mirrors. Hence, a metal mirror andbaffles are required to fully eliminate fluorescent -radiation heatloading of the object to be cooled.

Shadoved regionsFluoresceru radiaxion fieldIICooling element

refrigeration - using lasers to coolinstead of heat - becomes muchclearer.

For the first time, scientists areglimpsing the possibilities ofconstructing a solid-state opticalcryo-cooler that could be used incooling ultrafast computer circuits orfor removing heat from electronics inouter space. Researchers are talkingoptimistically about 'opticalrefrigerators' being used in satellitesto cool infrared cameras or insuperconducting relays for cellulartelephone calls, within only a fewyears.

The work is being carried out at theLos Alamos Laboratories, and thelatest news is being seen as a majorstep forward toward the goal ofcreating a "Los Alamos solid-stateoptical refrigerator," or Lassor, whichwould cool electronic devices andscientific instruments to at least liquidnitrogen temperature, 77° aboveabsolute zero - and eventually lower.

When light hits a solid object itusually deposits energy or heat. Butunder some circumstances, light canabsorb energy from the microscopicthermal vibrations in the solid, so

collects real-time information on thebath height.

By implementing fast, real-timesensors in the steelmaking process,researchers hope to reduce the timefor each 'heat', cut oxygenconsumption, and improve theefficiency and reliability of theprocess from heat to heat.

The team is testing several infraredlaser methods to measure thetemperature, water content, ratio ofcarbon dioxide to carbon monoxide -indicating how much carbon remains- and the presence of particles abovethe melt.

Carbon content is normallyanalysed later, before finalmetallurgy adjustments, and the finaldesired composition will vary forautomotive sheet metal, steel plate,and other products.

Steel mills currently measuretemperatures with single -use,platinum -alloy thermocouples,racking up about $2000 per day fortemperature checks.

Don Hardesty, Sandia CombustionResearch Facility, Sandia NationalLaboratories, MS 0167 Albuquerque,New Mexico, 87185-0167, USA.

decreasing the object's temperature.If an object excited by radiation at

one frequency, can be made to emitradiation at higher frequencies, whichcarry more energy, the object cools.

In previous experiments, heatinghas always far exceeded cooling. Butby using a tunable laser and modemfibre -optic materials, the researchershave managed to suppress the usualheating and make optical coolingdramatically apparent.

In effect the researchers havediscovered how to use laser light toexcite an object to special quantumstates in which it can trap thermalvibrations but can't create them.

The experiments are actually thefirst demonstration of a newcontinuous -solid-state cooling processsince the French watchmaker -turned -physicist Jean-Charles-AthanasePeltier discovered thermoelectriccooling in 1834.

In their experiments, the LosAlamos scientists shined a beam ofinfrared light at a 6mm-long sliver ofultra -pure glass impregnated with ionsof the ytterbium.

Ytterbium ions radiate over only asingle band of frequencies,


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RESEARCH NOTES

Design for afluorescent

cryocooler thatmight be used inspace. It is based

on using anytterbium -doped

heavy -metal -fluoride glass asthe fluorescent

cooling element.

frequencies that are much higher thanthe possible frequencies at which theglass could vibrate. So when the glassis pumped with laser light at the right

frequency, it is unable produce heat.The Los Alamos team managed to

produce a cooling power that was afew percent of the absorbed laser

power. That's not a lot in terms ofnormal cooling devices. But it is quiterespectable for cooling high-techdevices to extremely low, orcryogenic, temperatures.

Light for the Lassor would beprovided by efficient, compact, high-powered diode lasers in a device withno moving parts and weighing only a1kg. The technique would be ideal forspace, where the Lassors could cool awide variety of detectors andinstruments mounted on satellites.

Since they would be entirely solid-state, the devices would generate novibrations and could survive for yearsin the harsh environment of space.

Ultimately, optical refrigeratorsmay find homes in desk -topcomputers where they could enablesuperconducting circuits to operatehundreds of times faster than today'sconventional electronics.

Chaotic approach to better electronicsTo impose order on chaos - just takesa little more chaos. At least that's theconclusion of three US researcherswhose work is forcing scientists totake a new look at the operation andinteraction of both natural andartificial non-linear systems.Ultimately it could lead to methodsfor improving performance ofelectronic systems by exploitingvariations in components.

William Ditto, at the GeorgiaInstitute of Technology andcolleagues John Lindner of TheCollege of Wooster and Yuri Braimanof Emory University used computersimulations to study a variety ofcoupled non-linear systems, includinga series of chaotic pendula and asystem with a hundred identicaloscillators. The systems exhibitedchaotic behaviour over both time andspace (spatio-temporal chaos), and theactivity of each individual elementcould affect the behaviour of others.

To see what would happen if theyincreased the disorder and variabilityof the chaotic systems, the researchersmade each pendulum a differentlength, and programmed eachoscillator to respond in a slightlydifferent way.

They expected to see even moredisorder and even more turbulentbehaviour. But what they got wasorganised behaviour patterns comingout of the systems. It seems that the

diversity or disorder provided amechanism by which the systemscould organise themselves.

How the process works to controlchaos isn't fully understood yet,though it looks as if disorder may helpmove groups of chaotic elements intosimilar modes of behaviour.Neighbouring elements then begin tolock into the same mode, and "a localdomino effect" spreads thatbehaviour. The result is an organisedsystem of individual elements thatrepeats its behaviour in a complex butregular way.

The work looks to have directrelevance to electronics - Josephsonjunctions for instance. A small dcvoltage across such junctions, formedby separating two superconductors bya thin insulator, causes an ac currentto flow. Because the frequency of theac current is very sensitive to anyambient magnetic field, such devices.(called squids) can be used to measureextremely small magnetic fields. "Ourfigures of the spatio-temporalevolution of the velocities of arrays ofcoupled pendula can also representthe evolution of the currents acrossarrays of coupled Josephsonjunctions," Lindner told EW+WW.

More generally, the work hasimplications for any system consistingof arrays of identical or near -identicalelements, such as vlsi circuits and ccdarrays.

It demonstrates that if the elementsare coupled and are non-linear, thanthe behaviour of arrays of identicalelements may be qualitativelydifferent from the behaviour of arraysof slightly disordered elements.

"In fact, small amounts of disordercan literally chaos chaos to order,"says Lindner.

The work may turn out to be relatedto stochastic resonance, aphenomenon in which adding noise toa system actually improves its abilityto receive weak signals. Stochasticresonance is already findingapplications in electronic systems, andLindner believes engineers may oneday use disorder to enhanceperformance of electronic systems.

"For certain non-linear systems,maybe you can not only get awaywith greater variability in yourcomponents, but maybe that's whatyou want," he explains. "A cleverengineer may be able to exploit thisbasic phenomenon to lead to betterdevices. Surprising as that may sound,having a little inhomogeneity in asystem may provide betterperformance if the elements arenonlinear."

John Lindner is Associate Professor ofPhysics, The College of Wooster,Wooster, OH 44691, [email protected]


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CONSUMER ELECTRONICS

John Matthewsoutlines thetechniques beingused to cram moreimage informationinto less space andbandwidth.

Video technology consultancyJohn Matthews is a research and developmentengineer at Teltec Ireland and is based atDublin City University. Teltec Ireland is theNational Programme for Telecommunicationsin Ireland and represents a partnershipbetween leading third -level institutions andindustry. The Teltec Video Coding Group atDCU has conducted extensive research in thearea of low bit -rate video and image coding fortelecommunications and multimedia applica-tions. For further information, phone353-1-7045759, fax 353-1-7045508 or [email protected].

VideoCOMPRESSIONtechniquesIn recent years, advances in video compres-

sion techniques have been at the forefrontof the multimedia revolution. The variety of

video applications which are becoming avail-able was clearly evident at this year's Telecom95 show in Geneva, ranging from pc basedconferencing systems to high -end video ondemand products.

Multimedia is a general term covering theexchange of video, audio and data betweenpeople. New applications and products appearalmost daily, and there are standards in themultimedia world to ensure that equipmentand services from one manufacturer will oper-ate successfully with similar equipment fromother companies.

A number of standards are now firmlyestablished, including JPEG, MPEG1,MPEG2 and H.320. Most video-conferencingsystems over ISDN now conform to the ITU-T H.320 standard, although there are propri-etary systems.

MPEG1 is used for audio/visual storage oncd. JPEG is used for still image transmission,while MPEG-2 is aimed at higher end broad-cast systems. Apart from JPEG, these stan-dards define the rules governing the compres-sion of video and audio for storage ortransmission.

This article looks at the video aspects ofthese standards. These new standards andcompression algorithms have been developedto reduce the bandwidth required for videotransmission. In addition, emphasis has beenplaced on defining methods which can bepractically implemented This development hasbeen coupled with progress in the hardwareworld, where highly integrated single -chipsolutions for the algorithms have been broughtto the market.

While the video standards have some com-mon features - in particular the fact that they

all use discrete cosine transform - they aredistinctly different and are geared towardsdifferent applications. For example, JPEGcould be used for motion video applications,but it would never achieve the same real-timeperformance as H.261. This is because it doesnot have inter -frame and motion compensa-tion capability

Also, new standards will emerge, encom-passing even more applications. For example,H.263 is a video standard with many similar-ities to H.261 (the video standard for H.320)which will enable good quality video confer-encing over the ordinary telephone line. WithMPEG-4, there will be new functions, cou-pled with improved compression ratios andpicture quality.

In this article I outline the video standardsalready developed and summarise their dif-ferences and unique positions. In addition, Ialso review the up and coming standards.

Video compression fundamentalsCurrent standards - JPEG, MPEG and H.261- have a number of things in common. Themost important of these is that they all usethe discrete cosine transform, dct, in theiralgorithms. They each perform quantisationon the resulting dct coefficients, and imple-ment run -length coding on those quantisedcoefficients, Fig. 1.

So what is dct? It is a mathematical trans-form which translates digital video data fromthe spatial domain into the frequency domain.Typically, a coding algorithm will divide pic-ture data into blocks of 8 -by -8 pixels, where apixel is a picture element with a valuebetween 0 and 256. It then performs the dct oneach block. For each block of 8 by 8 pixels,the dct gives an 8 -by -8 block of frequencycomponents.

The rationale behind the dct is as follows: In



Second generation video coding techniques

Block -based coding methods havedisadvantages - in particular blockinessin pictures and the inability to deriveinformation on specific objects in thepicture. But is there an alternative?

Second generation video codingtechniques have been the subject ofmuch research in the nineties, and newtechniques such as segmentation,model based coding and object basedcoding are under intense investigation.

Segmentation is a technique in whichthe image is described in terms ofcontours and texture. Contours are

. abrupt changes in the gray levels of theimage, and texture can be thought of asthe roughness of the image - or theshade transition across the image. So asegmentation based scheme willattempt to describe an image astextured regions surrounded bycontours.

Model based coding techniques havebeen greatly influenced by progress inthe fields of computer vision andcomputer graphics. The underlyingmotivation in model based coding isthat an image is the projection of anilluminated 3-d object onto a 2-dplane. In object based coding an imageis subdivided into objects and eachobject is described in terms of itsshape, motion and colour.

In an object -based coding scheme, asource model provides an abstractmeans of describing the type of objectin the picture. This source modeldefines the parameter which will beused to identify objects during imageanalysis. For example, an object might

--' be rigid or flexible.The source modelwill also describe motion of objects -i.e. fixed direction or arbitrarydirection. So a picture is analysed andobjects are identified. Each object is

Frame in a video sequence

Zig-zag scan output7,2,5,1,0,1,0,1,0,0,0,0,2...

Run -length code output0 7 0 5 0 1 1 1 42...

Variable length coding

Object -based imageanalysis. Newtechniques for coding ofvideo signals are beinginvestigated as analternative to DCTblock based techniques.One such scheme isobject based coding,where objects areidentified in a pictureand are coded usingtheir shape motion andcolour parameters.

frame n

then described in terms of shapemotion and colour, see illustration.

Of course, certain parts of the picturewill not be classified as objects as theywill not conform to the source model.These areas are classified as modelfailure regions, and might be encodedusing a more traditional codingscheme. Among the objectives in anobject based codec is to have a higherpicture quality at comparable or lowerbit rates than block based codecs.These objectives are helped by anumber of factors.

The process of analysing an image toidentify objects is an exhaustive one,but once the objects have beenidentified, it does not take a lot ofinformation to describe them.Furthermore the only motion vectorswhich are transmitted are those relatingto objects.

Schemes are usually designed so thatobjects are bigger than the blockswhich would exist in correspondingblock based coding methods, so thereis potential for saving on motionvectors. Thirdly, when an object has

8x8 block withdigitised pixel values

90 22 73 94 18 36 41 6082 86 58 43 70 50 57 5673 25 62 61 39 43 54 55

100 80 67 53 42 51 56 7092 16 27 18 14 30 48 5970 52 38 20 24 17 40 29

105 90 40 23 7 3 4 14110 100 80 52 21 9 8 10

Zig-zag scan

C7 =7111r.nmumiummumrrimmmEumin

A Analysis frame n+1

Object Shape Motion Colour

Circularobject

Triangularobject

Abeen defined and is moving from frameto frame, very little update informationmay be required for that frame. So eventhough three parameters are necessaryin object based schemes, as against two- motion and colour - for block basedschemes, it is still feasible to operatesuch a scheme on a similar bandwidth.

A further feature of an object basedscheme is that it should be able toclassify the the objects, so optionallyonly the most important objects needbe transmitted in a low bit ratechannel. Editing would also be feasiblein such a scheme.

At present, most hardware researchin object based coding techniques iscarried out using digital signalprocessors or similar devices. There isstill a lot of work to be done both inthe areas of algorithm definition andin the implementation of thosealgorithms in hardware. However, it isan area which is attracting muchresearch interest, and this level ofinterest has been considerablyenhanced due to the interactivefeatures required in MPEG-4.

Lowerfrequencies ti 8x8 dct block Horizontal

frequencies60 21 8 5 3 -4 7

40 -3 15 7 4 -3 -2 0

14 7 18 -1 0 4 -2 5

7 6 7 12 -5 0 3

5 -7 14 6 3 2 4

4 -7 3 -4 0 -1 4

6 -5 0 -6 -2 3 2

3 0 -4 0 4 -5 -3Vertical

frequencies

Quantiser outpufor Q=8

7 2 1 0 0 0 0 0

5 0 1 0 0 0 0 0

1 0 2 0 0 0 0 0

0 0 0 1 0 0 0 0

0 0 1 0 0 0 0 0

0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0

Higherfrequencies

Fig. 1. DCT-basedvideo codingscheme. Thediscrete cosinetransform (DCT) isat the heart of thecoding schemesused in MPEG, JPEGand H.261. Thisfigure shows how an8 by 8 block of datais extracted from afield of video data.Note the presenceof significant lowfrequencies in the 8 -by -8 block oftransformcoefficients, withmost of the higherfrequencies going tozero afterquantisation.



File size of the JPEG original on the left is 1215Kbyte while that of the version on the right, compressed with loss, is only 61Kbyte.

the spatial domain, picture information isspread thinly over a large number of pixels. Inthe frequency domain, however, much of thepicture information will be contained in thelower frequency components. As a result, itmay be possible to discard some of the higherfrequency components, without sacrificing toomuch picture quality.

Performing the dct on the video data typi-cally concentrates much of the picture infor-mation into the lower frequency components.The dct itself does not compress data. An 8 -by -8 block of pixel data will provide an 8 -by -8 block of frequency components. The com-pression process starts with quantisation andrun length encoding.

Quantisation is a process where each of thedct coefficients is divided by an integer androunded towards zero. In a typical picture,many of the higher frequency components willhave low values, so their output after quanti-sation will be zero. The quantisation integer isuser definable, or is adaptable, its value beingdetermined by a control loop. In most cases,users can control how much of the high fre-quency components they wish to neglect. Thisis the start of the compression process.

The quantised coefficients are then zig-zagscanned and run length coding, or rlc, is per-formed. Output of the rlc process will be thevalues of each non -zero components, preced-

ed by the number of zero valued coefficientsbefore that component.

In most algorithms, further compression isachieved by the use of variable length coding,or vlc. Here commonly occurring strings fromthe run -length coding process are assignedshort code words, while less common stringsare assigned longer code words At this point,framing of the data can occur, so compresseddata is now ready for transmission or storage.

In motion video, further techniques are usedto remove redundancy from the data. The firstof these techniques is prediction. Instead ofcoding and transmitting data for full frames,frame differencing is used. The encoder willcode the difference between the current frameand a prediction of what that current frameshould be.

The easiest method would be to simply sub-tract the last frame from the current frame anduse the difference. However this method doesnot work well, because it doesn't take intoaccount the error build up in the transmissionchannel. So each encoder has an inbuilt modelof the decoder in a feedback path. It is there-fore a decoded version of the last encodedframe which is used for prediction purposes.

To further eliminate redundancy, motion,estimation and compensation is used. The pre-dicted frame is refuted to take into account themotion which is estimated to have occurred

between it and the current frame. This has theeffect of making the predicted frame as simi-lar as possible to the new incoming frame, sothe frame difference will be minimised evenfurther.

Most standards do not specify how to domotion estimation and compensation, so atrade off can be made between complexity andperformance.

Still image coding - JPEGStandard IS010918, more commonly referredto as JPEG, defines the techniques to be usedin the coding of still pictures.

JPEG is the most simple of all the standardsunder discussion. Because it caters for stills,there is no requirement for frame prediction ormotion compensation, so it does not need afeedback loop. The forward process consistsof dct, quantisation, zig-zag scan, and run -length and variable -length coding.

However, a number of different options inthe JPEG standard, allow users to tailor theirsystems for different levels of compressionand picture quality. Both lossless and lossycoding techniques are referred to.

In lossless coding, the picture can be rebuiltexactly as it was prior to coding. Lossless cod-ing techniques in JPEG are not based on thedct, but are 'prediction' based. Lossless codingis very limited in the amount of compression



which it can achieve however. Imaging formedical purposes is an example of a situationwhere lossless coding is required.

Lossy coding techniques are based on thedct. Among the options available are sequen-tial coding, progressive coding and hierarchi-cal coding.

Sequential coding is the simple dct processalready discussed. Progressive coding, as thename implies, allows a progressive build up ofpicture quality. In this mode, the quantisedcoefficients are sent in stages. Initially thelower frequency components are stored ortransmitted, followed by the higher frequencycomponents.

Another method is to selectively increase theresolution of the coefficients, so that the most -significant bits are first processed, followed bythe least -significant bits.

In hierarchical coding, resolution of the pic-ture gradually builds up. The advantage ofprogressive and hierarchical schemes forJPEG is that they allow the user to select avariable quality level for a still picture. This isimportant, for example, if a JPEG picture isbeing transmitted from one location to another.

If a slow transmission channel was used,then sending a very high resolution picturecould take a long time. As a result, it might bedesirable to send lower quality video. In a`browse' type application, the receiver couldthen select specific stills and request those ingreater detail.

Video conferencing and H.261The most relevant standard today for the videocompression part of a conferencing system isthe ITU-T standard H.261. Most commercial-ly available systems available today use tech-niques outlined in H.261. The standard detailsthe syntax for the coded bit stream and speci-fies how the decoder works.

Implicit in specifying the syntax anddecoder will be certain features of the encoder.

PAL or DISC4101sed Ptepreees>r

Otto

However many encoder options are left to theuser to implement. Examples of such optionsare the ways in which motion estimation andcompensation are performed. Figure 2 showsa typical H.261 encoder.

The compression algorithm in the H.261standard operates on YCrCb digital data.There are two resolutions specified for thesource data, namely CIF and QCIF, asdetailed in the Table. An H.261 compatibledecoder must be able to decode a bit streamwhich had QCIF as its origin, but CIF isoptional. Most systems accommodate bothresolutions. A system which encodes CIF datato a single ISDN B channel will compressvideo by approximately 60:1.

H.320 and H.261 are geared towards ISDN,so transmission of coded audio/visual data isnormally at a multiple of 64kbit/s - the band-width of one ISDN channel.

Typically, since the video and audio mustshare the channel, there will be some trade-offbetween audio and video quality - especiallyat low bit rates. Normally in a single ISDNchannel, 16kbit/s would be required for audio,so 48kbit/s would be left for video.

Video-conferencing systems based on pcstypically operate at lower bit rates, usually64kbit/s. Bigger stand-alone systems usuallyoperate at between 128 and 384kbits/s, andthey benefit from the higher resolution of CIFdata.

As with JPEG and MPEG, H.261 is a dctbased standard. Because it caters for motionvideo, frame prediction is used with motioncompensation in the encoding process.

A reasonably simple motion estimation andcompensation scheme is used. The currentframe data is divided into 16 -by -16 pixel`macro -blocks', each of which is compared toother 16 -by -16 blocks in the last decodedframe, to a displacement of plus or minus 15pixels in each dimension.

A calculation, such as the sum of the abso-lute differences between each correspondingpixel in the 16 -by -16 macroblocks is made.The nearby 16 -by -16 block which gives theminimum overall difference is used to deter-mine the best match. Motion vectors are thencalculated based on this match, and these mustbe sent to the decoder.

The predicted frame is adjusted using themotion vectors, and frame differencing thentakes place. In practice the predicted framewill be stored in memory, so the compensationcan occur by modifying the memory address-es. Finding the motion vectors, however is alengthy and computational process.

The variable length codes, produced by theencoder, are fed into the output buffer of thesystem. This buffer has a variable input rate,but also has a fixed output rate determined by

InIrk pxa

the bandwidth of the transmission channel.The amount of information entering the buffermust be controlled so that the buffer does notoverflow. If the buffer overflows picture infor-mation is lost, and corruption occurs.

Buffer control schemes can range frombeing very simple to extremely complex. Insimple terms, control is achieved by monitor-ing the buffer fullness, and adjusting parame-ters such as the quantisation values to maintaina steady input rate into the buffer. The systemalso decides whether or not to use frame pre-diction and motion compensation, and couldalso decide to drop the frame rate by skippingsome frames.

Problems generally occur when there is sud-den movement in the picture being encoded.Sudden or rapid movement is almost always aproblem for a number of reasons. Firstly, thebuffer level increases and can overflow. Thishappens because there is a larger frame dif-ference due to the high degree of motionbetween scenes, leading to more quantisedcoefficients.

More generally the motion compensationcan only deal with a limited amount ofmotion. The effect the viewer sees is a smear-ing on the screen where the movement isoccurring, and jerkiness in the picture is oftennoticed - especially when frames have beendropped. These are probably two of the mostannoying features in a system.

Another annoying feature is poor lip tospeech sync, where lip movement and audiooutput do not exactly coincide. This is causedby different delays for the audio and videodata through the system.

MPEG-1 and video CDMPEG-1 is an internationally accepted stan-dard for the compression of digital audio andvideo. The actual standard is an ISO-IEC stan-

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Fig. 2. Diagram of 11.261 encoder. The H.261encoder compresses video data for transmissionover ISDN in video conferencing applications.Frame prediction and differencing is used toenable compression of data to bit rates rangingfrom 64kbits/s up to 2Mbits/s. Motioncompensation also assists this compressionprocess by minimising the difference betweenthe current frame and the prediction frame.

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dard and the term MPEG (Moving PictureExperts Group) comes from the group whostarted work on the standard. There are threeparts to the standard: audio, video and system.

MPEG-1 was originally developed to pro-vide a standard for the storage of audio andvideo on digital storage media. The standardis optimised for operation at about 1.5Mbits/s.This is significant because it is the data ratefor an uncompressed cd and it is also suitablefor digital audio tape.

Typically the audio takes about 192kbits/s ofthis bandwidth, and some bandwidth is alsoneeded for the system data stream. As a result,there will be approximately 1.15Mbit/s avail-able for video.

Certain requirements in accessing storedvideo and audio have played a large part in thedevelopment of this standard. Access to thestored material is important and facilities havebeen inbuilt for random access, fast forwardand reverse, and reverse playback. The syn-chronisation of audio and video is also veryimportant and error robustness is also inbuiltinto the system.

Unlike video conferencing standards, MPEGtends to be quality controlled rather than bitrate controlled. Certain parameters are speci-fied which give a certain quality level, ratherthan, say, setting the system to operate at aparticular bit -rate such as the bandwidth of anISDN channel.

There are significant differences between theencoding process used for MPEG1 and thoseused for H.261. In H.261 for example, thereare two types of frames, namely intra and interbut in MPEG-1, there are three types.

The intra frame in MPEG, called the Iframe, is similar to the intra frame in otherstandards, and it is encoded without referenceto other frames. One difference exists howev-er: in an H.261 system it is desirable to avoidany intra coding. In MPEG however, intracoded frames are needed because they providethe points at which random access can takeplace in the decoded video.

The inter frame in MPEG is like the one inH.261. Basically a prediction is made of the

Video colour s aces and resolutionsWhen people think of colour, theusually think of red, green and blue.These are the primary colours and anyother desired colour can be obtainedby adding the required amounts ofthese primary colours together.

Since the advent of televisionhowever we have made use of the factthat the eye is much less sensitive tochanges in colour than it is to changesin brightness. So television signals aretransmitted as a black and white signalplus two colour difference signalsproviding information on how muchthe colour varies from white. Becausethe eye is less sensitive to colour, thecolour difference signals aretransmitted using a lower bandwidththan the monochrome signal.

The black and white signal is alsoknown as the luminance signal. It isusually referred to as the Y component.The colour difference signals arereferred to as the U and V componentsand they tell how much red and blueexists in a picture. The combination ofthese signals is known as the YUVcolour space. Since the total amount ofred green and blue add up to thepicture brightness, then the translationbetween YUV and gamma correctedRGB (referred to as R'G'B') can becalculated using the following matrix.

1-11 I- 0.299 0.587 0.1141FR'l

IUI=1-0.147 0.289 0.436 1 G' I

[ 0.615 -0.515 -0.1 IB'i

Note that even if the signals aretransmitted in the YUV space, it will benecessary to be able to convert back torgb for display on a video monitor.

Another important colour space isYCrCb. This colour space wasdeveloped as part of the CCIRRecommendation 601. Thisrecommendation defines the"encoding parameter of digitaltelevision for studios", and is a world

Table 1. Video resolutions for PAL originated signalsFormat Y horiz. Y vett Cr horiz. Cr vent. Cb horiz. Cb vett.CCIR-601 720 576 360 576 360 576CIF 352 288 176 144 176 144QCIF 176 144 88 72 88 72SUB QCIF 128 96 64 48 64 48

wide standard for digital componentvideo. Basically, YCrCb represent thesame colour space as YUV, but theindividual components in YCrCb arescaled and offset versions of thecomponents in the YUV space.

CCIR-601 video specifies a 4:2:2sampling format, and this means thatthere are only half the number ofsamples for each of Cr and Cb per lineof video as there are Y samples. So it istaking advantage of the fact that theeye is less sensitive to colour. In a lineof digital video sampled at 27MHzthere will be 720 luminance samplesand 360 each of the colour differencesamples.

When generating of CIF and QCIF,even further redundancy is built intothe colour difference sampling. Theformat is no longer 4:2:2, but is now4:1 :1. This means that there is one Crsample and one Cb sample for everyfour Y samples in the picture.

Table 1 gives the horizontal andvertical resolutions for CCIR-601, CIF,QCIF and sub-QCIF for. Given thatmost video coding systems will useCCIR-601 compatible video as theirdigital source, it is clear thatgenerating CIF or QCIF from CCIR-601represents significant compression byitself. Converting from CCIR-601 to CIFrepresents compression of 5:1, andconverting to QCIF gives compressionof 20:1.

The subsampling of the video signalto generate CIF or QCIF must be

implemented quite carefully. It is notsufficient to simply drop the pixels orsamples which are not required, and ifthis is done artifacts can result in thepicture due to overlap in the frequencyspectrum of the signal. As a result, aprocess known as decimation iscarried out on the video data. A similarprocess, interpolation, is usuallycarried out when upsampling CIF orQCIF data up to CCIR-601.

Decimation is a digital filteringprocess, and in such a process, thedata is usually filtered first, and thenresampled at the desired rate. In thecase of interpolation, where the signalis being upsampled, the data is usuallypadded with zeros to bring it up to thedesired sample rate and is thenfiltered. This happens in both thehorizontal and vertical dimensions.

There is a number of choices for thehardware designer who is required toproduce CIF or QCIF. The use of adigital signal processor is an option,but there are chip sets available toresample video. The GEC PlesseyVP520 is a dedicated CCIR-601 toCIF/QCIF convertor and it can alsoconvert back from QCIF/CIF to CCIR-601. Other devices for decimatingvideo are manufactured by Philips,Chips & Technologies, Brooktree,Raytheon and Harris - and others.



current frame, and this prediction is motioncompensated. The frame difference betweenthis prediction and the actual current frame istaken, resulting in the predicted frame, P.

A third type of frame is used in MPEG-1,known as the bidirectional B frame. B framesare interpolated from earlier and later I and Pframes. The way these bidirectional frames arecreated affects both the ability to randomaccess the video and the quality of that video.

The distance between I frames in a videostream affects the random access capability,while the distance between P frames affectsthe complexity of the system and the quality

of the video. Another interesting thing aboutMPEG-1 is that frames are not always sent inthe order that they are created, so the decoderwill need memory to enable the decoder toconstruct bidirectional frames. See Fig. 3 foran idea of how this happens.

Coding for broadcast systemsMPEG-1 was optimised for CD-ROM at bitrates of about 1.5Mbit/s. The international co-operation to develop MPEG worked well, sofollow-on work involved addressing broadcasttelevision sample rates using the CCIR 601recommendation. MPEG-2 was the result.

MPEG-2 is geared towards broadcast tech-nologies, and examples of where it will findapplications are catv, digital television, videoon demand and DBS. For video -on -demand,trials have been carried out worldwide andADSL networks were used in these trials.

MPEG-2 has different 'profiles' and 'levels'so its use can be tailored to a particular appli-cation. A particular profile will place limita-tions on the syntax of the encoded video,while a particular level will place limitationson parameters such as frame dimensions orsample rates.

Low level MPEG-2 involves the use of CIF

Hardware o tions for image corn ression

It could be said that design engineers arenow spoilt for choice when it comes tothe design of video circuitry. New chipsets are constantly entering themarketplace, catering for all of theestablished standards.

These chip sets are also becomingincreasingly more highly integrated. Solet us say you have just started workingon video, and you wish to design aJPEG, MPEG or H.261 circuit. Whosechips will you look at?

The diagram below shows some of theoptions your proposed system mightcomprise. Your first problem is digitisingthe video. It may need to bepreprocessed or scaled. It is then codedand stored or transmitted. After the videohas been decoded you may have to dosome post processing, ie convert fromCIF to CCIR and reconvert the signal toanalog PAL for display on a monitor.

Alternatively you may wish to displaythe video on the pc, so the video signalmust be merged with the rest of thegraphics going to the screen. I will lookbriefly at some of the options availablefor these tasks since an exhaustivesurvey is beyond the scope of thearticle.

For digitising PAL signals andconverting to CCIR-601, Philips,Brooktree or Raytheon all produceappropriate devices. These companiesnow offer highly integrated front endsolutions, such as the Philips SAA7110and the Brooktree 8t819. The SAA7110needs almost no external components,producing square pixel CCIR compatibledata, while the Bt819 allows scaling ofvideo to one -thirteenth of its originalsize. Auravision also have a number ofinteresting devices, such as the VxP501,which allows video capture with scalingand also support MPEG/JPEG playback.

For preprocessing, the GEC -PlesseyVP520 is a dedicated bidirectionalCCIR-CIF/QCIF convertor. Other devicesare available which are geared to pcvideo, such as the Philips SAA7195

video memory controller or the Chips &Technologies VideoPro chip set. Bothdevices are essentially video memorycontrollers which allow scaling of videofor windowing.

For JPEG coding, options includedevices from Zoran, LSI Logic, C -Cubeand Winbond. Silicon to support MPEG1is available from C -Cube, IC Works,SGS-Thomson, Hitachi, IIT andWinbond amongst others. For H.261,packages are available from C -Cube, IIT,GEC Plessey and Array Microsystems.The GEC Plessey chip set is a dedicatedH.261 coding/decoding chip set. ArrayMicrosystems produce the Videoflowchip set, based on risc architectures. It isone of a number of chip sets which willsupport several standards, in this caseJPEG, H.261 and MPEG-1, and uses ahighly parallel data flow architecture toallow multiple decoding when it acceptsseveral bit streams.

The IIT VCP can be used in bothH.261 and MPEG-1 codec applications,and will support MPEG-2 decoding. C -Cube has a range of devices which coverall the established standards includingthe CLM4200 H.261 codec and the

Analoguevideo - PA LINTS Cdecoder -4

CL480VCD MPEG1 system decoder. ForMPEG-2 encoding both IBM and C -Cubeannounced devices this year.

Another option for codec developmentis that of digital -signal processing TexasInstruments released their C80 this year.The C80 contains four parallelprocessing signal processors with a riscmaster processor, an integrated videocontroller and claims 2 BOPsperformance.

If a composite PAL signal is required atthe output of the system, again Philips,Brooktree and Raytheon should beconsidered, with each company havinga range of encoders suited to differentapplications. Devices which arebecoming more common in the marketnow are those which will accept videofrom an MPEG/JPEG decoder and willmerge that video with the normal pcgraphics for display on the monitor. TheAuravision VxP501 was mentioned, Itwas designed with interfaces for Zoranand C -Cube JPEG and MPEG devices.Other companies which are strong inthis area are Brooktree, PixelSemiconductors, MCT, Trident andPhilips.

Optionalpreprocessor

Analogue PA LINTS C Optionalvideo o encoder post processor

411-PC

monitorVideo manager

RAMDA C

Options -

MPEG/JPEGH.261

encoder

MPEG/JPEGH.261

decoder

Possible hardware requirements. A typical hardware video coding system will need todigitise analog video, and process that digital video using a /PEG, MPEG or H.261 encoder.The compressed video is then stored or transmitted. In PC based systems the decoded videowill be merged with the other PC graphics for display on the monitor. In a stand-alonesystem, however, the output may be a PAL signal for display on a composite monitor.



Actual picture order

2 3 4 5 6

I B B P B B

7

P

Order in which frames are transmtted

1 4 2 3 7

I PBBP5

B

6

B

I i ntra, B bidi-ectioral, P predicted

resolution with a bit rate for the encoded dataup to 4Mbit/s, while main level studio tvapplications will require CCIR 601 resolution.Most decoder chips will be capable of operat-ing at main profile, but higher profiles couldinclude features such as spatial scalability.

The syntax in MPEG-2 can be divided intotwo main categories. There is a scalable syn-tax and a non -scalable syntax.

The non -scalable syntax is structured as asuper -set of MPEG-1, but there are extra toolsfor handling interlaced video. This is requiredfor studio applications, because PAL andNTSC video sources are interlaced, i.e. twofields are interleaved to form a frame.

Typically MPEG-1 and H.261 use CIF res-olution. This is obtained by dropping one fieldper frame and and further dividing the remain-ing field. This lowering of video resolutioncauses a subsequent loss in video quality, sowhile its acceptable for pc conferencing sys-tems, it is not suitable for studio broadcast.

When handling interlaced video, MPEG-2allows a frame to be selectively treated as asingle picture. Alternatively it allows the twofields to be coded individually. It there is a lotof motion in a picture, it is generally better tocode the fields individually.

MPEG-2 incorporates all the functionsavailable in MPEG-1, such as random access,fast forward and reverse and reverse playback.All MPEG-2 decoders will in fact be able todecode an MPEG-1 bit stream.

The scalable syntax in MPEG-2 will findapplications in transmission media which donot have constant bit rate. Asynchronous trans-fer mode, or ATM, is one such application.

There are three types of scalability inMPEG-2, namely signal-to-noise ratio, spatialand temporal. Each of these scalable exten-sions uses the concept of a base layer and anenhancement layer. The lower base layer isused for a basic video quality, and the higherenhancement layer is used to improve thequality already available from the lower layer.This is useful in applications such as transferof video over an ATM network, or in generalover a channel with a variable bit rate.

An error -robust channel can be used totransmit the base layer video. However, theenhancement layer could be transmitted over achannel which was not so error robust, or waslikely to be congested. Since it is for enhance -

Fig. 3. Transmission ofMPEG 1 frames. MPEG-1 isparticularly suitable forvideo CD, and is optimisedfor operation at around1.5Mbits/s. It uses threetype of frame, Intra,Prediction andBidirectional. In order tofacilitate the MPEG-1decoder, these are nottransmitted in the sameorder as they are encoded.Frames 1 and 4 are neededto decode 2 and 3, andframes 4 and 7 are neededto decode 5 and 6.

ment only, it does not affect the basic videoquality if corrupted, or if it fails to reach thedecoder.

In temporal scalability, the base layer pro-vides a basic temporal resolution (frames persecond), and the higher layer is coded withtemporal predictions for further enhancements.The enhancement layer for spatial scalabilityprovides a coded difference signal based on aninterpolated prediction of the lower layer. Inthe case of signal-to-noise ratio scalabilityerror information produced in the encodingprocess might be used.

Video over the phoneIn March 1995, the ITU-T accepted a newstandard known as H.263. The title of thisstandard is 'Video coding for narrow telecom-munications channels at <64kbit/s'. The 11.263standard is geared toward use over the normaltelephone line. It will be possible to imple-ment it with a range of options up to andincluding use of a V.34 modem at 28.8 kbit/s.The umbrella standard for full audio-visualtransmission in this way will be H.234

It is expected that chips and products forH.263 will be available sometime next year.These products will probably be for the video-phone market, or for pc users who need realtime video communications but do not haveaccess to ISDN.

H.263 is similar to, but more complex than,H.261. Much of the work which was done todevelop the standard had its origins in theH.261 development. As with H.261, H.263uses block based methods for compressingand coding video signals.

The discrete cosine transform is used toderive frequency content information from theoriginal spatial information. Quantisation, dif-ferential coding between frames, run lengthand variable length coding techniques thenallow compression and coding. As with H.261,motion estimation and compensation can beused in the differential (Inter) coding process.

There are differences between H.261 andH.263 which allow 14.263 to operate moreeffectively at low bit rates. Firstly the pictureformat for H.263 is QCIF at 176 by 144 ele-ments or sub-QCIF at 128 by 96. Secondly thesyntax is different, and improved variablelength codes are used. The motion compensa-tion is also different, with H.263 allowing

half -pixel accuracy.A significant difference between the two

standards is the use of `13B' frames in H.263.The idea comes from the use of P and Bframes in MPEG. Basically, a PB frame con-sists of two pictures coded as one.

The P frame is similar to the normal intercoded frame in H.261. The B frame is how-ever derived using bidirectional predictionfrom the two adjacent P frames, fitting inbetween these two frames. Experimental workshowed that without significant gain in bitrate, a much better picture quality wasobtained using these PB frames.

When H.263 products actually arrive to themarketplace, it is possible that there will be arequirement for at least the decoder to bebackward compatible with H.261. This maynot present too much of a problem however,as H.261 can be seen to be a sub -set of thisnew standard.

The future - MPEG-4The standards already described all use blockbased coding. In such coding, the image isdecomposed into blocks which are encodedindependently of each other. There are sever-al problems and limitations attached to thisapproach. One is `blockiness' in the picture.Another is the fact that objects in the pictureare not defined, so a limited number of func-tions can be added to the system.

Work has already begun on a new standard,MPEG4, which will support new ways forcommunicating, accessing and manipulatingaudio-visual data. With an increasing trendtowards wireless communications, and ademand for more interactive communication,many new requirements are arising in audiovisual communications which are not cateredfor by existing standards.

One desirable feature in the new standardwill be that of content based accessibility andmanipulation. A user should be able to accessand manipulate video based on its content.This may only be possible if new schemes aredeveloped for the coding of that video.

Over the past few years, much research hasbeen carried out using advanced coding tech-niques, such as object based coding, and it ispossible that some of these techniques may beused in MPEG-4.

Because the development of this new stan-dard is at such an early stage, no specificmethod for doing this has been decided.However a desirable coding scheme will beone which can identify objects in a picture andcan track the movement of those objects.

It is hoped that MPEG-4 will enable manynew uses for multimedia, such as the retrievalof information from on-line libraries. One canimagine being able to browse through a mov-ing picture, clicking on an object in the picture- perhaps a book in a library or an item on ashelf - and being able to download moreinformation on that item.

We are however still a long way away fromthis scenario - the MPEG-4 standard is notexpected to be ratified until 1998.


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CIRL LE NO. 117 ON REPLY CARD


AUDIO

Hick powervalve audio

In this extract from hisbook Valve Amplifiers,Morgan Jones discussesways of designing valveaudio amplifiers capableof delivering more thanthe usual 10W.

While the amplifier discussed lastmonth was a good design, it has tobe admitted that 10W is not a great

deal of power, and more may be required. Thetraditional way of doing this was to use a morepowerful valve such as the EL34, or even theK7'88. Another method is to use Class AB;using these techniques, we can obtain 50Wfrom a pair of EL34 or KT66s, or 100W froma pair of KT88s. After this, we resort to trans-mitter valves at enormous cost.

The traditional method has disadvantages:

Higher powered valves are invariably dis-proportionately more expensive. They use high supply voltages, whichmakes the smoothing capacitors expensive,and the HT supply a major safety hazard. Higher powered valves tend to need higherimpedance anode loads, which makes thedesign of a good transformer difficult. Transmitter valves have savage driverequirements, and often need a power valve asa driver.

Fortunately, there are several ways out ofthis dilemma,

Lie about output power. In the late 1960sand early 1970s, some quite unpleasant audioamplifiers were made using transistors.Compared to the valve behemoths, these tran-sistor amplifiers were very small and light, butthey didn't actually sound any better. In fact,most sounded a lot worse so something wasneeded to make them sell. The one thing thatearly transistor amplifiers could do was to pro-vide plenty of power, and as a result the powerrating war started.

To make a truly powerful amplifier, a largepower supply is needed, but this is expensive.Classical music generally has peaks of only ashort duration, and few hi-fi enthusiasts lis-tened to anything else. Amplifiers weredesigned that could manage higher outputpowers, but only for a very short time. This

allowed power ratings to be increased further,and the 'music power' rating was born.

Music power works like this. Measure themaximum output power at 10% distortion orthe onset of clipping, with bursts of 1kHzdriving one channel only into a resistive load.By this means, it is perfectly possible to con-vert a 20W amplifier with a poor povSer sup-ply into a 50W model. If output is doubled toaccount for two channels, you can achieve a100W amplifier. At least four fallacies wereused in the previous

Build more efficient loudspeakers. This isan excellent solution, since inefficient loud-speakers frequently suffer from power com-pression. This is an effect whereby resistanceof the voice coil rises due to temperature. Asa result sensitivity is reduced until the coilcools down.

Drive the loudspeakers more effectively. Ifdrive units are driven by dedicated amplifierspreceded by an active crossover, many bene-fits result (Colloms, 1985). For the purposes ofthis discussion, it is sufficient to say that a twoway loudspeaker system, driven actively by10W amplifiers, will go surprisingly loud.

Parallel output valves. This solution pro-vides many advantages. If multiple pairs ofparalleled output valves are used, HT voltagecan be kept within safe bounds. This is thecase even at 320V if many pairs of EL84 areused.

With each additional pair of valves, thetransformer primary impedance falls, as doesthe turns ratio. This makes it easier to design agood quality component. Statistically, totalanode current per side is better balanced as thenumber of valves is increased. Deliberateselection will improve this still further.

Driving higher power output stagesWhether they are composed of paralleleddevices or not, higher powered output stages

ELECTRONICS WORLD February 1996

AUDIO

always require more driver circuitry.When the Williamson was investi-gated - EW+WW December 1995 -it was found that it had a dedicateddriver stage. However, the large totalnumber of stages made stability aproblem. Clearly, a better approach isneeded. As before, listing the require-ments will help solve the problem.

A low output impedance to drivethe increased input capacitance of theoutput valves - a cathode followermay be needed.

Capability for providing a largeoutput voltage with low distortion.This invariably demands some formof a differential pair.

Input0

.C4 Ill.T T r T

188C1

6SN7

IMO

Wide bandwidth and high gain arealso desirable. This is because itwould be preferable to use just oneset of coupling capacitors, ensuring ifstability. A cascode would be ideal,although a carefully designed pair of dc cou-pled differential pairs could be even better.

Putting these requirements together resultsin a cascode differential pair with direct cou-pled cathode followers. This design is some-times known as the Hedge circuit after its

4700

I MS -2

411 V 22 kg2 HSA2547nF I IFKP/1\I 7 450V I

471d2 47k0 33 ki2

HSA25 - HSA25 HSA25

102.5V

382V

31(51

A=17E 1 82CC

BC549

BC549

Feedback

0

27052W21

5600W2I

red LED

-12.6V

HT

22LOWH25

22 1(52

WH25

II -

original inventor, although the originalHedge circuit did not include cathodefollowers (Hedge, 1956), Fig. 1.

The differential pair is not the idealphase splitter, so extra care will betaken over this in order to obtain agood result. Anode load resistorsshould be matched, and generouslyrated to avoid drift. The constant -cur-rent sink should be made to have ashigh an output resistance as possible.Also stray capacitance to ground fromthe cathode should be minimised to

IH maintain a high impedance at high fre-quencies. Matching valves would beuseful if possible.

Each pair of valves requires a sepa-

OVrate heater supply. Sad, but true.Cathode followers need around 200V

-12.6V

Fig. 1. Cascade differential pair with directcoupled cathode followers. Sometimesreferred to as the Hedge circuit, this designdiffers because of the inclusion of cathodefollowers.

700V

superimposed on their heaters. Theupper pair of the cascode needs around100y, and the lower pair OV. Flirtingwith this rule will generate problemsrelated to heater cathode insulationbreakdown. Emission from the heater

to the cathode will be summed with the inten-tional cathode current. You have been warned.

The place to slug the dominant pole is at theupper anodes. Theoretically, a capacitorbetween the anodes does the job. In practicehowever, individual capacitors are necessaryto ensure gain roll -off.

+700V@37 mA

47nF47µF FKP1

11 33 ki2

HSA25220nFFKP1

47k52 750F 1=1111

47052

A=29E88CC

382V

75pF

47052

102.5 V

2700W2I

5600W21

-12.6V

14700

1/2 El 82CC

68100.1%

68100.1%

red LED

I I2V

I

KT88

220nFFKP I

1 kit1-+

I 001(S2 1

8.2 k51

8.2 kit

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KT88

Output transformer4k (a -a)

5600Fig. 2. Balanced input amplifier using a differential pairwith balanced feedback. This is injected into eachcathode via the introduction of a small resistor in serieswith each cathode and the constant current source.

Fig. 5.33 Balanced input amplifier using differential pair and balanced feedback

O

O+485 V@200mA

O

30Winto

80

O

0 OV

0 12.6V


AUDIO

As mentioned before, the only really satis-factory valve for use as the lower valve in acascode is the E88CC. Any other type willwaste ht.

Cathode voltage on the lower valves is usu-ally quite low, typically around 2.5V. This isinsufficient to allow a constant current sink tooperate linearly. For this reason, the tail of thesink is usually connected to a subsidiary neg-ative supply.

Feedback from the output can be applied toa grid, which makes calculations of the feed-back network much easier.

Power amps - a balanced alternativeAll of the amplifier designs discussed so faraccepted an unbalanced input signal presentedto the phase splitter. This generates a balancedsignal to drive the push-pull output stage. Ifthe pre -amplifier output is already balanced,there would not be a need for a phase splitter.Transmission of the signal from the pre -ampli-fier to the power amplifier in balanced formwould give a great advantage in rejection ofinduced noise.

The only possible contender for a balancedinput stage is the differential pair. But sincethe input signal is applied to both grids, weneed to fmd a means of implementing globalnegative feedback. The solution is to add asmall resistor in series with each cathode andthe constant current source, and inject a bal-anced feedback signal to each cathode, Fig. 2.

Cathode resistors reduce the common modeperformance of the differential pair becausethe cathodes are no longer tied tightly togeth-er. Because of this their value should be min-imised -a 4752 resistor is probably the lowestpractical value.

Having set the value of Rk, resistor RF canbe calculated. Fortunately, this calculation isnot nearly as traumatic as that for the IOWamplifier, because the constant current sourcetakes care of the dc conditions. Since each Rkcauses such a small amount of local feedbackit can be neglected.

If valve balance were perfect, there wouldbe no signal voltage at the top of the constantcurrent source. Therefore this can be treated asbeing at ground for the purposes of the fol-lowing calculation. Output of the amplifier isno longer firmly ground referenced, and bal-ances itself about the notional ground of theconstant current source. Each leg of the outputcan therefore be treated as a signal, referred tothis notional ground, of half the full outputvoltage.

The feedback Rk, RF combination is a sim-ple potential divider where the lower arm isloaded by the valve's rk, and the input signalto the divider is half the full output voltage ofthe amplifier. The required value of RF cannow be found using the normal feedbackequation and the potential divider equation,without having to invoke Kirchhoff. However,it is essential that these resistors are accurate-

ly matched to avoid unbalancing the circuit.Resistors with a 0.1% tolerance are recom-mended.

The disadvantage of this arrangement is thatthe output of the amplifier now has the cath-ode voltage of the input stage superimposedon both its output terminals. This will not mat-ter to the loudspeaker, even if the cathodesare at slightly different potentials. This is dueto the small cathode voltage being heavilyattenuated by the potential divider formed byRF and the loudspeaker voice coil. Also, prac-tical values of RF would reduce the likely off-set to 10mV or less. However, it does meanthat neither output of the amplifier may beconnected to ground, because this would upsetthe bias of the input stage.

Further readingColloms, M, 'High performance loudspeakers',3rd edn. Pentech Press, London, pp. 188-206,1985.Futterman, J, 'A practical commercial outputtransformerless amplifier', Journal of the AudioEngineering Society October 1956.Hedge, L B, 'Cascade AF amplifier', WirelessWorld, 283-87, June 1956.Mullard, 'Tube Circuits for Audio Amplifiers',reprinted by Audio Amateur Press, Peterborough,New Hampshire, 1993.Williamson, D T N and Walker, P J, 'Amplifiersand superlatives', Journal of the AudioEngineering Society, 2(2), 75-80, 1954.

Valve Amplifiers BOOKSValve amplifiersClassic power amplifiers is just one of the subjects covered in anew book entitled Valve Amplifiers, from which the abovearticle is extracted. With over 370 pages, Valve Amplifiers iswritten by Morgan Jones and covers,

Circuit analysis Basic building blocks Components Power supplies Power and preamplifiers Construction Safety

Valve Amplifiers is priced at £25. Please add postage at £2.50UK, £5 Europe or £7.50 worldwide. Send your request with acheque or postal order made payable to Reed BusinessPublishing Group Ltd, to Jackie Lowe, Room L333, QuadrantHouse, The Quadrant, Sutton, Surrey SM2 5AS. If ordering bycredit card, please quote card type, number and expiry datetogether with card -holder address. Post your order, fax on0181 652 8956 or e-mail it to [email protected].


Reference books to buyFor Audio Engineers

.1 111011,111111

AudioEngineer's

I:1111;1 \I I 1:11111\

Comprehensive- over 600 pages

Written by leadingauthorities from theaudio world

Easy to read, compiled formaximum accessibility

Concise and authoritative Covers topics from noise

measurement to studioinstallation

Subjects includeRecording, microphones

and loudspeakers

Digital audio techniques

Basic audio principles

Acoustics andpsychoacoustics

Audio and televisionstudios and their facilities

Radio and telephony

Invaluable reference work foranyone involved with audio -from broadcast consultant toserious enthusiast. AudioEngineer's Reference Book iswritten by an internationalteam of experts and edited byMichael Talbot -Smith -previously a trainer of audioengineers at BBC Wood Nortonand now a freelance audioconsultant and technical writer.

For TV & Video Engineers

Over sixty chapters on thelatest techniques in videoand television

Up to date reference on EMCrequirements, DBS and HDTV

Easy -to -use reference,eminently suitable forstudents

Topics range from materialsand construction to medicaland defence applications oftelevision.

Subjects includeFundamentals of colour TV

TV studios

High definition TV

Satellite broadcasting

Distribution of broadbandsignals

TV receiver servicing

Video and audio recordingand playback

Teletext

The W & Video Engineer'sReference Book will be ofimmense value to anyoneinvolved with modern tv &video techniques - in particularbroadcast engineers. The newformat makes it an excellentreference for students.Edited by KG Jackson and GBTownsend from contributionswritten by acknowledgedinternational experts.

Please supply me copies of theAudio Engineer's Reference Book,(ISBN 0 7506 0386 0)

Fully -inclusive price - UK £62.50, Europe £68, Worldwide

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COMPONENTS

&CarrierLock Off (1)

Michael Cox has beendesigning with a highlyintegrated solution tosync pulse generationand video genlocking -the SAA1101.

Table 1. Operating modes of the SAA1101are selectable via three logic levels..

X Y Z SYSTEM1 0 1 PAL B/G1 0 0 SECAM0 1 1 PAL M0 0 1 PAL N0 1 0 NTSC

+5V

5 MHz Osc

H Phase Comparator

External Svnc/

Field Reset

(dent Reset

Locking ontovideo sync

In any video system in which two or morepicture sources are to be combined - say,for mixing or special effects - the scanning

generators of the picture sources have to besynchronous. This means that the scanninglines must start and finish together both acrossand down the screen.

If the system is a composite colour one, thenthe subcarriers in PAL or NTSC must havethe same frequency and phase, to within adegree or two. In addition, in a PAL system,the positive and negative line alternationsequences have to be identical.

In older systems, a central sync pulse gen-erator was used, giving timing signals to allsources. More recently, each source carries itsown timing generator, which needs to be ref-erenced to other sources in the system. Thisprocess is known as genlock.

The design described here produces multi -standard line, field and composite sync pulses,all genlockable to an external composite -videoreference.

CHROMA ERROR

+5V

FSI 1 28 VDDFSO ZCSI rcso xOSCI CLOOSCO NORMVLE HDPH VDLM1 18181P

LMO CLPECS CS

RR CBSI BKVSS(OND) 151D

SAA1101

0 .5GND

SYSTEMSELECTLINKS01+6V

HonzDrive

Vert.Drive

MixedSync -

7 8KHz

(PAL SW)

MixedBlanking

BurstFlag

Fig. 2. Connectionsto the SAA1101simplified.Operating with just10pA quiescentcurrent from asingle 5V supply,the device canhandle input clocksup to 24MHz.

VCOClock5 MHz

ECS

Ph.Comp

divider

-/160

V Reset

Sub -carrierto Fh

dividers-/2,./625

Subcarrier VCXO

SAA1101dividers

H

V

Fig. 1. Dividers within the SAA1101 allow notonly separate and composite sync pulses to begenerated, but also allow pulses to begenerated for different tv standards.

The SAA1101 sync generatorAt the heart of the sync generator board is arelatively new chip known as the SAA1101,Fig. 1. It is a 28 -pin device, available in 0.6inspacing dil, or in small -outline sm package.

As Table 1 shows, by taking pins X, Y andZ to OV or to 5V, Fig. 2, the device can bemade to work in PAL, PAL M (Brazil), NTSCand SECAM. In addition the device can oper-ate in 524 or 624 line sequential mode for nonstandard use, by taking a pin (NORM) to +5V.

It can be set to maintain the frequency rela-tionship between subcarrier and horizontal fre-quencies, or not. This allows the subcarrierand horizontal oscillators to be locked sepa-rately which speeds up the genlock process.

GenlockingThere is a wide requirement for a genlockingsynchronisation generator. Any source, be itcamera, video -disc player or test signal gen-erator, may need to be lockable to an externalreference signal.

A broadcast synchronisation generator in astudio may need to lock to an external sourcesuch as an outside broadcast. The locking pro -


COMPONENTS

0 00 1

1 01 1

cess must therefore cause minimal disturbanceto viewers.

Normally, horizontal and subcarrier fre-quencies need to lock almost instantly, whiletwo lines per field are dropped or added untilcoincidence of the vertical sync block isachieved. This method is rarely used nowbecause of the almost universal use of framesynchronisers at studio inputs.

In a piece of equipment that is fed a refer-ence signal all the time, it is acceptable toreset the vertical counter to achieve rapid fieldcoincidence, Table 2. This philosophy isadopted in this design.

Design detailsThe starting point for the design is the type ofreference signal that is to lock up the syn-chronisation generator. In this case, it has tobe a colour composite signal. In practice, it isusually colour, black, which is 300mV sync,with colour burst but no video.

Refer to main circuit p117. Video input goesto a sync separator IC, the familiar LM1881.Note that it is driven by an emitter followersince it has a sync tip restorer that needs to bedriven by a low impedance source.

The device also falters if the input, for what-ever reason has low level sync, and a highlevel of burst. It slices the burst as if it is syncand causes chaos downstream of the separator.Hence a simple low pass filter has to be fittedto roll off the chroma before the separator.

Driving impedance requirements dictate thatthe filter is placed at the emitter followerinput, and R3/C33 form the filter. The separatorproduces a mixed sync output, and a clamppulse output suitable for colour burst gating.

Vertical output is not so useful as its leadingedge corresponds to the first serration in thebroad pulse train. This comes too late to resetthe field counter in the SAA1101 synchroni-sation generator chip.

Schmitt buffer U2, a 74HC14, inverts thesync signal to drive the ECS input pin of theSAA1101. Another section of U2 integrates thesync to produce a field pulse whose leadingedge occurs during the first broad pulse.Differentiating then produces a pulse ofaround 21.is width. These pulses also feed thefield reset pin, RR, of the SAA1101.

Internal countersThere are two sets of counters in theSAA1101. The first divides the 5MHz clock tohorizontal (15.625kHz for PAL) and vertical(50Hz for PAL) pulse trains. The seconddivides from subcarrier (4.43361875MHz) toFh. This is then compared with the Fh derivedfrom the 5MHz clock to produce an error sig-nal which corrects the 5MHz clock until lockis achieved. Table 3 shows clock frequenciesavailable by programming SAA1101 inputsCS 1 and CS2.

Table 2. SAA1101 modes.LMO LM1 Lock Mode

Subcarrierslow, ext H refslow, int H reffast, int H ref, V reset

Table 3. SAA1101 clock frequencies.CS CS Fck 625 lines 525 lines0 1

0 0 160 2.500MHz 2.5178420 1 320 5.000 5.0349641 0 960 15.000 15.1048931 1 1440 22.500 22.657340

When the synchronisation generator is freerunning, overall stability is that of the4.433MHz crystal oscillator. When it islocked, stability is that of the reference signalused for locking. Two pins on the SAA1101chip, LM0, LMI, select the mode of operation,Table 2.

To engage the subcarrier to horizontal lockmode, both Llio and LM1 need to be takenlow. When a reference signal is present, adetector circuit takes L140,1 high, invoking thefast sync lock mode.

Because the slicer input of the separator chiphas a sync tip restorer, absence of input makesthe output go low. In the ordinary way, thisleaves the ECS pin high. This is not a recom-mended operating mode, as it causes thedevice to continually slips fields. Accordingly,a resistor and diode, driven from the syncdetector, clamp ECS in the low state whenthere is no locking input to the sync generator.

There are two possibilities for the 5MHzclock oscillator - crystal control or LC timing.For speed of pull in, the LC type was chosen.The SAA1101 carries two separate oscillators,both equally suitable for crystal or LC stabili-sation, Fig. 2.

The internal phase comparator of theSAA1101 is an edge comparison type, with anoutput dc of 2.5V.

Because a +5V rail was available, a dc -to -dcconverter is used to generate a -5V rail for theerror amplifiers and chroma demodulator cir-cuits. Error amplifier outputs can then sit at anominal OV, with the varicaps' other electrodetaken to ±5V as necessary.

For the 5MHz clock oscillator, an erroramplifier is used, to act as a level shifter fromthe PH output pin to varicap D1. It also pro-vides a convenient point for a phase control.The error signal injects dc into the error ampli-fier, U88, and shifts the sync edge timing plusor minus a few microseconds relative to thereference input. This is an essential functionfor integrating a camera or other video sourceinto a practical system.

Smoothing of the error signal is carried outby a CR network on the PH pin itself, and by adamping network on the error amplifier feed-back loop. Variable inductor L5 is set for cor-rect frequency working, and then finely adjust-ed to give OV on the H -Error test point.

Chroma recoveryIn years gone by, various tv receiver chipswere available that would serve as subcarrieroscillators, phase -locked loops and identifi-cation recovery circuits. Sadly, it is now dif-ficult to find such chips where subcarrier andPAL identification are available to the outsideworld.

As a result, we have to revert to first princi-ples. The input reference signal is buffered by

Fig. 3. Limited chroma. In this design, chromain the active line is not so important, but aconstant -amplitude burst is useful.

Fig. 4. Chroma, demodulated using U axiscarrier.

+V

-V

Sampled Demod output

To error

Sample aC12 amp

Fig. 5. PAL switch recovery basics.

Fig. 6. Recovered PAL switch signaL

an emitter follower and drives a very simpleband-pass filter, L i/Cio. This removes mosttraces of luminance. Chroma output is thenamplified by an NE592, U5, and limited bytwo schottky diodes, D6,7, Fig. 3. We are notinterested in the chroma during the active line,but a constant amplitude burst is useful.

The limited chroma signal is now demodu-lated by an MC1496P, U6. Its carrier isderived from the oscillator within theSAA1101. Recovery amplifier, U8A, delivers


COMPONENTS

baseband demodulated chroma to a samplegate, U7, Fig. 4. Note that the recovery ampli-fier and error amplifiers are all sections of aquad BiFet op -amp, in this case, a TL084.

The only reason for this choice is that theyare cheap, they are reasonably easy to comeby - and they work. The sample gate is anMC4053.

Output from the demodulator consists ofalternate positive and negative burst pulses,together with any active chroma during linetime. The gate is turned on during burst time,and storage capacitor, C12, has a 7.8Hz squarewave on it, Fig. 5.

Fig. 7. Horizontal phasing - cancellation ofsync on locking input by sync out from thesync generator, using the A-8 display on anoscilloscope.

Fig. 8. Vector scope trace - subcarrier fromsync generator is reference, and signal islocking input.

Fig. 9. Prototype sync generator and genlockboard.

Error amplifier, U8D, amplifies this further,and drives the varicap that pulls the subcarri-er crystal oscillator into lock with the externalreference.

As there is a large amplitude square wave atthe chroma-error test point TP4, Fig. 6, this isdifferentiated, sliced by U8c, and used to steerthe sync generator chip into coincidence withthe PAL identification sequence of the refer-ence input.

Subcarrier oscillator output is buffered by asection of another schmitt buffer, U4c, andthen filtered by an LC circuit to give a sub -carrier output. Buffer output is also used todrive the chroma demodulator. In this way, theoutput subcarrier phase is related to that of thereference.

Pulling the LC filter circuit either side of res-onance provides a simple means of varyingsubcarrier phase over a range of 180° or so. Asimilar adjustment to L1 (input chroma filter)although not highly recommended, will allowfurther adjustment.

Output stagesMy application required negative going puls-es at nominal ttl level. As the SAA1101 out-puts are all positive going, a schmitt invertingbuffer such as the 74HC14 is ideal.

Because the lowest possible clock frequencyfor the SAA1101 is 2.5MHz, waveformsderived from it can only be in multiples of400ns. The CCIR specification for mixed syncwidth is 4.7ps, whereas the SAA1101 gives4.8ps. As sync is the most critical component- and the most easily measured - it is goodpractice to try to get it into the middle of theallowed range.

The diode/CR network between the mixedsync output of the SAA1101 and the outputbuffer delays the leading edge of sync byabout 100ns, while doing nothing to the trail-ing edge. The result is a centre tolerance syncoutput of 4.7ps.

As already mentioned, the 74HC14 makes agood subcarrier driver. By using capacitor tapson the resonant circuit, subcarrier output isseveral volts into low impedance.

Testing the prototypeIt is necessary to check the functioning of thelocking circuits. Check first that the two oscil-lators on the chip are running, and at roughlythe right frequencies. It helps to have a dual -trace oscilloscope of at least 20MHz band-width, and a vectorscope with external sub -carrier reference input.

Keep one trace of the 'scope on the lockinginput, and look at the H error test point withthe other. Adjust L5 until the oscillator comesinto lock, and then set it finely to give OV atthe test point.

Move to sync output, and set 'scope to A -B.It will be necessary to invert channel 2. Theobject is to cancel the sync on the locking sig-nal with that from the synchronisation gener-ator.

The H phasing control should be adjusted tobring the two sync signals into time coinci-dence when one sync cancels the other, Fig. 7.

Due to differences in rise times between thesignals, small 'ears' may be seen at the edges,but when these are symmetrical, coincidencecan be assumed.

Return 'scope to normal two channel work-ing. Next, check the `Demod Chroma' testpoint. It should bear some resemblance to thewaveform shown, Fig. 4.

Move to the `Chroma Error' test point,where a square wave at 7.8kHz should beseen. Set VC1 to make waveform symmetricalabout OV. Connect the subcarrier output to thevectors cope reference input. Loop the syncgenerator locking signal through the vectorscope channel 1 input.

It helps if colour bars are used for the lock-ing signal, as phase relationships can be seenclearly on the vector display. Check that

Components for the whole sync generator andgenlock circuit.ReferenceC2,3, C5, C9, 029.30R2

R3

R4, Rio, R25, 834.35,

R50-52, R56

C6

R7

Rg, R20,21, R26, R29-31,R36, R43

C7,8, C4

R9, /31, R45, R53, R59

R,1, R6

01,2

1.12,114

U3

R12-16, R42

C10, C15

R18,19, R22, R46, R60R23, R25

R24, R,7, R27, R32.33R38

VC1,2

R39, R37, R48A9R40, R5

R41, R47

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U6

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C25

04, 01, DIA

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023

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4k782pF, ceramic560k

lkO1 pF/35V tant

10k

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100pF ceramic2k2470R220R1k2

5-65pF, Murata ceramicIMO470k22kNE592, Philips,LM1496P, Nat Sem/PhilipsMC14053B, Motorola/HarrisTL084, Texas, etc4n750k, 3/sin sq cermetBAT81, Philips22pF, ceramic47pF, 16V radial100pH, axial,1nF, ceramic10pF, 25 v radial680815pH, Toko, 7mm variable3k3470nF, poly, 0.2in pitch470pF, ceramicBB809, varicap220pF, ceramic100k47nF, poly 0.2in15pH, axial47pH, Toko, 7mm variable,5MHz, 30ppm, 30pF,IQD, EuroQuartz(if L5 not used)led, red, 3mm12pF, ceramic10pF, ceramic2n2, poly, 0.2in pitch39pF, ceramic47pF, ceramic1N4148

X2 4.43MHz, 30ppm, 30pFAll resistors are 1%1/.41,9 metal film, (MR25)

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GENLOCK SPG FOR CTC-3X CAMERA

Size Document Number 3XSPG.SCH

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0 0Date:

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1

COMPONENTS

adjusting the core of L3 rotates the vectorscopedisplay, Fig. 8.

If a PAL coder is available, use the syncgenerator to provide all its service signals, andthen try to cancel the output waveform withthe locking input using the 'scope in A -Bmode. If it proves impossible to cancel theburst part of the signal after adjusting the sub -carrier phase, the PAL identification sequenceis wrong.

It is worth switching the coder on and off afew times to check whether there is a randomPAL sequence, or that it is always wrong. Arandom sequence suggest that the 7.8kHzrecovery circuit, Ugc, is not operating cor-rectly, and needs some attention.

ImplementationThe prototype board was a double -sidedboard, 3.1in by 5.5in, with a double -row 10 -pin 0.156in pitch edge connector.

This defined the size and connections to thereplacement. From Fig. 9 you will see thatthere is adequate space for all the circuitry, ona single pcb, without having to resort to sur-face mount components.

Lack of a negative rail in the wiring to thesync generator dictated the use of a NewportNME0505S dc -to -dc converter to provide afew milliamps at -5V for the op -amps andtransistor tails, U9 on the main circuit p117.

The complete circuit diagram of the syncgenerator card is shown on page 117.

Developing the generatorFor use in a broadcast videotape editing envi-ronment, it may be necessary to pay attentionto Sc/H phase.

In a PAL signal, subcarrier dot structurerepeats over eight fields. In most applications,it is only necessary to respect the four fieldsequence which is defined by the 7.8kHz PALidentification waveform.

For animation, or where invisible edits areneeded, it is necessary to pay attention to thephase of subcarrier with respect to the leadingedge of sync on line 1 of field 1. When thisrelationship is within ±20°, sideways motionon cuts is reduced to a minimum. To achievethis, it is necessary to have a further phasecomparison circuit to sample subcarrier phaseas stated, and to apply a correction to the Herror amplifier.

In some cases, a high degree of subcarrierstability in the free running, i.e. non-genlockedmode may be needed. Most crystals boughtoff the shelf are cut (AT) with a temperaturecoefficient that is approximately zero at 25°C.

If the board is in an environment that getsappreciably hotter, then the temperature coef-ficient gets larger, and the crystal drifts everfurther off frequency. Temperature compen-sated crystal oscillators, tcxo, are available,but usually on extended delivery.

The other solution is to use or make a crystaloven. The crystal has then to be specified towork at 50°C or 75°C, and will be cut to give

approximately zero temperature coefficient atthat temperature. It will be power hungry -perhaps requiring several watts - and will takesome time to reach a stable temperature.

Other outputs available from the SAA1 1 01 ,

not used here, are, clamp pulse (sync tip) 7.8kHz square wave. white measurement pulse.

In summary, the SAA1 101 is a significantimprovement on its two -chip predecessor, butit is not a real one -chip synchronisation gen-erator, However, it is unlikely that a true one -chip solution would offer the same designflexibility.

Further reading.Specifications of the world television systems canbe found in a CCIR document, published by theInternational Telecommunications Union (ITU) inGeneva.

Details of the NTSC system can be found inSMPTE Standard 170M, obtainable from,Society of Motion Picture and TelevisionEngineers, 595W. Hartsdale Avenue, WhitePlains, NY 10607, USA.

Details of the UK PAL I system can be found in"Specification of Television Standards for 625line System I Transmission in UK", published1992 by the Radio Communications Agency.Full details of the SAA1101 chip will be found inthe "Desk Top Video Handbook", published byPhilips Semiconductors.

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PC ENGINEERING

ModellinocabBen Duncan demonstrates

how the behaviour ofaudio loudspeaker cablescan be simulated withincreasing realism at audiofrequencies.

Most circuit simulators include atransmission line part. Themore sophisticated ones offer

several i . But for cable lengths below afew hundred metres at 200kHz, andpro -rata greater lengths at lower fre-quencies, cables do not behave liketransmission lines2. Traditionally, per-formance has instead been modeled bya lumped network.

Lumped modellingFigure 1 shows the simplest plausibleR -L -C lumped model, applied in threeseparate test circuits. Left and right ele-ments are arranged symmetrically. Thisis done to approximate the fact thatsubstantial cable capacitance is not nor-mally experienced without some seriesresistance, esr, and inductance of theorder of 1pH/m. These parasitics aresimilar to those found in a real capaci-tor.

Also, for simplicity, the model is a`half section' where parasitic values inthe return side (lower) have been 'fold-ed -around' into the send side. Overall,the sum of R, is the total measured val-ues of the send and return resistances ina real cable. This was a 2m length of2.5mm2 two core PVC insulated flex,as is commonly used for connectingmedium to high power amplifiers tofull range and bass speakers. But theinductance is defined differently, as thesend and return inductances at leastpartly cancel. Effective series induc-tance, ESL, is the same as transformerleakage inductance, and the total 2pH issplit either side of the capacitance,which is simply the measured value.

In this test setup, the sine source'soutput impedance is set at 1p52, so it

can drive the three loads with negligibleinteraction. On the right, these are a5.652 resistor, which is the resistive por-tion of a nominal 85I speaker; then a15in drive unit. In this macro, voicecoil resistance is external - so it couldbe stepped. The third load is a macro ofa typical two way speaker with passivecrossover.

Figure 2 is a magnified view of thefrequency response at each end. Thetop plot confirms that the response atthe source is flat. Below, the otherlargely flat response is into the resistiveload. At hf, it shows how the cable actsas a low pass filter, coming in above10kHz. This kind of response is oftenseen in catalogues for shielded cables.The response across the speaker modelsis more wild, and is a reflection of eachspeaker's impedance modulus.

With the 2m of cable, the broadestvariation is quite subtle at 0.13dB. Ifthe same cable was ten times longerand/or if two cabinets were wired inparallel, or if the resistance was higher,

Fig. 2. Effects predicted by thelumped model as seen on a ±-0.1dBscale. On the right, the 811 resistanceand two-way speaker cause hf rolloff, incisive enough to be obviouseven on a larger decibel scale. Theloudspeaker frequency responses arejust evident.

You can see that the 15in bassdriver resonates at 33Hz, and thetwo way speaker's bass driver isdoing the same at 73Hz. At 4kHz, theIf/hf crossover point is clear from theabrupt phase, followed by a steepinductive rise. Above, the cable's lowpass filtration cuts in.

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Fig. 1. Working in MicroCAP IV, the sine source on the left islike a test power amp with infinite current and VI outputsource impedance, so it can drive into three different loadsdown three cable models without its output voltage beingsignificantly modulated.

In the centre are three identical lumped speaker cablemodels, based on 2m of mains cable. These are connected to(top) the resistive part of an 80 driver; a model of a 15in bassdriver; and (bottom) model of a two way hi-fi speaker. Insidethese macros are Ic L, and Cs that closely simulate the sweptimpedance characteristics.

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PC ENGINEERING

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Fig. 4. Simulation permits differential measurements acrosslengths of cable that would be difficult or impossible inrealspace. Here, the shark fins indicate the leading -edgeenergy in the pulse that appears across the cable - not thespeaker.

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Fig. 5. The test condition is as Fig. 4, but the signal is a sinewave burst, stopping at 2ms where it is at OV. Due to phaseshift in the cables, the signal at the speaker end at this instanthas not reached OV.

The lower graph shows the ensuing losses and dampingbehaviour across the cable with a log (transient dB) scale. Thevoltage scale represents current. While smaller than the largesignal level (the 'barndoor'), these errors are in a sense infinite,relative to the zero volt stimulus.

the response variation would be muchmore prominent. Modelling can comeinto its own to demonstrate this. Thisplot highlights the fact that the penaltyfor inadequately low resistance - andinductance - cabling is not just powerloss but also the superimposition of aspurious frequency response deviations.

For Fig. 3, the sine source is changedfor a +10V pulse with a 1ps risetime,top left waveform, and transient analy-sis selected. The signal at the load end(offset slightly for clarity) is surpris-ingly well damped into the two-wayspeaker model, lower panel. This isbecause the speaker being modelled hasa Zobel network across its input, whichhelps to make the loading appear resis-tive at high frequencies. Comparisonwith the 5.60 load resistor's responsesupports this. The 15in bass speaker hasno Zobel network. As a result it is dom-inantly inductive at the 1ps rise timeperiod (reciprocal of 1MHz), and thereis accordingly a small parasitic oscilla-tion, confirmed by smaller timesteps.

Differential testingIn Fig. 4, the test signal is identical, butthe measurement condition is now dif-ferential across the cable. As a resultyou can see a representation of the cur-rent drawn, both into the load and intothe cable capacitance, and also the sig-nal that is abstracted by the cablebefore it reaches the speaker.

Differential testing is physically dif-ficult to perform meaningfully withunshielded, speaker cables of anylength. There is a risk of measuring rfcontamination. Looping back the cable -under -test for short, noise free sensingconnections also requires great care toavoid altering the cable's behaviour. Inthis simulation, the incoming signal isshown again in the top panel, as a tim-ing reference. Now you can see that theerror signal across the cable is practi-cally the same for the 80 resistor andthe two way speaker connections. Theerror for the bass speaker is muchsmaller as the inductance draws so littlecurrent on a pulse. As before, the oscil-lation tells us some of the parasitic ele-ments are resonant.

In Fig. 5, the test condition is thesame except that a two cycle sine waveburst has been substituted (upperpanel). In the lower panel, the timescale is a magnified portion. A log scalehas been selected so the behaviour canbe seen over a 100dB range (fivedecades). Looking at the 'barn door'centred on 1.15ms, this is the usualappearance of a half a sine wave in log-arithmic form.

In the upper panel, 2ms is a zero voltpoint where the test signal ceases. Inthe lower panel, the same signal at thespeaker ends is not at zero volts due to

phase shift. The different behaviours ofthe currents in each cable can be clear-ly seen. With the resistive load, the cur-rent damps immediately below the 1pVlevel. The bass driver's current quicklydamps to the level represented by lmV,after which is decays slowly. With thetwo-way speaker, the current oscillatesbefore settling to the same lmVpedestal, after nearly 1 ms.

Deeper modellingThe lumped model so far is but a crudefirst order approximation. It corrobo-rates with little of what critical musiclisteners hear when different speakercables are tried. Practical speaker cablesare stranded for flexibility. In the realworld, copper soon oxidises, or formsother complex (`fractal') molecules onits surface, for example chlorides.Copper oxide is a definite semiconduc-tor. As a result each strand has a longi-tudinal diodic connection with itsneighbour. Below the conductionthreshold, the oxide, which can be justa few atoms thick, forms a high valuecapacitor.

Occasionally and randomly, strandsare shorted along the cable length, dueto handling, bending and twisting. Theonly place where the strands are posi-tively ohmically connected is at theconnectors, and then only if the wire issoldered or properly crimped. InMicroCAP IV, a series of diodes called'Oxide' were written into the diodelibrary. They have forward thresholdsin the tens of millivolt region, andbreakdown voltages that are higher buton the same order.

Speaker wires have series inductanceand yet must carry substantial peak cur-rent, commonly up to 5 or 10A and insome designs, over 100A. Music com-prises many sine waves stopping andstarting, but series inductance seeks tocounter this. Worse, above 3kHz,where transient accuracy is most need-ed, skin effect intrudes.

This is easy to visualise as highlylocal eddy current loops within the con-ductor which subtract from current flowat the interior. In turn, this forces thelongitudinal, active current flowincreasingly into the outside 'skin' ofthe wire. The outcome is an additionalseries impedance that rises at+3dB/octave. This may be viewed as`the square root of an inductor'. In thegreen plot in Fig. 6, it is modelled usingan L -C ladder network. A Laplacefunction source may be used instead,but only in ac analysis, where Laplaces'violation of causality is not a problem.

Cable insulation acts as a capacitordielectric. Most affordable cablesemploy PVC insulation, which is high-ly polar and suffers high dielectricabsorption. For this reason, PVC is not

1 20 ELECTRONICS WORLD February 1996

PC ENGINEERING

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Fig. 6. Two special 'Skin' macros were constructed using L -R laddernetworks. Each represents the longitudinal, sectional inductancebetween strands or bundles of strands, in a stranded conductor.Distances are on the order of 0.3mm section x 1m long.

Here their Z versus frequency is compared to a pure 5nH inductorwhich slopes at +6d8/octave, exactly twice the rate of skin effect. Withordinary copper, skin effect can be seen coming in below 1 kHz, andbeing swamped by 'real' inductance above 70kHz. With lenving'spatented Supra ply, sectional skin effect is reduced and its onset isdisplaced over a decade up in frequency.

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Fig. 8. Effects of dielectric absorption are clear immediately after theburst sinewave signal ceases (upper panel, arrowerh. In the centrepanel, voltage across the capacitance of an ideal cable falls to OV within20ps and at a uniform exponential rate.

However, the discharge of voltage across a PVC dielectric has a dualslope and it takes at least 1ms, or 50 times longer, to come close to OV.The lowermost panel employs a log scale to show how it has onlydecayed to 33pV in this time.

used by capacitor makers. In Fig. 7PVC's dielectric absorption is modelledby hanging nested RC networks fromthe 'explicit' capacitance, which is a70pF. Each lm section has three of thesedistributed symmetrically. Figure 8compares the behaviour of PVC and aperfect dielectric.

Self -similar meshingFigure 9 is an end -on view of wirewhich shows how a stranded (or solid)conductor can be divided into annuli ofequal dc resistivity. Below, the fourannuli are transformed into arbitrary,equal longitudinal sections, where com-ing down the Y axis represents depth -

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Fig. 7. The RC networks on the right are modeling dielectric absorptionin a 0.3mm length of the PVC. On the left, a sine source is connectedvia a time switch. The point following the switch is shorted after thistime. As a result source impedance is zero. In the lower circuit, thestimulus and main capacitor are identical. Only the componentssimulating dielectric absorption are omitted.

towards -centre. Each annulusis simply in parallel at dc, but at hf,they are divided by skin effect.

The circuit fragment in Fig. 10 showsthe beginnings of a higher order cablemodel. It serves to remind us that ana-log electronics is ultimately fractal(self -similar) as elements are repeated-ly nested within each explicit R, L andC element. At the top left are the testsource and control components. Thetop line is the outside of the conductor,and the first cable section begins withthe 1pH inductance on the right of `V15'(this initial section omits skin effect forsimplicity). Thereafter LLsect.' is theseries or longitudinal sub -inductance,

Skin layer of strands

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Fig. 9. Top shows end -on view of a round, stranded conductor.Skin effect modelling requires annular sections to be mappeddown into two dimensions. For simplicity, annuli of equallongitudinal resistance, hence cross-sectional area areassumed, so the deeper sections are wider.

Lower shows the basic form of the two dimensional map.Each layer is isolated by skin effect. The kite -like device is myproposed component symbol designed to symbolise the cable'sshrinking effective ohmic diameter under the curved surface.Signal flowing through 2, 3, 4 is in parallel with the skin (1) atdc but increasingly delayed for transients.

beginning at the wire's surface.The circuitry below is deeper into the

wire, with the skin effect component, asin Fig. 6, between each layer. In seriesis the inter -strand capacitance 'Sc andthe oxide diodicity (various oxide


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Fig. 10. Realistic speaker cable modelling begins with the mesh of R,L, PVCcap macros, oxide diodes and skin effect macros seen here. The Y axis isconcentric depth, so the lowest layer, not visible hear, represents theinnermost strand. At the top left, a second speaker macro is arranged as acontrol. It receives the same test signal but free of cable.

Between the test signal (1AC) and the cable onset is a network throughwhich the cable's input is grounded after the pulse has finished. Itcomprises a small series resistor and a damped inductor, which simulatesthe output impedance of a typical power amplifier with high, globalnegartive feedback. The control speaker is grounded at the same instant.

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Fig. 12. In the lenving cable, simple patented techniques prevent diodic tybetween strands, so each mesh section is simplified. The Skin -4 macro isthe Blue (/eflying) plot in Fig. 6. One extra PVC capacitor coversincreased capacitance, while Lsect is cut by tenfold.

In a full -section model, Lsect would be unchanged in effective value,but each would be strongly mutualled to its opposite number byappending 'mutual' statements.

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15.0

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Fig. 11. Signal residue after the sinewave burst has stopped. Thepurple plot shows how signal across a speaker fed hypotheticallywithout any cable immediately falls to OV. The speaker at the end ofthe cable sections is not so favoured, blue. Initial error is about1/70th of the historic peak input signal.

This is partly due to finite damping at the amplifier output, red.The green plot looks across the cable to show its dominantcontribution. Clearly, with ordinary cable, the amplifier is loosing itsgrip on controlling the speaker's transient terminal voltage.

Transient Scope Monte Carloal

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Fig. 15. Model of lenving's Supra Ply cable correctly predicts anapproximately 20dB lower peak pertubation (-54dB arrowed, lower,where the decay angle changes). The upper plot shows that after 3.0ms,amplifier output error is of the same order or likely dominant.


PC ENGINEERING

diodes la, lb, lc). Some diodes are`wild -tied' to other layers, representinga real speaker cable, twisted andcrushed after treatment by humans.

Each layer has its own longitudinalsub -inductance, onto the neighbouringsection. The shunt resistors ensure theQ of each LLsect' is damped belowinfinity, to avoid unnecessarily pro-longing simulation. Along the top line,the cable's shunt capacitance includingthe dielectric absorption and leakageresistance, is distributed about. Sincethis, like the lumped one, is a single -ended model for simplicity, the capaci-tance is to ground. The cable comprisesfour longitudinal sections, ie. repre-senting 4m. The same Jensen two-wayspeaker model, as on the left, is con-nected after section four to ground.

Figure 11 shows the signal decayafter a three cycle sine burst. The modelis predicting a pre -referred error acrossthe cable that is 1.5% of 1V, or 1/66th ofthe peak signal level that did exist.Strictly, the error is very much higher,approaching infmity, for at least lms,and this is what sensitive listeners

notice with music, when the slurringhappens repeatedly.

In Fig. 12, the mesh values and skinmacro have been adjusted to simulatean advanced cable construction, patent-ed worldwide by Jenving of Sweden4.It has very high mutual inductancehence low loop inductance (`Lsect').Also, it is almost free from skin effectand has no diodicity. Hence it has neg-ligible capacitance between strands.These parasitics are replaced by smallresistances. Shunt capacitance is slight-ly higher but this has no ill effect ontransmitting current pulses into speak-ers; it only concerns poorly designedpower amplifiers.

Figure 13 shows how - excepting thesharp 'inductor spiking' for a fewmicroseconds after 3.00ms, which is aproblem for the amplifier's negativefeedback - the Jenving construction is`smears less'. That is, it allows a given,typical loudspeaker load to damp muchmore quickly and tidily. Events in the0-30ms period after a given musicalattack, can be highly audible, being inthe 'early arrival' window before mask-

ing room reflections arrive.Figure 14 and 15 complete the pic-

ture, confirming that ordinary cable canstore enough energy to be the cause ofmuch of the initial peaking in Fig 11.Verdict: Mr Nalty may have been rightall along5.

References1. B.Duncan, Mixed Mode Modelling,EW+WW, Sept '93.2. F.E.Davis, Effects of cable, loudspeakerand amplifier interactions, J.AES, June '91.3. M.O.Hawksford, The Essex Echo, Hi-FiNews, Aug '85, Aug & Oct 86 and Feb 87.4. B.Duncan, Loudspeaker cabledifferences - case proven, Proc.IOAVol.17, Nov '95. Also in Studio Sound,Dec '95; and Stereophile (USA), Dec '95.5. G. Nalty, 'Complex cables defyphysics', EW+WW, Jan 94

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February 1996 ELECTRONICS WORLD 2,

DESIGN BRIEF

Noteson free phasing

Needing a combination of simplicity, cheapness andvery high stability, oscillators for free -phasing electronicorgan notes make an interesting design challenge. IanHickman discusses his new solution to the problem.

practical analogue circuit design is fraughtwith snags, compromises and difficulties.These are well illustrated by the subject

of this article - keyed tone generators - suchas might be used in the two tone alarm gener-ator of an hf radio telephone or a hundredother applications.

One such application is tone sources in anelectronic organ. There are two main varietiesof electronic organ, namely divider organs,and free phase organs. Divider types use a dig-ital 'top octave generator' to produce thetwelve semitones of the equal tempered scale.All the intervals are, if not exact, at least veryclose, and of course 'set in concrete'.

Each semitone output is applied to a binarydivider such as the seven stage CD4024 toprovide the lower octaves. Advantages of thisapproach include cheapness and simplicity. Italso produces an organ which is always intune, but there are a number of snags as well.

With all twelve semitones of seven or moreoctaves available all the time, each individualnote has to be passed when the correspondingkey is pressed, or else blocked, by its ownkeying circuit. It is difficult to obtain sufficientattenuation when notes are not supposed to besounding, leading to a residual backgroundnoise aptly described by the term 'beehive'.Also, square waves contain no even harmon-ics, so some combining of different octaveoutputs for each note is necessary if a con-vincing variety of pipe -like sounds is to beachieved, adding to the complexity. This isespecially so where open diapasons are con-cerned.

However, for anyone wanting at least any-thing like the richness of sound provided by areal pipe organ, a major snag is the use ofdividers to provide the various octave pitches.For example, if while sounding middle C anoctave coupler is activated, then C' - the C

one octave above - will also start to sound.But since C was obtained by dividing C' bytwo in the first place, the two notes are lockedtogether and the octave is too perfect.

In fact, all you have done is to change theharmonic content of C: if you didn't hear the

02

Output

Fig. 1. One of the simplest audio oscillators ortone generators is based on the Wien bridge.

Fig. 2. Output of an oscillator based on Fig. 1shows little distortion.


DESIGN BRIEF

two notes starting to sound at different times,you would never know that there were sup-posed to be two separate notes sounding. Forthis reason more than any other there is still alively interest in 'free phase' designs, despitethe availability of palliatives such as phasemodulated delay lines which try to 'unlock'the various octaves.

An oscillator for free phase designsA true free phase organ needs a separate oscil-lator for each note of the rank - or for half thatnumber using an ingenious scheme for sharingone oscillator for each adjacent pair of semi-tones. This is on the premise that normalmusic does not require both to sound at oncel.For example, a flute stop would have 61 gen-erators. The usual arrangement is C - twooctaves below middle C - to C"' three octavesabove.

On an 'eight -foot rank' - so called becauseeight foot is the length of the lowest, pitchopen flue pipe of the five octaves - middle Csounds at that pitch. On the other hand on afour -foot rank, middle C would sound the noteC', and on a 16 foot rank, the note C,. To sim-ulate the richness of a pipe organ, severalranks of generators are needed, correspondingto the different stops on a real organ. Clearly,economy is a prime consideration in choosingan oscillator design, but equally important isstability. With 61 individual independent gen-erators per rank, retuning would otherwise bean endless chore.

Oscillator optionsIn the past, many electronic organ buildershave used LC oscillators, the inductor using agapped laminated core. This type of oscillatorhas the advantage of not needing a separatekeying circuit; it performs its own keyingfunction by switching the supply to the main -

R2

100k

C21n

R

1n 100k

R5

1M2

C R4R3 195k100k

taining transistor.Output is taken from a point in the circuit

where there is no change in dc level betweenthe on and off states. This avoids keyingthumps, while the smooth build-up and decayof the amplitude avoids the slightest sugges-tion of 'key clicks'. (These clicks plague manyother designs of keyed oscillators and keyingcircuits). Many such ranks are still in use, butthe size and cost of using LC oscillators pro-vides a strong incentive to seek alternativedesigns.

I decided to design a cheap simple keyedoscillator needing no separate keying circuit.Instead it only requires a single -pole normally -open switch for each key contact. Some pub-lished designs require, at each key, onechangeover contact plus two normally opencontacts. A single -pole normally -open contactis preferred to a normally closed option sincethe worst that dust can then do is to prevent anote from sounding when played. A normallyclosed contact can cause a note to be 'stuckon'.

One of the simplest possible oscillators con-sists of a Wien bridge and an op -amp, Fig. 1.Attenuation from the op -amp output to itsnon -inverting input via R1, R2, C1, and C2 isinfinite at 0Hz and infinite frequency, and aminimum of a factor of three at the frequencygiven by f=1/(27rRC), if R1=R2=R andC1=C2=C. This forms the narrow band posi-tive feedback path.

If attenuation in the broadband negativefeedback branch via R3 and R4 is less than 3:1the circuit will not oscillate. But if it is equalto (or due to the finite gain of the op -amp,slightly greater than) 3:1, then the circuit willoscillate. With no special amplitude stabilisingmeasures, amplitude of the oscillation willbuild up until limited by the output hitting thesupply rails. This causes little distortion if the

Flutestone bus

OutputSi1/4 CD4016

D

2M2

-7.5V

Fig. 4a) A keyed sine -wave generator. Using cmos switches for keying results incheapness and compactness.

+7.5V

Keycontact

SR: scaling resistor

;... .... ; .....

Output

Fig. 3. Adding trimmer potentiometer Rvpermits tuning of the oscillator withoutchanging the attenuation via the Wiennetwork - provided the resistance of the pottrack does not exceed a tenth of thereactance of C1. Ri=R2=100k.

positive feedback signal at the non -invertinginput barely exceeds the negative feedback atthe inverting input, Fig. 2.

Surprisingly, using the circuit shown, withan LM324 op -amp, there is no audible changein pitch as the supply rails are varied from±3V to ±15V.

To make a practical organ tone generator,some means of tuning is required, and this isby no means straightforward. Varying any oneof R1, R2, C1 or C2 will change the frequency,but will also change the attenuation in the pos-itive feedback path. Depending on which waythe attenuation changes, this can cause oscil-lation to stop. Alternatively it results in limit-ing so hard that the signal verges on a square -wave.

A two -gang resistor will do the job, but this

b) Output waveform is basically sinusoidal, suitable for usedirectly for stops of the flute family, upper trace. Begin andend transients are smooth and free from any incidental dcshift, lower trace.


DESIGN BRIEF

is hardly practicable on a one -per -note basis.Fortunately, as is so often the case in analoguecircuit design where only a small parameterchange is required, a little ingenuity can pro-vide the solution, Fig. 3.

If reactance of the capacitor at the operatingfrequency is ten times the track resistance ofthe potentiometer, the voltage at B will beonly 0.5% smaller than at A. Since these volt-ages are in quadrature, the voltage across theresistor will be a tenth of that across the capac-itor. However, as the wiper of the pot ismoved from A towards B, additional phase lag

Tone bus (clarinets)

From othernotes

Fig. 5a) Simple clipper circuit provides anapproximation to a square -wave forsimulating, say, a clarinet.

b) Comparing the 'square -wave', lower trace,with the input sine -wave.

c) Due to the limiting action of the diodes, theending transient of the square -wave output isextended compared to that of the sine -wave.

is introduced onto the signal fed to the op -amp's non -inverting terminal.

To compensate for this, maintaining zerophase shift from the op -amp's output to itsnon -inverting input, the frequency must fall.Due to the low Q of the RC network (its Q =1/3), a small change in phase shift causes amuch larger compensating change in fre-quency than would be the case with an LC cir-cuit.

At the operating frequency, the reactance ofC1 equals R1. So in Fig. 3, track resistance ofthe potentiometer should not exceed 10kaThis provides almost three semitones tuningrange, while a 4.7k0 pot provides over onesemitone.

A stable, tuneable oscillatorFrom my records I found that I developed thiscircuit in 1982, but I know that it has beenindependently derived by others2. It has a fur-ther advantage in that the wiper of the poten-tiometer feeds an op -amp input, ie a highimpedance. Except in the case of wire -woundtypes, the resistance from one end of a poten-tiometer to the wiper plus that from the wiperto the other end, exceeds the end -to -end trackresistance, due to wiper contact resistance.

Contact resistance is relatively less stablethan the track resistance, so tuning by makingpart of R1 or R2 a potentiometer would beimpracticable on stability grounds, quite apartfrom the incidental change in loop gain. As itis, C1, C2 can be polystyrene types, availablein El 2 values at 1% or more cheaply 2.5%selection tolerance. Resistors should all bemetal film types. Using polystyrene capacitorsand metal -film resistors, long term stability ofthe oscillators should be adequate to ensurethat only occasional retuning is necessary.

Over the temperature range 20°C to 60°C,the breadboard circuit exhibited a temperaturecoefficient of -o.02voc, using polycarbonatecapacitors. Frequency shift with change ofambient temperature can be expected to be -for all practical purposes - the same for allnotes, provided of course that the capacitorsused all have the same type of dielectric.

Designing a keyed oscillatorHaving arrived at a stable, tuneable oscillator,it remained to add a keying facility, which canbe achieved by altering the ratio of R3 and R4.This has to be effected by the key contact, butthe latter cannot be used to modify the com-ponent values directly, if - as is likely - it isrequired to add octave and suboctave couplers.These, when activated, sound the note anoctave above, and/or an octave below eachnote played.

Richness of sound is increased and, becauseof the inevitable slight departure from exactoctaves when using individual generators, cre-ates a desirable chorus effect just as in a pipeorgan. As a result, key switches should simplykey a dc control signal, instructing the gener-ator to sound when the corresponding key is

depressed. The circuit itself will be controlledby an electronic switch. Cmos switches arecheap and readily available and, like theLM324 op -amp, come four to a pack, forexample the CD4016.

Figure 4a) shows such a keyed oscillatorwhile Fig. 4b), upper trace, shows the outputwaveform, which is basically sinusoidal.Being so, it is suitable for use directly as the

From outputTone bus(Diapasons)

Fig. 6a) Circuit for adding second - and other- harmonics to the sine -wave.

b) Output of the above circuit, lower trace,compared with the sine -wave input, uppertrace.

c) Showing the fundamental at about 1.7kHz,the second harmonic about 10dB down -about right for an open diapason - and manyother harmonics. (10dB/division vertical,2kHz/division horizontal, span 0-20kHz.)


DESIGN BRIEF

02

basis of stops of the flute family. Figure 4b),lower trace, shows the starting and endingtransients. These are clean and smooth.Having no associated dc level shifts, they givecomplete freedom from key clicks and thumpsrespectively.

The note sounds when R5 is grounded viaSt, one section of a CD4016. In view of thesupply voltage rating of this device, the circuitis run on ±7V rails instead of the more usual±12 or ±15V. The 2.2Mi2 resistor of Fig. 4a)normally holds the control pin of S1 at -7V,the key contact raising this to +7V to soundthe note.

The rate of build-up of the tone depends onhow much greater than 3:1 is the attenuationfrom the op -amp's output back to its invertinginput when the key is depressed. The rate ofdecay is set by how much attenuation is lessthan 3:1 when the key is released. As a result,by suitable selection of R3, R4 and R5, attackand decay times can be separately adjusted.

Although Fig. 4a) behaves like a high Qtuned circuit, this is only because the feedbackis just too much or too little to allow it tooscillate. Where the frequency determiningnetwork has a high Q in its own right, forexample an LC oscillator, the build-up tran-sient will generally be as fast as the decay - orfaster if the maintaining circuit is heavilyovercoupled.

Creating other tone coloursWhile a near sine -wave is fine for flute typestops, waveforms with higher harmonic con-tent are needed to simulate many other pipesounds. A near square -wave, with its absenceof even order harmonics, is ideal for stops ofthe clarinet family. Figure 5a) shows a simpleadd-on circuit to provide it. One per note isrequired.

Figure 5b), lower trace, shows the 'square -wave', compared with the input sine -wavedriving it, upper trace. Due to its rathersmooth shape, the harmonics - especially thevery high ones - roll off rather faster than atrue square -wave, but it sounds very accept-able. Figure 5c) shows the ending transient,which - due to the limiting action of thediodes - is extended compared with the sine -wave. In practice, this is of no consequence,provided it is smooth, well controlled and free

Output-7.5Vs2

1/4 CD4016

C

2M2

-7 5V

TY>

33k +7.5V

Key contact(upper semitone)

+7.5V

Key contact(lower semitone)

from clicks or thumps. The ear is much lesssensitive to the end of a note than it is to itsbeginning.

For other types of sound, some second har-monic is essential, for example open diapa-sons. Being a quarter of a wavelength long,stopped diapason pipes are an exception, buteven these, if of large square cross sectiontend to show some second harmonic.

Figure 6a) shows an interesting shaper cir-cuit, originally published in an American mag-azine, and modified here with suitable com-ponent values for the available drive voltage.Figure 6b) shows the output voltage, lowertrace, compared with the input sine -wave,upper trace.

Experimentation with the relative values ofthe four resistors enables a wide variety ofwaveshapes, and hence of harmonic contents,to be achieved. However, when even har-monics are introduced, the circuit reduces thearea under positive -going half cycles morethan under the negative -going ones. Thismeans that it introduces a small dc compo-nent, which results in an offset at the keyedoutput relative to ground when sounding.

The result is a slight tendency to producekeying thump, mitigated somewhat by the factthat the driving sine -wave builds up and diesaway gradually. This effect is found in nearlyall schemes for introducing second harmonic,and the thump can be largely suppressed bypassing the output through a high pass filter.The filter need not be provided on a one -per -note basis, but on the other hand one per rankcannot be effective over the whole keyboard.

Figure 6b) type tone generator outputs cantherefore be combined on an octave basis,passed through an appropriate high-pass filterand the five filter outputs combined for feed-ing to further voicing and tone -forming filters.If passed through a high-pass circuit providingattenuation of the fundamental relative to theharmonics, a sound like a really fiery reed stopresults.

By these means, three different stop typescan be derived from a single rank of genera-tors, but of course in no way does this make itequivalent to three independent ranks.Drawing two of the three stops together sim-ply changes the harmonic content of a note. Ittherefore contributes nothing to the chorus

Fig. 7. Circuit Fig. 6 modified tosound either of two adjacentsemitones, according to whichkey is pressed. Addition of bothR6 and R7 keeps the loop gainthe same when S2 is closed,leaving the amount of clippingat the rails the same for eithersemitone (see Fig. 8a).

effect, whereas with two different speakingstops drawn on a pipe organ, two differentpipes sound for each note.

Nevertheless, it is convenient to have threedifferent tone colours available, even if draw-ing them in different combinations merelyprovides further different tone colours. In par-ticular, one output can be voiced as a veryloud stop and another as a quiet one. If theloud one were drawn, the quiet one would notbe heard anyway - even on a real pipe organ.

Cutting cost and complexityHowever simple the tone generator,therequirement for one per note per rank means alot of circuitry is needed.

The scheme of reference 1 sharing a gener-ator between two adjacent semitones is there-fore very attractive, but that used a relaxationoscillator. Changing the pitch of a Wienbridge oscillator is not so simple however, aspulling the frequency of a relaxation oscillator.This is because, as noted earlier, while chang-ing either R1 or R2 alone will change the fre-quency, it will also change the required ratioof R3 and R4.

What is needed is a way of simultaneouslychanging both R1 and R2, using -for economy- just a single pole switch, such as a singlesection of a CD4016. Here again, as theparameter change required is a small percent-age, one equal tempered semitone represents a5.9% change in frequency -a little ingenuitycan supply the answer, Fig. 7.

While the two additional resistors connectedto switch S2 will marginally increase the fre-quency of oscillation when S2 is open, valuescan be found which will cause a furtherincrease of exactly a semitone in pitch when itis closed. This occurs without changing thepositive feedback level. As a result the degreeof clipping is unchanged - compare the twosemitone outputs in Fig. 8a) - leaving the har-monic content virtually unchanged, Fig 8b).

In 8b), the semitone frequency separation ofthe two fundamentals is only just visible.However the separation becomes two semi-tones or about 12% at the second harmonic,and so on in proportion to the order of the har-monic. The starting and ending transients ofthe upper semitone are also unchanged, due tocircuit arrangement maintaining the same


DESIGN BRIEF

degree of clipping for both semitones.For experimentation purposes the actual fre-

quencies were regarded as unimportant, thesemitone shift being the essence of the exer-cise. But the two notes - in the region of1700Hz - correspond roughly to A" and A"flat. There is a small effect on the accuracy ofthe semitone change, depending on the settingof the tuning potentiometer. This amounts to a

Fig. 8a) Two sine -wave outputs, a semitoneapart.

b) As a consequence, amplitude and harmoniccontent of the circuit's sine -wave output isvirtually the same for both semitones.(10dB/div vertical, 2kHz/div horizontal, span0-20kHz.)

c) Delaying the removal of the semitone pitchchange control signal to avoid chirp on endtransient of the square -wave output whensounding the upper tone causes a hiccup inthe ending transient of the upper tone sine -wave output, audible as a slight key click.

few cents more or less than a semitone withthe tuning potentiometer at one extreme end ofits range or the other, where one cent repre-sents one hundredth of a semitone.

The two diodes in Fig. 7 are arranged so thateither of the two adjacent semitone keys willclose St. This causes the note to sound, butonly when the key for the upper note ispressed will S2 be closed, giving the higher ofthe two pitches. If both keys are pressed atonce, the upper semitone sounds. In someshared note schemes accidentally pressingboth keys together causes a totally different,unrelated note to sound.

With the optional capacitor (2nF) absent, thepitch will revert to the lower semitone imme-diately the upper semitone key is released.Consequently, this causes the tail of the noteto be at the lower semitone frequency.Strangely, this results in but the barest trace ofkey click on the sine -wave output, presumablybecause of the rapid decay of the tone, Fig.4b). However, the decay of the square -waveoutput is much slower, due to the limitingaction of the diodes, and this is clearly visiblein Fig. 5c).

On the square -wave output, the pitch changeduring the ending transient of the upper semi-tone gives a much more obtrusive key click.The 2nF capacitor suppresses this by delayingthe return to the lower pitch when the key isreleased. The optional resistor (33k) is neces-sary to control the capacitor charging current,otherwise a key click appears at the beginningof the upper semitone square -wave output.

Unfortunately, while the optional compo-nents suppress any key click on either semi-tone on the square -wave output, they create avery audible key click on release of the uppersemitone sine -wave output. This is caused bycharge injection in the switch circuit S2, fromthe control input to that section of theCD4016.

With the capacitor delaying the opening ofthe switch, it now occurs when the sine -wavehas all but died away. As the switch is con-nected directly to the op -amp's non -invertinginput, it shock excites the oscillator into ring-ing - visible on the upper trace (upper semi-tone) in Fig. 8c). By comparison, the lowersemitone sine -wave output is of course unaf-fected, lower trace.

Further enhancementsCharge injection in electronic switches is awell known phenomenon, and in later designsof switch ICs it has been greatly reduced, butthese would be too expensive in the numbersrequired for this application.

Clearly there is scope for further develop-ment here. For example, the capacitor at thecontrol input of S2 could be grounded notdirectly, but via another section of theCD4016. This additional section would beswitched on when square -wave was selected,but not for sine -wave. All additional switchsections would have their control inputs con-nected together and controlled by the stopswitches, being on for clarinet (square -wave)type stops but off for flutes (sine waves).

Having concentrated on the basic one -per -note, or one -per pair of notes tone generator, aword on controlling the generators from thekeyboard will not go amiss. For a very simpleorgan of just one rank, key switches can con-trol S1 for each note directly, and S2 - if usingthe shared generator scheme - via diodes as inFig. 7a).

If it is desired to incorporate octave and sub -octave couplers, this can be achieved byadding diodes and resistors. However thecomplexity increases alarmingly, especiallywith the shared generator scheme. It increasesfurther if it is desired to have two or moreranks of generators with the option of sound-ing these at different pitches. As a result, forall but the least ambitious designs some otherscheme is called for.

A microcontroller can be used to scan thekeyboard and set or clear latches controllingSi, and S2 if used, in accordance with the stopsdrawn. But a simpler approach is to employone of the variations on the multiplex scheme,which has been described many times in theliterature, for example Refs 3 and 4.

References1. Shared note F -P oscillator, Dr. J H Asbery,Electronic Organ Magazine (Journal of theElectronic Organ Constructors' Society) No. 154,December 1994, pp 14, 15.2. A Free Phase Organ, Dr. J H Asbery, EOM No.145, March 1992, pp 8-13.3. Electronic Organ Magazine, No. 98, page 12.4. Experimenting with Multiplex, T Hawkins,EOM No. 146, July 1992, pp. 12-15.


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12.9

RF ENGINEERING

Fractional -1Nsynthesis

Cosmo Little reveals the benefits of a little-knownfrequency synthesis technique that is cheaper thandirect synthesis - and requires much less power.

Afractional -N synthesiser is essentially asingle -loop digital synthesiser wherethe loop divider has been modified to

divide by an integer plus a fraction - insteadof by an integer alone. In this way, extendedfrequency resolution is obtained.

Because division by a fraction is not possi-ble, the divider approximates to the requiredfractional division ratio over a period of time.

'REF

Fig. 1. In the basicdigital loop, a voltage -controlled oscillatorrunning the outputfrequency is dividedby integer N.

(Kr) Loop filter

F(s)

Divider

KVCO -s

KrK,F(s)G(s)=

Transfer function eou-r G(s)nr 1+ G(s)H

ouT _ 1Reduction of nv or nd(P

1+ G(s)H

1H = -N

nr, nd, and n, are additive phase noise sources

Time to acquire phase lock (zero initial frequency error)

1 1

27rfn can

Time to pull in from frequency offset At

(27rAf)2

24ron3

f OUT

°OUT

(2'd order loop with phase detector)Note: this formula does not apply tophase/frequency detector

In this first article I review the operation ofthe single loop digital synthesiser, and willconsider the basic type of fractional -N synthe-siser. In the second article, we will concludethe review of fractional -N techniques, and willlook at practical implementations of themethod. Both articles will be illustrated byMathCad simulations which will be madeavailable to readers as the original MathCaddocuments. This will enable readers to experi-ment with the design of fractional -N synthe-sisers to suit specific applications.

Benefits of fractional -NThe fractional -N synthesiser is believed tohave been invented by Hewlett Packard in theearly eighties. It was used in a number of syn-thesisers - including the 3325A, whichachieved micro -hertz resolution with only onephase -lock loop.

The same concept has been used in otherinstruments, such as the Marconi 2022 signalgenerator, and can be used as the high reso-lution loop in a multi -loop synthesiser whichincreases the possible frequency range intothe gigahertz region.

Modem digital large-scale integration chipshave generated considerable interest in thedirect digital synthesiser, which has largelyeclipsed the fractional -N technique. never-theless, fractional -N has many advantages,and is worth serious consideration by anydesigner faced with the task of producing amedium performance frequency synthesiserwith small frequency resolution.

Fractional -N can be implemented muchmore cheaply than a direct digital synthesiser,or dds. It also uses much less power as it doesnot require fast logic or a fast video d -to -a


RF ENGINEERING

converter for the signal reconstruction.This article reviews the different evolutions

of the fractional -N synthesiser from the mostbasic idea of non constant division ratios in adigital phase -lock loop, pll, to the develop-ment of the two accumulator fractional -Nloop with its division by a choice of four dif-ferent integers and analogue correction.

Performance of the fractional -N loop is wellsuited to simulation on a general purposemaths package, as its performance limitationscan be investigated independently of perfor-mance limitations caused by the hardwareimplementation. In this article, analyses aresupported by MathCad documents.

Initially, I will review the basic digital loopfrom a performance point of view, and dis-cuss the basic trade offs between resolution,reference frequency suppression, phase noise,and tuning time. These relationships are notderived formally, as this has been done manytimes in existing literature.

Basic digital pllFigure 1 is a block diagram of a single loopsynthesiser. This will no doubt be fairly famil-iar to most readers. A voltage -controlled oscil-lator running at the desired output frequency,fo, is divided by an integer, N.

Phase of the output frequency from thedivider is then compared with the phase of areference frequency, and the phase error isconverted to a voltage error by the phasedetector. This voltage error is processed by theloop filter, which is usually an integrator andzero, with one or more higher frequency poles.

Output from the loop filter is now used tocorrect the vco frequency to hold the phaseerror at the phase detector to near zero. Thisloop can be formally analysed to predict suchbehaviour such as loop stability, forwardtransfer function - which describes how close-ly the phase fluctuations of the vco followthose of the reference - behaviour of the loopto phase errors added to the vco signal, ie sup-pression of phase noise of the vco, and manyother performance characteristics. I do notanalyse the digital loop in detail here, but I

have included references to the details.This is a summary of the most important

performance trade offs:

Frequency resolution. This equals the refer-ence frequency. Output frequency is frefxN

Natural loop frequency. This is defined asthe -3dB point of the closed loop gain. It is animportant parameter that affects several otherperformance measures. For generality it is bestconsidered as a fraction of fref.

Note that the digital loop is actually a sam-pled data system. Phase comparisons are onlyavailable at the rate of the reference frequency.As a result, in theory, the loop frequency can-not be higher than fret/2.

In practice, the loop frequency will need tobe fref/10, or even lower. The main reason forthis will be to suppress leakage of unwantedhigh frequency signals from the phase detec-tor. These occur at multiples of the referencefrequency, and will phase modulate the vco,producing spurious sidebands.

Some phase detectors are better than othersin this respect. The sample and hold detectoris generally considered to have the lowest ref-erence frequency feed through. However, thedigital phase/frequency comparator is stillused in a great number of single chip synthe-sisers. The choice of phase detector becomesimportant for another reason concerned withthe fractional -N mechanism, so I will return tothe discussion of phase detectors later.

Designing the loopThe natural loop frequency - and dampingfactor - may be calculated from the compo-nent values used in the type 2, second -orderloop filter. The circuit and equations are givenin Fig. 2. Real implementations, however,always have additional poles, and the simplestway to find the natural loop frequency, andalso the phase and gain margins, is to plot theclosed loop gain and phase. This is easy withtools such as MathCad.

The op -amp is modelled as an amplifierwith finite gain and one low frequency pole.

Component values in Fig. 2 for the fifth -orderloop are entered. The loop divider (N), phasedetector constant (Kp), and vco gain constant(Kv) are also entered. The document thenplots graphs of closed loop gain and phase,forward gain, reduction of vco phase noise,and loop filter response. This enables esti-mates of natural loop frequency, loop stabili-ty, reference frequency suppression, and vcophase noise to be made.

The natural loop frequency affects a numberof performance tradeoffs of the digital loop.Those that are most important to synthesiserdesigners are phase noise, spurious sidebands,and tuning time.

Phase noise of the vco can be divided intotwo regions, frequency offsets well within theloop natural frequency, and frequency offsetswell outside it. At frequencies well within theloop frequency, the vco is controlled by thereference frequency phase. Any phase fluctu-ation of the reference will appear on the vcooutput, multiplied by the loop division factor,N. In terms of sideband level, the increase inlevel from the reference to the vco will be20xlog(/V).

For example, if the reference has 100Hzsidebands at a level of -80dBc (80dB belowthe carrier) due to phase modulation , and N is1000, then the 100Hz sidebands will appearon the vco at a level of -20dBc.

Exactly the same calculation applies to noisesidebands. In the example a reference phasenoise level of -80dBc/Hz will be transferredto the vco at a level of -20dBc/Hz. If N is verylarge, the vco may well end up with worsephase noise than if it was free running.

This in fact was the case in an early versionof a low-cost signal generator made by afamous manufacturer. As far as I can remem-ber, the vco operated at 160MHz, with a com-parison frequency of 100Hz. In this case Nwould be 1.6 million, and the phase -noisemultiplication factor I24dB.

Within the loop bandwidth, which was onlyabout 10Hz, output of the signal generator hadso much residual fm that it produced an audi-ble wobble when used to test ssb receivers.

Alternative frequency synthesis techniques

Methods of frequencysynthesis can be divided intoa number of distinct types.

Direct frequencysynthesisers use onlyharmonic multipliers,mixers, and dividers togenerate their output. Nophase -locked loops are used.This type of synthesiserswitches in a few ps, but isextremely complicated, witha vast quantity of analoguecircuitry. They are essentiallyobsolete. Interested readersare referred to the blockdiagram of the HP5105 in

reference 3.Digital synthesisers use one

or more digital phase lockloops, ie a phase -lockedloop with a digital dividerbetween the vco and thephase comparator. Morethan one loop is commonlyused, with mixers inside andoutside the loops. A hugevariety of differentconfigurations have evolvedto provide small frequencyincrements with fast lock -uptime and good phase noise.

A large number offrequency synthesisers in

everyday use are single -looptypes. This includes alldomestic radios and tvs, andthe great majority ofcommercialcommunications equipmentoperating in the vhf, uhf andlow microwave bands. Theuse of multi -loop mixingtypes is mainly in laboratoryinstrumentation such assignal generators andspectrum analysers, and inhf transceivers.

The third type ofsynthesiser is the directsynthesisers. These

synthesise the outputsinewave by outputting asampled approximation ofthe waveform at a ratedetermined by a high -frequency clock. As all thecircuitry is digital, it issuitable for large scaleintegration. This type isbecoming more popularwith the astonishingincrease in density, andreduction in price, of LSIdigital chips. A directsynthesiser may be used ina single loop with mixerconfiguration to providesmall frequency incrementswith reasonable simplicity.


RF ENGINEERING

This made measurement of SINAD nearimpossible.

The manufacturer soon replaced this signalgenerator with a version that used a fractional -Nloop to avoid this problem.

Calculating phase noiseThis digression all helps to illustrate the prob-lems with digital loops with high loop divisionfactors.

Note that reference noise must includedivider noise and phase detector noise. If thisis not done, it is possible to make a large errorin the calculation of phase noise within theloop bandwidth. Reference oscillator phasenoise will be reduced by the reference dividerchain by the same factor 20xlog(R), where Ris the total divider ratio.

For example, a crystal oscillator at 10MHzmay have phase noise of -100dBc/Hz at a100Hz offset. If this was then divided downto 100Hz, you might assume that the phasenoise at the divider output would be-200dBc/Hz from the above formula. But thiswould be incorrect, as the divider noise flooris unlikely to be below -160dBc/Hz. Forexamples of divider and phase detector noise,see reference 1, p86.

Outside the loop bandwidth the vco isuncontrolled by the loop - except for theunwanted reference frequency componentswhich generate discrete sidebands. As aresult phase noise reverts to that of the freerunning vco.

A loop with low reference frequency is usedto obtain high resolution, and a low loop nat-ural frequency suppresses reference frequencysidebands. But with such a combination, thephase noise may be too high to meet thedesigner's initial specification. Nothing can bedone about this except to build a better vco.

Phase shift considerationsSpurious discrete sidebands have already beenmentioned. These are generally caused by ref-

erence frequency leakage from the phasedetector.

In an attempt to push the loop natural fre-quency higher, designers have come up withelaborate filtering schemes after the loop fil-ter/integrator. These often take the form oftwin -T notch filters tuned to the reference fre-quency and its second and even third har-monic.

These can be useful, but it is essential toconsider the effect of the phase shift of thesefilters on the loop stability. This could be doneusing the MathCad document for the pll, byadding the s -plane transfer function of a twin -T notch filter to loop filter function F(s).

Tuning time, which is the time to acquirephase lock after a new frequency has beenprogrammed, is a very complicated parame-ter to analyse. This is because it involvesnon linear operation of the phase detector,with the loop initially slipping cycles duringacquisition.

Phase detectors of the digital phase/fre-quency tristate comparator type will alwaysacquire lock. Even if there is a large initial fre-quency difference, they always provide anoutput to pull the vco in the correct direction.They are almost always used in commercialsingle -chip digital synthesisers, although oftenan alternative phase detector is provided foruse once the loop has locked.

Tuning time is always inversely proportion-al to the loop natural frequency. Some approx-imate formulae are given in Fig. 1.Multi -loop synthesisersTo summarise, a single -loop synthesiser issimple and economical, but has serious per-formance problems when fine frequency res-olution is required.

Many transceiver applications have fixedchannel spacings of 12.5 or 25kHz, and inthese cases it is possible to design single loopsynthesisers with vco frequencies up to200MHz with adequate performance.

The same applies to domestic radios where a

5th order

1

fPOLE47CL

1

hod=27rt5

t2 = R2(C +C2)

t3 = C2R2

RiC3tzt =

4

t5 = R3C4

fo = op amp low frequency pole

A = op amp dc gain

R2

2"d order

1

fn 27r

KvKo

Nti

Cl

RiCi

t2 = R2Ci

Fig. 2. Loop filter options in outline. Realimplementations always have additional poles.

channel spacing of 9kHz is used, in Europe ,on the amplitude modulation broadcast bands,and a channel spacing of 100kHz on the fmbroadcast band. But what about a general cov-erage short wave receiver?

In this case the receiver will probably useup -conversion to a first intermediate frequen-cy of 45MHz, with a vco range of 45 to75MHz. At least 50Hz resolution is requiredfor ssb reception. A single -loop synthesiserwill be terrible, as you can appreciate from theformulae provided.

The traditional solution is multi -loop syn-thesisers - synthesiSers with mixers in theloop. These can be incredibly complicated. Acircuit of an early Yaesu amateur transceiveris typical of Japanese transceiver design in theeighties. It uses four internal vcos - notincluding the output vcos - with four single -chip programmable divider/ phase detectors,five mixers, six fixed divider chips, and amass of loop filters, low-pass, and tuned filtersto try and control all the unwanted mixerproducts. To be fair to the Yaesu designers,current amateur transceivers use much simplerschemes, usually based on a direct digital syn-thesiser - dds - as part of a dual loop.

Direct -digital synthesis is a method of direct-ly generating a sine wave output by accumu-lation of phase, table look up of the sine func-tion, and reconstruction of the output with ad -to -a converter. Analysis of the dds wouldrequire another article, but it is not the univer-sal solution to synthesiser design that somemanufacturers of the chips might claim.

Due to the fast logic required - clock ratesof at least four times the output frequency arerequired - and the fast d -to -a converter, pricesof the chips are very high, around £20 to £40for the dds chip, and about the same for thed -to -a converter. Spectral purity is a problem,especially if the output frequency is multipliedin a digital loop.

Fractional -N in practiceFigure 1 provides some insight into how thefractional -N technique works.

If the loop divider is changed at the end ofeach reference cycle, ie when the N counteroverflows and reloads from its latch, the aver-age value of N taken over many referencecycles may be made a non -integer value.

Frequency of the vco is still be given byfvco=Nxfref, but now N is no longer integer,giving us fractional frequency resolution.

As an example, if N is 100, andfref is 1kHz,output frequency will be 100kHz. If, every 10reference cycles, N is changed to 101 for 1 ref-erence cycle, the long term average of the loopdivider will be (9x100+101)/10=100.1 andoutput frequency will be 100.1kHz.

You may already have noticed the weaknessof this idea. Assuming that a very -low loopnatural frequency is used, the loop can be con-sidered as if it were open. The vco is consid-ered to be on exactly the correct frequency, ie100.1kHz.

Now, after the first reference cycle we will


RF ENGINEERING

Phase lock loop comparison frequency Prof.- 103. Integer pad of loop dMder N - IN

Fractional part of loop diVider M 7. Accumulator modulus Modulo

Correction DAC modulus DAC =2.'

i = O.. (Modulo.8 - I) T =0 Ao =0 N Do N + I

rye° .=, ref ,c.) T ref 'WO = KM134-375ref

The next statement forms the vectorof values in the accumulator.

Special vector function definition that returns 1 if next entryin vector is less than current entry. Serves to mark OVFL(Vj) rhj <0,0, if(V, ,<Vi.1.0)"accumulator overflows. If index is <0, returns O.

Logic section to create vector of divisors based on accumulator overflow. Order of these statements is important.

NR N- ND ,f(OVFL(A,r)al,N D I,N II mean N = 10 027g18

Graphs of accumulator content and loop divisor

00.

vi100

10 60 00

Create vector of time errors due to non exact &Man.

Create correction voltage from accumulator A.Accumulator W truncated to no of DAC bits.

Create error voltage vector at output of phase detector.Phase detector constant assumed equal to 1.59Note that correction voltage is assumed to be accurate to 5%

Remove DC component from error voltage

Graphs of time error. correction. and voltage error//zo 60

MV .maz(V

so

10

SO

T timer' =T + TodVCO

Com - floor DAC fret)2 a I 59

DAC (mode]. ryCO

T

V - 2 x = 1 59 0 95.CorriT ef

do

Fourier transform of error voltage. Bin spacing I.REF/no of samples

G .2FFT(Vo..) longth(V -2.048.103 length(G) = 1.025.103 Hz

j =O.. length(G)- I WRITEPRN(f.1) =0 WRITE(freqincl) =Hz

spectrum of error voltage(y axis in volts eqiv to peak voltage of a transformed sine wave)

.15

Automatic adjustment of error voltagecorrection by synchronous rectification of Verror

003

002

0 01

0 01

so

fieflengthiV.)

12.A. I

Rect. -if1floori 1 ,V )' ,mod.doicrror `n.",

a

,r, Oh /1/4/ f1/4 / 1/4

/1/4 -

1/4

\ / \1 / \\ / \ / \ // 1/4

\00 //

\\ //

\\\ \-

1/4 / \\/

I \ / I\ //

1/4 / / 1/4

1/4/1

- :I 4 o/ -

la 130 Ib IW 1X0 200

meon(Rect) =0.01245

Left, simulation of the fractional -N loop with analogue correction.Right, a simple way to display the natural loop frequency. Componentvalues in Fig. 2 for the fifth loop are entered as well as values for theloop divider (N), phase detector constant (Kr), and vco gain constant(Kr). The MathCad document shows plotted graphs of closed loopgain and phase, forward gain, reduction of vco phase noise and loopfilter response.

loop fixed parameters:

op amp low frequency pole and open loop gain: fo .10 Ay .100000

loop filter component values: RI 4700 R2 =10000 CI = 1010' C2 =.5-10'3

Phase detector gain constant ( volts per radian), Kp =1.59

VCO gain constant (radians per volt second), Kv

VCO modulation pole(Hz), (mod :30-103

Loop division ratio, N - 10

Additional low pass pole(Hz), tole .20000

Frequency sweep,

- I cownum - its) II...,= 100 r.op = 1Art

'fmartrf"P'tn'' start)

calculated values:

1

2mft =CI -R1

=210 f.

t2 .R2.(C1 C2) t =C2 R2 1

'mod - 2.x.f .0dt pole

Ao. (1 4-st 2) (I1

F(s) -o.to.ti.t3i-s2.(Ao.trt34-103.to.ti+to42).-e(Auti +t *t2i-t0)4.1 1+"Polc)

0(a)KpKvF(s)

A(s) =0(3).1-1

Performance graphs:

Module. of dosed loop gain

...(1"(%)i)

100

t mod .520516.10

t po..7.95775.10'3

t 0.01592

t t .4.7.10

t 2 w 1.05.10

t3w5.10'

1C0

150

Phase of closed loop gain

180

100

100

to

roo

Transfer function( output phase to reference phase)

100

VCO phase noise reduction by oop

Loop filter response

"coOrN)1)

to too


RF ENGINEERING

have divided by 100. The time required for thecounter to overflow, and deliver the outputpulse to the phase detector, will be100x1/100100 or 999p s. The reference pulseor edge has a period of 1000p s. As a result,the first reference cycle has resulted in a timeerror of 1 p s at the phase detector, the divideroutput appearing earlier. This corresponds to aphase error of 6.28mrad.

The next reference cycle produces anotherincremental error of 1ps, giving a total error of2ps. Errors build up until the tenth referencecycle, at which point a divide by 101 is carriedout. Incremental error due to this division willbe -9ps, the divider pulse appearing later.

The total error is now zero. The error wave-form is a sawtooth, with a peak -to -peak ampli-tude of just less than 1/fi,c0. In the exampleabove, the range was from 0 to 9ps. In a realloop this would produce a net input to the loopintegrator, and the phase of the vco wouldshift to ensure that the error waveform had nodc component.

The error waveform is a sawtooth with aperiod of 100ms - 10 reference cycles - or afundamental frequency of 100Hz. This isequal to the gain in resolution of the loop. Inorder to filter out the error voltage, whichwould otherwise phase modulate the vco, it isnecessary to reduce the loop bandwidth. As aresult little is gained over using a loop with areference frequency of 100Hz in the firstplace.

Both cases are not quite the same, as in the

fractional loop phase comparisons are still at a1kHz rate. Also, the error voltage to be filteredout does not depend on the characteristics ofthe phase detector, as it does with referencefrequency feed through.

Amplitude of the time error waveform isequal to the reciprocal of the vco frequency,and is proportional to 1/N. However, theloop will multiply the error voltage by itsforward transfer function, which at low fre-quencies is equal to N. As a result the vcospurious sideband level will tend to be inde-pendent of N.

Cancelling error voltageIn order to make the fractional loop workproperly, initially, some means of controllingthe loop divider is needed to generate anyrequired frequency increment. Secondly somemeans of cancelling out the error voltage inthe loop is necessary.

Control of the divisor can be arranged byusing an accumulator, with a phase incrementadded into it at the end of each referencecycle. When the accumulator overflows, theloop divisor is changed from N to N+1. Eithera decimal or a binary modulus may be used.The value of the phase increment is called thefractional divider, or M. Output frequency isnow (N+Mlmodulus)xfre.

This relationship can be verified by trying afew examples. If M is set to 1 less than themodulus, the accumulator will overflow onevery reference cycle except 1. The loop will

divide by N+1 for (modulus -1) cycles andthen by N for 1 cycle.

Another situation that is of interest is whenM is not a factor of the modulus. For exampleM=7 and modulus is equal to 100. Now theaccumulator will overflow on the fifteenth ref-erence cycle, but will not contain zero. Thetime error waveform will be the sum of twosawtooths, one with a period of about fifteenreference cycles, and the other with a periodof 100 reference cycles. The lowest frequencycomponent will be fref/modu/us. If M is a fac-tor of modulus, the lowest frequency will beLefxM/modu/us.

Cancellation of the error voltage from thephase detector can be achieved easily since thecontents of the accumulator can be consideredas a binary - or decimal - integer exactly fol-lowing the error waveform. Parallel output ofthe accumulator is fed to a d -to -a converter, itsvoltage is scaled appropriately, and it is addedto the output from the phase detector. Thisexactly cancels the error voltage.

Now all the elements for the fractional -Nsynthesiser exist. Figure 3 gives a block dia-gram of one type of practical implementationbased on discrete logic. Other implementa-tions will be considered later.

Simulating analogue correctionRather than analyse this circuit in detail in thetext, it is easier to introduce the first of the twoMathCad documents shown. This is a simu-lation of a fractional -N loop with analogue

A/-Loopfilter

VCO

Notes: 1)

2)

POUT

3)

The accumulator is clocked on the overflowof the N divider

Depending on the state of the carry from theaccumulator, the N divider is reloaded witheither N or N + 1

The components in grey box are optionalcorrection loop for analogue correction

Adder

N latch

Multiplying DAC

Accumulator MSB

Accumulator

M latch

Multiplying DAC

Latch

fOUT

Fig. 3. Basic fractional -n synthesiser with additional d -to -a converter for scaling the correction by 1fiout.

AC amplifier

Synchronous rectifier

Low pass filter


RF ENGINEERING

correction. It should be fairly easy to under-stand to users of MathCad.

It is not possible to simulate a program loopwith MathCad. Instead, the simulation mustbe made in a linear manner, proceeding fromthe start to the end of the document. Thelength of the simulation is set by the rangevariable T, which must be a power of 2 sothat the Fourier transform will work. Theaccumulator modulus is set to 256, and thelength of the simulation to eight completecycles (2048).

Various vectors are generated, such as thevector of the accumulator contents and thevector of the loop divider. Most of these areillustrated by graphs. The effect of using ad -to -a converter to generate the correctionvoltage with a modulus less than that of theaccumulator may be simulated. This is quitelikely to be the case in a practical implemen-tation of the synthesiser, when the accumula-tor modulus may be much greater than 256.

The addition of the correction voltage to thephase detector output voltage is deliberatelymade in error by 5%. This is in order to makethe rest of the document more interesting.Those of you with MathCad can verify thatthe correction does in fact exactly cancel the

error by changing the factor 0.95 to 1.The large graph is the Fourier transform of

the error voltage as it is at the input to the loopfilter. This graph does not directly predict thespectrum of spurious sidebands of the vco, asthe error voltage will be modified by the loopforward transfer response.

The fractional frequency generated in thissimulation is 2734.375Hz. The major compo-nent of the error voltage is at this frequencyand its harmonics. Smaller components arevisible at spacing of 390.625Hz which isfref/256.

As the adjustment of the correction voltage.is very important for the elimination of spuri-ous sidebands, it would be useful if there wasa method of automatically balancing the errorvoltage to zero. This is in theory possible if weconsider that the polarity of the error voltagewill change if the correction is changed fromtoo large to too small. As it stands the errorvoltage will always be balanced about OV togive the requirement that the input to the loopintegrator has a mean of zero.

However if you synchronously rectify the acerror voltage using the most -significant bit ofthe accumulator, and then filter the resultingwaveform. you get a dc value proportional to

the unbalance of the correction. This may beused in a long time -constant feedback loop tocorrect the magnitude of the correction volt-age. This idea is shown in Fig. 3, and is sim-ulated in the last part of the document.

As I mentioned earlier, the magnitude of therequired correction must be scaled by lifout inorder to keep the adjustment of the correctioncorrect. This can be done by means of an addi-tional multiplying d -to -a converter, Fig. 3.

This concludes the discussion of the frac-tional -N loop operation. In a further article Iwill examine an important modification of thesingle accumulator fractional -N loop whichgoes a long way to reducing spurious outputs- even without analogue correction.

References1. Ulrich L., 'Digital PLL FrequencySynthesisers', Rhode, Prentice Hall.2. William F. Edan, 'Frequency Synthesis byPhase Lock', Wiley.3. Vadim Manassewitsch, 'FrequencySynthesisers, Theory and Design', Wiley.4. Alain Blanchard, 'Phase Locked Loops.Application to coherent receiver design'.

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ANALOGUE DESIGN

Designingcascade RC oscillatorsCascade RC oscillators are simple, stable, and offer very faststart up. David Griffiths explains how this long-established circuitconfiguration benefits from modern op -amp technology.

The new breed of dual op -amps with rail -to -rail output swing allows a very sim-ple implementation of the RC cascade

oscillator.In addition to the timing elements shown in

Fig. 1, the cascade oscillator needs little morethan three resistors and a single eight -pin IC,provided a stable supply voltage is available.Sadly, distortion performance is only aroundthe 2-3% level - mainly third harmonic.However, those concerned with sensor instru-mentation at fixed frequencies should wel-come the following:

Excellent stability of output amplitude,which is also highly predictable and has a verylow temperature coefficient.

Very stable timing relation, with ageing and

Tc Tc T ov

Fig. 1. In principle, the RC phase -retardcascade oscillator is similar to its CRphase -advancing counterpart.

Fig. 2. The common CR-network basedcascade oscillator relies on phase advance.

temperature, between sine and square waveoutputs, which is a boon in phase sensitivedetection schemes.

Almost instant start and settling character-istic, which allows burst operation of sensorsto minimise battery power consumption.

The RC cascade alternativeThe above principles were expounded inWireless World by L Nelson-Jonesl. He con-centrated not on the common high-pass CRcascade, but on the less well known low-passRC scheme. As a re -cap, Nelson -Jones' intro-duction went along the following lines.

Figure 2 shows the more common cascadeCR phase advance oscillator. If the invertinggain of the amplifier exactly equals the atten-uation of the cascade when it is giving 180°phase shift, then oscillations at that frequencywill be sustained by this arrangement.

This still leaves the awkward problem ofprecisely controlling the gain to maintain sta-ble oscillation amplitude. This could entailthermistor control, but then ambient tempera-ture changes have a big effect on the ampli-tude, and it is difficult to avoid prolongedamplitude ringing at switch -on.

In my opinion, a Wien bridge oscillator withthermistor gain control beats this approachhands -down - especially if the amplification isarranged as virtual earth amplifiers givingultra -low distortion as in the elegant schemedue to John Linsley Hood2.

Alternatively, gain control in Fig. 2 can beexercised with oscillation amplitude sensing orrectification. The ensuing voltage is thenapplied to vary the channel resistance of a fetused in the feedback path controlling ampli-fier gain. In my experience, this approachalways seems to give more amplitude tem-perature coefficient than initially expected, as

well as increasing distortion.The necessary 180° phase shift in the cas-

cade can be equally well achieved via phaseretardation generated by interchanging thepositions of R and C to give Fig. 1. Again, thesame less than ideal schemes could be used totry to control the gain at the critical value tomaintain oscillation amplitude stability.However, Nelson -Jones' insight was that, ifyou primarily want amplitude stability and canbear some distortion, then it is much better torun the maintaining amplifier as near as pos-sible as an ideal limiter.

Cascade transfer characteristicsAssuming that the maintaining amplifier is notclipping and has infinite input impedancecombined with zero output impedance, theanalysis is as shown in the equations panel.This gives mesh equations for both types ofcascade.

In the phase retard case, if the cascade isdriven at angular frequency coat amplitude VI,then the output amplitude V2 is related by,

= V2.{1- 5a2 - Act' -6a)} (1)

where a=coRC and j=-4-1. When a=.\/6, theimaginary term is zero and V1.---29xV2, show-ing the phase shift is 180°. Angular oscillationfrequency is therefore ca/RC. That is, thephase retard RC cascade oscillator will ideal-ly oscillate at a frequency 'f' given by,

27rRC

As an aside, in the case of the phase advancecascade, the expression for the frequency atwhich the imaginary term is zero has the 16on the bottom line. Despite this six -fold dif-ference in frequency for the two configura-tions using the same R and C values, attenua-

(2)f=


ANALOGUE DESIGN

tion at the 180° phase shift condition is again-29, as expected from symmetry considera-tions.

Substituting 2a, 3a, 4a and 5a into equa-tion (1) allows the attenuation to be calculatedfor the second, third, fourth and fifth harmon-ics of the oscillation frequency. This yieldsattenuation factors of 148.1, 443.6, 1004 and1916 respectively, and shows a misprint forthe third harmonic figure in the original arti-cle. This gives an attenuation of 5.1, 15.3, 34.6and 66.1 respectively compared to the attenu-ation of the fundamental at which oscillationcan occur. These figures agree with those cal-culated by Nelson -Jones.

The ideal caseIt is now appropriate to consider the ideal casewhere the inverting amplifier of Fig. 1 is giveninfinite gain and behaves as an ideal limiterwith its output voltage only at one or other oftwo levels. The phase -retard RC cascade is asa result driven with a square wave and thequestion arises as to the waveform thatemerges from it. Using the harmonic attenua-tion factors calculated above and expressingthe driving waveform as a Fourier series ofharmonically related sinusoids, the outputwaveform can be calculated as follows.

Orthogonality of sines and cosines whenintegrated over a complete cycle means that asquare wave of amplitude 'A' can be repre-sented by the Fourier series,

-4.A.[sin0 + -1.sin30 + -1.sin50 +3 5

OV

Fig. 3. With modern rail -to -rail -swing op -amps, this amplitude -stabilised RC oscillator achievesa sine -wave output of around 3.2V pk-pk from a 5V supply. Square -wave output is in antiphaserelative to the sine wave.

This means that if the amplifier in Fig. 1were ideally limiting between OV and +5Vsupply voltage, then the amplitude of the fun-damental harmonic contained 'in' the squarewave is 4x5/it=6.37V. The fact that it shouldbe greater than the swing permitted by theavailable power -supply voltage is intriguing.

An unforeseen time constant in an amplify-ing chain can knock the corners off fast risingedges. Knowing this, you might imagine thatthe corners just get progressively rounded offas the limited waveform progresses down thecascade. However, it does not happen like thisbecause the repetition rate of the square waveis fast compared to the cascade time constants.

At the first capacitor down the chain youcan see only a spiky sequence of exponentialrises and falls, without any 'flat bits' left fromthe square wave. The waveform on the secondcapacitor is remarkably close to being trian-gular. As a result, it is initially surprising that

an oscilloscope shows a presentable sine waveat the end of the cascade.

The Fourier series shows that in the idealcase the third harmonic is the lowest distortioncomponent that would be present and wouldhave a third of the magnitude of the funda-mental harmonic. We have already establishedthat this third harmonic is subject to 15.3times more attenuation in the cascade than thefundamental. As a result the third harmonic atthe output only contributes 1 part in 45.9 tothe signal, ie a distortion level of 2.18%.Calculation gives a fifth harmonic level of0.3%, with relatively negligible amounts ofhigher harmonics.

Implementating the designBecause of the attenuation in the cascade andthe need for it to be lightly loaded, a bufferamplifier is needed as well as the limiter.These could both be driven in parallel by the

RC Cascade oscillator performance

Measurements on a numberof units oscillating at about400Hz and using theLMC660 and AD822op -amps have shown an acamplitude temperaturecoefficient around the10-20ppmf C level. Thisoccurred over excursions of25°C above and belowambient temperature, inaddition to that imposed bythe tempco of the supplyvoltage. As a result, for manymeasurement situations,there is no need to useratiometric techniques tocompensate for drifts in thecarrier amplitude. This

allows you to base anadequately stable calibrationon simply measuring theoutput voltage from a sensor.

As might be expected fromthe toggled nature of thedriving waveform andpassive shaping, the circuitstart-up and settling are veryrapid indeed. At switch -on,the uncharged timingcapacitors hold the output ofICi low, ensuring that thelimiter output goes high.

After a delay of about oneand a half oscillationperiods, output of ICI is highenough to toggle the limiterand the oscillation cycle

starts. Observations on ananalogue oscilloscopesuggest that after two furthercycles the amplitude hassettled to within 1% of itsfinal value. This gives a totalstart-up time of around threecycles.

At frequencies up to about1 kHz, this circuit showsremarkably good constancyof phase relation betweenthe sine and square waveoutputs without having touse a comparator for /C2. Asa result a space saving dualop -amp can be used.

An AD822AN basedoscillator, again running at

about 400Hz, was carefullyexamined in this respect. Itshowed less than 0.2° shiftchange between the sine andsquare waves for a 30°C rise incircuit temperature aboveambient. Similarly good long-term stability can be expected,making this oscillator usefulfor applications with phasesensitive detection.

Since expected distortion isnot good, examination of thisaspect has been limited tousing a passive Tee to filter outthe fundamental and checkthat amplitude of the residue isconsistent with the theoreticalpredictions.


ANALOGUE DESIGN

cascade output, but it seems better to drive thelimiter from the buffer amplifier. This increas-es the overdrive to speed up the transitions,Fig. 3.

A single supply voltage rather than dual isshown because positive line regulators or ref-erences tend to have better constancy of out-put than their negative line counterparts. Thisis important in maintaining the ac amplitudestability which is a prime feature of thisoscillator.

Op -amp IC2 performs the limiting functionand must have an output which can swing towithin a few millivolts of its supply voltages.Resistors R2,3 are of equal value and as a

result fairly closely establish the mid -pointvoltage between these output limits. If theseresistors are 1% tolerance, then the toleranceon the mid -point voltage is also 1% - as theresistors are equi-valued. This is more thangood enough in view of other imperfections inthe circuit.

My first reaction was to decouple the mid-point of R2,3 to OV with a large capacitor toprovide a low impedance reference voltage.But the resistance of R1 in parallel with R2 canbe used to define the appropriate gain neededin the buffer amplifier - as well as generatingthe correct reference voltage for the limiter.This also ensures dc coupling round the oscil-

Cascade oscillator equations

4

v,

O

z2

Iz

z2

O

O

¶V2

The generalised cascade gives the following mesh equations:

U =1,(z, +z2) -12z2

0 = -/1Z2 + /2(4 +2Z2) -13Z2

0 =12Z2 -/3(21 + 2Z2)

(3)

(4)

(5)

Adding equ.(3) x Z2 to equ.(4) x (Z1 +Z2) eliminates /1, yielding,

ViZ2 =/2{(Z, +2Z2).(Zi +Z2)- Z22}- /3.Z2(Zi (6)

Substituting /2 from equ.(5) into equ.(6), and putting,

1 =3 Z2

eventually yields :

V -V2 I +6L +1} (7)1 - 2

In the CR phase advance cascade, Fig. 1, Z1 is given by Cat angularfrequency co and Z2 by R, yielding,

5 j 1V

1= V2{1- (02c 2R2 + (032c2R2 6)} (8)

The imaginary term is zero when co = 1, giving V1=-29 V2.

RCS

In the RC phase retard cascade of Fig. 1,

V1 = V2{1-5co2R2C2- jcaRC(co2R2C2-6)} (9)

Writing a=wRC, the phase shift 0 given by,

(a3- 6a)tan -t0 =

1-5a2 )indicating 180° phase shift when,

= RC

lator loop, enabling the circuit to be useddown to low frequencies limited only by prac-tical values for timing resistors and capacitors.

As we have already calculated that theamplitude of the fundamental component driv-ing the cascade is 6.37V, and know that it isattenuated by a factor of 29 in the network, thebuffer amplifier is presented with a signal of0.22Vpk_pk. With R at 1001(52 and R1 and R2 at151a gain of the /CI stage is 14.3, giving asinewave output of 3.2Vpk_pk.

Because of the gain of the /CI stage and thecomparatively high resistor values used, careneeds to be taken to reduce unintentionalcapacitive coupling from the square wave tothe input of /CI. If this is not done, thesinewave output will be adorned with spikeswhere the limiter toggles. A sensible layout,with a grounded pcb trace to guard this fedback voltage, is all that is needed.

If output from the cascade is 0.22Vpk_pk,then the junction of R2 and R3 must be goingup and down by the same amount. This wouldseem at first sight to be a hopeless referencevoltage for the limiter. However, when outputof the cascade is in mid -excursion it must ide-ally be at +2.5V, since it is fed by a 1:1squarewave of amplitude 5V. Under theseconditions, no current will flow in R1 since thejunction of R2 and R3 is already at +2.5V byvirtue of the current flowing through theseresistors from the supply line. This is exactlythe correct condition to toggle the limiter.

Op -amp criteriaSince load on /C2 is greater than 1001M, it islikely that any op -amp with rail -to -rail outputcapability will limit its output within some10mV of OV and +5V under these condi-tions. As a result, it would be satisfactory inthis respect. However, /C2 also needs tocome out of saturation quickly from eitherlimit and to slew rapidly in either direction atthe same rate.

The new (dual) AD822AN seems a goodchoice in these respects, but the older (quad)LMC660C has worked well in a productionrun. As for the +5V regulator, there is much tobe said for the LP29SOACZ-5.0. Housed in aTO -92 package, this inexpensive low -drop outtype offers 20ppm/°C typical temperaturecoefficient. It is however essential to remem-ber to decouple its output as detailed in thedata sheet.

Considerations for higher frequenciesWith performance at frequencies where thepropagation delay in IC2 becomes significantcompared to the cycle time, it should be notedthat this delay is equivalent to a phase lag. Asa result the cascade does not need to produce afull 180° phase shift to satisfy the Barkhausencriterion for oscillation that there be 360°phase change round the complete feedbackloop. This means oscillations will alwaysoccur at frequencies somewhat less than thatpredicted by equation (2).

Accordingly, attenuation of the fundamentalthrough the cascade will necessarily be some-what less than the value of 29 implied by


ANALOGUE DESIGN

equation (1) and give more output swing fromthe buffer amplifier than might otherwise beexpected.

With an AD822AN at frequencies up toabout 500Hz, discrepancies from the ideal dueto circuit delays are not large. At 400Hz thesinewave output amplitude is about 5% largerthan given by simple theory with about a 5°shift between the sine and square waves.However, as noted earlier, the temperaturecoefficient of the amplitude and phase shift isstill admirably low.

With timing element R at 301(Q and C at1nF, oscillation occurs at about 10kHz.However, the phase shift between sine andsquare waves is now such that in a phase sen-sitive detection scheme you would have to usea separate comparator to generate a goodswitching reference from the sinewave.

Time delay around the oscillation loop pro-duces an equivalent phase shift such that oscil-lation occurs at only 75% of the frequencygiven by equation (2) and the reduced attenu-ation through the cascade gives some 75%greater output than at low frequency, requiringthat R1 be reduced to about 68ka While thesefigures are consistent with the (awkward)equations, it is much easier to do a bit of trialand error under these conditions rather than tryto calculate the degree of trimming needed.

With this degree of non -ideality, you mightexpect the amplitude temperature coefficient

of the output to be very poor. But while it isworse than at low frequencies it is still accept-able for many applications. Output of a trialunit with an AD822AN increased by just 1%for a temperature rise of 30°C above ambient,ie about 0.03%/°C. At 25kHz this onlyincreased to about 0.06%/°C. a 2

Because of the dc coupling in the amplitudemaintaining and stabilising loop, operationdown to very low frequency is possible. Withtiming element R at 10MQ and C at 2.2pF,the resulting oscillation period of 60s is prob-ably near the practical limit, as electrolyticcapacitors can not be used because of theirleakage currents.

Start-up and oscillation at this frequency,Fig. 4, was captured with a logging dvm andcan be seen to be as described for audio fre- around the maintaining loop and, as a result,quency operation. Sinewave amplitude and the errors arising from this mechanism.frequency were well within the limits set bythe 1% resistor tolerances and the precision ofmeasuring and selecting equi-value timingcapacitors. This is no surprise since the op -amps behave close to the ideal under theseconditions.

If the oscillator output must be symmetricalabout OV, this is easily achieved by using dual±5V supplies, albeit with a reduction in the Referencesamplitude temperature cofficient, as discussed 1. L. Nelson -Jones. Wireless World, p536-539,earlier. Increased swing now required from the November 1965.limiter takes longer with the slew rate of a 2. J. L. Linsley Hood. Wireless World, p51-53,given op -amp. This somewhat increases delay May 1981.

5

4

3

0100 200

Tirnn /01300

Fig. 4. Start-up characteristic of a 60s periodRC cascade oscillator demonstrates extremelyfast stabilisation.

Acknowledgements to the directors of ChelseaInstruments for their permission to publish this work.

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139

ANALOGUE DESIGN

In Marcel van de Gevel'shigh-performancepower amplifier,quiescent current isstabilised via feedback,using a non-linearcommon -mode loop.

Fig. 1. Simplified output stageof a power amplifierincorporating a non-linearcommon -mode loop. Thecircuit may lookasymmetrical, but the sourcefollower and common -sourcestages behave similarly whencurrent driven.

CCMP122p

RCMP122R

5mA

Audio powerwith a new loop

In a conventional class (A)B amplifier, qui-escent current through the output devicesdepends on temperature differences

between the output devices and a temperaturesensor. The temperature sensor is usuallymounted on a heat sink.

Due to thermal resistance from the outputdevices to the heat sink, and thermal capaci-tance of the heat sink, there are large differ-ences in temperature after a sudden change inpower dissipation. Hence, quiescent current ofan audio amplifier changes every time themusic volume changes. Non -optimal quiescentcurrent causes extra distortion known as tran-sient crossover distortion'.

Designers of operational amplifiers some-times use a different technique for class (A)Bbiasing known as non-linear common -modeloop, or class -AB control loop2. However, cir-cuits described in reference 2, and in manyother articles, are not suitable for a discreteamplifier. This is because they use IC tech-niques like emitter -area scaled transistors.

With a different kind of non-linear network,

MI 7BC558

CMP222p

RCMP122R0

R29470

5mA

+Isignal

Output of the previous stage

Tr18BC558

vcc+

however, it becomes possible to use non-linearcommon -mode loops in an almost wholly dis-crete audio power amplifier. With this tech-nique, thermal problems like thermal runawayand transient crossover distortion can beavoided as can quiescent current adjustment.

Further, the technique can be applied tocommon -emitter or mixed common-emit-ter/common collector output stages, or theirmos equivalents.

Designing the output stageA simplified schematic of the output stage isdepicted in Fig. 1. Voltage source Vi producesabout 10V above the output voltage, so thatthe gate of Tr13 can swing above the positivesupply rail.

The circuit may seem rather asymmetrical,having a source follower for the positive sideof the signal and a common source stage forthe negative side. However, both mosfets arecurrent driven. Under current drive, sourcefollowers and common source stages behavealmost identically, Fig. 2.

Tr21

1 mA

Tr22

= R44220pCcmp3

56R

1 mA

Tr24 Tr

CR46T 220ptlP4 56R

Tr21, Tr22, Tr24, Tr25:4/5 CA3046Transistor array

Load


ANALOGUE DESIGN

The class -AB control loop - a non-linearcommon -mode loop - consists of a non-linearnetwork around Tr21,22, and Tr24,25, a currentmirror with two outputs Tr15_18 and outputmosfets Tr12,13

When current through Tr13 or Tr12 becomestoo small, the current through Tr21 or Tr24increases respectively. Gates of both mosfetsare charged by the current mirror until bothcurrents are again large enough. When the cur-rents through both mosfets become largesimultaneously, currents through Tr21 and Tr24become small.

Now, the bias currents of the previous stageare larger than the currents through the currentmirror and the gates of both mosfets are dis-charged until the smallest current becomessmall enough. When currents through themosfets are of the same order of magnitude,they both have an influence on the non-linearnetwork and a smooth transition from one out-put device to the other is realised.

Quiescent current is about 100mA. Whenthe current through one output device is large,current through the other device is still about45mA, indicating that my amplifier is clearlya non -switching type.

The influence of the class -AB control loopon the difference between the drain currents ofTr12,13, and thus on output current, is kept assmall as possible by always driving both mos-fets equally. When the current through onemosfet is at its minimum, and the normal dif-ferential -mode loop tries to discharge its gatefurther, the common -mode loop responds byincreasing the currents through the currentmirror.

ZI

The gate of the other mosfet now chargesquicker than it would have had currentthrough the mirror not increased. In otherwords, the drive current of one output mosfetis passed on to the other when this is neces-sary. In this way, sudden changes in gain -similar to the gm -doubling effect - are pre-vented.

Components Ccmpi4 and Rcmpl_2 improvestability of the non-linear common -mode loop.

Amplifier circuitryOne channel of the amplifier is shown in Fig.3, and the protection circuit and power supplyin Fig. 4. I built a stereo amplifier, consistingof two channels with a common protection cir-cuit and power supply. Output mosfets of bothchannels are mounted with electrical insula-tion on a 1K/W heat sink.

In the protection circuit, Tr37 has its ownstar -shaped heat sink, 60K/W or less. Theother transistors do not require heat sinking. Amodified bootstrap network comprising R25,D14,15 and C10 corresponds to V1 in Fig. 1.

In order to keep the current controlled dur-ing clipping, recovery from clipping, stewing,switch -on and switch -off, the gates are alwaysdischarged when currents through the currentmirror are small. For this reason, R12,14, D8and R33 and R24 have been incorporated intothe circuit.

An anti -saturation circuit comprising Tr14and D 8,19 prevents saturation of the currentmirror. Without this circuit, a 5A current spikeflows through Tr13 and Tr12 for a fewmicroseconds during recovery from clipping.

The normal differential -mode feedback loop

z,

consists of the differential pair Tr2,3, phasesplitter Tr9, common base stages Tr10,11, out-put mosfets Tr12,13 and the feedback networkcomprising R4,5 and C5.

Major poles in the loopWithout frequency compensation, the normalfeedback loop has three major poles, ie polesthat have an important influence on high -fre-quency behaviour. Circuits can have severalmajor poles, sometimes referred to as domi-nant poles. However, this can cause confusionas 'dominant pole' is often used to describethe very lowest poles.

Capacitances between the bases and emittersof Tr2,3 and Tr9 contribute two major poles. Inthe output stage, the high -frequency transfer ismainly determined by the gate to drain capac-itance - the third major pole. This capacitanceacts as a Miller capacitor, causing open -loopoutput impedance to drop to a few ohms. Italso makes the high -frequency transfer of thelast stage less sensitive to the widely varyingtransconductance factor of the output mosfets.

In theory, the three major poles could bemoved into their desired positions - for exam-ple, three equal negative real poles or third -orderButterworth positions - with two compensationnetworks6. Unfortunately, simulations with apole -zero extraction program and a root locusprogram show that the influence of all thenon -major poles and zeros together is toolarge. As a result, a less subtle approach isnecessary.

Heavy pole -zero compensation in the secondstage comprising L1, R13 and C7 reduces thenumber of major poles to two. This is

z

Fig. 2. By redrawing the circuit andapplying a Blakesley transformation,the source follower on the left isshown to be equivalent to thecommon source stage with theextra current source on the right. Aslong as the current gain factor ofthe mosfet is much larger thanunity, the influence of the extracurrent source is negligible.

Mosfets versus bipolar transistors

Mosfets are used because of their typically large current -gainfactor and good high -frequency behaviour. Readers who haveread Self's article on mosfets and bipolar transistors3 mightthink it foolish to choose mosfets, so I shall explain why hisarguments do not apply in this case.

As Self correctly points out, mosfets have a lowertransconductance than bipolar transistors -a majordisadvantage in some circuits. However, the transconductancedoes not matter much when the output devices are currentdriven, as they are in my circuit. Current gain on the other handhas a direct influence on loop gain, and should be large.

Self also says that the sudden transition from a zero to aquadratic voltage to current transfer gives nasty corners inclass -B gain plots. However, whether the voltage -to -currenttransfer of the output devices starts in a smooth way or not doesnot matter in my circuit. Output devices do not determine howthe current is divided between the two sides of the output stage.

Further, the voltage -to -current transfer of a real mosfet starts

in a much smoother way than the voltage to current transfer ofa PSpice power mosfet. Designers of low -power mos circuitryknow that mosfets do not switch abruptly from an 'off -state' tothe quadratic, strong inversion, region.

At low gate -source voltages, mosfets are in the so-called weakinversion or sub -threshold region, where gate -source voltage todrain current transfer is exponential4. As gate -source voltagerises, the mosfet's transfer gradually changes from exponentialto quadratic. The range where the transfer is neither exponentialnor quadratic is known as the moderate inversion region.

For example, measurements of a BUZ71A power mosfet showthat the mosfet is in weak inversion from below 1 pA up toabout 10mA. The mosfet is in moderate inversion from aboutten to a few hundred milliamps. PSpice simulation of anIRF240 mosfet using a PSpice library file shows no weak ormoderate inversion regions at all, which is physicallyimpossible. Unfortunately, there is no BUZ71A model in thislibrary.


ANALOGUE DESIGN

achieved by covering the pole of thefirst stage and lowering the band-

5g E

'width. Capacitor C5 generates a zero 1j'A

in the feedback network which pulls egthe root locus well into the left half

1plane. In the closed -loop response the :3',4.3 ,--, m 3 A

two major poles almost end up on the 1-t !,. fnegative real axis. i- 1

Output filter L2, R47 and C13 7 Na t2gi

"1)it

:4G

decreases the influence of strange gi ''a

load impedances and suppresses spu- E 2' S'rious high -frequency signals pickedup by the loudspeaker leads. Theinput filter formed using R1,2 andC1,3,4, suppresses high -frequency sig-nals and prevents slew -rate limitingwhen the amplifier is subjected tounrealistic test signals like squarewaves. The response of this filter isapproximately a second -orderButterworth one, with a cut-off fre-quency around 140kHz.

Experimentation has shown that theamplifier is stable with an 8S2 load, aloudspeaker load and an unrealisticbut often used 8S2//2µF test load.

The circuit around the TL071 is adc bias servo loop, which gives a sec-ond -order Butterworth high-passresponse with C2 and R3 - at leastwhen output impedance of thepreamplifier is zero. Damping of theresponse increases when outputimpedance is not zero.

Protection networkThe circuit around Tr19,20 is a simpleprotection network. When output cur-rent is greater than about 10A, thisthyristor-like structure triggers andturns off the output stage. It remainsturned off until the amplifier isswitched off for around thirty secondsand then switched back on again.

The collector of Tr2 connects toanother protection circuit, Fig. 4,which responds if current through Tr2is less than a quarter or greater thanthree quarters of the tail current. Thiswill only occur if the amplifier is clip-ping or if the amplifier has brokendown, otherwise feedback keeps thesignal levels small.

Transistors Tr27_32 comprise a dualcurrent window comparator - dual,because both channels of a stereoamplifier have one common protec-tion circuit. If current through Tr2 hasa too large or small a value for longerthan about 20ms, C15,16 discharge, theoutput relay switches off and three -

Fig. 3. Entire schematic of one channel of thenon-linear common -mode loop power amplifier.


ANALOGUE DESIGN

colour led D36 turns red. This process protectsthe loudspeakers and provides a warning.

When the amplifier clips, the three -colourled emits yellow/orange light for about a sec-ond. If it clips severely for prolonged periods,the output relay turns off and the led turns red.This is done because the harmonics generatedby the clipping amplifier are not good for thetweeters. A few seconds after the volume ofthe signal is reduced, the output relay turns onagain and the led turns green.

As usual, protection circuitry preventsswitch -on and switch -off plops from reachingthe loudspeaker. The time needed to chargeC15,16 determines the switch -on delay withR68 and C14 the switch -off delay.

Measurement resultsTotal harmonic distortion at 10kHz and 16Winto 812 - about 80% of maximum power -was measured to be about 0.006%, droppingto 0.0025% at 10W. The -3 dB points of the

From theleft

channel

0201N4148

B> 14From the supplytransformer

A>

fla10k

frequency response were about 1.1Hz and143kHz.

A simplified Quad/Baxandall-like subtrac-tive test8'9 showed that the distortion on a realmusic signal was much smaller than 0.1%.With these methods, the desired signal can beattenuated without attenuating noise and dis-tortion. With about 60dB suppression of thesignal, the residue still sounded like musicrather than distortion so the distortion levelmust be well below -60dB or 0.1%.

References1. T. Sato, K. Higashiyama and H. Jiko,`Amplifier transient crossover distortion resultingfrom temperature change of output transistors',AES preprints for 72nd convention, Oct 19822. Johan H. Huijsing and Frans Tol, 'Monolithicoperational amplifier design with improved HFbehavior', IEEE Journal of Solid -State Circuits,

R66100k

RS51k51/4W

0301N4148

R51

39k

Tr33

BC558

From theright

channel Ah 0408V2

400mW

Try Tr25BC558 BC558

1037

4xBC548

Tr25 - Tr32

037 - 0391N4448

R4s

3k3

P38

030 R503k3

R5433k

Tr26BC558

R67

47k

C14 Rsa270k

Tr34BC558

01s

Rss Rss 1p

39k 27k0

R57

1M

Vss

2/6 40106 031

1/6 1M540106

(IC4)

0321N4148

161p

vol. SC -11, no. 2, Apr 1976.3. Douglas Self, Tots versus bjts the linearitycompetition', EW+WW, May 1995, pp. 387-3884. Yannis P. Tsividis and Ken Suyama, `Mosfetmodeling for analog circuit CAD: problems andprospects', IEEE Journal of Solid -State Circuits,vol. 29, no. 3, pp 210-216, Mar 19945. D. Self, private communication, 19956. Ernst Nordholt, 'Design of high-performancenegative -feedback amplifiers', Elsevier,Amsterdam, 1983, republished by the DelftseUitgevers Maatschappij, Delft, 19937. A. N. Thiele, 'Load circuit stabilizing networksfor audio amplifiers', Journal of the AudioEngineering Society, Vol. 24, no. 1, Jan/Feb 1976,pp. 20-23, published earlier in Proceedings of theMEE Australia, vol. 36, no. 9, September 1975,pp 297-2998. A. R. Collins, 'Testing amplifiers with a bridge',Audio, Vol. 25, Mar 1972, pp 28, 30 and 329. P. Baxandall, 'Audible amplifier distortion is nota mystery', Wireless World, Nov 1977, pp 63-66

2/6 40106(IC4)

Y. 0331N4148

Vcc+

043D4148 1N4148

1N41

04224V

400mW

Rho2k2

R59 1/2W82k

Tr36BC546

.1.1Cer1100n

Relay24V 37mA

Tr37BC161 or BC461with heatsinkRth6OK/W

100n

R65

00k

R64220k C19

4µ7

Rx /C°_R

cl>

D34

1N4148

IC5 Q1/2 x 4538

R63820R

0351N4148

Tr35BC548

Re*',, 6 Green

Vc),,{:" IC5

1/2 x 4538

Vss /CLR

Fig. 4. Power supply and protectioncircuit, common to both channels of astereo amplifier. The relay is a doublepole type which switches both channelson or off.

220V50Hz

F3

0.8AT

Si

0'7

A

Pink Red

Pink Grey

Amplimo2 x 15V, 160VA

044SB254Bridge

20

V.++21V

21

4 x 4700µ35V

23

vcc--21V

12mA

R62180

ELECTRONICS WORLD February 1996 143

144

INTERFACINGWITH C

HOWARD HUTCHINGS

If you have followed our series on theuse of the C programming language,then you will recognise its value to thepractising engineer.

The book is a storehouse of informationthat will be of lasting value to anyoneinvolved in the design of filters, A -to -Dconversion, convolution, fourier and manyother applications, with not a solderingiron in sight.To complement the published series,

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programming. The programs having beentested and proved. It is a distillation of theteaching of computer -assisted engineeringat Humberside Polytechnic, at which DrHutchings is a senior lecturer.

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SuperFILTER synthesizes Active, Passive andDigital FIR\IIR filters and ports to SpiceAge forWindows' for a complete analysis.Super FILTER Version 3 for Windows provides the following features.1.

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£29.00£19.95£39.00

LOW COST 486DX-33 SYSTEMLimited quantity of this 2nd user, supurb small size desktop unit.Fully featured with standard simm connectors 30 & 72 pin. Suppliedwith keyboard, 4 Mb of RAM, SVGA monitor output, 256k cache andintegral 120 Mb IDE drive with single 1.44 Mb 3.5" floppy disk drive.Fully tested and guaranteed. onlyMany other options amiable - call for details. £399.00 (E)

FLOPPY DISK DRIVES 31/2" - 8"5/1" or 31/2" from only £18.95 !

Massive purchases of standard 51/4" and 31/2" drives enables us topresent prime product at industry beating low prices! All units (unlessstated) are BRAND NEW or removed from often brand new equip-ment and are fully tested, aligned and shipped to you with a 90 dayguarantee and operate from standard voltages and are of standardsize. All are IBM-PC compatible (if 31/2" supported on your PC).31/2" Panasonic JU363/4 720K or equivalent RFE £24.95(B)31/2" Mitsubishi MF355C-L. 1.4 Meg. Laptops only £25.95(B)31/2" Mitsubishi MF355C-D. 1.4 Meg. Non laptop £18.95(B(51/4" Teac FD-55GFR 1.2 Meg (for IBM pc's) RFE £18.95(B)51/4" Teac FD -55F -03-U 720K 40/80 (for BBC's etc) RFE £22.95(B)51/4" BRAND NEW Mitsubishi MF501B 360K £22.95(B)Table top case with integral PSU for HH 51/4" Flopp or HD £29.95(B)8" Shugart 800/801 8" SS refurbished & tested £195.00(E)8" Shugart 810 8" SS HH Brand New £195.00(E)8" Shugart 851 8" double sided refurbished & tested £250.00(E)Mitsubishi M2894-63 8" double sided NEW £275.00(E)Mitsubishi M2896 -63-02U 8" DS slimline NEW £285.00(E)Dual 8" cased drives with integral power supply 2 Mb £499.00)E)

HARD DISK DRIVESEnd of line purchase scoop! Brand new NEC D2246 8" 85 Mbytedrive with industry standard SMD interface. Ultra hi speed datatransfer and access times, replaces Fujitsu equivalent model.Complete with full manual. Only £299.00 or 2 for £525.00 (E)31/2" FUJI FK-309-26 20mb MFM I/F RFE £59.95(C)31/2" CONNER CP3024 20 mb IDE I/F (or equiv )RFE £59.95(C)31/2" CONNER CP3044 40mb IDE I/F (or equiv.)RFE £69.00(C)31/2" RODIME R03057S 45mb SCSI I/F (Mac & Acorn) £99.00(C)31/2" WESTERN DIGITAL 850mb IDE I/F Brand New £185.00(C)51/4" MINISCRIBE 3425 20mb MFM I/F (or equiv.) RFE £49.95(C(51/4" SEAGATE ST -238R 30 mb RLL I/F Refurb £69.95(C(51/4" CDC 94205-51 40mb HH MFM I/F RFE tested £69.95(C(8" FUJITSU M2322K 160Mb SMD I/F RFE tested £195.00(E)Hard disc controllers for MFM , IDE, SCSI, RLL etc. from £16.95

THE AMAZING TELEBOXConverts your colour monitor into a QUALITY COLOUR TV!!

TV SOUND &VIDEO TUNERCABLE COMPATIBLE'

The TELEBOX is an attractive fully cased mains powered unit, con-taining all electronics ready to plug into a host of video monitorsmade by makers such as MICROVITEC, ATARI, SANYO, SONY,COMMODORE, PHILIPS, TATUNG, AMSTRAD etc. The compositevideo output will also plug directly into most video recorders, allowingreception of TV channels not normally receivable on most televi-sion receivers' (TELEBOX MB). Push button controls on the frontpanel allow reception of 8 fully tuneable 'off air' UHF colour televisionchannels. TELEBOX MB covers virtually all television frequenciesVHF and UHF including the HYPERBAND as used by most cableTV operators. A composite video output is located on the rear panelfor direct connection to most makes of monitor or desktop computervideo systems. For complete compatibility - even for monitors with-out sound - an integral 4 watt audio amplifier and low level Hi Fiaudio output are provided as standard.TELEBOX ST for composite video input type monitors £36.95TELEBOX STL as ST but fitted with integral speaker £39.50TELEBOX MB Multiband VHF/UHF/Cable/Hyperband tuner £69.95For overseas PAL versions state 5.5 or 6 mHz sound specification.'For cable / hyperband reception Telebox MB should be connectedto a cable type service. Shipping code on all Teleboxe's is (B)

DC POWER SUPPLIESVirtually every type of powersupply you can rmagine.Over

10,000 Power Supplies Ex StockCall for info / list.

IC's -TRANSISTORS - DIODESOBSOLETE - SHORT SUPPLY - BULK

6,000,000 items EX STOCKFor MAJOR SAVINGS- CALL FOR SEMICONDUCTOR HOTLIST

VIDEO MONITOR SPECIALSOne of the highest specification

monitors you will ever see -At this price - Don't miss it!!

Mitsubishi FA3415ETKL 14" SVGA Muttisync colour monitor with fine0.28 dot pitch tube and resolution of 1024 x 768. Avariety of inputs allows connection to a host of comput-ers including IBM PC's in CGA, EGA, VGA & SVGAmodes, BBC, COMMODORE (including Amiga 1200),ARCHIMEDES and APPLE. Many features: Etchedfaceplate, text switching and LOW RADIATION MPR

specification. Fully guaranteed, supplied in EXCEL-LENT little used condition. Order asrn & Swivel Base £4.75 Only £119 (E) MITS-SVGAVGA cable for IBM PC included.External cables for other types of computers CALL

5000 Monitors from stock !!!HERCULES, EGA, CGA, VGA, SVGA - 6 to 26"+ Many special items - CALL with your needs !

Just In - Microvitec 20" VGA (800 x 600 res.) colour monitors.Good SH condition - from £299 - CALL for Info

PHILIPS HCS35 (same style as CM8833) attractively styled 14"colour monitor with both RGB and standard composite 15.625Khz video inputs via SCART socket and separate phono jacks.Integral audio power amp and speaker for all audio visual uses.Will connect direct to Amiga and Atari BBC computers. Ideal for allvideo monitoring / security applications with direct connectionto most colour cameras. High quality with many features such asfront concealed flap controls, VCR correction button etc. Goodused condition - fully tested - guaranteed - -ocDimensions: W14" x H123/4" x 151/2" D. Unly t (E)

PHILIPS HCS31 Ultra compact 9" colour video monitor with stan-dard composite 15.625 Khz video input via SCART socket. Idealfor all monitoring / security applications. High quality, ex -equipmentfully tested & guaranteed (possible minor screen burns). In attrac-tive square black plastic case measuring W10" x H10' x 13W D.240 V AC mains powered. Only £79.00 (D)KME 10" 15M10009 high definition colour monitors with 0.28" dotpitch. Superb clarity and modern styling..Operates from any 15.625 khz sync RGB videosource, with RGB analog and composite syncsuch as Atari, Commodore Amiga, AcornArchimedes & BBC. Measures only 131/2" x 12" x11". Good used condition. Only £125 (E)

20" 22" and 26" AV SPECIALSSuperbly made UK manufacture. PIL all solid state colour monitors,complete with composite video & optional sound input. Attractiveteak style case. Perfect for Schools, Shops, Disco, Clubs, etc.lnEXCELLENT little used condition with full 90 day guarantee.

20"....£135 22"....£155 26"....£185 (F)

SPECIAL INTEREST ITEMSMITS. FA3445ETKL 14" Industrial spec SVGA monitors £2452kW to 400 kW - 400 Hz 3 phase power sources - ex stock £POABroadcast Electronics Inc FX30 FM exciter 80-108 MHz £750Stanelco STA15 15kW RF Induction heater system £POAIBM 8230 Type 1, Token ring base unit driver £950IBM 53F5501 Token Ring ICS 20 port lobe modules £750IBM MAU Token ring distribution panel 8228-23-5050N £95AIM 501 Low distortion Oscillator 9Hz to 330Khz, IEEE £550Trend DSA 274 Data Analyser with G703(2M) 64 i/o £POAHP APOLLO RX700 system units £950HP6621A Dual Programmable GPIB PSU 0-7 V 160 watts £1800HP6264 Rack mount variable 0-20V @ 20A metered PSU £675HP54121A DC to 22 GHz four channel test set £POAHP7580A Al 8 pen HPGL high speed drum plotter £1850Marconi 6310 Programmable 2 to 22 GHz sweep generator £6500EG-NG Brookdeal 95035C Precision lock in amp £650OTC Ltd 1550 SM Stabilised IR laser calibration source £2250Ling Dynamics 2kW programmable vibration test system £POAComputer 16mm CCTV auto iris lenses 'C' mount - NEW £125Keithley 590 CV capacitor / voltage analyser £POARacal ICR40 dual 40 channel voice recorder system £3750Roken 80-250 240v single phase flow solder machine £1200ICI R5030UV34 Cleanline ultrasonic cleaning system £POAMann Tally MT645 High speed line printer £2200INTEL SBC 486/133SE Multibus 486 system. 8Mb Ram £1200Zeta 3220-05 AO 4 pen HPGL fast drum plotters £1150Nikon HFX-11 (Ephiphot) exposure control unit £1450Motorola VME Bus Boards & Components List. SAE / CALL £POATrio 0-18 vdc linear, metered 30 amp bench PSU. New £550Fujitsu M3041R 600 LPM band printer £1950Fujitsu M3041D 600 LPM printer with network interface £1250Perkin Elmer 2998 Infrared spectrophotometer £POAVG Electronics 1035 TELETEXT Decoding Margin Meter £3750Andrews LARGE 3.1 m Satellite Dish + mount (For Voyager!) £950Thurlby LA 1608 logic analyser £375Sekonic SD 150H 18 channel digital Hybrid chart recorder £1995Densei MUD 0185AH 1KVa UPS system with baits NEW £575System Video 1152 PAL waveform monitor £485Test Lab - 2 mtr square quietised acoustic test cabinets £300Kenwood 9601 PAL Vectorscope - NEW £650

Please call for further details on the above items

19" RACK CABINETSSuperb quality 6 foot 40U

Virtually New, Ultra SmartLess than Half Price!

Top quality 19" rack cabinets made in UK byOptima Enclosures Ltd. Units featuredesigner, smoked acrylic lockable front door,full height lockable half louvered back doorand louvered removable side panels. Fullyadjustable internal fixing struts, ready punchedfor any configuration of equipment mountingplus ready mounted integral 12 way 13 ampsocket switched mains distribution strip makethese racks some of the most versatile we

have ever sold. Racks may be stacked side by side and thereforerequire only two side panels to stand singly or in multiple bays.Overall dimensions are: 771/2" H x 321/2" D x 22" W. Order as:

OPT Rack 1 Complete with removable side panels. £335.00 (G)OPT Rack 2 Rack, Less side panels £225.00 (G)

32U - High Quality - All steel RakCai)-1Made by Eurocraft Enclosures Ltd to the highest possible spec,rack features all steel construction with removableside, front and back doors. Front and back doors arehinged for easy access and all are lockable with ..five secure 5 lever barrel locks. The front dooris constructed of double walled steel with a'designer style' smoked acrylic front panel toenable status indicators to be seen through thepanel, yet remain unobtrusive. Internally the rackfeatures fully slotted reinforced vertical fixingmembers to take the heaviest of 19" rackequipment. The two movable vertical fixing struts(extras available) are pre punched for standard'cage nuts'. A mains distribution panel internal-ly mounted to the bottom rear, provides 8 x IEC 3pin Euro sockets and 1 x 13 amp 3 pin switchedutility socket. Overall ventilation is provided byfully louvered back door and double skinned top sectionwith top and side louvres. The top panel may be removed or fittingof integral fans to the sub plate etc. Other features include: fittedcastors and floor levelers, prepunched utility panel at lower rear forcable / connector access etc. Supplied in excellent, slightly usedcondition with keys. Colour Royal blue. External dimensionsmm=1625H x 635D x 603 W. ( 64" H x 25" D x 233/4" W )

Sold at LESS than a third of makers price !!

A superb buy at only £195.00 (G)Over 1000 racks - 19" 22" & 24" wide

3 to 44 U high. Available from stock !!Call with your requirements.

TOUCH SCREEN SYSTEMThe ultimate in 'Touch Screen Technology' made by the experts -MicroTouch - but sold at a price below cost I! System consists ofa flat translucent glass laminated panel measuring 29.5 x 23.5 cmconnected to an electronic controller PCB. The controller producesa standard serial RS232 or TTL output which continuously givessimple serial data containing positional X & Y co-ordinates as towhere a finger is touching the panel - as the finger moves, the datainstantly changes. The X & Y information is given at an Incrediblematrix resolution of 1024 x 1024 positions over the entire screensize !! A host of available translation software enables direct con-nection to a PC for a myriad of applications including: control pan-els, pointing devices, POS systems, controllers for the disabled orcomputer un-trained etc etc. Imagine using your finger with'Windows', instead of a mouse !! (a driver is indeed available !) Theapplications for this amazing product are only limited by yourimagination!! Complete system including Controller, Power Supplyand Data supplied at an incredible price of only:Full MICROTOUCH software support pack £145.00 (B)and manuals for IBM compatible PC's £29.95 RFE - Tested

LOW COST RAM & CPU'SINTEL 'ABOVE' Memory Expansion Board. Full length PC -XTand PC -AT compatible card with 2 Mbytes of memory on board.Card is fully selectable for Expanded or Extended (286 processorand above) memory. Full data and driver disks supplied. RFE.Fully tested and guaranteed. Windows compatible. E59.95(A1)Half length 8 bit memory upgrade cards for PC AT XT expandsmemory either 256k or 512k in 64k steps. May also be used to fillin RAM above 640k DOS limit. Complete with data.Order as: XT RAM UG. 256k. £34.95 or 512k £39.95 (Al)

SIMM SPECIALS1 MB x 9 SIMM 9 chip 120ns Only £19.50 (A1)1 MB x 9 SIMM 3 chip BO ns £23.50 or 7Ons £24.95 (A1)1 MB x 9 SIMM 9 chip 80 ns £22.50 or 7Ons £24.00 (A1)4 MB 70 ns 72 pin SIMM -with parity- Only £95.00 Al)8 MB 70 ns 72 pin SIMM - no parity £159.00 Al)INTEL 486-DX33 CPU £55.00 INTEL 486-DX66 CPU £69.00 Al)

FANS & BLOWERSEPSON D0412 40x40x20 mm 12v DC £7.95 10 / £65PAPST TYPE 612 60x60x25 mm 12v DC £8.95 10 / £75MITSUBISHI MMF-D6D120L 60x60x25 mm 12v DC £4.95 10/£42MITSUBISHI MMF-08C12DM 80x80x25 mm 12v DC £5.25 10 / £49MITSUBISHI MMF-09B12DH 92x92x25 mm 12v DC £5.95 10 / £53PANCAKE 12-3.5 92x92x18 aim 12v DC £7.95 10 / £69EX -EQUIP AC fans. ALL TESTED 120 x 120 x 38 mm specify 110or 240 v £6.95. 80 x 80 x 36 mm - specify 110 or 240 v £5.95IMHOF B26 1900 rack mnt 3U x 19" Blower 110/240v NEW £79.95Shipping on all fans (A). Blowers (B). 50,000 Fans Ex Stock CALL

Issue 13 of Display News now available - send large SfIE - POCKED with bargains!

1'

-ELECTRONICS-VISA rr ESTABLISHED

25 YEARS

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LONDON SE19 3XF

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Nr. Thornton Heath 8Selhurst Park SR Rail Stations

DISTEL©The Original

REE On line DatabaseInfo on 20,000 + stock items!RETURNING SOON !

ALL IT ENQUIRIES

0181 679 4414FAX 0181 679 1927

All prices for UK Mainland. UK customers add 17.5% VAT to TOTAL order amount Minimum order £10. Bona Fide account orders accepted from Government, Schools,Universities and Local Authorities - minimum account order £50. Cheques over £100 are subject to 10 working days clearance. Carriage charges (A)=£3.00, (A1).£4.00(B)=E5.50, (C)=£8.50, (D)=C12.00, (E)=£15.00, (F)=£18.00, (G)=CALL Allow approx 6 days for shipping - faster CALL Scotland surcharge CALL All goods supplied to ourStandard Conditions of Sale and unless stated guaranteed for 90 days. All guarantees on a retum to base basis. All rights reserved to change prices / specifications without priornotice. Orders subject to stock. Discounts for volume. Top CASH prices paid for surplus grvvf.s. All trademarks etc acknowledged. © Display Electronics 1996. E &0 E 01/5

CIRCLE NO. 125 ON REPLY CARD 147

CIRCUIT IDEAS

Flasher for dogsThis circuit uses a single,

I momentary contact, push buttonto turn an led flasher on and off.

/Ci a and XI b with RI form abistable. Capacitor C1 charges, viaR2, to the opposite logical state ofthe input of ICia. When the switchis closed, C1 forces ICia to changestate. Positive feedback throughthe two gates then stores the newstate.

Oscillation of ICia and /Cib,when the switch is closed, isprevented by keeping resistor R1

100k

significantly lower in value thanresistor R2.

/Cie forms a gated oscillator andis the only reason for using twoinput nand Schmitts in the circuit.DI and R4 make the oscillator lowoutput period shorter than the highperiod.

/Cid corrects the polarity of theoutput and the two transistors act asa buffer. Transistor Tr2 will driveup to a couple of dozen ledsproviding the battery will stand it.Transistor Tr1 can be omitted if

only one led or two leds are used,but R5 may need to be reduced.

Quiescent current was under onemicroamp in the prototype. Tomaintain this, and allow /Cic tooperate correctly, C2 must be a lowleakage type.

The original design was poweredby two AAA cells and drives sixleds on a collar so that I can locatemy errant dog during night-timewoodland walkies!Steve BushEpsom

Frequency comparator with hysteresisAphase -locked loop IC, thePC74HCT4046, forms the core

of the comparator and provideshysteresis.

Potentiometer VR1 sets thevoltage on the IC's voltage -controlled oscillator, C1 and R1being the timing components. Vcooutput goes to one input of thephase/frequency comparator andinput f1 to the other. Output of the

5.0

4.9

4.8

4.7

4.6

4.5

4.4

VC2 4.3Volts 4.2

comparator goes to the circuitoutput via a low-pass filter and byway of the feedback resistor Rf tothe bottom of R1.

When the input is at a lowerfrequency than the vco output FH,the comparator output is low; whenit exceeds the vco output, thereverse applies and the voltage atthe junction of R1 and Rv increases,decreasing the current through RI,

since the voltage at pin 11 equalsthat at pin 9.

This decreasing current lowers thevco frequency FL, so that FH-FL isthe hysteresis.

FL/FH=1-11c2/(VCOin(1+Rf/Rv))where VC2 is a function of R2 and Rf.

W DijkstraWaalreThe Netherlands

4.1

4.0

3.9

3.8

3.7

3.6

3.5

3.40

R2 = 5k

R2=10k

100 200 300RFkil

PC74HCT40463 1

Vcc

R3

3k9

VR1 'Reference10k frequency'

R4

3k9

Frequency comparator provides hysteresis adjustable400 500 by resistor values.


COMPUTER ICSTMS 9900NL-40 PULLS E20 eaS9900 NEW AMD EQUIVALENT £30 eaMC6802 PROCESSOR £2 eaTMS320 £5 TMS320 1 SHOT £3AM27CO20-125L1 SURFACE MOUNT EPROM USED/WIPED £1.50MX16C450 UEART £5P8271 BBC DISC CONTROLLER CHIP EX EQPT £252817A-20 (2K x 8) EEPROM ex egetD41256C-15 2561(01 PULLS 9 FOR E580C31 MICRO £2P8749H MICRO £5D8751-8 NEW £10MK48Z02-20 ZERO POWER RAM EQUI V 6116LP £4USED 41256-15 ElUSED 4164-15 50pBBC VIDEO ULA £108051 MICRO £125FLOPPY DISC CONTROLLER CHIPS 1771 £16FLOPPY DISC CONTROLLER CHIPS 1772 £17.5068000-8 PROCESSOR NEW £6-406384-8 £5ALL USED EPROMS ERASED AND BLANK CHECKED2716-45 USED £2 100/E12732-45 USED £2100/£12764-30 USED £2 100/£1.6027C256-30 USED £227C512 USED £2.501702 EPROM EX EQPT2114 EX EQPT 50p 4116 EX EQPT 70p6264-15 8k STATIC RAM £2Z80A S10-0 £1.257126312 DIGIT LCD DRIVER CHIP £2 ea2816A-30 HOUSE MARKED £2USED TMS2532JL £2.50 2708 USED £2HM6167LP-8 65p68000-10 PROCESSOR £68255-5 £1

2114 CMOS (RCA 5114) £1.60WD16C550-PC UART £6ZN427E-8 £427C256-26 USED £1.50

REGULATORSLM338K.. £6LM323K 5V 3A PLASTIC £3LM323K 5V 3A METAL £3LM350K (VARIABLE 3A) £378H12ASC 12V 5A £5LM317H T05 CAN £1

LM3177 PLASTIC T0220 variable £1

LM317 METAL £2.207812 METAL 12V 1 A £1

7805/12/15/24 30p7905/12/15/24 30pCA3085 TO99 variable reg 2/E178HGASC+79HGASC REGULATORS MO eaLM123 ST93 5V 3A TO3 REGS £3 seUC3524AN SWITCHING REGULATOR IC (10p78L12 SHORT LEADS 10/£1LM2950ACZ5.0 SOP

CRYSTAL OSCILLATORS307.2KHz 1 M000000 1M8432 2M457600 3M6864 4M0000005M000000 5M06800 5M760000 6M000000 6M1440 7M0000003M372800 7M5 8M00000 9M216 10M000 10M0 12M000000 14M31814M3818 16M00 17M625600 18M00000 18M432 19M050 19M219M440 20M000 20M0150 21M676 22M1184 23M587 24M000025M1748 25M175 25M1889 27M + 36M 27M00000 28M32232M000000 32M0000 *S/MOUNT 33M3330 35M4816 38M10040M000 41M539 42M000000 44M444 44M900 44M0 48M0000050M00 55M000 56M00920 64M000000 66M667 76M1 80M084M0 01.50 ea

CRYSTALS321(768 1AAHZ 1M8432 2M000 2M1432 2M304 2M4576 3M0003M2768 3M400 3M579545 3M58564 3M600 3M6864 3M932164M000 4M190 4M194304 4M2056 4M433614 4M608 4M9152 5M0005M0688 6M000 6M041952 6M200 6M400 7M37280 8M000 8M064008M448 8M863256 8M8670 9M3750 9M8304 10M240 10M24510M368 10M70000 11M000 11M052 11M98135 12M000 12M513M000 13M270 13M875000 14M000 14M318 14M7450 14M745615M0000 16M000 17M625018M432 18M432 20M000 21M30021M400M15A 24M000 25M000 26M995 BN 27M045 RD 27M095 OR27M145 BL 27M145 YW 27M195 GN 28M4696 30M4696 31M469631M4696 34M368 36M75625 36M76875 36M78125 36M7937536M80625 36M81875 36M83125 36M84375 38M900 48M00051M05833 54M1916 55M500 57M7416 57M7583 69M545 69M55096M000 111M800 114M8 120M000 El ea

TRANSISTORSMPSA922N2907ABC477, BC488BC107 BCY70 PREFORMED LEADSfull spec f1 E4,,100 £30/1000BC557, BC238C, BC30813 £130 £3.50 1002N2907 PLASTIC CROPPED £1'15 £41100EIC54813 SHORT LEADS (3.100£20.1000

10E110/E110E1

POWER TRANSISTORS0C29 £2 ea2SC1520 sim BF259 3/E1 100/E22TIP 141/2 £1 se TIP 112/42B 2/£1SE9301 100V 1 DA DARL SIM TIP121 2/£1PLASTIC 3055 OR 2955 equiv 50p 100/E35BUZ31 POWER FET TO -220200V 12.5A 2/£1

TEXTOOL ZIF SOCKETS28 PIN USED £3 40 PIN NEW E10SINGLE IN LINE 32 WAY CAN BE GANGED FOR USE WITH ANYDUAL IN LINE DEVICES COUPLING SUPPLIED 2/£1.50

KEYTRONICSTEL. 01279-505543FAX. 01279-757656

PO BOX 634BISHOPS STORTFORD

HERTFORDSHIRE CM23 2RX

MISCELLANEOUSXENON STROBE TUBE £1.802 VOLT 920 A/hr LEAD ACID CELLS, UNUSED, UNFILLED 18" HIGH12" u r, WEIGHT 48Kg each, RUBBERISED CASE, GAULTLETEDTUBULAR PLATE CONSTRUCTION, FOR DEEP CYCLE, HIGHCURRENT USE, MADE FOR BRITISH NAVY, 800 CELLSAVAILABLE, PHONE FOR PRICING ALSO AVAILABLE FILLED &

Narrow angle infra red emitter LED55C 2/£1UM6I 16M -2L surface mount 1000 available ElZ8OB PIO 7000 available Cl each, qty. price 30/50pCNY65 OPTO ISOL 3000 available 50pOPTO ICS also available TLP550 TLP666GF68 way PLCC SKT 1500 available £1 each100 wa PLCC SKT 100 available E1.50 each1250pF POSTAGE STAMP COMPRESSION TRIMMER £1XI R4:1054P-3 serial Eprom 10,700 available....... £1,600701, £251100, 01/3LM324 (Quad 741) 4/£1MINIATURE FERRITE MAGNETS 4x4x3mm 10/£1TL071 LO NOISE OP AMP 5 for E7TL081 OP AMP 4 for E147000u 25v SPRAGUE 36D E3.50 (E2)12 way dui sw MR El1ONF 63V X7R PHILIPS SURFACE MOUNT 100K available

E30/4000SWITCHED MODE PSU 40 WATT UNCASED QTY. AVAILABLE +555A, +12V 2A, 12V 500mA FLOATING

E9.95 (02)220R 2.5W WIREWOUND RESISTOR 60K AVAILABLE

050/1000CMOS 555 TIMERS 2J£12/3 M LITHIUM cells as used in compact cameras 2/E1.50ICM7126CPL CMOS 31/2 DIGIT LCD DRIVER CHIP E2eaLITHIUM CELL 1/2 AA SIZE 2 FOR ElPASSIVE INFRA RED SENSOR CHIP + MIRROR + CIRCUIT E2 eaEUROCARD 28 -SLOT BACK PLANE 96/96 -WAY 525 ea"PROTONIC 24 VARIBUS" 16.7"x 5" FIBREGLASS MULTILAYERPTH PCBEUROCARD 96 -WAY EXTENDER BOARD CIO ea290x 100mmDIN 41612 96 -WAY NB/C SOCKET PCB RIGHTANGLE £1.30DIN 41612 96 -WAY NB/C SOCKET WIRE WRAP PINS E1.30DIN 41612 64 -WAY A/C SOCKET WIRE WRAP PINSDIN 41612 64 -WAY A/C PLUG PCB RIGHT ANGLEDIN 4161264 -WAY NB SOCKET WIRE WRAP (2 -ROW BODY) ElBT PLUG +LEAD 3/E1MIN. TOGGLE SWITCH I POLE do PCB type 5/£1LCD MODULE sim. LM018 but needs 150 to 250V AC for display40 x 2 characters 182 x 355 13mm El 06-32 UNC 5/16 POZI PAN SCREWS E1/100NUTS E1.25/100PUSH SWITCH CHANGEOVER 2/£1RS232 SERIAL CABLE D25 WAY MALE CONNECTORS

£5.90 ea (£1.30)25 FEET LONG, 15 PINS WIRED BRAID + FOIL SCREENS

INMAC LIST PRICE £30AMERICAN 2/3 PIN CHASSIS SOCKET 2/E1WIRE ENDED FUSES 0.25A 30/E1NEW ULTRASONIC TRANSDUCERS 32kHz E2/prPOWERFUL SMALL CYLINDRICAL MAGNETS 3/E1BNC 500HM SCREENED CHASSIS SOCKET 2/£1SMALL MICROWAVE DIODES AEI OC1026A 2/£1D.I.L. SWITCHES 10 -WAY £1 8 -WAY 80p 4/5/6 -WAY 110p

180VOLT 1WATT ZENERS also 12V & 75V 20/£1MIN GLASS NEONS 10/£1RELAY 5V 2 -pole changeover looks like RS 355.741 marked STC47WBost Cl eaMINIATURE CO -AX FREE PLUG RS 456-071 2/E1MINIATURE CO -AX PCB SKT RS 456-093 2/EIPCB WITH 2N2646 UNUUNCTION WITH 12V 4 -POLE RELAY El400 MEGOHM THICK FILM RESISTORS 4/E1STRAIN GAUGES 40 ohm Foil type polyester backed balco gridalloy E1.50 ea 10+ ElELECTRET MICROPHONE INSERT 2/£1Linear Hall effect IC Micro Switch no 613 SS4 sim RS 304-267

£2.50100+ 01.50HALL EFFECT IC UGS3040 + magnet £11 pole 12 -way rotary switch 4/£1AUDIO ICS LM380 LM386 £1 ea555 TIMERS El 741 OP AMP 6/E1ZN414 AM RADIO CHIP 80pCOAX PLUGS nice ones 4/£1COAX BACK TO BACK JOINERS 3/£1INDUCTOR 20011.5A 5/E11.25" PANEL FUSEHOLDERS 3/£112V 1.2W small w/e lamps fit most modern cars 10/E1STEREO CASSETTE HEADMONO CASS. HEAD £1 ERASE HEAD 509THERMAL CUT OUTS 50 77 85 120°C £1 eaTHERMAL FUSES 220°C/121°C 240V 15A 5/£1TRANSISTOR MOUNTING PADS TO -5/T0-18 E3/1000TO -3 TRANSISTOR COVERS 10/£1PCB PINS FIT 0.1" VERO 200/£1TO -220 micas + bushes 10/50p 100/E2TO -3 micas + bushes 15101Large heat shrink sleeving pack £2IEC chassis plug filter 10A £3POTS SHORT SPINDLES 2K5 10K 25K IM 2M5 4/£140k U/S TRANSDUCERS EX-EQPT NO DATA El/prLM335Z 10MV/degree C ElLM234Z CONST. CURRENT I.0 ElBNC TO 4MM BINDING POST SIM RS 455-961 £1MIN PCB POWER RELAYS 10.5v COIL 6A CONTACTS 1 pole do

ElBANDOLIERED COMPONENTS ASSORTED Rs, Cs, ZENERS

£5/1000LCD MODULE 16 CHAR. X 1 LINE (SIMILAR TO HITACHI LM10)... £5OPI1264A 10kV OPTO ISOLATOR £1.35 ea 100+ Cl ea'LOVE STORY' CLOCKWORK MUSICAL BOX MECHANISMMADE BY SANKYO £1 eaTelephone cable clips with hardened pins 500/£210,000uF 165 PCB TYPE 30mm DIAx31mm 2/£1EC CHASSIS FUSED PLUG B -LEE L2728 3/£12A CERAMIC FUSE 1.25" QB 10/£146 WAY IDC RIBBON CABLE 100 FOOT REEL E5+CARR20mm PCB FUSEHOLDER 5/E1IEC CHASSIS FUSED PLUG B -LEE L2728 3/E1ASTEC MODULATOR VIDEO + SOUND UM1287 £2.25BARGRAPH DISPLAY 8 RED LEDS £1.50NE567 PHASE LOCKED LOOP 2/E1

DIODES AND RECTIFIERSA115M 3A 600V FAST RECOVERY DIODE 4/E1

1N5407 3A 1000V 8/E11N4148 100/£1.501N4004 SD4 lA 300V 100/£31N5401 3A 100V 10/£1IN5819RL 20K Ex stock 1000+10pBA158 lA 400V fast recovery 100/£3BY254 800V 3A 8/£1BY255 1300V 3A 6/£16A 100V SIMILAR MR751 4/E1

1 A 600V BRIDGE RECTIFIER 4/EI4A 100V BRIDGE 3/£16A 100V BRIDGE 2/£110A 200V BRIDGE £1.5025A 200 V BRIDGE E2 10/£1825A 400V BRIDGE £2.50 10/0222KBP02 IN LINE 2A 200V BRIDGE REC 8/E1BY297 10/£1103PC304 BRIDGE REC 3A 400V 41E1

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TRIACS DIACS 4/£1NEC TRIAC ACO8F 8A 600V TO220 5/£2 100/£30TXAL225 8A 500V 5mA GATE 2/E1 100/E35BTA 08-400 ISO TAB 400V 5rnA GATE 90pTRAL2230D 30A 400V ISOLATED STUD £5 eaTRIAC 1 A 800V TLC381T 16k AVAILABLE 5 FOR Cl E75/100

PHOTO DEVICESHI BRIGHTNESS LEDS CQX24 REDSLOTTED OPTO-SWITCH OPCOA OPB8152N5777TIL81 PHOTO TRANSISTORTIL38 INFRA RED LED4N25, OP12252 OPTO ISOLATORPHOTO DIODE 50PMEL12 (PHOTO DARLINGTON BASE ri/c)LED's RED 3 or 5mm 12/£1LED's GREEN OR YELLOW 10/E1FLASHING RED LED 5mm 50pHIGH SPEED MEDIUM AREA PHOTODIODE RS651-995OPTEK OPB745 REFLECTIVE OPTO SENSORRED LED - CHROME BEZELOP11108 HI VOLTAGE OPTO ISOLATOR

STC NTC BEAD THERMISTORSG22 220R, G13 1K, G23 2K, G24 20K, G54 50K, G25 200K, RES 20°CDIRECTLY HEATED TYPE El eaFS22BW NTC BEAD INSIDE END OF 1" GLASS PROBE RES 20°C200R El saA13 DIRECTLY HEATED BEAD THERMISTOR 1k res. ideal foraudio Wien Bridge Oscillator

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IC SOCKETS14/16/18/20/24/28/40 -WAY DIL SKTS El per TUBE8 -WAY DIL SKITS 02 per TUBE32 -WAY TURNED PIN SKIS 3 for ElSIMM SOCKET FOR 2 x 30 -way SIMMS £1

POLYESTER/POLYCARB CAPS330nF 10% 250V AC X2 RATED PHILIPS TYPE 330 E20/100100n, 220n 63V 5mm 20/E1 100/E310n/15n/22n/33n/47n/66n 10mm rad 100E3.50100n 250V radial 10mm 100/£3100n 600V Sprague axial 10/£1 100E6 (El)2p2 160V rad 22mm, 2p2 100V rad 15mm 100/£1010n/33n/47n 250V AC x rated 15mm 10E11 p 600V MIXED DIELECTRIC 50p ea1110100V rad 15mm, 1110 22mm rad 100/£60.22p 250V AC 02 RATING 4/£1

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RF BITSSAW FILTERS SW662/SW661 PLESSEY SIGNAL TECHNOLOGY379.5 MHZ £1.50 eaFX3286 FERRITE RING ID 5mm OD 10mm 10 for £1ASTEC UM1233 UHF VIDEO MODULATORS (NO SOUND) 1250STOCK E1.50MARCONI MICROWAVE DIODES TYPES DC2929, DC2962,DC4229F1/F2 El EAXTAL FILTERS 21M4 55M0 £2 eaALL TRIMMERS 3 for 50pVIOLET 5-105pFRED 10-110pF GREY 5-25pF SMALL MULLARD2 to 22pF 3 FOR 50p E10/100TRANSISTORS 2N4427, 2N3866 80p eaCERAMIC FILTERS 4M5/6M/9M/10M7 60p eaFEED THRU' CERAMIC CAPS 1000pF 10E1SL610 Eh

6 VOLT TELEDYNE RELAYS 2 POLE CHANGEOVER £2

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74N16 TAGS CAR PHONE 0/P MODULEEOUIV MHW806A-3 RF IN 40mW 0/P6 -.8w 840-.910mHz £3 ea

MONOLITHIC CERAMIC CAPACITORS

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10n 50V 2.5mm 100E4.50100n 50V 2.5mm or 5mm 100/f6100n ax short leads 100E3100n ax long leads 100E5100n 505 dil package 0.3" rad 100/£8

NE564 El QUARTZ HALOGEN LAMPSP8749H USED WIPED £2TL084 4/E1 12V 50watt LAMP TYPE M312 Et ea HOLDERS 60p eaIR2432 SHARP 12 LED VU BAR GRAPH DRIVER £1.25 6V 50watt

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Ilk


CIRCUIT IDEAS

Control software flow through pc's serial portMany pc application programs usespecial defined keys (for example

Alt+R) to select different procedures. In themanufacturing environment, sometimes it isinconvenient to access the keyboard directly.

For instance, an application program maydefine 'push any key to repeat test'. It makesmore sense to use just a regular push buttonrather than a keyboard. The diagram belowshows how to use the pc's serial port toconnect eight push buttons. Pushing any oneof those buttons will lead the program to aspecified application procedure.

This power -less approach is controlled viaa C program - right.Yongping XiaTorranceUSA

This circui reads eight buttons through the pc'sserial port.

#include <dos.h,

#include <conio.h>

#include <stdio.he

#define MCR 4 /. modem

#define MSR 6 /* modem

void app_1(void)/* your

printf("button 1 is


printf("button 2 is


control register */

status register */

1st application */

pushed");

2nd application

pushed");

3rd application

print("button 3 is pushed");


printf("button 4 is


printf("button 5 is


printf("button 6 is


printf("button 7 is

1

void app_8 (void)/* your

printf("button 8 is

void main(void)

* /

"1

4th application */

pushed");

5th application */

pushed");

6th application */

pushed");

7th application */

pushed");

8th application */

pushed");

int base_address1=0x3f8;/* COM1 address

int base_address2=0x2f8;/* COM2 address

Simple power flasherr or a simple task, a simple circuit.

This is a flasher circuit for amains -powered lamp.

Initially, the capacitor isdischarged and starts to chargethrough the 3.3k0 resistor,triggering the scr. The lamptherefore comes on and stays onwhile current from the capacitorsustains the scr. As the capacitordischarges, the lamp goes off.

Mains220 - 230VAC

Load 200W maxresistive

Using a 60W bulb, frequency isaround 1.1Hz at nominal mainsvoltage and temperature, decreasingslightly with a 25W lamp; dutycycle ratio is 1:1. Capacitancelargely determines frequency and itmay be found that a different gateresistor is needed for other scrs.D Di MarioMilanItaly

3k35W

Very simple circuit to flasha 60W lamp at about 1Hz.

100o350V

int datal, data2;

dot

clrscr();

outportb(base_address2.MCR, Ox01);

/* set COM2's DTR high and RTS

low */delay(1);

datal=inportb(base_address2+MSR)/16;

delay(10);

data2=inportb(base_address2+MSR)/16;

if (datal==data2)

switch(data2){

case Ox08:app_1();

break;

case Ox02:app_2();

break;

case Ox01:app_3();break;

case 0x04:app_4();

outportb(base_address2+MCR, 0x02);

/* set COM2's DTR low and RTS

high */

delay(1);

datal=inportb(base_address2+MSR)/16;

delay(10);

data2=inportb(base_address2+MSR)/16;

if (datal==data2)

switch(data2){

case Ox08:app_5();break;

case 0x02:app_6();break;

case Ox01:app_7();

break;

case 0x04:app_8();

}

delay(200);

iwhile(!kbhit());/* hit any key to quit

Frequency -dependentnegative conductance

Current conveyors do not suffer from the bandwidthrestriction with feedback seen in common op -amps,

so that this fdnc is able to work at much higherfrequencies. Further benefits of using cc amplifiersinclude stability with inductive and capacitive loads.

Input impedance is -co2B, where B = RiR2R3CiC2.K L Sunil KumarVisakhapatnamIndia

yin

Zin zX z

XY

z

X

Using current conveyors instead of op -amps in this fdncincreases its bandwidth and improves stability withreactive loads.


BROADCAST MONITORRECEIVER 2

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We have taken the synthesised all mode FRG8800 communi-cations receiver and made over 30 modifications to provide areceiver for rebroadcast purposes or checking transmitterperformance as well as being suited to communications useand news gathering from international short wave stations.The modifications include four additional circuit boardsproviding *Rechargeable memory and clock back-up*Balanced Audio line output *Reduced AM distortion *Buf-fered IF output for monitoring transmitted modulationenvelope on an oscilloscope *Mains safety improvements.The receiver is available in free standing or rack mountingform and all the original microprocessor features areretained. The new AM system achieves exceptionally lowdistortion: THD, 200Hz-6kHz at 90% modulation -44dB, 0.6%(originally -20dB, 10%).*Advanced Active Aerial 4kHz-30MHz *PPM10 in -vision PPMand chart recorder *Twin Twin PPM Rack and Box Units*Stabilizer frequency shifters for for howl reduction *10Outlet Distribution Amplifier 4 *Stereo Variable EmphasisLimiter 3 *Stereo Disc Amplifiers *Peak Deviation Meter*PPM5 hybrid, PPM9 microprocessor and PPM8 IEC/DIN -50/+6dB drives and movements *Broadcast Stereo Coders.

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I -C port or Mbus & Watch dog facilities Large Proto-typing area for user circuits Up to 5 chip selects available Program in C, Modula-2 & Assembler Real Time multitasking Operating System 059 or MINOS with free run time license

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monitor ROM, Terminal program, Downloader, a singlecopy of MINOS. Extensive example software, and freeunlimited technical support all for 1295 + VAT.

Cambridge MicroprocessorSystems Limited

Unit 17-18, Zone 'D', Chelmsford Road Ind. Est.,Great Dunmow, Essex, U.K. CM61KGPhone 01371 875644 Fax 01371 876077

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CIRCUIT IDEAS

Retuning local -oscillatorcrystalsn a receiver using a crystal -tuned

I local oscillator, changing channelfrequency requires the crystal tobe fine tuned to produce the sameIF. This circuit assists in theprocess.

A reference frequency of10.7MHz, generated by a simplecrystal oscillator, is coupledcapacitively to the mixer bysimply putting the end of its outputcoaxial cable, near the filter.

If an unmodulated signal is now

RF amp

BC108

68p

1k

Paral el mode Colpitts oscillatorused as reference signal

injected at the receiver input, anominal 10.7MHz IF is producedwhich beats with the 10.7MHzreference oscillator output, thebeat being heard at the receiveroutput. Adjusting the localoscillator for zero beat gives thecorrect lo frequency. Use thecircuit for either single or doubleconversion superhets.Glyn RobertsWalsallWest Midlands

Basic single conversion superhet receiver

Remove shieldingapprox. 2cm

U or similar

Mixer Filter IF amp Detector AF amp

Localoscillator

101

An incorrectly set local oscillator will affectthe mixer output frequency.The difference between mixer and reference signalswill produce an audible beat note.

Beat oscillator helps to retune crystal -based receivers to different channels.

Telephone line monitorExploiting the tendency exhibitedby some n -p -n transistors to

oscillate when connected inreverse, this circuit uses one tomonitor a telephone line and givewarning of untoward activity. Innormal operation, the circuit hasno effect on telephone calls, takingabuse such as reverse voltages,spikes and wrong connections inits stride.

Normal conditions show as arapidly flashing green led, whichstops flashing when a call is madeor received. A high-pitched soundshows that reverse polarity is

applied on the line side and theconnection of another telephone inparallel or a short circuit on the lineside sound fades and the led stopsflashing. Disconnection or a blownfuse gives a low -frequency tone fornearly two minutes.

Conversation triggers the ledevery few minutes and ringing ordialling causes it to flash at adifferent frequency. Normally, thespeaker is virtually out of circuit toprovide privacy.D Di MarioMilanItaly

Linear square andtriangle generatorConstant -current charging and discharging linearises

the triangular output from a 555 -based functiongenerator.

When the timer output is at Vec, the timing capacitorcharges through the p -n -p transistor current mirror. As theramp reaches 2V,c/3, the 555 output goes to ground and,since the capacitor voltage is now higher, the capacitordischarges through the n -p -n current mirror until the rampreaches I/cc/3. Charging current is adjusted by R. Outputfrequency is variable up to 2.1MHz.Lee SzymanskiStamfordLincolnshire

1/2Vcc

Matched pairs

Gnd

Square -waveoutput

FET input Triangular output

5116

8V21W

Telephoneset

Telephone monitor gives an indication of fault conditions orunusual activity on the line.


Um ue o r - corn vent e on rorn

ELECTRONICS ELECTRONICS ELECTRONICS LECTRONICSWORLD WORLD WORLD ---e7ti; WORLD+ WIRELESS WORLD

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Distortion from power -amp supplies

Winning power switching circuits

Enhance RS232

Transmission lines explained

Tesla's ht generator

ELECTRONICSWORLD+ WIRELESS WORLD

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PC engineering:signal analysis

24ear esteem

DSP demystified

Analogue signalproressmg

Linsley -Hoodromments onmosfets

IF indllostopprobe using sat

AUGUST 1995

20Hz active subwoofer

Getting more from RS232

PC engineering: signal analysis

24cm antenna

DSP demystified

Analogue signal processing

GPS designer's kit

RADIO &ELECTRONICS

ENGINEER'SPOCKET ROOK

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CIRCUITIDEAS

POCKETBOOK

OPTICAL STORAGE - present and pendi

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FREE Circuit Ideas pocket book Part 2

ISDN - inside the world network

Linsley -Hood's attenuator for audio

Evidence for the slew -rate debate

Self -tuning 50Hz filter for

instrumentation

ELECTRONICSWORLD

New audiopowersolution

I:Lc:aP 5'

InteractionAnaloguefillers

Al IsebalancedamplifierAnalysingIm noise

SEPTEMBER 1995

New audio power solution

Analogue design for a single -rail

MicroCap 5 reviewed

Nulling coil interaction

New balanced amplifier design

Analysing fm noise

BACKISSUESBack issues of ElectronicsWorld are £2.50 in the UKand £3.00 elsewhere*. Priceincludes postage. Pleasecomplete the coupon andsend with correct payment to:Electronics World, QuadrantHouse, The Quadrant,Sutton, Surrey, SM2 5AS

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+ WIRELESS WORLDJune 1.5 V-10

irsr17,'rca.7.7S(Fr:rTri-modalaudio powerNticrorellexloudspeakerAudio powerICs exposed

Researchingvia InternetNew

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It 'I.Versatile £220 i/o controller for £99

JUNE 1995

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Microreflex full -range loudspeaker

Audio power ICs exposed

Researching via the Internet

New concept in i/o control

30% OFF - 10A nieltheetor MG transistor t

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FREE Circuit ideas pocket book

Sweeper for 0 to 200MHz

IEEE488 testing made easy

Current probe for switching mosfets

Valve audio

Analysing circuits via energy

DC circuit design

+ WIRELESS WORLD

Mean ratemonitorSignalewCeedntre

Coaxial tableanalyserDual mirrorfor fasteraudio

ModulatinglinearlyOscillatorinnovations

JULY 1995

PC Interfacing

Signal Centre reviewed

Coaxial cable analyser

Dual mirror for faster audio

Modulating linearly

Oscillator innovations

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Power andMap(Linsley -Roodnoise recliner

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NOVEMBER 1995

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Optoelectronics investigated

Isolate RS232

14.4kbaud fax/data modemPower and Class -C

Linsley -Hood noise reducer

Applying the ZR78L05 regulator

Issue (Month/Year) Quantity Price Total

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CIRCUIT IDEAS

Edge detector/doublern a similar manner to that of theI

circuit by Mike McGlinchy(Aug.1994 Circuit Ideas), thiscircuit responds to both transitionsof square input, but this one is self -clocked and a little simpler,although it does have one extra IC.

Delay RDCD gives control of

Vccinv

dir

to

2fo

output pulse width t, and may besplit between sections a and b ofthe 74HC86 to equalisepropagation delay, allow smallercomponents or increase pulsewidth.

It is essential to use cmos logicbecause of the source -current

dir inv

74HC74

limitation to RD when positive -going and the logic zero thresholdwhen negative -going. Values in thetable are for a 10V supply.John A HaaseColorado State University

Edge detector producing output pulseson both transitions of the input atfin/2 and 2fin, positive or negative.

/0

>1/2f.

tw, ns 50 70 150 230 400

CD, pF 0 0 24 50 100

RD, 1,...(2 0 4.7 4.7 4.7 4.7

Low -battery monitor shuts down gracefullyAfter detecting a low -batterycondition, this circuit allows a

definite time for emergencyhousekeeping tasks before shuttingdown a controlling processor,rather than waiting until batteryvoltage decreases further. Currentdrawn while quiescent is a fewmicroamps, so that discharged cellsare protected. Accurate voltagemonitoring, achieved by the closetolerance of a comparatorthreshold, allows the battery -lowwarning to be positioned exactly onthe knee of the NiCad dischargecharacteristic.

Low -dropout linear regulator ICIsupplies 250mA to the outputpower line, dropping only 350mVat 200mA; IC2 is a dualcomparator/±1% voltage reference.If the fraction of the battery voltageat the junction of R1 and R2 fallsbelow the internal 1.182Vreference voltage, OUTB goes high,serving as a warning and alsocharging C1 through R3. When thevoltage at pin 3 rises to thereference voltage, OUTA shuts ICIdown. To obtain ±25mV ofhysteresis, make R4 49.91(51 and R52.4%2.

If, for example, R3 is 1MS2, C3 is

calculated by Vth=VOUTBwhere Vourg is 4.9V and is R3C1.For a is delay, r is 3.6s and C1 is3.6pF. Alternatively, a standard3.9p F gives a delay of around Is;use a low -leakage type. Duringshutdown, C1 becomes charged and

needs about 6s to discharge whenoperation resumes.Craig Falkenham andLarry SuppanMaxim Integrated Products LtdThealeBerkshire

Bi5 - 6 cells '7

I

OUT

ICtMAX667

SET

GND SHDN

R3

INB- V+OUTA

OUTB REF

102MAX923

INA+ HYS

6

C2

o 5V/200mA

o Low -batterywarning

On detecting lowbattery voltage,this very frugalcircuit issues awarning signaland shuts apower line downafter a precisetime interval,rather than afterthe usual,somewhatindefinite timetaken for thebattery voltage todecrease evenfurther.

154 ELECTRON ICS WORLD February 1996

ANCHOR

+44

EATON

TheNottingham

2075

Tele:(0115)

FrequencyResolution

Cattle

Fax:NOISE

10Mhz toMax

Gain Measurements

EMC

SURPLUSMarketNG2

+44 (0115)986 4041

+44 (0115)GAIN

1800Mhz withoutInput to +20dbm.

range of 2075to 0.1 Mhz.

Specs toEMS Specs

Supplied with

-20db

NoiseMIL

98624hr986

ANALYSERExternalNoise

10Mhz

-STDto

Case

UK

+ 7618E

± 0.2db with(tunes

RE02,CS06,in Noise"

Ltd .... ...

ORSURFk,

NOISE GENERATORto 18Ghz

± 0.05dbresolution

±0.5MhzVSWR <1.5:1

VDE

£3250

3GY.4902/

answerphone

tp >50dbto

<7db461,

CS01,and

Depot

4667

equipment,Measurement

1800Mhz+0.002db/Mhz.

CE03,CS02,

"Topics

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LETTERSLetters to "Electronics World" Quadrant House, The Quadrant, Sutton, Surrey, SM2 5AS

Reflections onoptical linksn his article 'Reflections onOptoelectronics' in the Novemberissue, Ian Hickman says thatincreasing the gain of the photodiodeamplifier by 40 dB extends the rangeof the optical link by a factor of 100,for example from 2m to 200m. Idon't agree with this assertion.

Assume, for the moment, in termsof linear units rather than decibelsand consider Fig. 12a) of the article.Amplifier A2 has a voltage gain of100, so if we transfer the oscilloscopeprobe from the output of Al to theoutput of A2 and we want to observethe same signal amplitude, than thecurrent produced by the photodiodehas to be reduced by a factor of 100.

Current produced by thephotodiode is proportional to theincident light power, which thereforehas to be reduced by the same factor.

A ratio of 1:100 in incident lightpower corresponds to a ratio of 10:1in distance, so Fig. 12c) displays the

simulated output of A2 at a range of20m rather than 200m.

If we want to argue in terms of thesometimes deceiving decibel, wehave to point out that the photodiodeis a non linear transducer which canbe thought as made up by anelectrically linear receiving antennafollowed by a quadratic detector.

The antenna establishes a linearrelation between the alternatingelectric field associated to incidentlight and the voltage produced; thedetector establishes a linear relationbetween the dc current produced byitself and the mean square of thealternative voltage produced by theantenna.

In fact, as the incident light poweris proportional to the square of therelevant alternative electric field, wecan verify the linearity of the relationbetween the dc current produced bythe photodiode and the incident lightpower.

So a 20 dB loss in the incidentlight power (relevant to a 10:1distance ratio) causes a 40dB loss inthe signal current, just recovered by

amplifier A2.To recover the signal loss due to a

100:1 ratio in distance, the amplifierA2 should have to gain 80dB;unfortunately at a range of 200m theoutput signal of A2 would appear astotally buried by noise since thesignal to noise ratio was just enoughat a range of 20m, as displayed byFig. 12c).Carlo CarliFerraraItaly

Clarified linearmodulationIn his letter of Dec 1995 concerningmy article 'Modulating Linearly' -July 1995 - Mr West makes thepoint that "intermodulation productsare usually generated at the poweramplifier final stage".

I entirely agree, indeed, the secondparagraph of the article runs "In anhf ssb transmitter, it is likely to bethe transmitter power amplifieroutput stage that is principallyresponsible for... intermodulation

products." It goes on to point outthat as clean a test signal as possibleis desirable for test andmeasurement purposes.

Nevertheless, it is true that hf ssbpower amplifiers only produce theamount of intermodulation productscommonly observed, because theyare permitted to do so by currentregulations 25dB below either tonefor R3E, J2E and H3E withoutprivacy device; 35dB with privacydevice and for A3E, B8E, R7B, B7Band B7W, per CCIRRecommendation 326.

There is no incentive formanufacturers to produce 'cleaner'power amplifiers, bearing in mindthat this would involve extra costs.

However, if this were necessary,the required techniques are alreadyto hand. The Polar Looptechnique1,2 was intended to permitthe use of ssb with 5kHz channelspacing at vhf, should this standardever be introduced. Power amplifierintermodulation products of 55dBbelow either tone weredemonstrated, and the principle

But EMC testing isnot requiredIn Letters, Dec. '95, Chris Bore makes aninteresting point regarding emc emissions. Heappears, however to be misinformed on the emcdirective requirements. Equipment does not haveto be tested - contrary to what many test houseswould have you believe.

Conformance can be shown by submitting aTechnical Construction (TCF) to notified body, oryou can self -certify if you are confident that itmeets the standards.

Secondly, common sense shows that 2W is notsensible limit for input power. The point of emcis to stop interference to radio communications.A device radiating more than a few tens ofmilliwatts on a broadcast or communicationsband would clearly see interference.

However, it is still reasonable to assume thatdevices using sufficiently low power could notemit over the test limits - digital watches forexample.

The same would apply to items using lowclock speeds and slow logic, as radiatedemissions are only measured above 30MHz formost products. If you can show calculations tojustify this, you could use the TCF route or self -certify on this basis - there would be no need fora change in the regulations.

Still on the subject of emc, I've found a verycheap way of assessing emissions. From a hamradio shop, for less than £300, you can get ascanning receiver covering 1MHz to 1GHz witha signal strength meter. This is obviously notvery accurate, but it does tell you everything

needed for development work - ie are thereemissions, if so where, and if I make a changedoes the level go up or down? If you cannot`hear' your product on this, it is reasonable toassume it won't interfere with anyone else's.Mike HarrisonLoughtonEssex

EMC critique deservedChris Bore's letter regarding emc and low powercircuits has already received some comment inanother trade journal, namely ElectronicsWeekly.

Criticism of his thesis has given examples suchas oscillators or a photographic flash gun whichcould produce interference at spot frequencies.And one way of checking an IR remote controlis to listen for the interference it can induce intoan am radio at zero range.

However, his main point deserves sympatheticconsideration for any low power item whoseonly interference output (if any) would be whiteor pink noise. After all, the measurement band isup to I GHz.

As Mr Bore said, let someone competent do thecalculations, and come up with some usefulfigures, including allowance for power deliveredto load. The 2W must be power available tocause interference and represent deviceinefficiency.R HigginsonEdgbastonBirmingham

Arguments on EMCpartly rightI think that Chris Bore's arguments are soundwhen cw or quasi-cw rf signals are beinggenerated from conventional power supplies.Forty years ago, a young graduate showed, to hisjoy, how to generate short pulses of 10kV and200kA using a modest 1kW for less than oneminute from the mains. It soon became necessaryto measure these pulses, and in a short timeconducted interference pulses of 1000V and 100A(105W) were easily but inadvertently produced.

Pulsed power has moved into everyday use - forexample high power lasers, and electric traction.As the rise time approaches Ins or less, thepossibility of radiating an appreciable part of thepulse power from leads only a few centimetreslong becomes likely in bad designs. Switchedmode power supplies are using ever faster andshorter pulses and have internal pulse powersexceeding their average input and output powers.

I must admit to having enjoyed this subject,especially the challenge of separating a I012Wsource from a diagnostic of 10"6W (180dB). Butnow that emc regulations have moved into thethird of the `Three Cultures'1, I am thankful at nothaving to justify it in terms of the Europeanregulations.E. ThorntonGloucester

Reference1. Maurice Ramsey, 'Three Cultures', PhysicsWorld, p72, Aug 1994. (UK Institute ofPhysics).


LETTERS

would be directly applicable at hf.The same sort of reduction in odd

order intermodulation levels couldbe achieved by the related CartesianLoop system, which I believe wasalso developed at Bath University.

These techniques require theresolution of a sample of thetransmitter output into its real andimaginary components atintermediate frequency in order toclose the loop. This naturallyrequires a fair amount of kit, so inthe absence of mandatoryregulations requiring that sort ofperformance, it is not surprising thatextensive use has not been made ofthese schemes.

In the mid 'eighties, I developed asimpler arrangement, which wasapplied to a 150W broadband hfpower amplifier module. The latterwas designed to be multicoupled upin stages, to provide various powersup to 1kW PEPS. This also reducedthe third order intermodulationproducts to 60dB or more below PEP.

Even with this degree of transmitteroutput stage linearity, it remains truethat the main use for an ultralinearmodulator is in test and measurement.For any out of band intermodulationproducts produced by the modulatorwill usually be adequately suppressedby the following sideband filter. Theexception is where modulation is

performed without a sideband filter,for example by quadraturemodulation.

However, I cannot agree that oddorder intermodulation products addto the intelligibility of speech per se.Indeed they degrade it. Theimprovement in hf communicationsin difficult conditions arises fromthe fact that, with a very poor signalto noise ratio, the degradation due tointermodulations is more than offsetby the improved signal to noise ratiobrought about by the increasedaverage radiated power. Theinstantaneous compression providedby intermediate -frequency clippingfollowed by a second sideband filter- compared with the slower

compression provided by a VOGAD- is very effective at emphasisingthe quieter components of speechsuch as unvoiced consonants -particularly sibilants - whichotherwise get lost in the noise.

References1. Petrovic V and Gosling W, 'PolarLoop Transmitter', ElectronicsLetters, 1979, 15,(10),pp. 286-8.2. V Petrovic and C N Smith, 'TheDesign of VHF SSB Transmitters'IEE Conference on CommunicationsEquipment and Systems, April 1982,pp. 150-5.3. 'Single Sideband

Transmitters', UK Patent 2209639Bgranted 1 May 1991, assigned toSiemens Plessey Electronic SystemsLtd.Ian HickmanWaterloovilleHampshire

Complete loonyI am fairly sure that loonier mindsthan mine will point out that MorganJones' valve power amplifier designshown on page 27, January isflawed.

The "concertina" phase splitterconcept works adequately at lowfrequencies but falls over in thehigher ranges: the splitter anodepresents a much higher driveimpedance than that of the cathodemirror. While signal levels look thesame at low frequencies, the Millereffect present with high gain, highcapacitance audio power pentodesknocks off the sharp signal edges inthe top half of the circuit. It is muchbetter to use a double triode virtualearth phase split circuit whichproduces a symmetrical output inevery respect.

But it is all academic really. Whobut a complete loony suffering fromterminal nostalgia would seriouslyconsider valves for anything? Whichis probably the reason that Mr Jones

didn't consider dynamic outputimpedance... But then it takes one toknow one.Frank OgdenConsulting Editor

Fields and healthIn his response to Roger Coghill'sletter - EW+WW May, 1995 - yourcorrespondent Colin Davidson offersto ensure that the IEE will give thewidest possible publicity to anyevidence concerning possiblerelationships between low-level,low -frequency electromagneticfields and health - EW+WW Dec,1995.

There is indeed, abundantevidence of the existence of a directrelationship between all forms ofelectromagnetic field and livingtissue. The demonstration of thisrelationship relies on concepts ofcoherent polyphase computationrather than on crude measures offield strength.

It is principally governed by a bi-linear modulo -four arithmetic as anexpression of phase conjugatequadrature rather than by decimalmathematics. The IEE would bewell advised to study the subject ofbioelectronics with close attention,since the ultimate expression ofthese effects is that of heuristic

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LEITERS

electromagnetic resonance as thedriving force of evolution.

The Institution should thereforecontact the Department of Health orSir John Maddo, editor of Nature, towhom much relevant informationhas already been supplied.REP ClementClement Neuronic SystemsPowys

Sallen & Key misread?Before accusing me of departingfrom the truth, or at least of drawingwrong conclusions, Mr. Skirrow(Letters, December) would have donewell to read my November lettermore carefully, even to repeat mysimple experiment. The distortionfigures I tabulated were measuredwith no capacitors at all in circuit. Idid not try the 5532 op -amp, butanyone interested could easily do so.It just seemed odd to me that after allthese years the S&K circuit continuesto appear in data -sheets without ahealth warning.

I also wrote to one of the Americanop -amp manufacturers, and havesince heard that the explanation isthought to be the variation of inputbias current with common -modeinput level. I have also heard fromone or two interested readers whohave detected audible distortion inS&K circuit.

Mr Skirrow criticises my use of110k resistors, saying that 3k3 wouldbe optimal, but not why. No doubt3k3 would reduce distortion, becauseof the very effect I reported, andprobably make it negligible for manyapplications. But why put up withthis constraint - and the cost of largercapacitors - when a better circuit isavailable?

The replacement Rauch 1kHzcircuit referred to in my previousletter is shown here, nominal Q=1.47,and F. gain unity. It adds nodetectable second harmonic (<2ppm)and uses capacitors easily available inpolystyrene.A. D. RyderBoltonLancashire

Foster -Seeley related?Your recent articles on valveamplifiers and Richard Brice's articleon the Seeley -Foster discriminator,Dec 1995, have awakened interest andnostalgia. I built a Williamson

amplifier while still a student atuniversity, and a valve fm tuner a fewyears later. Though at the timegrasping their essential operatingprinciples, my main memories wereof not really understanding theoperation of the fm discriminator.Time may not have fully solved thelatter problem.

Richard Brice's equivalent circuitfor the loosely coupled IF transformerbears a remarkable resemblance to adisastrously designed pulsetransformer in which the leakageinductance L(1+k) greatly exceeds theprimary inductance -kL.

I found it academically interestingto try to explain the 90° phase shiftdiscussed in his article withoutresorting to his more rigorousanalysis. Clearly, when closely(perfectly) coupled the leakageinductance is zero and AB in hisfigure represents the primaryinductance and the identical reflectedsecondary inductance of the perfecttransformer. Input and output voltageswill be in phase.

When loosely coupled, AB (-kL)represents the low valued couplinginductance of the intermediate -frequency transformer, the voltageacross which drives the right-hand sideof the equivalent circuit. This latterconsists of a series resonantcombination of capacitance C and

inductance L(l+k) whose overallseries impedance is zero.

There is however a loss term, theright-hand parallel resistance R, whichI would transform into the timehonoured series equivalent seriesresistance r, in series with L and C.

Voltage generator AB therefore seesto its right-hand side a pure resistancer, and a current will flow in phase withVAB. This means that the currentthrough L and C at resonance is inphase with V. I assume that r,though small, is larger than joicL, anddoes not significantly load thecoupling inductance. The voltageacross L (or C) will be 90° out ofphase with the current through themso there will be a 90° phase shiftbetween points A and C.

Coupling inductance kL is in serieswith the primary inductance L on theleft-hand side and their voltages willtherefore be in phase. Hence,providing the coupling inductance isnot appreciably loaded, V10 and Vout,will be 90° out of phase.

Nostalgically, after about 10 years,the transistor arrived and the monoWilliamson was replaced by a stereopair of Tobey and Dinsdales. Thephase -locked loop took over the fmdiscriminator after a further couple ofdecades.E. Thornton.Gloucester

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9Tektronix 704 -500MHz ..... from E850Telequ lament £183 - 50MHz dual ch ......... £200

Other scopes available too

IIGEGE3=33111Advantest 4133A- 10KHz-20tH E6995Advantest 41338 - 10KHz-20tH - (60GHz with ext. mixers) £7995Hewlett Packard 1417 8552B +8555A (10MHz-18GHz) £1600Hewlett Packard 1821 with 8559A (10MHz-21GHz) ........... ......... C3750Hewlett Packard 853A with 8559A (0.01-21GHz) £4250Hewlett Packard 3562A - dynamic signal analyser, dual channel £7500Hewlett Packard 3580A - 5Hz-50KHz £995Hewlett Packard 3582A - 25KHz analyser, dual channel C2500Hewlett Packard 370913 - Constellation Analyser with 15709A High

Impedance Interlace (as new) 16750Hewlett Packard 8505A- Network analyser (503KHz-1.3GHz) £4000Hewlett Packard 8565A (0.01-22GHz) 4000Hewlett Packard 8590A KHz-1.56Hz ..... . _ . ...... £4250Hewlett Packard 8754A Network Analyser- 4-1300MHz .Hewlett Packard 35601A- Spectrum Analyser Interlace ............Marconi 2370 -110MHzMarconi 2371 30Hz 200Milz £12501

Rohde & Schwarz - SWOB 5 Polyskop 0.1-1300MHzPol rad 641-1 - 10MHz-18GHz

Schlumberger 1250- Frequency response analyser . ........Tektronix 496P- 1KHz-1.8GHz programmable......... ......Tektronix 2710 -KHz-1.8GHz..... .... ............ . ....... .............. . £4250

MANY MORE ITEMS AVAILABLE -SENDLARGE S.A.E. FOR LIST OF EQUIPMENT ALL

EQUIPMENT IS USED - WITH 30 DAYSGUARANTEE. PLEASE CHECK FOR AVAILABILITY

BEFORE ORDERING - CARRIAGE& VAT TO BE ADDED TO ALL GOODS

158


ELECTRONICS WORLD+WIRELESS WORLD February 1996

NEW PRODUCTS CPlease quote "Electronics World"when seeking further information

ACTIVEA -to -D and D -to -Aconverters12 -bit a -to -d. Analog's AD9042analogue -to -digital converter samplesat 41Msample/s minimum while givingtrue 12 -bit performance with aspurious -free dynamic range of 80dBat half the sampling rate;intermodulation distortion is 90dB atthe Nyquist frequency. Powerconsumption is 575mW from a single5V supply. The device is made inAnalog's XFCB technique, which isextremely fast complementary bipolar.Analog Devices Ltd. Tel., 01932266000; fax, 01932 247401.

Discrete active devices6.4GHz power fets. Hewlett-Packardhas the 1M5964-xL series of internalmatched gallium arsenide power fets(Imfets) to operate in the 5.9-6.4GHzcomms band. Typical output is over4W and the devices contain internalmatching networks. Hewlett-PackardLtd. Tel., 01344 366666; fax, 01344362269.

Fast diodes. BAS family diodes fromITT provide extremely fast switchingand are extremely versatile. Theseextreme diodes have forward voltagesof 1V at 100mA and 1.25V at 200mA,with reverse breakdown at 120V -250V. Power dissipation is 200mW at25°C. ITT Semiconductors. Tel.,01932 336116; fax, 01932 33148.

Linear integratedcircuitsMultiplexers. Analog's ADG608/609are eight -channel and differential four -channel multiplexers for 3V, 5V and±5V supplies. Economy is served bythe provision of an on resistance ofunder 30Q and less than 0.5nAleakage current, so making themusable in precise circuitry that oftenrequires several more components.Power consumption lies between0.1pW and 1.5pW, depending onsupply, and operation is free fromlatch -up to 100mA or more. There arealso ADG438F/439F, with eightsingle -ended channels and fourdifferential inputs. Both devices arefault -protected, but without the usualloss of performance. Analog DevicesLtd. Tel., 01932 266000; fax, 01932247401.

Memory chipsFlash proms. EDI has a range offlash simm and plcc modules basedon a standard JEDEC 80 -pin simm or68 -pin plcc arrangement, with a 32 -bitdata bus in capacities up to 32Mb.

The proms work on 5V and give bothmore board space and increasedmemory up to 256Mb, with accesstimes of 100-150ns. EDI (UK). Tel.,01276 472637; fax, 01276 473748.

Microwave componentsCoaxial attenuators. AtlanticMicrowave's new range ofattenuators comprises SMA, 2.92mmand Type N units for frequencies fromzero to 40GHz. Attenuation is from0.5dB to 60dB, with accuracy at 30dBof ±0.75dB. Rating is 2W at 25°C andversions with cooling fins to handleup to 50W. They are normallymale/female in -line, but can bemale/male or female/female andthere is a hexagonal body section, ifrequired, to allow accurate setting ofcoupling torque. Atlantic MicrowaveLtd. Tel., 01376 550220; fax, 01376552145.

Travelling -wave -tube amplifier.Thorn Microwave Devices announcesthe PTX7439 amplifier, which uses a9-10.5GHz (other frequencies toorder) travelling -wave tube matchedto an encapsulated, switched -modepower supply. The amplifier isdesigned for battery -powered andairborne use, offering an efficiency of30% minimum at a power output of45dBm. Built-in circuitry allowsmonitoring of correct operation. ThornMicrowave Devices Ltd. Tel., 01815735555; fax, 0181 5691839.

Broad -band klystrons. TMD hastwo new klystrons for future airbornesystems, featuring small size, highefficiency and phase stability invibration and shock. PT5184produces 50kW at 5% bandwidth in Xband with 1.5kW of average power,periodic permanent -magnetfocussed, although a solenoidallyfocussed version is being developedthat will produce 100kW peak and5kW average output. PT6470 gives1-3kW peak at 2% bandwidth in Xband at a very high duty ratio. ThornMicrowave Devices Ltd. Tel., 01815735555; fax, 0181 5691839.

Optical devicesWafer inspection. For theinspection of silicon wafers at highmagnification, Vision Engineering

_ASSIFIED

has introduced a wafer loader for its5E Dynascope optical inspectionsystem. It uses the WEDSemiconductor Wafer Handler forrapid operation and precisepositioning of wafers before cuttingand encapsulation. VisionEngineering Ltd. Tel., 01483223417; fax, 01483 223297.

PASSIVEConnectors and cablingPrinter connectors. Fujitsu's FCN-240R series of parallel PC -to -printerconnectors conform to IEEE P1284 -Cstandards, European CE Mark andthe CG standard and are a directreplacement for Centronicsconnectors. They are protectedagainst emi and esd. There are right-angled sockets for pcb mounting andplugs come with light plastic shells ordie-cast covers. Rating is1Adc/240Vac with a contactresistance of 30m0; insulationresistance is 1GQ. Inelco Ltd. Tel.,01734 810799; fax, 01734 810844.

Comms cable. Montrose/CDT ofMassachusetts has a new line ofpairs -in -metal -foil cable designed tocomply with new crosstalk standards.Each pair is individually shielded bythe foil and the whole braided overallwith a pvc or zero -halogen jacket.EMAXX 300 shows a -55dBperformance at 300MHz, whileEMAXX 400 gives the sameattenuation at 400MHz. The cablesare smaller than comparable types.Montrose/CDT. Tel., 001 (508) 7913161; fax, 001 (508) 793 9862.

Mains/phone/data services. Rendaroffers an integrated electrical servicessystem to enable 'Plug -and -go'installation of the three types ofservice in an office complex, basedon two, four and six gang UK and IECsocket styles with variable orientationand a choice of switching and fuseoptions. Rcd, mcd and filter modulesare available for protection againstearth leakage, overcurrent andtransients and the system is easilyadapted in the light of future needs.

Synchronous dram. Designedto match 64 -bit memory busbandwidth, two synchronousdrams from Smart can beused to make main memoriesto run faster than anypreviously available. They areorganised as 1M by 64 and2M by 64 and offer athroughput of 900Mbyte s,both being 168 -pinunbuffered dimms with serialpresence detection. SmartModular TechnologyTel., 01908 234030fax,01908 234191

Rendar Ltd. Tel., 01243 866741; fax,01243 841486.

DisplaysColour lcd controller. For colourliquid -crystal displays, a controllercard from Inelco allows the display of22981 colours. It has 512K of dramon board and comes with utilitysoftware. Since the video bios is user -programmable, driving parameterssuch as refresh rate and resolutioncan be varied to suit. A SmartMapfacility allows the intelligentconversion of colour to a grey scale intext mode to solve the problem ofapplications being optimised forcolour crts. The card fits any 16 -bit,ISA-compatible slot. Inelco Ltd. Tel.,01734 810799; fax, 01734 810844.

FiltersRelay filters. Solid-state filterscontribute enough 150-400kHz noiseto come between the domesticEN50081-2 and the industrialEN50081-2 standards. Relay makerCrydom has introduced relays withfilters to suppress this noise in singleand three-phase applications, simplybeing connected across incoming lineor phases. One filter suffices forseveral relays at currents over 15A.Noise reduction at 50A is from70dBpV to 35dBpV at 150kHz and to


NEW PRODUCTS CLASSIFIED

Please quote "Electronics World"when seeking further information

40dBpV at 250kHz at 30A. CrydomEurope. Tel., 0181 763 0550; fax,0181 763 0499.

HardwarePC card cover. Molex's Snapper is aone-piece, stainless -steel cover forPCMCIA PC cards that needs noepoxy or tape to fit the card to theframe. It is usable with Types I and IIcards in such applications asmodems needing shielding. No heator pressure is needed; a small arborpress closes and secures the cover,which is complete with 68 -circuitstandard interface connector,grounding clips and i/o connectors,also available with solder tails. Arange of cable assemblies and i/oconnectors is available and other kitsfor different PC cards. MolexElectronics Ltd. Tel., 01420 477070;fax, 01420 478185.

Shielded touch screens. LucasDuralith resistive touch screensprovide electrostatic and magneticinterference shielding. They complyfully with emc legislation, nowmandatory, and will protect thescreen and other components against

EMC filters for 3 -phase. FN 258is a filter for three-phaseindustrial frequency inverterswith a universal voltage ratingof 480V by Schaffner, meetingEN 133200 and the American UL1283. The filters are in ninevariants for currents from 1 A to180A and, since its temperaturerating is 10°C higher than usual,it can be used in mostconditions without de -rating.Two -stage filtering provides foroutput cables up to 75m inlength. Schaffner EMC Ltd. Tel.,01734 770070; fax, 01734792969.

discharge from an external object -afinger - charged to several kilovolts.The emi shielding not only protectsthe screens but reduces emissions.Anders Electronics plc. Tel., 01713887171; fax, 0171 3872951.

Embedded PC chassis. IMSannounces the MBPC-641 Microboxchassis of about the size of a shoebox to contain an embedded industrialPC controller safely and in a smallspace. It has a four -slot PC/AT busbackplane, a 65W power supply withfans and a number of connectors fori/o. There is a range of plug-in286/386/486 cards with solid-statedisks to fit the chassis, with threeslots spare. Integrated MeasurementSystems Ltd. Tel., 01703 771143; fax,01703 704301.

Test and measurementSurge testing. A surge generatorfrom Seaward, the THOR testselectrical and electronic equipment forsurge immunity by replicating largesurges of the type caused by powerbursts, lightning and some othersources. Outputs are selectable from0.5kV to 4kV at up to 16A and anoscilloscope connection is provided.The unit is controlled by amicroprocessor to give easy operationand a library of test routines. SeawardElectronic Ltd. Tel., 0191 586 3511;fax, 0191 586 0227.

Non -contact profile measurement.UBM offers the UBR200 non -contactmeasurement system, which can beused with a Microfocus optical sensorto replace the stylus in a profilometer,so reducing the risk of damage andincreasing speed of measurement. Nomodifications are necessary and thesystem works exactly as before.Microfocus automatically controls lensposition to maintain focus on theobject's surface and a second systemmonitors lens position, which is areplica of the surface profile. Tworanges are produced: ±500pm and±50pm, the laser power beingselected to match. AdvancedProducts and Technologies Ltd. Tel.,01865 724863; fax, 01865 725831.

Laser fault finder. ME301 by theSpanish company Molher Electronicais a visual fault locator using a laser tofind several types of fault in opticalfibres, emitting a red glow to indicatea point of high loss in the fibre causedby tight bends or crimps, badconnections, poor splices or breaks,and will identify fibres. Output isselected for cw, low -power cw and a2Hz pulsed signal, the selection beingindicated by a led. A timer can beselected to allow five minutes ofoperation. Molher Electronics sa. Tel.,0034 1 462 25 62; fax, 0034 1 465 5382.

Gas monitoring. The cost of areagas monitoring for health and

building applications is reduced byCBISS's Intelligent Sampling SystemMk 2, which collects samples of up tofour gases in eight areas. Since thatis equivalent to 32 monitoring points,the cost is brought down to £140 perpoint. Gas comes in through ptfe ornylon tube to the central analyser,which allows alarms and data loggingto be carried out centrally without theuse of additional modules. Auto -zeroand calibration are incorporated anddetector faults are shown and theirresults ignored. Windows softwarefor data acquisition is supplied. Awide range of gases can be detected.CBISS Ltd. Tel., 0151 3431543; fax,0151 3431847.

Analogue/digital dmm. From Di-loG,the DL -295 digital multimeter, whichmeasures voltage, current,resistance, frequency to 200kHz andtemperature in the -40°C to 1370°C.In addition to the 3.75 -digit readout,there is also a 43 -segment analoguebar -graph display with a 'zoom'facility for precise readings. Otherfacilities are a comparison functionbetween reference and measuredvalues, lowest and highest readingsover time and a hold facility. Di-loGLtd. Tel., 01707 375550; fax, 01707393277.

Function generators. YokogawaFG200/300 are synthesised functiongenerators with touch -screen control.The FG200 series has sweep andmodulation on two independentchannels at 0.000001Hz-15MHz andup to ±10V, the FG300 types alsoproviding arbitrary sweep andwaveform definition. All waveformparameters can be set independentlyfor the two channels. An extra on theFG300 instruments is a floppy drivefor waveform output or input. MartronInstruments Ltd. Tel., 01494 459200;fax, 01494 535002.

PC -to -storage -oscilloscopemodule. Converting a PC into a22kHz digital storage oscilloscope,the Allison 0 -Scope takes the form ofa module to connect to the printer portand software. Features include aspectrum analyser mode and thenormal facilities offered by the PC forsaving traces and printing can beused. Allison envisages the 0 -Scopebeing used in audio, data logging, carelectronics and the like. AllisonTechnology Corp. Tel., 001 800 9809806; fax, 001 713 777 4746.

Am/fm signal generator. TheTopward 8015 2MHz frequencygenerator offers both amplitude andfrequency modulation at a cost of£159. Its features include 5mV-20Vpkoutput on sine, square, triangular,ramp and pulse waveforms, a polarityinversion switch, variable dc offsetand variable duty ratio on ramps andpulses. There is an internal 400Hzmodulation oscillator, with provisionfor an external source. Tandem

Keypad for lefties. If you arebored with the number pad onthe right of your keyboard, try theCherry G80-3700- one that cango anywhere. It is a separate padto link directly with ordinary IBM-compatible keyboards by way ofa PC pass -through port. It hasthe usual number pad keys, plusfour programmable function keys.It is claimed to be of benefit forleft-handed operators. CherryElectrical Products Ltd. Tel.,01582 763100; fax, 01582768883.

Technology Ltd. Tel., 01243 576121;fax, 01243 576119.

LiteratureTest gear. TTi has a new catalogueof other people's instruments -arange of equipment from the world'smakers, including oscilloscopes,power supplies, audio analysers,video test equipment and mainsanalysers. Manufacturers includeTektronix, Stanford and Hitachi.Thurlby Thandar Instruments Ltd.Tel., 01480 412451; fax, 01480450409.

Power components. A new 150 -page catalogue is produced by Pico,containing details of surface -mountedand plug-in transformers andinductors, dc -to -dc converters andpower supplies. The transformersection has a wide selection of audioand ultra -miniature components.Ginsbury (UK) Ltd. Tel., 01634290903; fax, 01634 290904.

Panel meters. Europa Componentshas produced a 20 -page catalogue ofCrompton Greaves DIN standardpanel meters, which meet theDIN57411 sheet 1NDE0411 pt1,proving that not only are specificationnames becoming longer, but thatthese meters are suitable for veryharsh surroundings. Main product isthe S100 range, which is adaptable tomost requirements, being of moving -iron and moving -coil types,conforming to all manner of otherspecifications, all contained in glass -filled polycarbonate cases with ablack bezel. Europa Components &Equipment plc. Tel., 0181-953 2379;fax, 0181-207 6646.

Modems and GPS. Rockwell offers a50 -page handbook and guide to itsrange of modems and GlobalPositioning System devices, boardsand evaluation products. It contains a




glossary of terms in the telecomms,datacomms and navigation fields.Telecom Design Communications Ltd.Tel., 01256 332800; fax, 01256332810.

Telecomms. A short catalogue fromStanford Telecom gives details ofproducts in the areas of demodulationand spread -spectrum asics andboards, frequency synthesiser boardsand subsystems, forward errorcorrection at up to 45Mb/s and digitalcommunications. BFI IBEXSAElectronics Ltd. Tel., 01622 882467;fax, 01622 882469.

Computer -based instruments.National has a catalogue of softwareand hardware to form instrumentationand industrial automation based onthe use of computers. In over 600pages, the catalogue is in sixsections: software, data acquisition,GPIB, VXI/MXI, industrialcommunications and customereducation. National Instruments UK.Tel., 01635 572400; fax, 01635523154.

Three books on VMEbus. Threereference books and an 'editedhighlights' from a market report on the

Slotted opto-sensor. Omronbelieves its EESX 1101 range oftransmissive, slotted opto-sensors to be the smallestavailable. The whole thing isonly 4.3 by 4 by 5mm and ledand phototransistor each fit intoa width of 1.15mm, leaving a2mm wide slot. A Fresnel lensfocuses the led output on thedetector to give a high current.Devices are of two kinds: astandard phototransistor or aphoto-ic output for improvedswitching speed, the latterhaving an amplifier andregulator, with a Schmitt. OmronElectronics Ltd. Tel., 0181 4504646; fax, 0181 450 8087.

VMEbus are available from VitaEurope. There is a product directoryto about 3000 products from aroundthe world, a 300 -page handbook forengineers and programmers and theVME64 specification for 8 to 64 bitparallel -bus architectures. All thebooks cost around £35 and the reportis free. VITA Europe Ltd. Tel., 01329841272; fax, 01329 846166.

PIC guide. Polar Electronics hasupdated the Beginners Guide to theMicrochip PIC, but it is still at the oldprice of £19.95 from cataloguecompanies such as Maplin, Farnell,RS and Rapid. It is now spirally boundto lay flat and contains information onhardware and software design,assembly and debugging. The priceincludes a disk of useful designsoftware. Most of the new informationpresented is on the 16Cxx family. Forvolume purchases, speak to Ian Ewinor Peter Greenslade at Resource,Polar Group on 01525 858200, fax:01525 858101.

Wire, cable and tubes. Alpha Wireintroduces the Master Catalogue,which takes the form of a guide to theselection and specification of wire,cable and tubing for the electronicsindustry. In 400 pages, the publicationis in ten sections and includesshrinkable tubing, coaxial cables, Iancables, and all kinds of more familiarproducts such as hook-up wire. Thereare also 38 pages of technical data,including information on cableshielding. Alpha Wire Ltd. Tel., 01932772422; fax, 01932 772433.

MaterialsTamper detection. Electrolube offersBloc'Lube, which gives the gameaway when someone who shouldn'tattacks a screw or tuned coil. It isapplied to the component, remainingtacky for a while until final adjustmentis made and drying brittle, so that anyfurther attempt at adjustment cracks itand shows. You can get most of it offwith a screwdriver and any bits leftwith a solvent. Electrolube Ltd. Tel.,01734 403014/031; fax, 01734403084.

Solder paste. Loctite's new solderpastes are particularly formulated foruse in precise, miniature circuitry. The3824, 3825 and 3828 are of naturalrosin, mildly activated and exhibit0.2mm 'slump' on 0.7mm pads afteran hour at room temperature. Nocleaning is needed after reflowsoldering and the wet strength isretained for long periods. Loctite UKLtd. Tel., 01707 821000; fax, 01707821200.

Printers and controllersThermal printer. A 42 -column versionof Epson's M-TS60 thermal printer,the M-TS63, is now available. Itoperates in both directions to print two

lines at the same time at a rate of2.4lines/s. In spite of the width andhigh speed, the unit's price is only70% that of comparable printers. Theunit measures less than 10cm wideand comes with a serial RS -232Cboard to provide a paper feed switch,self test, 5V power supervisor andhead -jam and motor -stall protection.Able Systems Ltd. Tel., 01606 48621;fax, 01606 44903.

Another thermal printer. Fujitsuclaims the world paper speed recordfor its FTP600 series thermal line dotprinters at 100mm/s, running at 40%of the power needed by earlier types.The printers are available in 2in, 3inand 4in versions, producing 480, 640and 832dots/line. FTP621/631/641are produced as mechanisms only orcomplete with interface or as a setwith microcontroller and gate array.Paper cutting mechanisms areoffered. lnelco Ltd. Tel., 01734810799; fax, 01734 810844.

Production equipmentHot jet handpiece. The Royel 100hot jet handpiece is suitable for reflowsoldering or solder paste reflow insurface -mounting application,shrinking tubing and component test.It can be operated from a variable airflow and digital feedback -controlledpower unit such as the HJ1000 or oneof the Royel workstations. An N -typethermocouple gives continuousreadout of air or gas temperature.Production Equipment Sales Ltd. Tel.,01323 811694; fax, 01323 811528.

Power suppliesMicropower dc -to -dc converter.SC1652CS from Semtech is aconverter designed for lcd biascontrast application, having an 87%efficiency. It is an inverting typedriving an external switch to generateprogrammable negative voltages,output being scaled to -40V or moreby two resistors. Quiescent current is80pA or 0.7pA when shut down.Semtech Ltd. Tel., 01592 773520; fax,01592 774781.

100W dc -to -dc converter. Abbott'sSMH50 and SMH100 modulescomplete the family of 200kHz singleand dual output converters of 50, 100and 200/280W ratings, withcomplementary emc filters, transientfilters and ac/dc front end modules.Standard input is 18-36V and outputscover the 2-48V range. There is nocurrent de -rating up to 100°C. AbbottElectronics Ltd. Tel., 01233 623404;fax, 01233 641777.

Low -loss regulators. Input/outputdifference voltage of Sanken's SI-3001N is voltage regulators is 1V andpower dissipation 1.5W with no heatsink; output current is 1.5A. Protectionagainst over current, too high an inputvoltage and overheating. The series is

Three-phase harmonicanalysis. Fluke's 41B PowerHarmonics Analyser is a hand-held instrument measuring truerms voltage and current,frequency and power factor anddisplaying three-phase power.Display is as a waveform, as abar -graph showing the level ofharmonics present or as anumeric value, data beingdownloaded if required. PIDA.Tel. (and fax), 0756 799737.

suitable for use when a constantoutput voltage is needed withouton/off control. Allegro MicroSystemsInc. Tel., 01932 253355; fax, 01932246622.

Lower -cost switchers. Calex says itsnew 100W switched -mode powersupply, while retaining all theadvantages possessed by that type ofdesign, now costs about the same asan unregulated transformer type. itsoutput is 24V, 5A and is proof againstshorts; ripple less than 50mVpk-pk;regulation less than 1% overall; andmains buffering greater than 20ms at5A. The supply conforms to therelevant interference, emission andsafety standards. Calex ElectronicsLtd. Tel., 01525 373178; fax, 01525851319.

Lamp transformers. Meant to drivethe cold -cathode fluorescent lampsused in flat -panel displays,transformers by Coiltronics come inpower ratings of 2.5, 4, 6 and 14W ina variety of mounting styles. They areusable with floating or tied -secondarydesigns and give up to 30mA at40-80kHz. Output is sinusoidal andemi/rfi consequently low.Microelectronics Technology Ltd. Tel.,01844 278781; fax, 01844 278746.

DC -to -DC converters. Melcher's IMRfamily of converters offers ranges of 3,6 and 15W and is for use inreasonable environments. Single ordouble outputs are 5V, 12V or 15Vdc




and input range is 2:1. The smallestunit comes in a 24 -pin dil package,the other two being in 2in squaremodules, both types having standardpinouts. Open and short circuitprotection is provided and i/o isolationis 500Vdc. Melcher Ltd. Tel., 01425474752; fax, 01425 474768.

Switches and relaysSolenoid. BLP's new PED Series 66is a low-cost device suited to uses inwhich a high force:stroke ratio isneeded, but where there isn't muchspace. It measures 30 by 16 by14mm, has a 3W continuous ratingand pulls a load of 0.1kgf at 10mmstroke; 1.1kgf at 1mm. Coils are for 5,6, 12, 24 and 48V and the solenoidsare available in push and pullversions. BLP Components Ltd. Tel.,01638 665161; fax, 01638 660718.

Television componentsCharacter generator. From Philips,the PCA8516 stand-alone on -screendisplay generator, which allows thedisplay of up to 256 high -resolutioncharacters from a font containing 253custom characters. On a 12 by 18dot-matrix area, the device displaysJapanese and Chinese writingsystems and adjacent cells can becombined vertically and horizontally tomake icons and semi -graphics. It isprogrammable to suit all commontelevision scan formats. PhilipsSemiconductors (Eindhoven). Tel., 0031 40 722091; fax, 00 31 40 724825.

Transducers andsensorsBending actuator. For largedisplacements at low voltages, Philipsoffers the CMA (ceramic multilayeractuator), which is a piezoceramicstrip with electrodes to cause it tobend under applied voltage andactuate external equipment such asvalves. Since the piezo layers arevery thin, drive voltages from 10V to60V produce electric field strengthsup to 3kV/mm; conventional types ofactuator would need up to 1 kV to givethe same field strength. Speed ishigher and the device is smaller thanis usual, requiring only voltage driveand therefore much less power.Philips Components. Tel., 00 31 40722790; fax, 00 31 40 724547.

Linear actuator. Electro-Thrust is alinear actuator combining thesimplicity of a pneumatic type with theprecision of a mechanical cylinder. Itis programmable, repeatable to within±0.013mm and comes in strokelengths in the 50-1000mm range.Velocity can be controlled to speedsup to 1250mm/s at thrusts of up to7200N. The actuators are available inframe sizes of 32, 50 and 80mm innine metric ISO mounting styles. Therange of leadscrew pitches and driveratios makes for easy matching to anapplication, as do the four rod endchoices. Parker Hannifin plc, DigiplanDivision. Tel., 01202 699000; fax,01202 695750.

. Vision systemsStereo vision. Sundance has a dualdigital video interface module, theSMT318, to provide stereo vision inembedded systems. It provides adigital data -capture node forTMS320C4X TIM -based systems andcan be used as the interface to twodigital cameras. The two interfacesgive a peak acquisition bandwidth of60Mbyte/s and linking them gives asingle 16 -bit interface. Independentcontrol of each channel is providedand there are 10 general-purpose,programmable i/o lines. The interfacecan be used with Pulnix, Dalsa andEEV cameras. SundanceMultiprocessor Technology Ltd. Tel.,01494 431203; fax, 01494 726363.

COMPUTERComputer board -levelproductsPentium motherboards. Cosworth,from Apricot, is an ISA/PCImotherboard for the full Pentium Profamily, the relevant sockets, clock andbus speeds up to 66MHz beingprovided. There is on -board memoryof up to 1Gbyte in 3.3V dimms and aCirrus Logic Alpine GD543x or 544xchip set copes with graphics. Dual -mode PCI IDE ports with two socketsare provided for hard disks or AtapiCD-rom drives. Apricot ComputersLtd. Tel., 0121 717 7171; fax, 0121717 3692.

Data acquisitionPlug -and -play. A new multi -functiondata acquisition board from National,the 1Msample/s AT -M10 -16E-1 isplug -and -play ISA-compatible anduses the company's E Seriesarchitecture to eliminate jumpers,switches or potentiometers. There are16 single -ended inputs, 16 pseudo -differential inputs with a sharedcommon or eight 12 -bit full differentialinputs; two analogue outputs have 12 -bit resolution, eight digital i/o linessink 24mA on each line and there aretwo 24 -hour counter/timer channels.National Instruments UK. Tel., 01635572400; fax, 01635 523154.

Data communicationsWireless Ian chipset. Harrisintroduces a four -member chipset,Prism, for 2.4GHz direct -sequence,spread -spectrum, wireless Iansystems, to be used as the core oftransceivers for Type II PCMCIA andISA network adaptor cards for 4Mb/sworking. Features offered include aresistor -programmable filter,programmed timers and thresholdlevels in the baseband processor.Harris Semiconductor UK. Tel., 01276686886; fax, 01276 682323.

Development andevaluationRom emulator. Nexus's ROMbox is arom emulator designed to assist codeand hardware development by

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allowing rom image downloading at200kb/s from a PC, and also byproviding aids to debugging of bothhardware and software. Tracefunctions are included for addressmatching and a bidirectional linkobviates the need for an extra serialport for development. Up to 16ROMboxes can be daisy -chained on asingle cable to support 128b buses.The unit can be plugged into a 32 -pinor 28 -pin rom socket and adaptors areavailable for plcc sockets, theconnection to the PC parallel portbeing by a single cable. Two versionshave memory of 1Mb and 4Mb. NexusElectronics Ltd. Tel., 01223 576100;fax, 01223 576619.

Device drivers. A Windows tool fromIAR, DriveWay-51, is launched as 'thefastest way to generate device driversfor the 8051 family". It is produced inassociation with the Israeli companyAiSys and allows integration of on -chip peripherals into designs,automatically producing documentedand tested driver C source code foreach 8051 peripheral. Test functionsand documentation are generatedautomatically, as is an on-line datasheet on the chip's peripherals,modes, registers and pins. You willneed 5Mbyte of hard disk space and4Mb of memory. IAR Systems Ltd.Tel., 0171 9243334; fax, 01719245341.

Computer peripheralsRS -485 as GPIB. National's GPIB-485CT-A is an external box thatmakes a computer with an RS -485port behave as a full -function IEEE488.2 controller, an RS -485 deviceappearing as a GPIB device, thesystem being effective over a distanceof up to 4000ft. National alsoannounces the PCI-GPIB, a plug-inGPIB instrument control board forcomputers with PCI bus runningWindows 95. It handles data transferrates to 1.5Mbyte/s and implementsthe HS488 GPIB protocol forprogrammed i/o transfers at3.7Mbyte/s or more. With this board, acomputer is able to monitor andcontrol several thousand pieces ofequipment. National Instruments UK.Tel., 01635 572400; fax, 01635523154.

SoftwareWaveform generator. ThurlbyThandar introduces aWindows -based package,WaveForm DSP, to supportarbitrary waveform generationon the Model TG1010 functiongenerator, which is a 10MHzdirect digital synthesiser. Thepackage creates, analyses andedits waveforms, which havebeen made by anycombination of drawing,mathematical expression,output from a dso, or takenfrom a library or pasted fromother applications; waveformsmay be drawn by mouse andsmoothed with curve -fittingalgorithms. It switches easilyfrom the time to the frequencydomain, both possessingediting, drawing and libraryfeatures. Thurlby ThandarInstruments Ltd. Tel., 01480412451; fax, 01480 450409.

Computer securityData protection. Jetico, Inc., ofFinland, produces the Best Crypt+data protection system for PCcompatibles, which is said to providethe most secure storage and yet offereasy access control to the encrypteddata on disk, where it behavestransparently to an authorised userfrom any application program. Thehardware is an add-on board and thesoftware contains Control Panel forMS-DOS and Windows. Encryption isby means of the Russian Federalstandard GOST 38147-89, which is,apparently, well known as anuncrackable algorithm, being 105°times more uncrackable than theAmerican standard. And it isn't anygood trying to guess a password,because they have thought of that,too, and made it impossible to get iteven by looking over someone'sshoulder. Jetico Inc. Tel., 00358-31-316-5215; fax, 00358-31-316-5901.e-mail [email protected] M.


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February 1996 ELECTRONICS WORLD+WIRELESS WORLDCIRCLE NO. 132 ON REPLY CARD

163

APPLICATIONSPlease mention Electronics World when seeking further information.

Load dump generators for emc testingA utomotive generators that cope with the

inew ISO 7637 standard and the morestringent emc test requirements in a moderncar are the subject of Schaffner applicationnote INS0002.

Entitled Discussion on load -dumpgenerator designs and suitability forautomotive EMC testing, the note describeshow NSG500x emc test generators are of usein evaluating automotive emc.

Transient and burst generators typicallyneed to generate very fast rise times andshort pulse widths. A typical transientgenerator is shown in Fig. 1.

Pulse shaping components are typicallypassive components - capacitors, inductors,resistors - because current solid statetechnology cannot generally provide thepulse shape control with the rise times andenergies involved. As a result of this output

resistance Ri is typically specified as avariable value to allow for some controlover the energy delivered to the equipmentunder test - RL in Fig. 1. This mechanismhowever provides very limited energycontrol on the output. If you take the casewhere RL=R, it is clear that half the pulseenergy is dissipated internally in thegenerator rather than the equipment undertest, or eut. In addition pulse amplitude atthe eut would be half the value programmed.

In the case of the load dump generator forthe NSG5000, because rise times and pulsewidth requirements are in the millisecondregion, this pulse generator is based entirelyon solid state technology. This means pulseshape and energy content, delivered to theeut, are fully programmable. As a result, testpulses delivered to the load can be muchmore predictable. This provides the user

pulse shaping components

switch(usually solid state)

Nl

ene gy storage

pulse amplifier

control ----1

Rsense1

0.010

output impedanceRi > EUT

10-0

energystorage

NSG 5005generator

load dumpsupressor

O

RL

EUT

L

EUT

RL

Fig. 1.Simplified blockdiagram of atransientgenerator. Bothtransient andburst generatorstypically haverequirementsfor generatingvery fast risetimes and shortpulse widths.

Fig. 2. Simplifiedschematic of theNSG 5005 operatingin current mode. Anin -line sense resistordevelops a feedbackvoltage to controlthe pulse amplifier.

Fig. 3. Centralised loaddump suppressor in thetest harness to the EUThelps simulate the type ofenvironment that the EUTmight meet in anautomobile.

with test modes previously not possible withtraditional passive circuit designs.

Operating modesThe instrument is intended for three basicmodes of operation, one of which is currentmode output.

This mode of operation could beconsidered a new departure in terms of thetype of pulses and pulse specifications thatare presently specified in the ISO 7637standard. However, outputting a currentpulse shape is a much more accuraterepresentation of what actually happens witha load dump from an alternator in a modernautomobile.

An in -line sense resistor is used to developa feedback voltage to control the pulseamplifier, Fig. 2. The value of this resistor isvery small so it does not dissipate asignificant amount of energy.

In this mode the pulse shape wouldnormally be defined into a short circuit.Once the eut internal resistance is lowenough to allow the maximum programmedpeak current to flow then the pulse shapeprogrammed will be replicated exactly at theoutput. Voltage developed at the outputterminals, ie the equipment under test, isdetermined by load impedance RL.

Maximum output voltage available fromthe NSG5005 is 200V so the unit will clamparound this level if no other limiting deviceis present in the test circuit. A morecommon situation would be to include acentralised load -dump suppressor in the testharness to the eut, Fig. 3. Again this alsohelps to represent the environment that theeut might meet in the automobile moreaccurately.

If the eut load represents a high inductanceor capacitance then the current shape may bedistorted from that programmed.

The note also describes the normal voltagemode output and the voltage mode withexternal Ri resistance unit. Maximumperformance limits of the NSG5005 being amaximum pulse amplitude of 200V, pulsewidth of 500ms and a maximum current of200A.

An appendix describes how pulse shapecharacteristics depend on the eut load andhow quickly it drains energy from thegenerator.

Schaffner EMC Ltd. Ashville way, MollyMillar's lane, Wokingham, Berkshire.Tel, 01734 770070, fax, 01734 792 969.


APPLICATIONS

Surge protection solutionsTransient voltage protection products are

I the subject of a data and applicationsmanual from Protek Devices. Dedicated toengineering solutions for the transientenvironment, the manual is split into five

1000

10

Industry Standard,Low CapacitanceSoul State

- Protector

Prot.* -CX 12LC

0 1 2 3 4 5

Von Signal Operating Voltage - VoltsCapacitance in protection devices can be asource of significant signal attenuation.

sections covering tvs diodes, Discrete TVSdiodes, power tvs assemblies and highpower surge suppressor modules. The fifthsection covers application notes.

An interesting device designed to protectinterfacing equipment from inducedlightning or switching transients is detailedin section 4. Called the CX 12LC module,the device is a two stage, hybrid surgeprotector with a low clamping voltage, highenergy handling capabilities and anoperating data range up to 100Mbit/s. It isdesigned for high data rateapplications over theoperating voltage range of acomputer.

Coupling capacitorsinserted across the data linemust be very low to preventsignal distortion or loss ofdata on the LAN network.The diagram (left) shows acomparison of twoprotection products insertedin the data line for transientvoltage protection. Thebottom line is for the CX12LC, and the top line is for

a more standard device. Due to the drasticchange in capacitance of the product, topline, signal distortion, loss of data or evenaccess to the computer may be a problem.

Protek Devices, 2929 Fair Lane, Tempe,Arizona 85282, USA, Tel, 602-431-8101,fax, 602-431-2288.

In a typical data line application, as shown,video and serial data transmission lines aresusceptible to lightning strikes and surges fromac power lines. The CX 12LC is designed toprotect against such surges.

CX 12WLow OW. Modulo

DATA HIGHWAY

CX 12LCLem Caw Maki,

Transmission On 75 Ohm Coaxial Line

Up to 7500 Feet

'Uncrackable' electronic lockClaimed to be the world's firstunpickable electronic lock,

the dynamic key alarm micro -DKA1 - from ElectronicResearch and design Ltd lendsitself to many securityapplications.

The device is particularlyapplicable to keyless lockdesigns relying on radiotransmission. Such lock systemshave traditionally beenunsuitable for high -securityapplications.

Detailed in its technical databrief, the DKA1 is said toincorporate levels of security thathave only recently becometechnically feasible. The systemincludes generation III militarytype encryption techniques basedon the manufacturer's time -basedmulti -level encryptiontechnology. This is said to beuncrackable - even by the mostadvanced 'grabber predictors'.

When originally programmed,a base time seed code isgenerated. This is different forevery key and forms the starttime -seed. This seed is thenclocked in real time and aproportion of the encryption

mechanism is 'weighted' by thecurrent time seed variables.These variables are constantly

changing. This means that theencryption engine parameters arechanging all the time. Together

ARRAYMULTIPLEXER

POINTERTABLE

LOOK UP TABLE

RANDOMENCRYPTIONFUNCTIONARRAY

MOVING TIME SEED

LOCALPATTERN

ADJUSTER

B ENCRYPTIONENGINE .1

,1JINTERMEDIATE CODE .1

LOCAL

PATTERNADJUSTER

B

B

ENCRYPTIONENGINE .2

4

4

INTERMEDIATE CODE .2

LOCALPATTERNADJUSTER

DKA1 time based multilevel encryption functiondiagram.

ENCRYPTIONENGINE .3

FINAL CODE

with the third level encryption onencryption coding techniques(multi level), this combines tomake it impossible tocalculate/predict consecutivecodes. Even with knowledge ofthe multi -level encryptionalgorithm, it would still beimpossible to decode the currenttime based multi -level encryptioncode without the knowledge ofthe current time seed. This canonly be known by that particularkey's run-time file in thedecoding to which it was initiallysynchronised.

Conversely, because thedecoder has an identical run-timefile and the same moving timeseed, it is able to de -encrypt theincoming code and observe anycomparison, see diagram.

The brief also details thedevice's specifications, alarmfeatures and diagnostics.

Electronic Research andDevelopment, K&K House,Station Approach,Rickmansworth Road,Watford, Herts, WD1 7LU.Tel. 01923 240525, fax220011.


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motor and control circuit £23.00 14p 100+ 9p.....1000+Hand held transistor analysm it tells you which lead is the luf 250vdc 20p each

base, the collector and emitter and if it is NPN or PNP 15p 100+ 10p.....1000+of faulty £33.45, I uf 50v bipolar electrolytic axial leads 15p each

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Nickel Metal Hydryde AA cells high capacity with aso resistors, please send SAE for listmemory. If charged at 100ma and discharged P.C. 400W KU (Intel part 201035-001) with standard250ma or less I INtnAH capacity (lower capacity for motherboard and 5 disk drive connectors. fan andhigh discharge rates) £3.75 mains inletioudet connectors on back and switch on

Special offers, please check for availability. the side (top for case) dims 212x149x149mmStick of 4 42x1 6mm Nicad batteries 171x16mm die with excluding each

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7 segment common anode led display 12mm £0.45 DIP switch 3PCO 12 pin ERG SDC-3-025) 60p eachLM 337k TO3 case variable regulator £1.95 40p 100+

£1.44 100+ Disk drive boxes for 5.25 disk drive with mom for a powerGaAs FET low leakage current S8873 £12.95 each supply, light grey plastic. 67x268x247mm

£9.95 10+, £7.95 100+ £7.95 or £49.50 for 10BC250 P channel mosfet £0.45 Hand held ultrasonic remote control £3.95I3559 transistor £3.95 per 100 CV2486 gas relay, 30x10mm dia with 3 wire terminals, willBC547A transistor 20 for £1.00 also work as a neon light 20p each741.505

hisinvertor £10.00 per 100 .... ..... .... ..... ....... ...... .... .......................... ....£7.50 per 100

All products advertised are new and unused unless otherwise stated.Wide range of CMOS TTL 74HC 74F Linear Transistors kits. Rechargeable batteries, capacitors, tools etc

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MATHCADcets a plusAllen Brown found the latest release of Mathcad asignificant step forward. But was he equally pleased withthe DSP Function -Pack soption?

The well known maths softwarepackage Mathcad has recentlybeen upgraded to version 6, and

renamed Mathcad Plus 6. Version 6 isan enhancement of version 5 withsome very interesting developments -

Computing a Symbolic Derivative

Rs), 21.3. 44(42

Ra) -== 2- 2,0e(s)sia(a)da

eats

'17- f(.) - -32 c4(1) sax(r)dal

11104.41aprIC =

Fig. 1. A new featureof Mathcad Plus 6 isthe inclusion ofQuicksheets. Each onegives an example ofhow a Mathcadfunction can be used.This example showshow the firstderivative can beobtained.

E E1,11.11- 1

Je C. 1- I (4 -Oaf (21.1V3)1

Fig. 2. Program loops and structures can be included in aMathcad object; they have similar constructs as found intraditional programming languages.

not least the ability to executeprogram loops. In addition, Mathcadis one of the few 32 -bit programs thatruns under Windows 3.1. It also runsunder Windows 95, albeit with apatch program.

The new version retains the basicinitial design of using the pc screen asa scratch pad where the user is able toexpress and solve equations, drawgraphs and construct tables. Thepackage makes most of these tasksrelatively easy. It is also able toperform analytical operations via theMaple Library. Although this featurewas introduced a few version ago, itstill remains as a powerful and usefulfeature of the package.

Newcomers to the software willprobably find the immense array offunctions and options bewildering. Itis not a software package that the newuser will learn overnight. It willprobably take you several weeks tomaster it. However there are a numberof design features, in addition to thenormal help menus, that will help yougain an insight into the package'spotential.

Because of its very general nature,Mathcad can be used by anyone whohas a need to manipulate numbers orperform modelling tasks. To add to itsappeal, the package can be boughtwith a variety of 'function packs' thatcontain functions developed for

specific applications. In this review Iwill be looking at the signal -processing function pack.

QuickSheets for faster learningOne innovation introduced intoMathcad Plus 6 is the concept of theQuickSheet. It is well known that oneof the most effective methods oflearning is through the use ofexamples and this is the principleemployed in the QuickSheet facility.The user is provided with a table ofcontents, each entry leads to a furthermenu and eventually to an example ofhow a function is used. An example isshown in Fig. 1 illustrating how thederivative function is operated.

Examples, showing how the variousfunctions and operations work withinMathcad, can be viewed. Moreimportantly, many of the examplesare easy to follow.

Programming methodsOne of the problems with previousversions of this package was itsinability to perform programs withconditional loops. In version 6, thisdeficiency is remedied by theintroduction of a set of programmingfunctions. These include 'for','while', 'if', 'break' and 'otherwise'.They are evoked from theprogramming constructs palette andan example of how the program is


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Signal processing function pack

The makers of Mathcad provide manyspecial purpose function packs. One ofparticular interest to electronics engineersis dedicated to signal processing.

Each pack is a collection of specialfunctions compiled into a dynamic linkedlibrary (DLL) that is accessed by the soft-ware. Although the SIGNAL -PROCESS-ING PACK comes with a small bookletwhich lists the functions, when installed aSignal Processing Electronic Book is load-ed on the PC.

All information regarding the operationof the pack is accessible by entering the'Electronic Book'. This provides numerousexamples of how each function in thepack can be used. Having an electronicbook dispenses with the need for yetanother paper manual. If you want copiesof specific pages from the electronicbook, you merely print them as required.The only irritating aspect of the Mathcadselectronics books is the pale blue fontwhich makes them difficult to read.

Sixty four functions in the signal -pro-cessing pack fall into the following cate-gories,

Transforms Spectral analysis Time series analysis Spectral analysis Digital filtering.

constructed in shown in Fig. 2.Also shown, as an insert, is the

programming palette. The whilestatement is very useful for iterating aloop until a condition is met at whichpoint the program stops executing. Asan extra safeguard the break functioncan be included to ensure that theloop terminates in the event of thenormal exit condition not beensatisfied.

As with other programminglanguages, loops can be nested withinother loops to give several variabledependencies. It does however take awhile to get used to the programmingtechnique. As with all programminglanguages, it is necessary to think ofyour problem in terms of the languageconstructs. But first you must be veryfamiliar with the operation of theconstructs.

Handling non-lineardifferential equationsOne of the exciting aspects ofMathcad Plus 6 is the facility forsolving nonlinear differentialequations numerically. AlthoughMathcad has been a very effectivetool for modelling linear processes,

Fast Fourier transforms and inverse FFTsalready form part of the Mathcad packageand the signal -processing pack have sev-eral spectral analysis functions that com-plement these. These include cepstrum,for finding harmonics in spectra, costr,sintr and cosine and sine Fourier trans-forms. There is also a discrete Hartlytransform which is similar to the FourierTransform except it does not use complexmaths.

A number of window functions areavailable for shaping input data beforeany spectral analysis is performed on it.These are important for resolving smallspectral peaks lying in the shallows ofmuch larger ones.

Although many of the functions are use-ful one has the feeling that they could beeasier to use and this is particularly true ofthe digital filter functions. These operatein a rather strange manner. Normally theuser will known what the stop band atten-uation is, the pass band ripple and thetransition frequency width between thebands. Filter design software should thenprovide the number of coefficients (num-ber of filter taps) and value of the coeffi-cients.

In the signal -processing pack, the user isexpected to provide the number of coef-ficients. Not only that but once the coef-ficients have been generated there is no

most real world problems arenonlinear. Man has a history of tryingto impose linearity upon nature whichis intrinsically nonlinear.

The principal function for tacklingnonlinear differential equations is`rkfixed'. This function evokes thefourth -order Runge-Kutta algorithmwhich can be used to solve any order,and even systems, of nonlineardifferential equations.

Figure 3 shows how the functionmodels relaxation oscillations in asemiconductor laser. There are otheralgorithms available in the packageand their application depends on thenature of the nonlinear differentialequations to solve, and on theaccuracy of the required solutions. Ingeneral, systems of nonlineardifferential equations can be classifiedas 'smooth', 'slowly varying' and`stiff'. The function for tacklingsmooth systems is bulstoer, afterBulirsch-Stoer, and for slowlyvarying is Rkadapt, a modifiedversion of the Runge-Kutta algorithm.Stiff systems can be solved by using`stiffb', again after Bulirsch-Stoer, or'stiff? after Rosenbrock.

Solving nonlinear differential

direct, easy method for displaying thetransfer function of the filter. The userneeds this to determine whether the filtersatisfies the specifications. To add to theconfusion, the coefficients generated arelarger than unity. As a result, they do notlend themselves to easy quantisation forimplementing on fixed point DSP chips(see Fig. 7). This makes me wonderwhether an engineer was consulted whenthe signal -processing pack was designed.

To make matters worse, there are nofunctions for designing elliptical filters.This is a nuisance since this type of filteris used frequently for sharp cut-off filterswith minimal tap count.

Generating Coefficients for Chebyshev Pus Bond Filter N 11

C = diebylt N ,0.01) 13 opus(

0 0.005 1 0.004 1 0.003 1 0.002 1 0001 1 0.031 1

.0 -3 06 0 -3.036 0 -3.018 0 -3.004 0 -2.096 0 -1 49-

-0.01 4.314 4.246 -0.006 4.191 11.004 4.151 4.002 4 lr .0 031 0 939

-3.032

_-.008

0 -2.958 0 -2.896 0 4.849 0 -2.821 0 0

0.005 0.982 0.004 0.949 0.003 0.921 0.002 A! p.001 0 886 0 0

Fig. 7. Mathcad's signal -processingfunction pack has functions fordesigning digital filters. Howeverwhen the coefficients of an infiniteimpulse response (IIR) filter aredisplayed, the format is notimmediately useful to a digital filterdesigner.

equations can be achieved providedthe user has knowledge of the initialconditions. If this information is notavailable, it may be possible to usethe `sbvla' or the `bvalfie functionswhich employ 'boundary value'techniques.

Given partial knowledge of a

a . I IA Ais r tadelinsudworn

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Fig. 3. One of the powerful tools found in the new version isthe option of solving nonlinear differential equations. In thisexample the relaxation oscillations of a semiconductor laserare modelled. As the phonon density P increases theelectron density N decreases and vice -versa.


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syn.ole trewsMen NAN Ronan

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Fig. 4. Mathcad uses a symbolic calculator to performanalytical evaluations of equations. This figure shows a fewexamples of what can be done with the calculator.

;,.. (5. rres(%))ces(4.) . (5 reese0aj) air.(8,0 Z,n,n . r.im()

An wimple d.parametric surfacs

Fig. 5. Customary 3D plots can be generated with Mathcad,but their ease of construction could be improved. Not onlythat but object rotation to obtain a different perspective is notat all convenient.

Fig. 6. For imaginative users, Mathcad now has the provisionfor generating video clips which can show how a plottedfunction changes as one of the variables is allowed to changefrom frame to frame.

problem these functions allow you todetermine appropriate initialconditions that can be used in theapplication of functions justmentioned. Collectively thesefunctions form quite an impressivearsenal with which to solvedifferential equations.

Symbolic calculationsMathcad 6 Plus retains the ability tosolve equations symbolically. It uses

the Maple engine from the Canadiancompany Waterloo. Its performance isusually quite impressive. When the pcis configured for 32 -bit disk access,the speed of execution of the`symbolic calculator' is surprisinglyfast. Its popularity in education goeswithout saying. Judging by the fallingstandards in mathematical skills bystudents entering universities, thisaspect of the package will be seizedon with great enthusiasm.

The software is able to perform awhole array of symbolic processingoperations including integration,polynomial expansion, simplification,partial fraction expansions and manyother general symbolic algebraicfunctions. However, sometimes thesymbolic expansions do not performeven on simple expressions.

I had to conclude that it mostlyprovides an answer but not always.Figure 4 illustrated a number ofsymbolic operations that weresuccessfully performed by Mathcad.

Graphing and plottingGraphing options offered by Mathcadare not too dissimilar to those offeredin general purpose graphics packages.These days, high quality data plottingsoftware is freely available. As aresult, the package has a lot incommon with most graphics packages- contour plots, polar plots, threedimensional solid modelling withrotation and bar charts.

However, it should be mentionedthat producing a surface plot is not aseasy as I would like. It is stillnecessary to construct a matrixbeforehand, which is not the mostintuitive method of generating a three-dimensional plot.

On the whole, facilities forgenerating and manipulating three-dimensional plots are rather clumsy.An example of a colour codedparametric plot is shown in Fig. 5.There is also a provision for importingimages, however this facility is by nomeans free of problems as it failed tofunction properly. Not all bit -mappedimages are recognised.

An interesting addition in the newversion is the option to generateanimation plots. This feature employsthe Microsoft multimedia facilities forvideo clips, .AVI files.

Figure 6 shows how easy it is tocreate an animation. A function isdefined with a variable called FRAME.

Once the animation has been evoked adialogue box appears, on the right ofFig. 6, where the range of FRAME isdefined. The user also chooses thenumber of frames per second.

Once the plotting area has beenselected, the animation process begins.

.1.11

j Wax 1 4 re

SAW )owa... 1 4 on,

Five screen captures from an AVI fileproduced by MathCad illustrate thepackage's animation capability.


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The frames are then compiled into.AVI video, Fig. 6, top left, and playedat will. This could be useful fordynamic solid modelling to illustratevibration modes in something like anoptical fibre.

The software is quite impressivewhen solving simultaneous equationsusing the lsolve function. Solvingsimultaneous equations boils down tosolving the matrix equation,

x=A-1vFor example, if this represents 500

simultaneous equations with 500unknowns, v, and 500 solutions, x,Mathcad takes just over 14s to solve itwhen running on a 120MHz Pentium,representing 28ms for each unknownelement in x. Bearing in mind that thematrix A contains a quarter of amillion floating point elements, it canbe said that the pc has come of age forcomputational operations.

Solving simultaneous equations is afrequent requirement for statisticalwork. In the new version, there is also

a substantial range of statisticalfunctions. Should the need arise toimport or export data to and fromWindows applications, the packagehas a facility for creating dynamic dataexchange, DDE, interfaces. This is auseful component if the user isinterested in using Mathcad to processdata direct from a data acquisition cardin real-time.Summing upLooking at all the features thatMathcad Plus 6 has to offer, onewonders what the next version willhave in store. There could be improved3D plotting. It still remains a very welldesigned software product that willcontinue to find appeal amongst manydifferent kinds of users. Whether youwant to perform simple calculations orquite involved nonlinear modelling thepackage is a very approachableproduct.

The user guide has passed throughseveral iterations and the volume forthe new version is an invaluabledocument for any user - experienced

or otherwise. The 694 page guidecontains many examples and is veryreadable. It certainly complements thehelp file.

My enthusiasm for the signal -processing function pack however isnot so forthcoming. Although it hasmany useful functions, many lackfunctionality and are basicallyunwieldy and difficult to use. Thesedays there are many software packagesfor designing and analysing digitalfilters. Unfortunately the signal -processing function pack falls far shortof most of them.

AvailabilityAdept Scientific Micro Systems Ltd,6 Business Centre West, Avenue One,Letchworth SG6 2HB, Tel. 01462-480055, fax 01462-480213. Price-Mathcad Plus 6, £395 excluding VAT,Signal Processing Function Pack,£195 excluding VAT. Educationaldiscounts are available in some cases.

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4.6mw LASER POINTER. BRAND NEW MODEL NOW INSTOCK!, supplied in fully built form (looks like a nicepen) complete with handy pocket clip (which also actsas the on/off switch.) About 60 metres range! Runs on2 AAA batteries. Produces thin red beam ideal forlevels, gun sights, experiments etc. just £39.96 refDEC49 TRADE PRICE £28 MIN 10 PIECESBULL TENS UNIT Fully built and tested TENS (TranscutaneousElectrical Nerve Stimulation) unit, complete with electrodes and fullinstructions. TENS is used for the relief of pain etc in up to 70% ofsufferers. Drug free pain relief, safe and easy to use, can be used inconjunction with analgesics etc. £49 Ref TEN/1COMPUTER RS232 TERMINALS. (LIBERTY)Excellentquality modern units,(like wyse 50,$) 2xRS232, 20 function keys, 50thro to 38,400 baud, menu driven port, screen, cursor, and keyboardsetup menus (18 menu's). £29 REF NOV4.RUSSIAN MONOCULARS Amazing 20 times magnification,coated lenses, carrying case and shout der strap.£29.95 REF BAR73

PC PAL VGA TO TV CONVERTER Converts a colour TV intoa basic VGA screen. Complete with built in psu, lead and sAvare.. Idealfor laptops or a cheap upgrade.Supplied in kit form for homeassembly. SALE PRICE £25 REF SA34EMERGENCY LIGHTING UNIT Complete unit with 2 doublebulb floodlights, builtin charger and auto switch. Fully cased. 6v 8AHlead acid req'd. (secondhand) £4 ref MAG4P11.SWINGFIRE GUIDED MISSILE WIRE. 4,200 metre reel ofultra thin 4 core insulated cable, 28Ibs breaking strain, less than 1mmthick! Ideal alarms, intercoms, dolls house's etc. £13.99 ref EP51ELECTRIC CAR WINDOW DE-ICERS Complete with cable,plug etc SALE PRICE JUST E4.99 REF SA28ASTEC SWITCHED MODE PSU BM41012 Gives +5 @ 3.75A,+12g 1.5A, [email protected]. 230/110, cased, BM41012. £5.99 ref AUG6P3.

AUTO SU NCHARGER 155x 300mm solar panel with diode and 3metre lead fitted with a cigar plug. 12v 2watt. E8.99 REF SA25.TOP QUALITY CENTRIFUGAL MAINS MOTORS SALEPRICE2 FOR JUST E2.60 REF SA38ECLAT RON FLASH TUBE As used in police car flashing lightsetc, full spec supplied, 60-100 flashes a min. £6.99 REF SA15.24v AC 96WATT Cased power supply. New. E9.99 REF SA40MLITARYSPECGEIGERCOUNTERS Unused anstraightfromHer majesty's forces. SALE PRICE E44 REF SA16MICRODRIVE STRIPPERS Small cased tape dnves ideal forstripping, lots of useful goodies including a smart case, and lots ofcomponents. SALE PRICE JUST E4.99 FOR FIVE REF SA26SOLAR POWER LAB SPECK L You get TWO 6'x6' 6v 130mAsolar cells, 4 LED's. wi re, buzzer, switch plus 1 relay or motor. Superbvalue let SALE PRICE JUST E4.99 REF SA27

RGBICGA/EGAfTTL COLOUR MONITORS 12' in goodcondition. Back anodised metal case. SALE PRICE E49 REF SA16PLUG IN ACORN PSU 19v AC 14w , £299 REF MAG3P 10POWER SUPPLY fully cased with mains and o/p leads 17v DC900mA output. Bargain price E5.99 ref MAG6P9ACORN A RCHIMEDES PSU +5/ a 44A. on/off sw uncased,

SOMR OP OUR PRODUCTS MAY BE UNLICENSABLE IN THE UK

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selectable mains input, 145x100x45mm E3.99 REF MAG7P213.8V 1.9A PSU cased with leads Just £999 REF MAG10P3200 WATT INVERTER Converts 10-15v DC into either 110v or240v AC. Fully cased 115x36x 156mm, complete with heavyduty power lead, cigar plug, AC outlet socket. Auto overload shutdown,auto short circuit shut down, auto input over voltage shutdown, autoinput undervoltage shutdown (with audible alarm), autotemp control,unit shuts down if overheated and sounds audible alarm. Fusedreversed polarity protected. output frequency within 2%, voltagewithin 10%. A well built unit at an keen price. Just E64.99 ref AUG65.

UNIVERSAL SPEED CONTROLLER KIT Designed by us forthe C5 motor but ok for any 12v motor up to 30A. Complete with PCBetc. A heat sink may be required. £17.00 REF: MAG17

COMPUTER COMMUNICATIONS PACK Kit contains 100mof 6 core cable, 100 cable clips, 2 line drivers with RS232 interfacesand all connectors etc. Ideal low cost method of communicatingbetween PC's over a long distance. Complete kit £8.99.VIEWDATA SYSTEMS made by Phillips, complete with internal1200/75 modem, keyboard, psu etc RGB and composite outputs,menu driven, autodialler etc. SALE PRICE E12.99 REF SA18AIR RIFL ES.22 As used by the Chinese army for training puposes,so there is a lot about! £39.95 Ref E F78. 500 pellets £4.50 ref EFS°.

PLUG IN POWER SUPPLY SALE FROM £1.60 Plugs in to13Asocket with outputlead. three types available. 9vdc 150mAE1.50ref SA19, 9vdc 200mA £2.00 ref SA20, 6.5vdc 500mA £2 ref SA21.VIDEO SENDER UNIT. Transmits both audio and video signalsfrom either a video camera, video recorder, TVor Comp uter etcto a nystandard TV set in a 100' range! (tune TV to a spare channel)12v DCop. Price is E15 REF: MAG15 12v psu is £5 extra REF: MAGSP2*FM CORDLESS MICROPHONE Small hand held unit with a500' range! 2 transmit power levels. Reqs PP3 9v battery. Tuneableto any FM receiver. Price is £15 REF: MAG15P1*MINATU RE RADIO TRANSCEIVERS A pair of walkie talkieswith a range up to 2 km in open county. Units measure 22x52x 155mm.I nduding cases and earp'ces. 2xP P3 req'd. £30.00 pr.REF: MAG30

*FM TRANSMITTER KIT housed in a standard working 13Aadapter!! the bug runs directly off the mains so lasts forever! why payE700? or price is E15 REF: EF62 (kit) Transmits to any FM radio. FPI BUG BUILT AND TESTED superior design to kit. Suppliedto detective agencies. 9v battery req'd. £14 REF: MAG14

TALKING COINBOX STRIPPER COMPLETE WITHCOINSLOT MECHANISMS originally made to retail at£79 each,these units are designed to convert an ordinary phone into apayphone. The units have the locks missing and sometimes brokenhinges. However they can be adapted for their original use or used forsomething else?? SALE PRICE JUST E2.50 REF SA23GAT AIR PISTOL PACK Complete with pistol, darts and pelletsE12.95 Ref EF82B extra pellets (500) £4.50 ref EF80.6"X12" AMORPHOUS SOLAR PANEL 12v 155x310mm130mA. SALE PRICE E4.99 REF SA24.

FIBRE OPTIC CABLE BUMPER PACK 10 metres for £4.99ref MAG5P13 ideal for experimenters! 30 m for E12.99 ref MAG13P1

MIXED GOODIES BOX OFMIXED COMPONENTS WEIGHING 2 KILOS

YOURS FOR JUST £6.994X28 TELESCOPIC SIGHTS Suitable for all air rifles, groundlenses, good light gathering properties. £19.95 ref RI7.

RATTLE BACKS Interesting things these, small piece of solidperspex like material that it you try to spin it on the desk it only spinsone way! in fact if you spin it the 'wrong' way it stops of its own accordand go's back the other way! £1.99 ref GI/J01.

GYROSCOPES Rememberthese?well we have found a companythat still manufactures these popular scientific toys, perfect gift or foreducational use etc £6 ref EP70HYPOTHERMIA SPACE BLANKET 215x 150cm aluminisedfoil blanket, reflects more than 90% of body heat. Also suitable for theconstruction of two way mirrors! E3.99 each ref 0/L041.LENSTATIC RANGER COMPASS Oil filled capsule, strongmetal case, large luminous points. Sight line with magnifying viewer50mm dia, 86gm . E10.99 ref 0/K604.RECHARGE ORDINARY BATTERIES UP TO 10 TIMES!With the Battery Wizard! Uses the latest pulse wave charge systemto charge all popular brands of ordinary batteries AAA, AA, C, D, fourat atime!Led system showsw hen batteries are cha rged. automaticallyrejects unsuitable cells, complete with mains adaptor. BS approved.Price is £21.95 ref EP31.

TALKING WATCH Yes, it actually tells you the fime at the press ofa button. Also features a voice alarm that wakes you up and tells youwhat the time is! Lithium cell included. E7.99 ref EP26.

PHOTOGRAPHIC RADAR TRAPS CAN COST YOUYOUR LICENCE! The new multiband 2000 radar detector canprevent even the most responsible of drivers from losing theirlicence!Adjustable audible alarm with 8 flashing leds gives instant warning ofradar zones. Detects X, K, and Ka bands, 3 mile range, 'over the hill''around bends' and 'reartrap facilities. micro sizejust4.25"x2.5"x.75',Can pay for itself in just one day! £79.95 ref EP3.SANYO NICAD PACKS 120mmx 14m m 4.8v 270 maH suitablefor cordless phones etc. Pack of 2 just £5 ref EP783" DISCS As used on older Amstrad machines, Spectrum plus3'setc E3 each ref BAR400.STEREO MICROSOPES BACK IN STOCK Russian, 200xcomplete with lenses, lights, filters etc etc very comprehensivemicroscope that would normally be around the £700 mark, our priceis just £299 (full money back guarantee) full details in catalogue. Ref95f300.

SOLAR POWERED CAR VENTILATOR Simply fits along thetop of the glass in a side window and provides a constant supply offresh air in hot sunny conditions! keeps your car cool in summer.£19.95 ref s/vent.

WE BUY SURPLUS STOCK FOR CASHFREE CATALOGUE100 PAGE CATALOGUE NOW

AVAILABLE, 45P STAMP OR FREEWITH ORDER.


172 ELECTRONICS WORLD+WIRELESS WORLD February 1996

PORTABLE X RAY MACHINE PLANS Easy to constructplans on a simple and cheap way to build a home X-ray machine!Effective device, X-ray sealed assemblies. can be used forexperimental purposes. Not a toy or for minors! £6/set. Ref F/XP1.TELEKINETIC ENHANCER PLANS Mystify and amaze yourfriends by creating motion with no known apparent means or cause.Uses no electrical or mechanical connections, no special gimmicksyetproducespoative motion and effect. Excellentfor science p rojeds,magic shows, party demonstrations or serious research &development of this strange and amazing phychic phenomenon.£4/set Ref F/TKE1.ELECTRONIC HYPNOSIS PLA NS & DATA This data showsseveral ways to put subjects under your control. Included is a fullvolume reference text and several construction plans that whenassembled can produce highly effective stimuli. This material mustbe used cautiously. It is for use as entertainment at parties etc only,by those experienced in its use. £15/set. Ref F/EH2.GRAVITY GENERATOR PLANS This unique plandemonstrates a simple electrical phenomena that produces an anti-gravity effect. You can actually build a small mock spaceship out ofsimple materials and without any visible means- cause it to levitate.

10/set Ref F/GRA1.WORLDS SMALLEST TESLA COIL/LIGHTENINGDISPLAY GLOBE PLANS Produces up to 750,000 volts ofdischarge, experiment with extraordinary HV effects, 'Plasma in ajar', St Elmo's fire, Corona, excellent science project or conversationpiece. £5/set Ref F/BTC1/LG5.COPPER VAPOUR LASER PLANS Produces 100mw ofvisible green light. High coherency and spectral quality similar toArgon laser but easier and less costly to build yet far more efficient.Thisparticulardeagnwas developed atthe Atomic Energy Commisionof NEGEV in Israel. £10/set Ref F/CVL 1.VOICE SCRAMBLER PLANS Minature solid state systemturns speech sound into indecipherable noise that cannot beunderstood without a second matching unit. Use on telephone toprevent third party listening and bugging. £6/set Ref FNS9.PULSED TV JOKER PLANS Little hand held device utilisespulse techniques that will completely disrupt TV picture and sound!works on FM too! DISCRETION ADVISED. £8/set Ref F/TJ5.BODYHEAT TELESCOPE PLANS Highly directional longrange device uses recent technology to detect the presence of livingbodies, warm and hotspots, heat leaks etc. Intended for security, lawenforcement, research and development, etc. Excellent securitydevice or very interesting science project. £8/set Ref F/BHT1.BURNING, CUTTING CO2 LASER PLANS Projects aninvisible beam of heat capable of burning and melting materials overa considerable distance. This laser is one of the most effident,converting 10% input power into useful output. Not only isthis devicea workhorse in welding, cutting and heat processing materials but itis also a likely candidate as an effective directed energy beamweapon against missiles, aircraft, ground -to -ground, etc. Partidebeams may very well utilize a laser of this type to blast a channel inthe atmosphere for a high energy stream of neutrons or otherparticles. The device is easily applicable to burning and etchingwood, cutting, plastics, textiles etc £12/set Ref F/LC7.MYSTERY ANTI GRAVITY DEVICE PLANS Uses simpleconcept. Objects float in air and move to the touch. Defies gravity,amazing gift, conversation piece, magic trick or science project. £6/set Ref F/ANT1K.ULTRASONIC BLASTER PLANS Laboratory source of sonicshock waves. Blow holes in metal, produce 'cold' steam, atomizeliquides. Many cleaning uses for PC boards, jewllery, coins, smallparts etc. £6/set Ref FAJLB1.ULTRAHIGH GA IN APAP/STETHOSCOPICM IKE/SOUNDAND VIBRATION DETECTOR PLANS Ultrasensitive deviceenables one to hear a whole new world of sounds. Listen throughwalls, windows, floors etc. Many applications shown, from lawenforcement, nature listening, medical heartbeat, to mechanicaldevices. £6/set Ref F/HGA7ANTI DOG FORCE FIELD PLANS Highly effective circuitproduces time variable pulses of accoustical energy that dogscannot tolerate £6/set Ref F/DOG2LASER BOUNCE LISTENER SYSTEM PLANS Aloes youto hear sounds from a premises without gaining access. £12/set RefF/LLIST1

CRAWLING INSECT ROASTER PLANS Harmless highfrequency energy pulses destroy pests as they crawl intothe energy field! £4/set Ref F/RCR1LASER LIGHT SHOW PLANS Do it yourself plans show threemethods. £6 Ref F/LLS1

PHASOR BLAST WAVE PISTOL SERIES PLANSHandheld, has large transducer and battery capacity with extemalcontrols. E6/set Ref F/PSP4INFINITY TRANSMITTER PLANS Telephone line grabber/room monitor. The ultimate in home/office security and safety! simpleto use! Call your bane or office phone, push a secret tone on yourtelephone to access either: A) On premises sound and voices or B)Existing conversation with break-in capability for emergencymessages. £7 Ref F/TELEGRAB.BUG DETECTOR PLANS lsthat someone getting the goods onyou? Easy to construct device locates any hidden source of radioenergy! Sniffs out and finds bugs and other sources of bothersomeinterference. Detects low, high and UHF frequencies. £5/set Ref F/BD1.

ELECTROMAGNETIC GUN PLANS Projects a metal objecta considerable distance -requires adult supervision £5 ref F/EM L2.ELECTRIC MAN PLANS, SHOCK PEOPLE WITH THETOUCH OF YOUR HAND! £5/set Ref F/EMA1.PARABOLIC DISH MICROPHONE PLANS Listen to distantsounds and voices, open windows, sound sources in 'hard to get' orhostile premises. Uses satellite technology to gather distant soundsand focus them to our ultra sensitive electronics. Plans also show anoptional wireless link system. £8/set ref F/PM5

2 FOR 1 MULTIFUNCTIONAL HIGH FREQUENCY ANDHIGH DC VOLTAGE, SOLID STATE TESLA COIL ANDVARIABLE 100,000 VDC OUTPUT G EN ERATOR P LANSOperates on 9- 12vdc, many possible experiments. £10 Ref F/HVM7/TCL4.

'AUTO .BRANCI1RCENTERST

MINI FM TRANSMITTER KIT Very high gain preamp, suppliedcomplete with FET electret microphone. Designed to cover 88-108Mhz but easily changed to cover 63-130 Mhz. Works with a common9v (PP3) battery. 0.2W RF. £7 Ref 1001.ELECTRON IC SIREN KR Impressive 5 watt poweroutput. Idealfor car/bike alarm etc. 6-12v dc max current 1A, 1.2khz £6 Ref 1003.340V POWER SUPPLY KR Variable, stabilized power supplyfor lab use. Short circuit protected, suitable for profesional or amateuruse 24v 3A transformer is needed to complete the kit. £14 Ref 1007.

1 WATT FM TRANSMITTER KIT Supplied with piezo electricmicrophone 8-30vdc. At 25-30v you will get nearly 2 watts! £12 ref1009.

FM/AM SCANNER KR Well not quite, you have to turn the knobyour self but you will hear things on this radio that you would not hearon an ordinary radio (even TV). Covers 50-160mhz on both AM andFM. Built in 5 watt amplifier, inc speaker. £15 ref 1013.MOSQUITO REPELLER KR Modem way to keep midges atbay! Runs for about a month on one 1.5v battery. £7 Ref 1015.3 CHANNEL SOUN D TO LIGHT KR Wireless system. mainsoperated, separate sensitivity adjustment for each channel, 1,200 wpower handling, microphone included. £14 Ref 1014.MOTORBIKE/CYCLE TREMBLER ALARM KIT Adjustablesensitivity, preset alarm time, auto reset. Could be connected to hornetc. £12 Ref 1011.

0-6 MINUTE TRIER KIT adjustable, will switch up to 2A mains.Perfect for alarms, photography, etc. £7 Ref 1020.4 WATT FM TRANSMITTER KIT Small but powerful FMtransmitter, 3 RF stages, microphone and audio preamp included.20 Ref 1028.

STROBE LIGHT KR Adjustable from 1-60 hz (a lot faster thanconventional strobes). Mains operated. £16 Ref 1037.ULTRASONIC RADAR KIT Ideal as a movement detector with arange of about 10 metres, automate your cat flap! 12v dc. £15 Ref1049.

LIQUID LEVEL DETECTOR KR Useful fortanks, ponds, baths,rain alarm, leak detector etc. Will switch 2A mains. £5 Ref 1081.

COMBINATION LOCK KIT 9 key, programmable, complete withkeypad, will switch 2A mains. 9v dc operation. £10 ref 1114.PHONE BUG DETECTOR KIT This device will warn you ifsomebody is eavesdropping on your line. £6 ref 1130.ROBOT VOICE KIT Interesting circuit that distorts your voice!adjustable, answerthe p hone w ith a different voice! 12vdc £9 ref 1131TELEPHONE BUG KIT Small bug powered by the 'phone line,starts transmitting as soon as the phone is picked up! £8 Ref 1135.FUNCTION GENERATOR KIT Produces sinusoidal, saw toothand square waves from 20-20khz, separate level controls for eachshape. Will produce all 3 together. 24vac. £16 ref 1008.

3 CHANNEL LIGHT CHASER KR 800 watts per channel,speed and direction controlssupplied with 12 LEDS (you can fit Macsinstead to make kit mains, not supplied) 9-12vdc £17 ref 1026.12V FLOU RESCENT LAMP DRIVER KIT Light up 4 foottubesfrom your car battery! 9v 2a transformer also required. £8 ref 1069.VOXSWITCH KIT Sound activated switch ideal for making buggingtape recorders etc, adjustable sensitivity. £8 ref 1073.INCARSOUNDTO LIGHT KIT Putsome atmosphere in yourcarwith this mini 3 channel sound to light. Each channel has 6 led's. £10ref 1086.

7W 111 Fl AMPLIFIER KR Useful, powerful, ideal for audiosystems, intercoms etc. 12-18vdc £7 ref 1025.

Check out ourWEB SITE

http://www.pavilion.co.uk/bull-electricalPREAMP MIXER KIT 3 input mono mixer, sep bass and treblecontrols plus individual level controls, 18vdc, input sens 100mA. £15ref 1052.METAL DETECTOR KIT Range 15-20cm, complete with case,9vdc. £8 ref 1022.SINGLE CHANNEL SOUND TO LIGHT KIT Mains operated,add rythum to your party for only £8 ref 1006.SOUND EFFECTS GENERATOR KIT Produces sounds rangingfrom bird chips to sirens. Complete with speaker, add sound effectsto your projects for just £9 ref 1045.GUrTARPREAMP KIT Complete with tone controls, small enoug hto fit in any guitar, based on TL082 IC, 9-12vdc £8 Ref 1091.16 WATT FM TRANSMITTER (BUILT) 4 stage high power,preamp required 12-18vdc, can use ground plane, yagi or opendipole £69 ref 1021.TELEPHONE AMPLIFIER KIT Very sensitive amplifier whichuses a pickup coil (supplied) will let you fellow a conversation with outholding the 'phone. E11 ref 1059.HUMIDITY METER KR Builds into a precision LCD humidity

'SOME OF OUR PRODUCTS MAY BE UNLICEBSABLE Ut THE UK

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PC TRIER KIT Four channel output controlled by your PC, willswitch high current mains with relays (supplied). Software suppliedso you can program the channels to do what you want whenever youwant. Minimum system configeration is 286, VGA, 4.1,640k, serialport, hard drive with min 100k free. £24.99DIVINING RODS Expensive technology cannot challenge the foolproof art ofwater divining, passed dow n from gen eration togeneration.Seeing is believing. Use in the home, garden, countryside or desert,it's divinely simple! E4.99 a pair ref E/3.

HUGE BUBBLE MAKING KIT You'll be amazed at the the sizeof the bubbles you can acheive with this bubble making kit. Once youhave gotthe knack it is possible to make bubbles of up to 40 feet long.£11.99 ref E19.

FM CORDLESSM ICROPHON E This unitis an FM broadcastingstation in minature, 3 transistor transmitter with electret condensermic+fet amp design resultin maximum sensitivityandbroadfrequencyresponse. 90-105mhz, 50-1500hz, 500 foot range in open country!PP3 battery required. £15.00 ref 15P42A.MAGNETIC MARBLES They have been around for a number ofyears but still give rise tocuriosity and amazement. A pack of 12 isjust£3.99 ref GI/R20STETHOSCOPES A fully functioning stethoscope for all thoseintricate projects. Enables you to listen to motors, pipes, heartbeats,walls, insects etc. £6 ref MAR6P6.

NICKEL PLATING KR Proflesional electroplating kit that willtransform rusting parts into showpieces in 3 hours! Will plate ontosteel, iron, bronze, gunmetal, copper, welded,silver sddered orb razedjoints. Kit i ncludes enough to plate 1,000 sq inches. You will also need

a 12v supply, a container and 2 12v light bulbs. £39.99 ref NIK39.

SHOP WOBBLERSISmak assemblies designed to take D sizebatteries and 'wobble' signs about in shops! £3.99 Ref SEP4P2.

OMRON ELECTRONIC INTERVAL TRIERS.NEW LOW PRICES TO CLEAR!!!

Minature adjustable timers, 4 pole o/o output 3A 240v,HY1230S, 12vDC adjustable from 0-30 secs. £4.99HY1210M, 12vDC adjustable from 0-10 mins. £4.99HY126OM, 12vDC adjustable from 0-60 mins. £4.99HY2460M, 24vAC adjustable from 0-60 mins. £2.99HY243H, 24vAC adjustable from 0-3 hours. £2.99HY2401S, 240v adjustable from 0-1 secs. £4.99HY2405S, 240v adjustable from 0-5 secs. £4.99HY24060m, 240v adjustable from 0-60 mins. £6.99DRINKING BIRD Remember these? hook onto wine glass (sup-plied) and they drink, standup,drink,standup ETCI £4 each Ref EF1SOLAR POWER LAB SPECIAL You get TWO 65(6' 6v 130mAsolar cells, 4 LEDs, wire, buzzer, switch plus 1 relay or motor. Superbvalue kit just £5.99 REF: MAG6P8BUGGING TAPE RECORDER Small voice activated recorder,uses micro cassettecomplete with headphones. £28.99 ref MAR29P 1.

PLUG IN ACORN PSU 19v AC 14w , £2.99 REF MAG3P10POWER SUPPLY fully cased with mains and o/p leads 17v DC900mA output. Bargain price £5.99 ref MAG6P9

9v DC POWER SUPPLYStandard plug in type 150ma 9v DCwithlead and DC power plug. price for two is £2.99 ref AUG3P4.13.8V 1.9A psu cased with leads. Just £9.99 REF MAG10P3INFRA RED REMOTE CONTROLLERS Originally made for hispec satellite equipment but perfect for all sorts of remote controlprojects. Our clearance price is just £2 REF: MAG2MAINSCABLE Precut black 2 core 2 metre lengths ideal forrepairs, projects etc. 50 metres for £1.99 ref AUG2P7.COMPOSITE VIDEO KIT. Converts composite video into sepa-rate H sync, V sync, and video. 12v DC. £8.00 REF: MAGBP2.UNIVERSAL PC POWER SUPPLY complete with flyleads,switch, fan etc.200w at £20 REF: MAG2OP3 (265x155x125mm).GYROSCOPE4bout 3' high and an excellenteducationaltoyforallages! Price with instruction booklet £6 Ref EF 15.FUTURE PC POWER SUPPLIES These are 295x135x6Omm,4 driVe connectors 1 mother board connector. 150watt, 12v fan, iecinlet and on/off switch. £12 Ref EF6.VENUS FLYTRAP KR Grow yourown carnivorous plantwith thissimple Id £3 ref EF34.TWEETERS r diameter good quality tweeter 140R (ok with theabove speaker) 2 for £2 REF: MAG2P5 or 4 for E3 REF: MAG3P46x12" AMORPHOUS SOLAR PANEL 12v 155x310mm130mA. Bargain price just £5.99 ea REF MAG6P12.FIBRE OPTIC CABLE BUMPER PACK 10 metres for £4.99ret MAG5P13 ideal for experimenters! 30 m for £12.99 ref MAG13P1

ROCK LIGHTS Unusual things these, two pieces of rock that glowwhen rubbed togetheri belived to cause raird£3 a pair Ref EF29.3' by 1' AMORPHOUS SOLAR PANELS 14.5v, 700mA 10watts, aluminium frame, screw terminals, £44.95 ref MAG45.ELECTRON IC ACCUPUN CTURE KrT Builds intoan electronicversion instead of needles! good to experiment with. £7 ref 7P30SHOCKING COIL KR Build this little battery operated device intoall sorts of things, also gets worms out of the ground! £7 ref 7P36.FLYING PARROTS Easily assembled kit that builds a parrot thatactually flaps its wings and flies! 50 m range £6 ref EF2.HIGH POWER CATAPULTS Hinged arm brace for stability,tempered steel yoke, super strength latex power bands. Departurespeed ofammunition is in excess of 200 miles per houri Range of over200 metres! £7.99 ref R/9.BALLON MANUFACTURING KIT British made. small blobblows i nto a large, longlasting balloon, hours of funl£3.99 ref GI/E99R

WE BUY SURPLUS STOCK FOR CASH

FREE CATALOGUE100 PAGE CATALOGUE NOW

AVAILABLE. 45P STAMP OR FREEON REQUEST WITH ORDER.

( IRCLE NO. 139 ON REPLY CARO


CLASSIFIEDTEL 0181652 3620 FAX 0181 652 8956

ARTICLES WANTED

WE WANT TO BUY!!IN VIEW OF THE EXTREMELY

RAPID CHANGE TAKING PLACEIN THE ELECTRONICS

INDUSTRY, LARGE QUANTITIESOF COMPONENTS BECOMEREDUNDANT. WE ARE CASH

PURCHASERS OF SUCHMATERIALS AND WOULD

APPRECIATE A TELEPHONECALL OR A LIST IF AVAILABLE.

WE PAY TOP PRICES ANDCOLLECT.

R. HENSON LTD.21 Lodge Lane, N.Finchley,

London N12 8JG.5 Mins, from Tally Ho Corner.

TELEPHONE0181-445-2713/0749FAX 0181-445-5702

**WANTED**Test equipment, Electronic Scrap,Valves, Transmitters/Receivers,Factory & Warehouse Clearance.

Confidentiality Assured.

TELFORD ELECTRONICSPhone: 01952 605451

Fax: 01952 677978

TOPPRICESPAID

For all your valves,tubes, semi

conductors and IC's.Langrex Supplies

Limited1 Mayo Road

CroydonSurrey CR0 2QP

TEL: 0181-6841166FAX: 0181-684 3056

WANTEDTest equipment, receivers, valves,transmitters, components, cableand electronic scrap and quantity.

Prompt service and cash.M & B RADIO

86 Bishopgate StreetLeeds LS1 4BB

Tel: 0113 2435649Fax: 0113 2426881

ELECTRONICSVALVES &

SEMICONDUCTORS

Phone for a mostcourteous quotation

We are one of the largeststockists of valves etc,

in the U.K.

COLOMORELECTRONICS LTD

170 Goldhawk Road,London W12 8HJ

England.Tel: 0181 743 0899Fax: 0181 749 3934

VALVES, and CRTs AVAILABLEONE MILLION VALVES stocked for Audio, Receiving, Transmit-ting & RF Heating. Rare brands such as Mullard & GEC available.

Also MAGNETRONS, KLYSTRONS, CRTs and SOCKETS.Large stocks of Russian & Sovtek items.

Please ask for our free catalogues of valves or CRTs.

VALVES, etc. WANTEDMost types considered but especially KT88 (£48), PX4/PX25(BO), KT66 (£35), KT77 (£15), EL34 (£10), EL37 (£9), ECC83 (f3).Valves must be UK manufacture to achieve prices mentioned.Also various valve -era equipment e.g. Garrard 301, (up to) £80.

Ask for a free copy of our wanted List.

BILLINGTON EXPORT LTD., Billingshurst, Sussex RH14 9EZ.Tel: 01403 784961 Fax: 01403 783519

VISITORS STRICTLY BY APPOINTMENT. MINIMUM ORDER £50 plus VAT

ARTICLES FOR SALE

FOR SALE - MULTICORE CABLE.Various lengths of 8 way heavy dutySound Cable, also 100m lengths of 4way Data Cable, plus 500m RG62 a/v.Offers. (01707) 263953.

KL SystemsMicrocontroller based electronic controlsystems. Specialising in the applica-tion of Zilog Z8 technology. Software,hardware and consultancy. Z8 devel-opment system available for £100.

Tel: 01642 480620or see Internet for further details.http:11www.wp. cornIKLsystems

SURPLUSSALE

THIS MONTH'S SALE INCLUDES: -Spectrum Analysers, Oscilloscopes,

Signal Generators, Voltmeters,Power Units, Frequency Counters,

Receivers, Transmitters, Ex PMR Equipment,Photographic & Video Equipment, Components,

& Miscellaneous items etc.

ALL EQUIPMENT IS SOLD AS SEEN.ALL PRICES EXCLUDE V.A.T.

NO MINIMUM ORDER.

RING TODAY FOR THIS MONTH'S CATALOGUE.

WANTEDSURPLUS ELECTRONIC

COMPONENTS ANDEQUIPMENT

We also welcome the opportunity to quote forcomplete factory clearance

B. BAMBER ELECTRONICS5 STATION ROAD, LITTLEPORT, CAMBS.

Phone: ELY (01353) 860185Fax: ELY (01353) 863245

174.

CLASSIFIEDTEL 0181 652 3620 FAX 0181 652 8956

ARTICLES FOR SALE

J. )

SUPPLIER OF QUALITY USEDTEST INSTRUMENTS

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CONTACT

Cooke InternationalELECTRONIC TEST & MEASURING INSTRUMENTS

Unit Four, Fordingbridge Site, Main Road, Barnham,Bognor Regis, West Sussex, P022 OEB

Tel: (+44)01243 545111/2 Fax: (+44)01243 542457CIRCLE NO. 140 ON REPLY CARD

VISA

OPERATING & SERVICE MANUALS

CONTACT

Cooke InternationalELECTRONIC TEST & MEASURING INSTRUMENTS

Unit Four, Fordingbridge Site, Main Road, Barnham,Bognor Regis, West Sussex, P022 OEB

Tel: (+44)01243 545111/2 Fax: (+44)01243 542457CIRCLE NO. 141 ON REPLY CARD

INDEX TO ADVERTISERSPAGE PAGE PAGE

Anchor Surplus 155 Halcyon 145 Quickroute Systems 90

BK 109Hart 93 Ralfe IBC

Bull Electrical 172,173Interconnections 101

Seetrax 118Iosis 90 Smart 135

Clinical Engineering 163 Johns Radio 95 Stewart of Reading 166CMS 151 JPG 166 Surrey 151Cricklewood 109

Kanda 163 Stag 101Crossware 90

Crownhill Associates 123Kestral 171 Telford 109

Keytronics 149 Telnet 158

Danmere 151 M B Radio 101 Those 145

Dataman OBC Microlease 157 Tie Pie 167

Display 147 Milford 171 Tsien 163

Farnell 97 Number One 166 Ultimate Technology 99

Flight IFC Pico 139 Warwick 145

75

)fib

Eight year EW indexHard copy or diskIncludes over 600 circuit idea references

Whether as a PC data base or as hard copy,SoftCopy can supply a complete index ofElectronics World articles going back over thepast eight years.

The computerised index of Electronics Worldmagazine covers the eight years from 1987 to1995 - volumes 94 to 101 inclusive - and isavailable now. It contains almost 2000references to articles, circuit ideas andapplications - including a synopsis for each.

The EW index data base is easy to use andvery fast. It runs on any IBM or compatible PCwith 512k ram and a hard disk.

Even though the disk -based index has beenexpanded significantly from five years to eight,its price is still only £20 inclusive. Pleasespecify whether you need 51/4in, 3.5in DD or3.5in HD format. Existing users can obtain anupgrade for £15 by quoting their serial numberwith their order.

Hard copy Electronics World indexIndexes on paper for volumes 100 and 101 are availableat £2 each, excluding postage.

[g] Circuit

Remote motor controlResistance multiplierSCR InverterSample -and -infinite holdSchmitt trigger, prog. thresholdsSelf -ID for plugs and sensorsSensor, Linear CurrentServo, High -torque positionServo, Simple

ingle-pot Pularitu B GainSoft -start filament driverSpeech compressorSquare wave generator, 1:Status detection over twoStepper Motor ControllerStepper Motor ControllerStepper Motor DriverStereo expanderSwitch, Low voltage

Photo copies of

Electronics World articles

Photo copies from back issues of

Electronics World are available at a

flat rate of £3 per article or 50p per

circuit idea, both excluding

postage.

ad just

Ideas

SIMULATOR, INSERTION 8 RETURN LOSSC J Hall

May 1992, p422

"Simultaneous insertion and returnloss plots".Modelling a return -loss bridge atthe relevant port allow plot ofinsertion loss, and, withoutfurther computation, return lossplot simultaneously.

R

n'l Design: RF

Directional couplers, hybridGigahertz Systems on a ChipHF receiver performanceHF receiving loop, improvedHepa for RF power amplifier designHigh quality punch for radiocommsHybrids in RF combinersImpedance transformationMeasuring DetectorsMeasuring with TDR

Microwaves, Mew wave /2Noise source, self -calibratingPolyphase SSBRF Design RevolutionRF Power Measurements in milliwattsRF Transistors, Using /1

RF Transistors, Using /2

RF Transistors, Using /3RF filter for electro-explosives

MICROWAVES, NEW WAVEMike Hosking

81 Concepts, circuits 8 deApril 1994, p276

112 The Laws of MicrostripMay 1994, p410

03 Lumped components 8 uaJune 1994, p472

114 Active devices for millwaves.July 1994, pS71

BE Oscilator and amplifierAugust 1994, p666

Fl-Hel, FZ-Search F3-Meno F4 -Edit F5-0ther F10 -Exit TAB

Ordering detailsThe EW index data base price of £20includes UK postage and VAT. Add anextra £1 for overseas EC orders or £5 fornon -EC overseas orders.

Postal charges on hard copy indexesand on photocopies are 50p UK, £1 forthe rest of the EC or £2 worldwide.

For enquiries about photocopies, etc,

please send an sae to SoftCopy Ltd atthe address below.

Send your order to SoftCopy Ltd., 1Vineries Close, Cheltenham GL53 ONU,tel 01242 241455, or e-mail [email protected]. Pleasemake cheques payable to SoftCopy Ltd- not EW or Reed Business Publishing.Please allow up to 28 days for delivery.

ELECTRONIC UPDATEContact Malcolm Wells on

0181-652 3620New Flight ElectronicsInternational Catalogue SetYou now have access to the world's latest:* Electronics Training Equipment* Microprocessor Training Equipment* Test and Measurement Equipment* PC Cards

via "Flight's" latest catalogue set.

We are specialists in the provision ofinnovative top quality electronicstrainers, breadboards, test andmeasurement, PC cards andmicroprocessor evaluationequipment.

Our extensive range covers everyneed, call today for your freecatalogue set.


Fat Thendiy seroce 3 ,ast Oct. vettphone Feedback

NEW Feedback T&MCatalogue

The latest edition of the Feed-back Test & Measurement cata-logue is now available. Over 60pages packed with more than800 products divided into over20 sections. The catalogue isindexed for both product andmanufacturer and is fully illus-trated. Whether you are lookingfor an individual product, a com-plete workstation, or a solutionto a particular Test & Measure-ment need the NEW Feedbackcatalogue will sove your prob-lems, send for a copy NOW!


A regular advertising feature enablingreaders to obtain more informationon companies' products or services.

NEW CATALOGUEThe new 1996 NationalInstruments InstrumentationReference and Catalogue isavailable now. Discover how todevelop integrated systems fortest and measurement andindustrial automation. Includesdetails of over 500 software andhardware products for PCs andworkstations. Includes valuabletutorials on data acquisition andinstrument control.

NATIONAL INSTRUMENTSTel: 01635 523545


1995 MASTER PRODUCTCATALOGUE NOW OUT!

Test and instrument control solutions.48 pages of full description and technicaldata on our own range of solutions to yourPC and PS2 interfacing problems; IEEE488(GPIB) * 010 * Timer/Counters * RS232 *RS422/485 * A/D * D/A * plus OptoIsolated versions. New Parallel/SerialRS232, Opto Dual RS232, Motion Control,Converter and Repeater for 1995!ISO 9001 Quality guarantee UK design and manufacture 36 month no -quibble warranty Telephone hotline support Competitive pricing on the page Intelligent solutions 8 friendly service /

BRAIN BOXESUnif 3f Wavertree Boulevard South

Wavertree Technology ParkLiverpool L7 9PF

Tel: 0151 220 2500 Fax, 0151 252 0446


SPECTRUM ANALYSERS ralfe electronics exclusively

professional

HEWLETT PACKARD

IR

HP141T 1.25GHz system (85528, 85548) £1250

18GHz system 1 £1500

HP8557A 350MHz (fitted in 1820 mainframe) £1500

HP3580A 5Hz-50kHz audio frequency spectrum analyser

HP3582A audio frequency fft analyser dual -channel

HP8568A high -specification 1.5GHz spectrum analyser

MARCONI 2386 100Hz-26.5GHz (in 1Hz steps!)

TEKTRONIX 496P 1.8GHz spectrum analyser, GPIB programmable

TEKTRONIX 7L12 1.8GHz, w tracking gen & mainframe 7622A

36 Eastcote Lane South Harrow Middx HA2 8DB England TEL (+44)0181-422 3593 FAX (- 44)0181-423 4009

EST41

YRS

DISTRIBUZIONE E ASSISTENZA, ITALY: TLC RADIO, ROMA (06) 871 90254

750 to £1250

£2000

£7500

£15000

£4500

£2000

MARCONI INSTRUMENTS

2019A synthesized AM/FM signal gen 80kHz-

1040MHz (2000

2305 modulation analyser 50kHz-2.3GHz f2500

2828N2829 digital simulator/analyser £500

2382 spectrum analyser hi -spec 100Hz-400MHz £8500

2386 spectrum analyser, hi -specification,

100Hz-26.5GHz £15000

2926 TV generator & inserter (NTSC variant) £500

6460/6421 power meter & sensor 10MHz-12.4GHz £350

6500 amplitude analyser c/w 2c 6514 waveguide detectors

6960 microwave power meter with 6910 power sensor

IOMHz-20GHz

0A2805A pan regenerator test set

TF2910/4 non-linear distortion (video) test set

TF2910 TV interval timer

TEST EQUIPMENTANRITSU MF76A 18GHz microwave frequency counter

BRUEL & KJAER 1023 sine generator

BRUEL & KJAER 1027 sine random generator

BRUEL & KJAER 2619 preamplifier complete with 1/2" mic

BRUEL & KJAER 2619 preamplifier complete with 1/2" mic

BRUEL & KJAER 2511 vibration meter (field set with 1621 filter)

BRUEL & KJAER 2317 portable level recorder

BRUEL & KJAER 2607 measuring amplifier

BRUEL & KJAER 2609 measuring amplifier

BRUEL & KJAER 2308 analogue X -Y pen recorder

BRUEL & KJAER 2639 preamplifier

CHASE LFR1000 interference measuring receiver 9kHz-150kHz

DATRON 1061 & 1061A- various, digital millimeter & 10E6 - call from £500

IDACOM PT502 protocol analyser (Hewlett Padtard E391013 with E3936A) £3000

JJ INSTRUMENTS CR600 2 -channel pen recorder £350

£1500

£1250

£1750

£500

£500

£1000

£1500

f600f750

£750

£325

£850

ralfe electronics exclusivelyprofessional T&M C)

SEND FOR LATEST STOCK LIST. WE FAX LISTSAND SHIP WORLDWIDE. ALL FULLY LAB -TESTED

AND NO -QUIBBLE GUARANTEED.o.

IS09002 ACCREDITED STOCKISTCERT. 954713 MEASUREMENT & TEST EQUIPMENT CERT.. 95/013

£2500

£900

£750

£500

£250

KIKSUI 8520 frequency response analyser 20Hz-200kHz

PHILIPS PM8272 X -Y & Y -t dual -channel pen recorder

RACAL -DANA 1992 frequency counter 1.3GHz IEEE option

SYSIAONDCNER 1330 synbested *lel generator 100Hz-1GHz GPIB

TEKTRONIX AA501/SG505distorkin analyser (complete Mth TM503)

TEKTRONIX P6303 o'sxce prcbas NEW 250M-lz X1010 itsith readculpti

WAVETEK 2520 synthesized signal generator 200KHz-2700MHz

WANDFEL & GOLTERMANN PS20 level generator

£500

£850

£700

£1350

Er 250

£50ea

£2500

£500

1\

i o:

. . . . :IIT`J I i WV i r : 0

1640B serial data generator

3561A dynamics signal analyser (opt 01)

3764A digital transmission analyser

3312A function generator

3400A voltmeter, analogue 10Hz-10MHz

3580A audio frequency spectrum analyser

3581C selective voltmeter

3582A dual -channel spectrum analyser 0.02Hz-25.5kHz

3779D primary multiplex analyser

41406 pNmeter, DC voltage source

41800A active probe 5Hz-500MHz

4339A high resistance meter c/w lead set 161178

4275A multi -frequency la meter

4951C protocol analyser with 1817A pod

53346 frequency counter w option 010 high -stab

5386A 3GHz frequency counter

54100A 1GHz digitizing oscilloscope

6012A power supply 0-60V 0-50A 1000W

6114A precision power supply unit 0-20V/2A, 20-40V/1A

6253A dual power supply 0-20V 0-1A twice

6443B power supply 0-120V 0-2.5A

6825A bipolar power supply/amplifier-20V to

+20V, 0-1A

80078 pulse generator 100MHz

8018A serial data generator

8082A pulse generator 250MHz -

8111A pulse generator 20MHz

816A slotted line 1.8-18GHz with 809C & 4478 probe

8349B microwave amplifier 2-20GHz

8444A tracking generator with option 059

85024A active probe

850328 N -type calibration kit

8568A spectrum analyser 100Hz-1.5GHz

86408 signal generator w opt 01 & 03

(variable audio osc 8 rpp)

87510A gain -phase analyser 100KHz-300MHz

8901A modulation analyser with option 02/010

8903A audio analyser

£500

£5500

£2000

£500

£250

£1000 to £1500

£1250

£2000

£3000

£4000

£750

£2000

£3500

£1000

£1250

£1500

£2250

£650

£650

£250

£400

£350

£950

£1000

£2000

£1250

£500

£4000

£1250

(1000

£1000

£7500

£1250

£6500

£3500

£2000

SPECIAL OFFER THIS MONTH ONLY ON HEWLETT PACKARDDIGITAL TRANSMISSION TESTERS, PROTOCOL ANALYSERS

Examples: HP37724A SDH/PDH portable test sets -Condition as new, price £5000 (were listing at ca £20K!) - also37772A optical interfaces available for STM-1, £1500 (list over 6K).

4957PC PROTOCOL ANALYSER CARDS4972A LAN PROTOCOL ANALYSER4995A LANPROBE II £500 EACH

(L1ST>£2K)J2219A/? J2170A, NETWORK ADVISOR8157A OPTICAL ATTENUATORS

1200-1650mm £1000 EACH

64000 -SERIES MDS:

64700A, MAINFRAMES WITH:647476, 64771 G, 64703A, 64704A, 64751A, 64172B, 64748A, 64748C,64787B, 64604A, 64783A, 64172B, 64746J, 64744A/C/E, 64780A.

SEND FOR COMPLETE LISTING AND QUOTATION

IS09002 ACCREDITED STOCKIST- MEASUREMENT & TEST EQUIPMENT

THE WORLD'SMOST

POWERFUL,PORTABLE

PROGRAMMERSCompare the Dataman S4 with any

other programmer and you'll see

why it's the world's undisputed number one.

S4 is capable of programming 8 and 16 -bit

EPROMs, EEPROMs, PEROMs, 5 and 12V FLASH,

BOOT -BLOCK FLASH, PICs, 8751 Microcontrollers and

more. 54 also emulates ROM and RAM as standard!

S4 is the only truly hand held programmer that ships

complete with all emulation leads, organiser -style

manual, AC charger, spare library ROM, both DOS and

Windows terminal software, and arrives fully charged

and ready to go! Who else offers you all this plus a three

year guarantee?

Customer support is second to none. The very latest

programming library is always available free on the

Internet, and on our dedicated bulletin boards.

Customers NEVER pay for upgrades or technical support.

Dataman-48Dataman-48 programmer adds Pinsmart®

to provide true no -adaptor programming

48 -pin DIL devices. Dataman-48 connects

CreditCard Hotline01300 320719Orders received by 4pm will normally be despatched same day. Order today, get it tomorrow!

straight to your PC's parallel port and works great with

laptops. Coming complete with an integral world

standard PSU, you can take this one -stop programming

solution anywhere!

As with S4, you get free software upgrades and technical

support for life, so now you don't need to keep paying

just to keep programming.

The current device library contains over 1500 of the most

popular logic and memory devices including GALs, PALs,

CEPALs, RALs, 8 and 16 -bit EPROMs, EEPROMs, PEROMs,

FLASH, BOOT -BLOCK, BIPOLAR, MACH, FPGAs, PICs and

many other Micro -Controllers. We even include a 44 -pin

universal PLCC adaptor.

If you need to program different packaging styles, we

stock adaptors for SOP, TSOP, QFP, SDIP as well as

memory emulation pods.

Order your Dataman programming solution today via

our credit card hotline and receive it tomorrow. For more

detailed information on these and other market leading

programming products, call now and request your free

copy of our new colour brochure.

The Dataman ChallengeTry the Dataman S4 or Dataman-48 withoutobligation for 30 days. ffyou do not agree that these

are the most effective, most useful, most versatile

additions you can make to your programming

toolbox, we will refund your money in fidl.

ON REPLY CARD

Dataman Programmers L

Station Road, Maiden No ton.

Dorset DT2 OAE. UK

Telephone +44/0 1300 320719

Fax +44/0 1300 321012

BBS +44/0 1300 321095 (24hr)

Modem V.34/V.FC/V.32bis

Home page: http://www.dataman.com

FTP: ftp.dataman.com

Email: [email protected]

the fastest growing electronics title in the uk …€¦ · 012 a02/ 00.2 p13 p14 a03/ p0.3 4 a 4,...

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