pique offer - Digital -readout temperature sensor

ELECTRONICSWORLD+ WIRELESS WORLDAugust 1995 £2.10

20Hz activesubwooferGetting morefrom RS232

PC engineering:signal analysis

24cm antenna

DSP demystified

Analogue signalprocessing

Linsley -Hoodcomments onmosfets

RF oscilloscopeprobe using sm

Exclusive - GPS designer's kit

Denmark DKr. 65.00Germany DM 15.00

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EXPRESS

CONTENTS

636 FEEL THE BASSJeff Macaulay's 100W sub -woofer has a-3dB point of 20Hz, yet the box is small.

643 DISCRETE -TIMEKEY TO DSPDiscrete -time linear systems explainedusing a practical approach, byHoward Hutchings.

656 AF ANALYSISVIA THE PCWhat started as a pc loudspeakermeasurement tool is fast becoming ageneral-purpose If analysis suite.

659 SWITCHERS FORTHE MASSESUsing a public -domain design tool andchips designed for ease of use, almostanyone can design an smps.

664 FINDING GPSVersatile modular GPS receiver -available at a special price to EW+WWreaders - is suitable for fixed pc stationsor portable navigation systems.

669 130 MHz ACTIVE PROBESM devices are ideal for an 10x activerf scope probe due to their small size,but can they be easily prototyped?

671 GETTING MOREFROM RS232Douglas Clarkson expands on RS232covering a -to -d conversion through to amulti -drop comms link.

682 HARMONY INTHE BANDA look at the Government's spectrumreview by reporter Svetlana Josifovska.

684 EXPERT WITNESSAudio expert John Linsley hood adds hisexperience to the mosfet v bjt case.

A special offer for John LinsleyHood's book 'The Art of LinearElectronics' appears on page 685.

687 TEMPERATURE BYTESTemperature to a 9bit serial word fromone chip - a design kit for which isavailable to EW+WW readers at aspecial price.

699 HIGH PERFORMANCEANTENNA FOR 24CMWide beam, wide -band antenna designfeaturing useful gain, from John Cronk.

REGULARS

627 COMMENTJug wine or Chambertin

628 NEWSCordless camcorder, new i/o processorfor pcs, Cash over the net, one -electrontransistor, vhdl delay.

633 RESEARCH NOTESFrog logging, morphing robot, camera ona chip, audio chip progress.

650 CIRCUIT IDEASResonant back-up source, video amp andsync stripper, hf buffer, duplex link,x -point switch.

675 LETTERSGPS vulnerability, bike lamps, power -lines, audio.

691 DESIGN BRIEFIan Hickman shows that analogue signalprocessing still has considerablelife left in it.

703 NEW PRODUCTSPick of the month - classifiedfor convenience.

Next month:Top designer Walt Jung discusses working with single -rail op -amps, Ian Hegglunpresents a high-performance audio power amplifier based on square -law techniquesand Douglas Clarkson looks at isolated RS232 links.

SEPTEMBER ISSUE - ON SALE 31 AUGUST

Cover - Trevor Bailey

A GPS designers kit - that can formthe basis of anything from a pcbased GPS data analyser to aportable navigation aid - is one ofthis month's special reader offers,page 664.

Heat -in, bits out -a combinedthermometer/thermostat chipoperating from -55 to 125°C. Adesigner's kit based on this chip isalso the subject of a uniquereader offer.

August 1995 ELECTRONICS WORLD + WIRELESS WORLD 625

"moving from schematic to layout- could not be easier"

Electronics World & Wireless World Jan 1995

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FREEDemoPack

Available.

JPGHigh. quality stepping motor kits (all including step- 74LS05 harinver.or £10.00 per 100

ping motors) Co top mdependent control of 216 stail:9508wnzp2m.ttom.oto.rldbzfttc...orta the parallel port) sLoillJU'd 8,111:44F8p.a.M'TnfAd711:plifishree

sheet £1.95Ready built £99.00 AM27S02 £1.25 each ((90p

Software support and 4 digital inputs kit £27.00 10p 100+ (Op 1000+air light gun terminated with a jack plug andPower interface 4A kit £36.00 Sinclair

Power interface 8A kit £46.00 PPS clip gives a signal when pomted at 50HtStepper kit 4 (manual control). includes 200 step Dickering light with output wave form chart

stepping motor and control circuit £23.00 £3.95We are now stocking a range of stepping motors and DC -DC convertor Reliability model V12P5 I2v in 5v

kin to chive them, please ask for the stepping 200rna out 300V input to output Isolation withmotor data sheet for full information. data £4.95 each or pack of 10 £39.50

Invertor toroidal transformers 225VA 10.5-0-10.5 Hour counter used 7 digit 240V AC-50Hr £1.45primary 0-260-285 secondary £29.95 QWERTY keyboard 58 key good quality switches

LEDs 3mm or 5mm red or green 7p each new £6.00Yellow llp each Ai ax A82903 -C larar _stepping motor 14v 7.5' step

Cable ties, Ip each, £5.95 per 1000, £49.50 per 10,000 27ohm 68mm diabody13.3mm shaft £8.95High quality photo resist copper clad epoxy glass or £200.00 fora box of SOboards Polyester ca.n/tors box type 22.5mm lead pitchDimensions single sided double sided 0.9uf 250vak 18p each 14p.....100+ 9p 1000+3x4 inches £1.09 £1.25 Iuf 250vdc 20p each4x8 inches £2.75 £2.99 15p....100+ 10p....1000+6x12 inches £6.20 - luf 50v bipolar electrolytic axial leads 15p each12x12 inches £12.25 - 7.5p 1000+

Rechargeable Batteries 0.22uf 250v polyester axial leads 15p eachAA (HF7) 500mAH ....... AA 500mAH with solder 7.5p 100+

£0.99 to £1.55 Polypropylene luf 400vdc (Wuna MKPI 0)AA 700mAH £1.75 C(HP11) 1.8AH ... £2.20 27,5mrn pitch 32x29x17mm case__ 75p eachC 2AH with solder tags D(HP2) 1.2AH £2.60 ' 60p 100+

£3.60 PPS 8.4V 110mAH Philips 123 series solid aluminium axial leads - 33ufD 4AH with solder tags £4.95 10v & 2.2uf 40v 40p each

£4.95 Sub C with solder tags.... 25p 100+1/2AA with solder tags £2.50 Philips 108 series long life 22uf 63v axiaL.... 30p each

£1.55 1/3 AA with tags (Philips 15p 1000+AAA (HP16) 180mAH CTV) £1.95 Multilayer AVX ceramic capaciton all 5mm pitch

£1.75 100v 100pf, 150pf, 220p ,1E 10,000pf (10n)Standard charger charges 4 AA cells in 5 hours or 10p each 5p 100+ 38p 1000+

4Cs or Ds m 12-14 -hours + lePP3 (1, 2, 3 or 4 500pf compression trimmer 60pcells may be charged at a time) £5.95 40 of 370var motor start capacitor (dialectrol type

High power charger as above but charges the Cs and containing no pcbs) £5.95 or £49.50 for 10Ds in 5 hours. AAs, Cs and Ds must be charged in Solid carbon resistors very low inductance ideal for2s or 46 £10.95 RF circuits - 27ohm 2W, 68ohm 2W 25p each

Nickel Metal Hydryde AA cells high capacity with no 15p each 100+memory. If charged at 100ma and discharged at We have a range of 0.25w 0.5w 1w and 2w solid250ma or less 11WmAH capacity (lower capacity carbon resistors, please send SAE for listfor high discharge rates) £3.75 P.C. 400W PSU (Intel part 201035-001) with sten-1100mAll £5.75 dard motherboard and 5 disk drive connectors,

Special offers, please check for availability. fan and mains inlet/outlet connectors on backStick of 4 42x16mm Nicad batteries 171x16mm dig and switch on the side (top for tower case) dims

with red & black leads 4.8v £5.95 212x149x149mm excluding switch £26.00 eachComputer grade capacitors with KM". terminals £138.00 for 6

5000 60v £4.95 MX180 Digital multimeter 17 ranges 1000vdc115V AC 80V DC motor 4x22nim shaft 50mra dig x 750vac Mohm 200mA transistor Hfe 9v and

60 long body (excluding the sh 3 pEaft)

it has a repla- 1.5v battery test £12-95ceable thermal fuse andlirushes AMD 27256- _ roros £2.00 each £1.25/100+

£4.95 each (£3.95 100+) DIP switch SPCO 12 pin (ERG SDC-3-023) 60p each40p...100+7 segment common anode led display 12mm £0A5 Disk drive boxes for 5.25 disk drive with room for a

LM 357k TOO cane variable regulator £1.95 power supply, light grey plastic, 67x268x247mm(£1.44 100+) £7.95 or £49.50 for 10

GaAs FET low leakage current 58873 .... £12.95 each Hand held ultrasonic remote control £3.95(£9.05 10+. £7.95 100+) CV2486 gas relay, 30x10ann dig with 3 wire termi-

85250 P channel modet £0.45 nals, will also work m a neon light 20p eachBC559 transistor £5.95 per 100 £7.50 per 100

All modems advertised are new and unused unless otherwise stated.Wide range of CMOST11. 74HC 79F Linear Transistors kits. Rechargeable batteries, capacitors, tools etc

always in stock. Please add £1.95 towards p&p. VAT included in all prices.

JPG Electronics, 276.278 Chatsworth Road, Chesterfield S40 2B11Access/Visa (01246) 211202 Fax: 550959 Callers welcome

CIR( II \O. Ur; ON REPLY CAW

SMART CARD READER/PROGRAMMEROn board ISO 7816 Card Reader Socket (Videocrypt etc). Software runs on IBM/PCenabling the user to Read & Write to IS07816 and 2/3 chip D2mac Satellite cards. Boardalso contains a PIC16C84 programmer. Ideal smart card development tool £79.95Requiries external power 15-20v AC or CD @250 ma. (optional extra £6.50)

MICRO -ENGINE MCS80C31/51 Development board.Tiny 72mm x 42mm PCB contains socketed 44 pin CPU, turned pin Rom socket, 12 MHzxtal and ports 1, 3 output on IDC connector. Ideal for stand alone projects or developmentwork. Supplied with CIRCUIT & MCS8051/52 development software £49.95

PIC ICE II* In Circuit Emulator for PICI6C54-55-56-57-71-84.Replaces all 18 or 28 pin PICs. All ports Bi-directional, OSC2 output, RTCC input. Onboard A/D converter for PIC167C1. Supplied with PICDEV54 and PICDEV7I software,manual, connecting leads & headers, ASM examples, and hardware circuit projects.

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PIC ICE STD In -Circuit Emulator for 18 pin PICs only no A/D.Plugs into the printer port, appears to the target system as a normal Pic device includingOSC2 and RTCC in/out. Runs in real time from the IBM PC changes made to File registersreflected on target. Supplied with Development software PicDev 54-57 and PicDev 71/84

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PIC PROGRAMMER* Programs Picl6C54-55-5656-71-84. Centronics port interface.Powerful editing software to Read, Write & Copy Pic devices including data memory inPicl6C84. Top quality components used throughout including production ZIF socket. Nowincludes a Text Editor/Assembler for all above PICs. £79.95Requires external power 15-20v AC or DC @250ma. (optional extra £6.50).

MEGAPROM programmer, EPROMS, E2PROMS, and FLASH memories from 28 (2716)to 8 Meg (27C080). Runs on IBM/PC via the centronics port using standard printer cable.Works on all PC compatibles, laptops, and notebooks. No special port requirements. Topquality components used throughout including production ZIF socket £99.95Requires external power supply 18-25v AC or DC @250ma. (optional extra £6.50).

EPROM EMULATOR Works on ANY computer with centronics printer port. Data sentto the printer appears in the target board Eprom socket. Emulates from lk to 32k Byte(27C256) roms, board switchable. Very fast download. Works with or without ourDevelopment software. £59.95

DEVELOPMENT SOFTWARE.Develop software on your IBM/PC for other Microprocessors, Controllers, Pic's etc.Software has fully integrated Text Editor, Assembler, Disassembler, and Simulator. Codecan be downloaded directly to our EPROM Emulator. All software supplied with sampleASM files, and user documentation manual.Available for the following:- £19.95 eachMCS8051/52/552 MCS8048/49 PICI6C71/84P1C16C54/5/6/7 HD63/6809 R6502All hardware carries a 12 months parts and labour Guarantee. No Vat payable. Please add£1.50 for Carriage.

Starred items also available from FARNELL (Leeds).

CREDIT CARD ORDERS SAME DAY DESPATCH

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ELECTRONICS WORLD+WIRELESS WORLD August 1995

COMMENT

EDITORMartin Eccles0181-652 3128

CONSULTANTSJonathan CampbellPhilip DariringitonFrank Ogden

DESIGN &PRODUCTIONAlan Kerr

EDITORIALADMINISTRATIONJackie Lowe0181-652 3614

E-MAIL ORDERSjackie.loweetbp.co.uk

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 INJ

SUBSCRIPTIONQUERIES01444 445566

NEWSTRADEDISTRIBUTIONMartin Parr0181 652 8171

BACK ISSUES

Available at £230

ISSN 09594332

REED

'el PUBLISHING

Jug wine or Chambertin?I t was early June in Montreux. The Organisers of the19th International Television Symposium and

Technical Exhibition were holding a lakeside party towelcome the press. Hungry hacks were grabbing any-thing edible from passing trays of nibbles. At anexchange rate of less than 2 francs to the pound - andno provision made for helping visiting journalists toeat - free food was everyone's first priority.

Exhibition organiser Joe Flaherty stood up. Flahertyis Senior Vice President in charge of Technology atCBS Inc, and for ten years he has been the drivingforce in the USA behind HDTV and the digital tvGrand Alliance.

"Europe's DVB will be a digital version of MAC. Itwill be a disaster", Flaherty pronounced, "When, as issure to happen, perhaps at the Olympics, broadcastersstart transmitting in high definition, existing sets willgo dark. You can't ever let sets go dark".

All round the area the press dropped food andgrabbed notebooks.

Flaherty then explained his point. Europe's DigitalVideo Broadcasting standard, which will be frozenthis September to allow a service launch in 1997, doesnot provide the same upgrade path from StandardDefintion to High Defintion that the Grand Aliancesystem offers. The SD digital receivers sold from DayOne will not be able to receive an HD broadcast, anddecode it as an SD signal. This, Flaherty repeated, willmake DVD "a disaster".

"In the future Europe won't be able to receivehigh -definition pictures from the same transmissionchannels. And it won't be long before someone putsout HD programming. You can go on drinking jugwine until you taste the Chambertin...".

As the word spread round Montreux of Flaherty'soutburst, members of the DVB project, which is nowbacked by over 160 companies, were asked to com-ment, often in open seminars. The diversity of com-ment told its own story. As Henry Price, BBC Head ofEngineering Information put it back in the UK.

"There is a huge amount of confusion over all this",NTL already provides the analogue transmitters usedby the UK's commercial tv companies, and hasoffered to build the BBC's netowrk. Tony Gee, NTL'sMarketing Manager for digital broadcasting, admittedthat the issue of whether DVB receivers sold on DayOne will later be able to decode HD programmes fordisplay in SD is "a key question". But he was unsureof the answer. "My understanding is that the likeli-hood is no" says Gee, suggesting that broadcasterscould simulcast the same programme in both HD andSD formats.

Richard Wiley, Chairman of the FederalCommunication Commission's Advisory Committeeon Advanced Television Service, boasted "In the USno set will ever be dark. We are making sure of that.The Grand Alliance handles both HD and SD trans-missions perfectly. The cost of adding HD compati-bility to an SD set is only marginal".

George Waters, Director of the Technical Divisionof the European Broadcasting Union, agreed with

Wiley's low cost estimate and added that "Joe wasright to stimulate discussion. The US has approachedthis from the top down; Europe has approached thisfrom the other way round because the project beganwith cable and satellite. There's a new awareness inEurope. We have to look at the situation again."

So why, if there is now doubt over the standard, isEurope rushing towards finalisation in September1995? Why not wait another six months or even ayear to sort out the issue of HD/SD downwards com-patibility? Who is driving the rush?

"The BBC", said George Waters, turning to look atMichael Starks, BBC Controller of Digital Feasibility.Starks looked sheepish, and remained silent.

Does the BBC really believe there will be rioting inthe streets of London if it delays the start of digital tvbroadcasting by six months? Does anyone in the elec-tronics trade or general public really care about a sixmonth delay, especially if it means Day One sets arefutureproofed?

Starks listened to the questions and remained evenmore sheepishly silent. With the help of engineersfrom NTL and the BBC it has now been possible topiece the scenario together.

The DVB originally planned to specify a hierarchi-cal system, but it was dropped for three reasons.

It puts up the cost of even the basic receiver,because it needs more memory. Also, if the broad-caster tries to guarantee good reception for portable tvsets, by adding a very robust signal with a low datarate, even high quality SD receivers with roof aerialswill lock onto the low resolution picture. And hierar-chical coding is very inefficient. It wastes so muchspectrum space, that the broadcaster might as well doas NTL's Tony Gee suggested at Montreux, and trans-mit the same programme twice over, once in standarddefinition and once in high definition.

But the Grand Alliance thinks it has licked all theseproblems.

Meanwhile the BBC favours a third option.Programmes will be shot in 1250 line definition,down -converted to 625 line signals and transmitted athigh bit rate, probably 9Mbit/s, which is half thecapacity of a uhf channel.

Adanced tv sets will then artifically double thenumber of picture lines to simulate HDTV. Howevergood the up -conversion this option still cuts Europeoff from true 1250 line HDTV.

While everyone scurries around, giving differentreasons for not doing what the Americans think theycan do, Jim Norton, Chief Executive of theRadiocommunications Agency, warns that simul-casting SD and HD will be a no -no. But Norton alsooffers a neat and simple solution.

"The tv manufacturers should borrow an idea fromthe computer world, and provide every digital tv withan upgrade slot. That way owners can bolt on what-ever upgrade circuits they need in the future".

Is it too late for the DVB group to write such a sen-sible approach option into its final standard?Barry Fox

Electronics World + Wireless World is published monthly. Bypost, current issue £2.25, back issues (if available) £2.50.Orders, payments and general correspondence to L333,Electronics World + Wireless World, Quadrant House, TheQuadrant, Sutton, Surrey SM2 5AS. Tlx:892984 REED BP G.Cheques should be made payable to Reed BusinessPublishing Group.Newstrade: Distributed by Marketforce (UK) Ltd,247 Tottenham Court Road London W1P OAU 0171 261-5108.Subscriptions: Quadrant Subscription Services, OakfieldHouse, Perrymount Road, Haywards Heath, Sussex RH163DH. Telephone 01444 445566. Please notify change ofaddress. Subscription rates 1 year (normal rate) £30 UK and£43 outside UK.USA: $52.00 airmail. Reed Business Publishing (USA),Subscriptions office, 205 E. 42nd Street, NY 10117.

Overseas advertising agents: France and Belgium: PierreMussard, 18-20 Place de la Madeleine, Paris 75008. UnitedStates 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 postagepaid at Rahway NJ Postmaster. Send address changes toabove.Printed by BPCC Magazines (Carlisle) Ltd, Newtown TradingEstate, Carlisle. Cumbria, CA2 7NRTypeset by Wace Publication Imaging 2-4 Powerscroft Road,Sidcup, Kent DA14 5DT

©Reed Business Publishing Ltd 1995 ISSN 0959 8332

August 1995 ELECTRONICS WORLD + WIRELESS WORLD 627

UPDATE

Video signal(composite)

Optical link makes camcorder cordlessitachi has launched a camcorder

I I incorporating an optical linkwhich is intended to make playbackmore convenient. The systemcomprises a camera with integraltransmitter and a remote receiverwith connections to a tv or vcr.

A composite video signal isclamped, pre -emphasised thenfrequency modulated onto a 11.5-

13.5MHz carrier; both stereo audioaudio channels also undergo pre -emphasis and frequency modulation,onto carriers at 950kHz and 550kHz.

The signals are combined andemitted by two infrared leds. In thereceiver, the signal is sensed by aphoto -diode and the process reversedafter signal amplification.

Usable range of the link is 3m, at

Audio signal(right)

Audio signal(left)

To help i/osubsystems keep up

with advances in x86microprocessor

performance, Intel islaunching anintelligent i/o

processor withdedicated PCI bus

facilities.

ClampPre -

emphasis

Pre -

emphasis

Transmitter

Pre -

emphasis

FM

modulation

FMmodulation

FMmodulation

Frequency11.5 - 13.5MHz

950kHz

550kHz

Transmitting and receiving systems of the camcorder one-wayoptical link. Both audio and video signals are transmitted.

Receiver

Lim.FM

modulation

-

LPF De -

emphasis

BPFFM

modulationLPF De -

emphasis

BPFFM

modulationLPF De -

emphasis

Infrared

Video signal(composite)

- Audio signal(right)

- Audio signal(left)

(dB)

Video 50signal

S/Nratio 40

3002 3 4(m)

Distance

As distance between the opticaltransmitter increases, so does noise.Past 3m, the s:n ratio falls below 42d8and starts to become a problem.

which point the video signal-to-noiseratio is at a threshold 42dB. Themaximum capture angle is about 60°.

Coincidentally, NC Professionalhas launched a portable videopresenter, also capable of opticallinking. Its built-in ccd camera isdesigned to provide the electronicequivalent of an overhead projector,so banishing cables is particularlyapt. The principle is the same as theHitachi optical link but with greaterquality and range, and no audio isinvolved.

New pc co -processor helps i/o keep upAn intelligent i/o processorunveiled by Intel addresses more

exacting applications demanded bypresent pc technologies such as x86microprocessors and PCI local bus.

According to Elliot Garbus, Intel'stechnical marketing manager,

Embedded Systems division, the bestexample of this is the evolution of thepc architecture for use in applicationserver systems: "This move toclient/server architectures has putgreat strain on the i/o."

Moreover, advancements in i/o

1960 RP Processor Data Flow RequirementsLocal klemory

0N

\

technologies for net working andstorage has also increased i/odemands. These include 100Mbit/sEthernet and ATM; and for storagethe Ultra -SCSI and 100Mbyte/s FibreChannel standards.

Called the i96ORP, the new device,device is based on the i960Jx core,which is rated at 31Mips (VAX)given a 33MHz clock. It incorporatesa 4Kbyte instruction cache, and2Kbyte data cache.

The i/o processor is designed to off-load the demands placed on the hostprocessor, while offering i/oexpansion via a secondary PCI localbus. In addition to the core and PCI-to-PCI bridge, the i96ORP featurestwo dma controllers, addresstranslation units, pci bus arbitrationlogic, a memory controller and a I2Cinterface.Intel plans to announce further i960core upgrades and produce other,more tailored product variants.Roy RubensteinElectronics Weekly

628 ELECTRONICS WORLD + WIRELESS WORLD August 1995

UPDATE

Cash transactions over InternetUyK electronic purse companyMondex is believed to be

squaring up to its European rivalEuropay to provide secure, chip -based financial transactions over theInternet.

Last week Europay joined Forceswith technology giant IBM to developa smart card based payment systemfor commercial transactions over theInternet.

This mirrors the plans of Mondex,led by NatWest Bank, Midland Bankand BT, which according to oneindustry source wants to provide itsown electronic funds transfer servicesover the Internet.

Europay, which is backed by creditcard firms Mastercard and Visa, ismaking the running and IBM hasalready devised an open paymentprotocol, named Internet KeyedPayment Protocol - iKP - that is fullycompatible with leading operatingsystems such as Windows, OS/2,Macintosh and others.

It has proposed this protocol to theWorld Wide Web organisation andthe Financial Services TechnologyConsortium in an effort to make it anindustry standard.

Another contending protocol is Visaand Microsoft STT's, which needs aproprietary system to run.

Widescreen plus plusThe obvious advantage of a tv

with a 16:9 Widescreen aspectratio is that 4:3 ratio programmes -i.e. standard tv pictures - can beexpanded to fill the screen. Initially,PALplus condenses pictures to aletterbox across the middle of thescreen. It does this by extractinginformation and encoding it in theblack area to enable the full imageto be reconstituted. But this as aresult of this, a 4:3 aspect -ratiopicture is only expandable by addingblank lines.

Now Philips is planning toovercome this with WideScreen Plus

tvs. A 16:9 letterbox image containsonly 432 active lines by comparisonwith the 576 of a full picture. Henceexpansion requires one extra line forevery three received.

With WideScreen Plus this isachieved by interpolation. Theincoming picture signal is digitisedand stored, then processed to createlines composed of elements fromexisting lines. For example, A, B,and C lines are written to screen asA, 2/3 of A+1/3 of B, 2/3 of B+1/3 ofC, and C. This returns the verticalresolution to near normal.

Unfortunately, the system does not

In order to allow electroniccommerce over the Internet, speciallydesigned card -readers fitting to PCsor multimedia boxes, are already indevelopment. "A range of devices areunder development: multi -functionaltvs, fax pcs and television setcombinations and not just onedevice," said a Europayspokesperson.

According to Adrian Cannon,general manager of smart card andreader provider CP8 Transac UK "Weare likely to join in an alliance as thebanks are our customers."Svetlana Josifovska,Electronics Weekly

compensate for the loss ofhorizontal resolution - as PALplusdoes - but perhaps that is somethingfor the future.

In the meantime WideScreen Pluswill coexist with PALplus andenable standard letterboxprogrammes to be viewed withimproved quality.

A

B

C

Blank

Standard letterbox

Neural net speeds up fingerprint matchingTo catch a thief - or any other re -offending criminal - can take a

matter of minutes with a little helpfrom the UK -based DSP firm,Cambridge Neurodynamics Limited(CNL).

The company has developed aneural network Integrated AutomaticFingerprint Recognition System(IAFRS), that can match a tenfingerprint (tenprint) set to one from atotal of a million stored in a centraldatabase.

The system comprises an encoder,image analyser and image matcherwhich are linked via a LAN. Once atenprint has been scanned in, it isstored as a greyscale image in a 40:1compressed format using C -Cube'sCL -550 JPEG device. In order toreceive/transmit noise -free imagesfrom/to remote locations, CNL alsoexecutes its proprietary compressionalgorithms on the images. Techniques

such as the wavelet -based modifiedfast lapped transform encoding, anderror resilient entropy coding areused. These avoid blocking artifactsthat result from the compression,smoothing away image irregularitiesand spreading errors throughout theimage.

The encoder/analyser isimplemented as a board containingfive 80MHz Texas InstrumentsTMS320C50 DSP chips. Theprocessor are linked in parallel, eachexecuting a different part of CNL'salgorithm. For a basic unit theseprocessors can deliver peakprocessing speeds of. 600Mips.

The unit extracts and encodes 16 ofthe most identifiable physicalcharacteristics of the fingerprint. Theunit uses a neural network to extractthe statistics from a large scale image.Neural networks are used becausethey are seen as one of the best

To partly compensatefor the loss of oneline in four whenviewing standardimages onWidescreen, aninterpolator is used tospread usefulinformation over allfour lines.

A

NBB/C

C

Widescreen plus

methods of data analysis for poorquality inputs, which can be unclear,smudged or superimposed.

The matcher is based on the sameprocessing board as the encoder, butruns a different algorithm to identify akilobyte of information with one froma million -image library of fingerprintinformation. The matching offingerprints can take 15 minutes onaverage, whilst the encoding takesapproximately one minute per set.

The system, being scalable, can beexpanded as required. Currently theIAFRS is being used by the SouthYorkshire police, but its applicationsgo beyond policing. It can be used inballistics and DNA. matching (forwhich there is currently no extensivedatabase), immigration and passportcontrol, banking and social securityapplications.Svetlana JosifovskaElectronics Weekly

August 1995 ELECTRONICS WORLD + WIRELESS WORLD 629

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ELECTRONICS WORLD+WIRELESS WORLD August 1995

UPDATE

One -electron transistorgets warmer

Hitachi's quest to build electronicI circuits from structures that, use

a single electron has taken asignificant step forward. Researchersat its Cambridge lab,with CambridgeUniversity, demonstrated a single -electron transistor device working at77K rather than the 4.2K. ProfessorHaroon Ahmed of CambridgeUniversity, said: "When we next talkabout developments it will be whenwe can demonstrate roomtemperature operation. We don'twant these things to remain noveltiesbut have exciting, real applications."The 77K device is a thin metal wireon a silicon -dioxide substrate. Thegold -palladium islands are the so-called Coulomb blockades letting

single electrons cross the gate. Theislands have a "world record"diameter of 2nm. But to get roomtemperature operation the dots wouldhave to be five times smaller, saidAhmed. "The important thing is toreduce the capacitance of theCoulomb blockade by using differentmaterials rather than making themmuch smaller." The group has alsodemonstrated an inverter at 4.2K andis striving to build more complexlogic primitives.

Researchers have demonstrated asingle -electron transistor operating at

77K rather than 4.2K and work isunderway towards a

room -temperature version.

VHDL model standard suffers further delayWork in the IEEE group strivingto specify analogue system

modelling extensions to the VHDLdigital design language has slowed toa crawl for the second time in 12months. Finalised specifications ofthe 1076.1 extensions is now unlikelybefore the early next year, pushingratification to at least end 1996.

Onlookers from the EDA industryand Asic user community are deeplyfrustrated with the latest delays. Itwas hoped, in September last year,that a language specification couldhave been released at the time of lastweek's Design AutomationConference.

Stan Krolikowski, senior member ofthe IEEE VHDL community, isdisappointed. "It's really frustrating:we have all the concepts mapped outbut there seems little progress ingetting them implemented," he said."The mood of the working group

seems to be changing fromdemocracy to mob rule with seniormembers seemingly unable to worktogether."

Krolikowski says the danger is thatanalogue extensions to the Veriloglanguage - about to become an IEEEstandard - will be available first,confusing potential users. "At thisrate we'll have analogue Verilog out along time before 1076.1, and that willreally change the picture."

But Ernst Christen, vice chairmanof the 1076.1 committee, defendsprogress saying the process is slowingdown because it depends on volunteerwork. "We have to let the volunteerscatch up with the two of us being paidto develop the language. That's whatmakes the schedule unpredictable.But we absolutely have to haveconsensus because we are bound bythe IEEE process and because thelanguage has to survive without being

continually modified."Christen says the current bottleneck

is validation of the fledgling languageand not design of the language itself.There are quite a lot of open issuessuch as frequency domain ac analysis- we haven't seen anythingsubstantial there yet - but 75% of ourinvestigations have reached their firstdrafts and 20% have produced resultsand been provisionally approved."

But in some areas arguments stillrage about language semantics andsyntax. "Language design is an art,not a science," said Christen. Thereare various ways of doing the samething and it is the task of the languagedesign committee to weigh thebenefits of one approach over others.We have to consider if it is consistentwith the main body of the existingdigital language, whether it providessufficient functionality and usability.It's not a black and white process."

TDM optical net promises multi-Gbit/s performanceAfibre-optic network transmittingmulti -gigabit per second data

using optical time divisionmultiplexing has been demonstratedby researchers at BT laboratories.

The BT network avoids thebottleneck associated with convertingoptical signals to an electrical form atswitching centres. Instead, long

distance transit traffic passes throughswitching centres in optical pulseform. By performing channelmultiplexing and extraction processesat high speed using optical devices,much higher aggregate data rates canbe attained, potentially as high as100Gbit/s.

Andrew Ellis, senior professional in

networks research said: "The keyadvantage of this experiment is notthe long distance capability or eventhe high capacity that can beachieved, but the ability to routetraffic flexibly on demand withoutneeding a lot of costly electronicswitching."

August 1995 ELECTRONICS WORLD + WIRELESS WORLD 631

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632 ELECTRONICS WORLD+WIRELESS WORLD August 1995

RESEARCH \OTESJonathan Campbell

Simple electronics takes a leapApplication of relatively simpleelectronics is being credited with

helping discover previously unknownpopulations of frogs. EcologistMichael Dorcas, working with hiselectrical -engineer father Eugenehave built a 'frog -logger' using atape -recorder that automatically turnson and off at particular times and usesa voice clock to audibly time stampthe start of each sampling interval.

In what is described as a dramatic"success" for the device, a breedingpopulation of barking tree -frogs hasbeen discovered where the specieswas previously represented by asingle road -killed specimen -despite 19 years of field work. Otherextensive monitoring work is beingcarried out with colleagues at theEcology Laboratory, operated by

University of Georgia.One problem remains with the

`frog -logger': you have to sortthrough a lot of tapes to find theright croak. So Dorcas is nowworking with Ontario HydroTechnologies to perfect computersoftware that can identify animalvocalisations, making it much easierfor scientists to analyse their data.

Fortunately, frogs are easier toanalyse than birds, say, becausetheir are fewer species and theircalls are less variable. That isfortunate, because scientists believethat monitoring the diversity andrelative abundance of frogs andtoads could serve as an overallindicator of the entire environment.

Frog dying to be logged.

Morphing robot with the amorphous role

Theconcept of a robot that can

change its form in response to itsenvironment has been the basis foreverything from a hit children'scartoon series to the blockbuster filmTerminator II. But a robot system builtup from interlocking body blocks thatcan slide over each other could be thestart of a shape changing reality.

The interlocking -cube idea has beenproposed by Joe Michael of London.He has just patented a design of cubewith a mechanism that push out andretract wedges from all its faces. Thewedges lock into place in other cubes

and a complete structure can be builtup like a series of Lego bricks.

But the clever part has been todesign a mechanism to allow thecubes to move over each other.Michael uses a gear wheel to engagewith the serrated edge of a wedgewhen it is place, enabling the wedge -and hence the block - to be moved.

Obviously movement is onlypossible when locking wedgesperpendicular to the direction ofintended movement are disengaged.But Michael says that the design willenable the blocks to move while

August 1995 ELECTRONICS WORLD + WIRELESS WORLD

holding tools etc.The first working prototype has yet

to be built and so most of the practicalproblems remain to be faced. ButMichael is supremely optimistic atpresent, proposing his design assuitable for use in microsurgery,using nanorobots, up to massivemachines to be used for bridgebuilding.

Whatever the actual potential, theattraction of a robot able to flow itselfthrough a keyhole and then reformitself in a room has obvious attraction- to film makers if no-one else.

Sliding cubestructure couldallow a robot toslip in and out ofalmost anywhere.

RESEARCH NOTES

50

L (mH)

45

40

Lc

35

300

induction loopyOdd electromagnetic effectssurface every so often,

prompting scientists to reviewinduction theory and re-examineFaraday's law. Now apparentgeneration of a positive emf as wellas back emf in experiments on amotor operated by an LCR circuit are

.3"Dischargestartingpoint

10 20

How inductance ofthe electromagnetrelates todisplacement of thecore from theelecrtromagnet. Rateof change of theinductance dependson the magnetic fieldsand is greater in theattracting mode.

Tq (g -m)33

Tq: I = 3A

30 40 50 60

d (mm

35

30

25

20

15

10

0

L (mH)

32

3

3

29

280

causing physicists to scratch theirheads once more.

The effect has come to light as aresult of work by Osamu Ide todevelop a motor operated bydischarge of a capacitor in an LCRcircuit ("Increased voltagephenomenon in a resonance circuit ofunconventional magneticconfiguration, J App Phys, Vol 11,pp. 6015-6020).

Ide's motor is designed to make useof the force of attraction between acurrent -carrying coil and a movablemagnetic core. That attraction,resulting from a capacitor discharge,is converted to a rotary motion, andunconsumed magnetic energy isrecycled as electrical energy by

Tq: I = 4A

10 20 30 40 50

Tq (g -m)

15

10

060

d (mm)

recharging the capacitor.But what Ide has noted, is that the

capacitor recharge voltage depends onthe precise configuration of thesystem, so that under a certainmagnetic configuration, it is biggerthan normal theory expects.

The construction of Ide's motor isunusual, but relativelystraightforward. He starts with a basicLCR circuit, with a silicon controlled

Silicon technology will catch sun -spot flaresC ilicon processing techniques developed from....)microchip manufacture are being exploitedby Sandia National Laboratories to maketelescope imaging grids with features up to 100times smaller than possible using traditionalmanufacture.

Liga -a German acronym for lithography,plating and molding - is being used at Sandia tocreate moulds for electroplating deep structuresmade of metal, or for casting ceramics, plasticsor other polymers.

The telescope will be used on a Nasa missionto image the sun's solar flares, tracking particlesthat burst in a sudden release of power fromareas where sun spots arise. Neither gamma norneutron rays produced by these solar outburstshave been imaged before.

Using liga, the telescope will be less than halfthe length initially anticipated, measuring overallless than 2m long. The smaller size allows it tobe launched on the cheaper spacecraft Pegasus.Orbiting almost 400 miles above Earth, thetelescope will capture images through a series of12 mesh grids and detectors. As the telescoperotates through space, it will provide a three-

dimensional view of radiation from solar flares,in a manner similar to a pinhole camera. Proof -of -concept grids have already been electroplatedat Sandia, and the next step is to produceperfect, large -area structures, and assemble andcharacterise flight instruments.

Other Sandia liga projects include a disk drivesuspension arm for IBM and a high-performancestepping motor that involves creating a largenickel -iron alloy part with fine resolution teeth.

Space camera ...thatdoesn't take up any

Adevice claimed to be much smaller andcheaper than current state-of-the-art

electronic imaging systems but comparable inperformance is being developed by Nasa as partof its space program.The camera on a chip is a considerable leapbeyond current charge -coupled devices,according to Eric Fossum, leader of the teamwho developed the active pixel sensor at Nasa's

rectifier (scr) used as a switch so thatinstead of the usual voltage andcurrent oscillations, a negative chargeis retained in the capacitor afterdischarge. The scr automatically turnsoff after the half -cycle current,recharging the capacitor to a rechargevoltage which is smaller than theinitial voltage due to resistance loss inthe circuit.

Ide has then replaced the inductancewith two pairs of electromagnets,which form the stator around a rotorhaving two ferromagnetic cores. Themagnetic fields attract the cores,producing motion, but as the coreapproaches the magnets, combinedinductance increases and the magneticflux moves, affecting the dischargecurrent and recharge voltage.

The total recharge voltage shoulddecrease because the system producesmechanical output as the core moves,but Ide found an increase in theaverage current and recharge voltagewhen the magnetic field in theelectromagnets was opposing, ieN-S:S-N).

His explanation is that his motordemonstrates that two types of emf(actually suggested by other workers50 years ago) - motional emf causedby cutting of the magnetic flux andinduced emf caused by Faraday'slaws - are independently at work.

In Ide's motor the two emfs have acontradicting effect, with themotional emf having a positive effecton the recharge voltage.

Jet Propulsion Laboratory (JPL), Pasadena.JPL has so far signed a technology cooperation

agreement with AT&T Bell Laboratories, whileseveral other companies are said to be seekinglicensing agreements to commercialise thetechnology.

Up to now, ccds have been used mostly invideo camcorders and space -craft, and have ledto relatively low-cost, compact imaging systemscompared to Vidicons and other tubetechnology. CCD technology has also advancedas the microelectronics industry has improved itsquality and fabrication techniques. But ccddevices with a million pixels, or pictureelements, are still expensive to make, costingabout $1000 per million pixels in low -volumeapplications.

Active pixel sensors, by contrast, are madewith main -stream cmos microelectronicstechnology which can reduce the cost to under$200 per million pixels.

The active pixel sensor developed at JPL forspace applications is designed to use less powerand has lower susceptibility to radiation damagein space.

634 ELECTRONICS WORLD + WIRELESS WORLD August 1995

RESEARCH NOTES

Solid progress to portable audioAre you concerned that themechanical component of current

audio technology is limiting your in -sport audio activity? Do you fmd youare frustrated with the limited choice(?) of tape and cd formats? Then aprototype solid state audio systembeing developed by researchers atNEC could be just for you.

The basis of the system, which theJapanese team is calling silicon audio,is a semiconductor memory cardequipped to store compressed audiodata ("The Silicon audio: an audio -data compression and storage systemwith a semiconductor memory card,"IEEE Transactions on ConsumerElectronics, Vol 41, No 1, pp.186-194).

Advantages seem to be that there isno need for any mechanics; unliketape, random access is possible, while

AudioInput

Audio

unlike cd, users can re-record.A general purpose dsp and

specially -designed gate array chip, isused for decoding data on the cardand the system will both play -backand record.

For audio compression, thedesigners propose using thempeg/audio layer H algorithm,handling a 20kHz bandwidth.

Length of recording time isobviously a function of the size ofmemory card available and theemployed bit -rate. In the prototypework, encoding is being carried out at96kbps/ch, giving a reasonablecompromise between recordingcapacity and sound quality.

So far the developers have built aplay -back machine able to store12min of music on a 16Mbyte card.But their eventual aim is 60min

recordings, which they say is wellwithin the capability of fast evolvingcard memory technology.

Silicon audio is being proposed as acomplete portable multimedia systemspanning teaching, guides, news andbooks, and integrating sound, speech,text, still pictures and even images.

However, the current close linksbetween technology progress andfashion have not been missed by theresearchers either. In parallel withdetailed electronic development, theteam has been trying out a variety ofpackaging colours and graphics toattract the eye of potential consumers.Only when that is finalised, will webe able strap on our new toy and go"jogging, skiing, biking and evenroller-blading", while we listen tosomething other than our ownlaboured breathing.

output

Analysis filterbank

Scale factorselect

information

FFT

Scale factorcalculation

V

Psycho -acousticmodel

0. Linear0. quantization

Bit

reduction

Side informationcoding

Dynamicbit allocation

oatCL

E

d¢CDU.,71

Encoder

Synthesiser filter4

Dequantization4

Bitstream unpacking 44bank error detection4 4

4A A

Bit allocationSide information

Scale factors decoding

Decoder

Hot GaAs technology gets a coolerWidespread application of galliumarsenide devices in portable

telephones phones is testament to their lownoise amplification characteristics -advantages that are expected to see GaAsuse spread to high speed switchingnetworks and digital logic. But difficultiesin removing the heat generated in GaAspower amplifier chips has so far led tocompromises in design which haveimpacted on yield.

But work at Motorola looks to have gonesome way to solving that problem, byshrinking the heat transfer path from thehot zones in the active area of the device

CUMaaaaaaaaaaaaa

Storage media/trans. line

'Silicon audio', giving arecording/p ay -back capabilitywith no moving parts.

to the heat sink, and bypassing the bulk ofthe GaAs itself. ("A novel active areabumped flip chip technology forconvergent heat transfer from GaAs powerdevices, Debabrata Gupta, IEEETransactions on Components, Packagingand Manufacturing technology - Part A,Vol 18, No 1, pp.82-86).

The technique relies on plating bumps ofgold onto the active area of a flip chipdevice. Bumped amplifier flip chipsbonded to aluminium nitride substrates candissipate heat fluxes up to 300W/cm2 withan acceptable rise in junction temperature.

Drain SourceGate

Plated goldthermal bump

Heat flow tothermal bump

Gate

Gallium arsenide power amplifier

Drain

Profiled bumps could be the answer to heatdissipation problems in GaAs power amplifiers.

August 1995 ELECTRONICS WORLD + WIRELESS WORLD 635

AUDIO

Feel thebassWith this active 100W sub -woofer design -featuring a -3dB point of 20Hz - Jeff Macaulayonce more demonstrates how inadequacies inloudspeaker cabinet systems can becompensated for electronically.

Although the quality of audio electronics hasnow advanced to a state of near perfection,loudspeaker systems have not kept pace.

The main problem is still the reproduction of bass- especially in domestic surroundings. Largespeaker systems are not usually practical, but bassreproduction requires large enclosures, when con-ventional design techniques are applied.

Historically, most of the effort in speaker designhas been expended on understanding how drivers

and enclosures interact to produce predictableresults. Generations of engineers have contribut-ed to this work, culminating in the Theile-Smallmodel, which now forms the basis of low fre-quency speaker design.

Briefly, the model compares the response of thespeaker system to that of a high-pass filter. Thisenables the response to be accurately predicted. Infact the response curve of an unmounted speakeror one mounted in a sealed box is that of a secondorder high-pass filter in the bass. This responseshape is dictated by the fundamental bass reso-nance, possessed by all speakers, between thecone mass and speaker surround compliance.

Although a driver may have a desirably low res-onant frequency when measured in free air,mounting it in a sealed enclosure raises the reso-nant frequency because of the added stiffness ofthe enclosed air. Unfortunately some kind ofenclosure is necessary because the radiation fromthe front of the cone is in antiphase with that fromthe rear. Consequently, because of the long wave-lengths of bass sounds the two outputs diffractaround the driver and cancel each other out, akind of acoustic short circuit occurs.

Below the resonant frequency, response rolls offrapidly, reaching an ultimate slope of12dB/octave. An obvious thought is to make theresonant frequency in free air lower to reduce thecut-off frequency in the enclosure. Unfortunatelythe efficiency of a speaker is proportional to thecube of its resonant frequency. Although you cantrade off efficiency and bandwidth, the benefitsare limited. The result is that most domesticspeaker systems are limited to a -3dB point of70Hz or more. At least an octave of bass is lost.

636 ELECTRONICS WORLD + WIRELESS WORLD August 1995

AUDIO

Driving amplifierThere is a parallel train of thought which seeksto modify the behaviour of a speaker systemby altering the response of the driving ampli-fier. Three main areas of research have beenpursued.

Motional feedback. Probably the most wellknown is motional feedback. Here a trans-ducer is fitted to the speaker cone and theinformation obtained is used to control thecone in a classic feedback circuit. This tech-nique has many advantages. The distortionand lack of bandwidth of a small box can beovercome. On the down -side, the system canbe easily overdriven by bass transients andrequires special transducers and electronics.

Damping. Another way of controlling thecone is based on the idea of damping. Poweramps are designed with a zero -impedance out-put to control the speaker cone. The idea isthat speaker resonance can be damped out byconnecting a zero impedance source of sig-nals. Unfortunately the voice coil resistance isalways in series with the resonant sound radi-ation circuit.

Figure 1 shows the equivalent electrical cir-cuit of a speaker mounted in a sealed box.Here the various reactive elements combine toproduce a parallel tuned circuit. Resonance ofthese elements produce the well known rise inimpedance at the speaker's fundamental reso-nance.

If these elements were to be fed directlyfrom a zero -impedance source, the bass reso-nance would be completely suppressed.Although voice coil resistance cannot be phys-ically removed from the circuit, an amplifier'soutput impedance can be made negative tocancel it. When this is done the speaker reso-nance is completely suppressed and the conemotion becomes independent of frequency.

The result is that the sound pressure level,

VIN

Rvc VC

Voice coil LM Cc C

Motional impedance

Equivalent circuit to speaker insealed enclosure.

LM = B2L2. CSCBCS+CB

Where Cs = cone suspension complianceCB = compliance of enclosed air in box

Cc = MaB212

RA = B2L;

Where Ma = mass of air load onspeaker

Where TA = radiation resistanceapplied to speaker

E = BLU where

B = magnetic flux densityL = voice coil lengthV = velocity of voice coil

Fig. 1. Parallel tuned circuit - the equivalentelectrical circuit of a speaker mounted in asealed box.

A new filter configuration for audioA standard second -order filter response can be simulated with a second -orderbandpass filter and an integrator.

The bandpass filter needs to have the same centre frequency and Q as thesecond -order filter, or speaker response to be simulated. The flat response audiosignal is fed first through the bandpass filter then an integrator. A second -orderhigh-pass response is obtained.

If the integrator is replaced with a differentiator, a second -order low-passresponse is obtained. To simulate a reverse speaker response, all that is requiredis to replace the bandpass filter with a band -reject type of the same turnoverfrequency and Q.

A practical difficulty with such a circuit is insertion loss, but it avoids the use ofhigh -gain circuits in the equaliser. As the gain of a high-pass filter at dc is zero,an infinite -gain amplifier would be needed to obtain full equalisation. Inpractice, this is not necessary since each halving of input frequency brings afourfold increase in cone excursion to maintain the same sound pressure levels.

Obviously this soon gets out of hand and at sub audio frequencies, excursionrequirements will eventually exceed the displacement limits of the speaker.

'11

dB

dB

6a0\ Vo = dViN

dx

ctia

=),Differentiator

f

Vo

f

ft , oo

Bandpass filter

fo Oo

Integrator Bandstop filter

dB

dB

fo 00

High pass 2ndf

order filter

Equaliser response

Synthesising a second -order high-pass filter from a differentiator and bandpass filter.For equalisation purposes, an inverse response can be generated by combining abandstop filter and integrator.

spl, measured in front of the driver, increasesat a steady 6dB/octave for a constant drive sig-nal amplitude. In other words, the speaker actsas a differentiator. This is exactly how a per-fect massless piston would behave - if such adevice could be built. Furthermore, near per-fect transient response is obtained and becausethe non linear compliance of the speaker sur-round is controlled this results in a consider-able reduction of distortion.

All that is required to obtain a flat responsefrom the speaker is to integrate the input sig-nal. It is a sobering thought that if perfectspeakers were available, our power amplifierswould have to become power integrators todrive them. In fact the only reason that loud-speakers have a flat response is that the bassresonance tilts the response downward by6dB/octave above the resonant frequency.

As with motional feedback systems, specialamplifiers with positive current feedback arenecessary. To be effective, the speaker induc-tance also has to be cancelled if new unwant-ed resonant peaks are to be avoided. One

advantage over the motional feedback systemis that the speakers are stock items. No specialfeatures are required.

Equalisation. Although it is true to say thatequalisation is used as an adjunct to bothmotional feedback and damping systems, itcan also be used on its own. The main diffi-culty is that although Theile-Small softwarecan predict the roll -off curve of any speakersystem, suitable equalisers are rare.

Sixth -order alignmentAlthough equalised speakers are not in gener-al use, the sixth -order alignment has gainedacceptance. This speaker system is a reflextype using a vent to provide bass boost. Thesystem is adjusted for an over -dampedresponse curve which is then boosted back toflatness by an auxiliary under -damped secondorder high-pass filter as Figure. 2 shows. Notonly can the system extend lower into the bassregion, but the subaudio noise limiting the sys-tem's excursion ability is rejected.

August 1995 ELECTRONICS WORLD + WIRELESS WORLD 637

AUDIO

OdB

Underdamped hi passfilter \

System response

Overdamped boxresponse

fFig. 2. Sixth -order alignment. Systemresponse is extended by an external filter.

Equalised speakers have most of the advan-tages of the other systems described. Transientresponse is improved because this is simply afunction of the rate of roll -off imposed by thesystem. Provided that sensible limits areobserved, the extension in bass response canbe as great.

Unfortunately, the total harmonic distortionof the system is not improved. However this isno great advantage since it has been shownthat 40% of second harmonic distortion below80Hz is inaudible on programme material.Modern drivers tend to produce far less oddharmonic distortion than older models. Thesefacts, taken together, indicate that sub -resonantoperation works well - a fact borne out byexperience.

R2

C2

VIN IF11

A1-

f000

Circuit detailsElectronics textbooks are full of circuitry toproduce the classical filter configurations. Buta reversed second -order response is notamongst them. The only filter that I know ofthat can simulate this response is the Linkwitzfilter.

Unfortunately this filter tends to be compo-nent critical, and as often as not, componentshave to be selected by experimentation - atime consuming process. I find this unsatis-factory, so I have developed a new type of fil-ter. The key to understanding this new circuitis that the standard second -order filterresponse can be simulated with a second -orderbandpass filter and an integrator, see panel.

A practical filter of this type is shown in Fig.3. Since band -reject filters tend to have awk-ward component. values, I have used a multi-ple -feedback bandpass filter, or mfb. Band -reject response is produced by subtracting thebandpass response from the input signal in A2.Since the mfb filter is inverting this can bedone with a shunt feedback amplifier withoutfear of unwanted signal interaction. The inte-grator function is performed by shunting thefeedback resistor. Although sealed box sys-tems can be very effective when operated insub -resonant mode, greater efficiency wouldbe a distinct advantage.

The Microreflex system described in an ear-lier article' is efficient and has excellent bassperformance for its size. It makes use of the

R5*

WO/

R6

C3-I I-

o o/p

* R5 2Q02R4

Fig. 3. Amplifier Ar, with Rr, R2 Cr and C2, forms a bandpass filter with the same turnoverfrequency and Q as the speaker system. The required bandstop response is obtained bysubtracting the bandpass from the input by A2. Capacitor C3 and R6 produce an integratorresponse to produce equalisation.

a s I Iroquerricy ltsiz)

Computer simulated response of the speaker alone shows significantroll -off to well over -20dB at 20Hz, bottom curve. Adding activeequalisation, upper curve, results in almost flat response down to20Hz, as is evident from the middle curve. When the high-pass filter isinserted, 20Hz becomes the -3dB point.

reflex principle but in a grossly undersizedbox. Such a system exhibits a roll -off charac-teristic closely resembling those of a closedbox. This means that it is easy to equalise.

To understand the Microreflex enclosurerequires some understanding of standard reflextypes. In a reflex enclosure, rear radiationfrom the cone is used to reinforce the outputfrom the front. As discussed earlier, radiationfrom the front of a speaker cone is inantiphase with that from the rear.

For rear energy to be useful, some methodhas to be found to phase invert the rear sound.In a reflex enclosure this is done by makingthe enclosed air resonate at a fixed frequencyby means of a vent. The mass of the air in thevent resonates with the compliance of the airwithin the enclosure. It forms a mechanicaltuned circuit which is excited by the rear ofthe cone.

Above the enclosure resonance, the vent'sradiation is in phase with the front of the cone.Below the resonance the vent and cone radia-tion move out of phase producing a rapid bassroll -off. The system operates as a fourth -orderhigh-pass filter.

At very low frequencies, the cone is unload-ed by the air in the enclosure and thus largesub audio cone fluctuations can occur, unlesssuitable filtering is applied. The advantages ofa reflex system over a sealed box are alsoapplicable in the Microreflex system.Primarily the speaker's resonant frequency isvirtually unchanged by reflex loading, leadingto lower distortion at bass frequencies.Secondly the excited enclosure resonance actsas a heavy acoustic load reducing both coneexcursion and distortion.

Most importantly however is the increasedefficiency it provides relative to a sealedenclosure. Unfortunately it is a waste of timetrying to extend the bass response of a prop-erly designed reflex enclosure below its cut-off frequency. All that happens is that the conemoves further but the antiphase vent outputcancels any improvement.

To take advantage of the reflex system, theenclosure has to be redesigned. It so happensthat when the enclosure is made small enoughthe natural fourth order filter roll -off charac-teristic changes to a second order roll -off, justlike a sealed enclosure.

Active equalisation is used in the sixth -orderspeaker system discussed earlier. Enclosureresonance is lowered and the overall responseis then boosted flat again. Before equalisationis applied, the response of the system resem-bles an over damped fourth -order filter. Toobtain a flat response the enclosure has to becarefully matched to the driver. Althoughsixth -order systems are usually smaller andproduce deeper bass, the design still requiresset enclosure volumes and driver parameters.

When the enclosure size is too small, as inthe Microreflex, the response becomes that ofa second -order filter. This yields responsecurves that are far from flat. However this isnot a limitation. The equalisation applies adrive signal that corrects both the amplitudeand phase of the natural response, rendering

638 ELECTRONICS WORLD + WIRELESS WORLD August 1995

AUDIO

the system response flat.Small reflex enclosures have a useful char-

acteristic. That is, that the second -order roll -off extends to below the enclosure resonance.Investigation reveals that the enclosure reso-nance's Q has been reduced, leading to lowerphase shift, and the vent output supplementsthe driver down to and below the enclosureresonance. This is important because it allowsbass to be extended towards the sub -audioregion. Provided that the excursion limit of thecone is observed, the performance of the sys-tem can be predicted with the standard Theile-Small model.

This article describes a small -sized activesubwoofer with a -3dB point extending downto 20Hz. Computer simulation, and testingshow that the system is thermally limitedwithin its working range.

Subwoofer systemsTo be effective, a subwoofer needs to shift alarge volume of air at low frequencies. Twoapproaches are possible. Either a large diam-eter driver can be used, or several smallerunits operating in phase. High efficiency isalso helpful to offset the amount of equalisa-tion required. Large speakers with the rightqualities are hard to find so four 8in PF8IHRtypes are used.

Speaker size is dictated by the need to reflexthe enclosure to a suitably low frequency. A1.5ft3 enclosure was chosen, tuned to 40Hz.By wiring the drivers in series/parallel, Fig.4,an 8S1 impedance was obtained with a refer-ence efficiency of 97dB/W. The resulting rawfrequency response of the system was pre-dictably dire closely resembling a closed boxsystem with a Q of 1.3 and a resonant fre-quency of 124Hz.

Examination of the alignment shows that thevent and driver are still operating in phasedown to below 20Hz. The vent provides sev-eral decibels more in the deep bass than the

L

R2

22k

RR i

22k

VR1

4.7k log

R

01

02

-v

A8 & A9 = HY60 modules

To ampand eq. +Vboard

To ampand eq.board

L

N

Fig. 4. Wiring the drivers in series/parallel results in an overall impedance of 80 from four 8S1drivers. Pairs of drivers are driven in antiphase and mounted face-to-face.

same system operated as a sealed box.Moreover the system is capable of providing95dB spl at lm at 30Hz. Further examinationof the large signal characteristics showed thatthe system was thermally limited, rather thandisplacement limited, to 20Hz.

With correct equalisation, the bass responsecan be rendered flat. Auxiliary bass filteringbelow 20Hz ensures that the displacementlimits imposed by the drivers are not exceed-ed. Although the vent resonance reduces dis-tortion from the speakers at low frequenciesthey are used in push-pull pairs. This effec-tively eliminates even -order distortion fromthe system.

Integration into an existing systemThe other interfacing problem posed by sub -woofer systems is integrating it into an exist-ing set-up. Having solved this problem sever-al times, I have found some useful practicalguidelines.

100k

82n 82n

R4 100k

IC1 & IC2 = - A7 = 2 x TL074

A2R5

82k

03

R8\AAA.47k R7

120k

Fig. 5. Equalisation circuit allows cone excursion to be moreusefully employed, producing more bass.

82n

82n

R 43k

R9

1.5M

C. Rio

15n 47k

Imposing a low -frequency crossoverbetween the subwoofer and existing speakersis counter productive. To prevent any prob-lems with the stereo image the subwoofer'srange should not exceed 120Hz. At these fre-quencies the existing speakers will be alreadybeginning to roll off with unpredictable ampli-tude and phase shifts. Add to this equallyunpredictable resonant modes in the listeningroom and you have a problem that virtuallydefies analysis.

The best solution that I have found is toleave the existing speakers alone and make thesubwoofer roll -off variable. A low Q secondorder low pass filter is the best. With a littleadjustment seamless integration of the systemis possible.

The power rating of the system is 100Wcontinuous. With four drivers there is a choiceas to the impedance chosen. By wiring thesein series/parallel I kept this at 80 to providestandard loading. However it is not strictly

R11

10k 22k lin 10kganged

+15V

OV

-15V

104

" add decoupling asadvised on data sheet

August 1995 ELECTRONICS WORLD + WIRELESS WORLD 639

AUDIO

A = 305 x 584 x 15mm x 2 C -B = 305 x 584 x 15mm x 2C = 305 x222 x 15mm x 1D= 305 x 275 x 15mm x 1E= 412 x 305 x 15mm x 1

E

Fig. 6. Enclosure details.Two drivers, face-to-face,mount in each aperture.Prototype was from15mm shelving, but18mm medium densityfibreboard isrecommended.

AA

335 305

4 holes184mm dia.

584

Frequency Relative(Hz) response

(dB)

Max powerinput (W)

Max infinitebaffle response(dB)

5 -74.59 49.37 38.9510 -49.16 39.66 63.4315 -33.90 35.64 78.2220 -25.80 71.03 89.3225 -22.00 100 94.6030 -19.31 100 97.2935 -16.97 100 99.6340 -14.84 100 101.7645 -12.86 100 103.7450 -11.02 100 105.5855 -9.31 100 107.2960 -7.72 100 108.8865 -6.24 100 110.3670 -4.87 100 111.7375 -3.62 100 112.9880 -2.50 100 114.1090 -0.65 100 115.96100 0.66 100 117.26120 1.85 100 118.45150 1.95 100 118.52200 1.31 100 117.91

Bass units - special offerSemiconductor Supplies International is offering sets of four PF81HR bass units needed for thesubwoofer at the special price of £42.77 - exclusively to EW+WW readers mentioning thisarticle. This price is fully inclusive of vat and UK next -day delivery. Normally, the set wouldretail at £55.27 fully inclusive.

Send postal order or cheque to Semiconductor Supplies International at Dawson House, 128Carshalton Road, Sutton, Surrey SM1 4TW, or ring or fax with credit card details, tel 0181 6431127, fax 0181 643 3937. Note that SSI's part number for these speakers is L031.

necessary to use 100W drive. In practice anyamplifier which can deliver 30W or more issuitable. In a domestic environment, usingmore than a few watts input will not impressthe neighbours.

The complete circuitThe whole circuit, Fig. 5 is built around twoquad TL074 op -amps. Right and left channelsare passively mixed via resistors Ria across thelevel potentiometer VR1. It makes sense toobtain the input from the right and left speak-er outlets of your main amplifier. This way thesub woofer correctly tracks the system output.

The signal is first buffered by AI beforebeing fed to the high-pass filter built aroundA2. Component values chosen for this circuitestablish the -3dB point at 20Hz. This heavilyattenuates out -of -band sub -audio signals.Without the filter these may have sufficientamplitude to push the drivers beyond theirexcursion limits. Not having the cones aim-lessly pumping in and out allows the coneexcursion to be more usefully employed, pro-ducing bass.

From A2's output, the signal feeds theresponse equalisation circuitry built around A3and A4. Op -amp A3 forms a band-pass filterwith the same turnover frequency and Q as thesystem. Output of the bandpass filter is sub-tracted from the input signal to produce abandstop filter.

Because A3 inverts, A4 acts as a differentialamplifier. Resistors 49, together with C5, inte-grate the signal. This produces accurate equal-isation, flattening the system's response.

Final equalisation is provided by a variablelow-pass filter, built around A5. This strips offout of band signals . Potentiometer VR2 -adual ganged type - makes this stage's cut-offfrequency continuously variable between 40and 120Hz. The Q of the filter is set at 0.5 forthe best transient response within the sub -woofer's passband.

Although the subwoofer gives a goodaccount of itself when driven from a low -power amp a reasonably substantial powerinput is required to drive it to its limit. A100W amp was required and this was pro-duced by using a pair of ILP HY60 modules inbridge mode.

To use the amps in this way requires a phasesplitting circuit, A6 and A7. Input signals arefed into A6's non inverting input. As this iswired as a buffer, the output signal is appliedacross R13. Op -amp A, is wired as a shunt -feedback amp. With R13 and R14 having equalvalues, A7 output is equal to A6 but shiftedthrough 180°. The circuit is powered by astandard ±15V power supply using 7815 and7915 regulators.

Enclosure detailsAn ideal material for the enclosure is 18mmmedium density fibreboard, mdf, Fig. 6. Thematerial is not too critical, but ensure that theinternal volume is kept constant if you usematerial of a different thickness. The enclo-sure must be completely airtight.

I implemented the tuning vent by forming apartition within the cabinet and an undersizedtop panel. Although the vent is rectangular, it

Theile-Small analysis of thesubwoofer shows highacoustic output above35Hz. Additional roll -offimposed by 20Hz high-pass filter ensures 100Wrating throughout therange. The PF81HR has aVAS of 1.462f13, a QTS of0.45 and an f5 of 45Hz.

operates as a circular type of equivalent area.The speakers are mounted in two pairs. One

pair with the magnets external to the case, theother pair conventionally. Its also important toensure that the drivers make an airtight seal tothe case. With the rear mounted pair they canbe simply screwed up against their gaskets.

Both the front pair and rear pair are wired inseries. Both pairs are then connected in paral-lel for an 852 load. The rear pair of speakersare wired out of phase with the front pair togive push pull operation.

A neat and airtight way of taking the con-nections through the case is to use M5 screwsfitted with solder tags. The electronics can bemounted inside the enclosure if need be. Arather neater result is obtained if the circuitryis mounted in an ABS case which is thenscrewed onto the rear panel.

This last method gives easy access to theelectronics without having to rip apart thecase. It also makes the task of keeping theenclosure airtight easier.

Finally I would commend this design tothose of you who yearn for a decent bassresponse, but who are unwilling to give houseroom to large enclosures. Everyone who hasheard the sub -woofer has been favourablyimpressed.

Reference1. Macaulay, J., Bigger bass - smaller box,EW+WW, June 1995, pp469-475.

640 ELECTRONICS WORLD + WIRELESS WORLD August 1995

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displays used in this set-up -8411a -8412 - 8413 - 8414 - 8418 - 8740 - 8741 - 8742 - 8743 -8746 - 8650. From E1000.

Racal/Dana 9301A-9302 RF Millivoltmeter - 1.5-2GHz - £250-£400.Racal/Dana Modulation Meter type 9009 - 8Mc/s -1.5GHz - ENO.Marconi RCL Bridge type TF2700 -£150.Marconi/Saunders Signal Sources type - 6058B - 6070A - 6055A - 6059A - 6057A - 6056 -

£250-£350. 400Mc/s to 18GHz.Marconi TF1245 Circuit Magnification meter + 1246 & 1247 Oscillators -£100-£300.Marconi microwave 6600A sweep osc., mainframe with 6650 PI - 18-26.5GHz or 6651 PI - 26.5-

40GHz - £1000 or PI only £600. MF only £250.Marconi distortion meter type TF2331- £150. TF2331A - £200.

Tektronix Plug -Ins 7A13 - 7A14 - 7A18 - 7A24 - 7A26 -7A11 -7M11 -7511 -7D10 -7S12 - Si- S2 - S6 - S52 - PG506 - SC504 - SG502 - SG503 - SG504 - DC503 -DC508 - DD501 -WR501 - DM501A- FG501A-TG501 - PG502- DC505A - FG504 -7B80 + 85-7B92A

Gould J3B test oscillator + manual -£150.Tektronix Mainframes - 7603 -7623A-7613-7704A-7844-7904- TM501 - TM503 -TM506 -

7904A - 7834 - 7623 - 7633.Marconi 6155A Signal Source -1 to 2GHz - LED readout -£400.Barr & Stroud Variable filter EF3 0.1Hz- 100kc/s + high pass + low pass - £150.Marconi TF2163S attenuator - 1GHz. £200.Farnell power unit H60/50 -£400 tested. H60/25-£250.Racal/Dana 9300 RMS voltmeter - £250.HP 8750A storage normalizer -£400 with lead + S.A or N,A Interface.Marconi TF2330 - or TF2330A wave analysers -£100-050.Tektronix -7S14 -7T11 -7S11 -7S12 - S1 - S2 - S39 - S47 - S51 - S52 - S53 -7M11.Marconi mod meters type TF2364 - £250.HP 5065A rub id ru m vapour FX standard -£1.5k.Systron Donner counter type 60546 -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 - £850.Farnall electronic load type RB1 030-35 -£350.Racal/Dana counters 9904 9905 9906 9915 9916 - 9917 - 9921 - 50Mcis - 3GHz - £100-

£450 -all fitted with FX standards.HP4815A RF vector impedance meter c/w probe - £500-f600.Marconi TF2092 noise receiver. A, B or C plus filters -£100-£350.Marconi TF2091 noise generator. A, B or C plus filters -£100-£350.Marconi 2017 S/G 10Khz -1024MHz.HP180TR, HP182T mainframes £300-£500.Philips panoramic receiver type PM7900 -1 to 20GHz - £400.Marconi 6700A sweep oscillator + 18GHz PL's available.HP8505A network ANZ + 8503A S parameter test set + 8501A normalizer - £4k.HP8505 network ANZ 8505 + 8501A + 8503A.Racal/Dana VLF frequency standard equipment. Tracer receiver type 900A + difference meter

type 527E + rubidium standard type 9475- £2750.HP signal generators type 626 -628- frequency 1OGHz-21GHz.HP 432A - 435A or B - 436A - power meters + powerheads - Mc/s -40GHz- £200-£1000.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 20Mc/s -£1500.HP 3336A or B syn level generator -£500-£600.HP 35868 or C selective level meter - £750-£1000.HP 3575A gain phase meter 1Hz - 13Mc/s - £400.HP 8683D S/G microwave 2.3 -13GHz- opt 001 - 003 - £4.5k.HP 8660 A -B -C syn S/G. AM + FM + 10Kc/s to 110Mds PI - 1Mc/s to 1300Mc/s - 1Mc/s to

2600Mc/s - £500-£2000.HP 8640B S/G AM -FM 512Mc/s or 1024Mds. Opt 001 or 002 or 003-£800-£1250.HP 86222BX Sweep PI - 01 - 2.4GHz + ATT- £1750.HP 8629A Sweep PI -2 -18GHz - £1000.HP 862908 Sweep PI -2 - 18GHz- £1250.HP 86 Series PL's in stock - splitband from 10Mds- 18.6GHz-£250-E1k.HP 8620C Mainframe - E250. IEEE -£500.HP 8615A Programmable signal source- 1MHz- 50Mds - opt 002 -Elk.HP 8601A Sweep generator .1 -110Mc/s -E300.HP 3488A HP- IB switch control unit- £500 + control modules various -£175 each.HP 8160A 50Mds programmable pulse generator -£1000.HP 853A MF ANZ -£1.5k.HP 8349A Microwave Amp 2 - 20GHz Solid state -£1500HP 3585A Analyser 20Hz- 40Mds-£4k.HP 85696 Analyser .01 -22GHz - £5k.HP 3580A Analyser 5Hz -50kHz-£1k.HP 19806 Oscilloscope measurement system - £600.HP 3455A Digital voltmeter - £500.HP 3437A System voltmeter - £300.HP 3581C Selective voltmeter - £250.HP 5370A Universal time interval counter -f450.HP 5335A Universal counter - 200Mc/s - £500.HP 5328A Universal counter - 500Mds - £250.HP 6034A System power supply- 0 -60V -0 - 10 amps - £500.HP 5150A Thermal printer - £250.HP 1645A Data error analyser -£150.HP 4437A Attenuator -£150.HP 3717A 70Mc/s modulator -£400.HP 3710A - 3715A - 3716A - 3702B - 370313 - 3705A - 3711A - 3791B - 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- £600.HP 3770A Amp delay distortion analyser -f400.HP 3780A Pattern generator detector - £400.HP 3781A Pattern generator - £400.HP 3781B Pattern generator (bell) - £300.HP 3782A Error detector - £400.HP 37826 Error detector (bell) - £300.HP 3785A Jitter generator + receiver - E750 -E1 k.HP 8006A Word generator -£100-£160.HP 8016A Word generator - £250.HP 8170A Logic pattern generator - £500.HP 59401A Bus system analyser -£350.HP 59500A Multiprogrammer HP -113 -£300.Philips PM5390 RF syn - 0.1 - 1GHz - AM + FM -£1000.S.A. Spectral Dynamics SD345 spectrascope 111 - LF ANZ -E1500.Tektronix R7912 Transient waveform digitizer - programmable - £400.Tektronix TR503 + TM503 tracking generator 0.1 - 1.8GHz-£1k- or TR502.Tektronix 576 Curve tracer + adaptors - £900.Tektronix 577 Curve tracer + adaptors -£900.Tektronix 1502/1503 TDR cable test set - £1000.Tektronix AM503 Current probe + TM501 m/frame - £1000.Tektronix SC501 - SC502 - SC503 - SC504 oscilloscopes - £75-f350.Tektronix 465 - 4658 -475 -2213A 2215 2225 2235 2245 - 2246 -£250-£1000.Kikusui 100Mc/s Oscilloscope COS6100M -£350.Nicolet 3091 LF oscilloscope -£400.Racal 1991 -1992 -1988 -1300Mc/s counters - £5130-£900.Fluke 80K-40 High voltage probe in case- BN £100.Racal Recorders - Store 4 - 4D -7 -14 channels in stock - £250 - £500.Racal Store Horse Recorder & control - £400-£750 Tested.EIP 545 microwave18GHz counter -£1200.Fluke 510A AC ref standard - 400Hz - £200.Fluke 355A DC voltage standard - E300.Wiltron 610D Sweep Generator + 6124C Pi - 4- 8GHz - £400.Wiltron 610D Sweep Generator + 61084D PI - 1Mds- 1500Mcis - £500.Time Electronics 9814 Voltage calibrator - £750.Time Electronics 9811 Programmable resistance -£600.Time Electronics 2004 D.C. voltage standard -£1000.HP 8699B Sweep PI YIG oscillator .01- 4GHz -£300.8690B MF -f250. Both £500.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.B&K 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-Thurlby- 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: (01214) 684001. Fax: 651160

CIRCLE NO. 109 ON REPLY CARD

August 1995 ELECTRONICS WORLD+WIRELESS WORLD 641

BULL CLEAROUT SALEWIRELESS VIDEO BUG KIT Transmits video and audiosignals from a minature CCTV camera (included) to anystandard television! All the components including a PP3 batterywill fit into a cigarette packet with the len s requiring a hole about3mm diameter. Supplied with telescopic aerial but a piece ofwire about 4" long will still give a range of up to 100 metres. Asingle PP3 will probably give less than 1 hours operating time.£99 REF EP79. (probably not licensable!)GOT AN EXPENSIVE BIKE? You need one of our bottlealarms, they look like a standard water bottle, but open the top,insert a key to activate a motion sensor alarm built inside. Fitsall standard bottle carriers, supplied with two keys. SALEPRICE £7.99 REF SA32.GOT AN EXPENSIVE ANYTHING? You need one of ourcased vibration alarms, keyswitch operated, fully cased just fitit to anything from videos to caravans, provides a yearsprotection from 1 PP3 battery, and protect it! UK made. SALEPRICE £4.99 REF SA33.DAMAGED ANSWER PHONES These are probablybeyond repair so they are just£4.99 each. Mainly response 200machines. REF SA30COMMODORE GAMES CONSOLESJusta fewof theseleft to clear at £5 ref SA31. Condition unknown.COMPUTER DISC CLEAROUT We are left with a lot ofsoftware packs that need clearing so we are selling at discvalue only! 50 discs for £4, thats just 8p eachNour choice ofdiscs) SALE PRICE £4 ref EP66IBM PS2 MODEL 150Z CASE AND POWER SUPPLYComplete with fan etc and 200 watt power supply. SALEPRICE £9.95 ref EP67DELL PC POWER SUPPLIES 145 watt, +5,-5,+12,-12,150x150x85mm complete with switch, flylead s and I EC socketSALE PRICE £9.99 ref EP551.44 DISC DRIVES Standard PC 3.5" drives but returns sothey will need attention SALE PRICE £4.99 ref EP681.2 DISC DRIVES Standard 5 25" drives but returns so theywill need attention SALE PRICE £4.99 ref EP69PP3 NICADS New and unused but some storage marks.SALE PRICE £4.99 ref EP52SOLAR PANELS 3v output with two flyleads, 100x60 mmpack of 10 SALE PRICE £6.99 ref EP56DELL PC POWER SUPPLIES (Customer returns)Standard PC psu's complete with fly leads, case and fan, packof two psus SALE PRICE £5 FOR TWOII ref EP61GAS HOBS AND OVENS Brand new gas appliances,perfect for small flats etc. Basic 3 burner hob SALE PRICE£24.99 ref EP72. Basic small built in oven SALE PRICEE79 refEP73BITS AND BOBS We have a quantity of cased modems,multiplexers etc different specs but ideal strippers. SALEPRICE £4 each ref EP63RED EYE SECURITY PROTECTOR 1,000 watt outdoorPIR switch SALE PRICE E9.99 ref EP57ENERGY BANK KIT 100 6"x6" 6v 100mA panels, 100diodes, connection details etc. £69.95 ref EF112.CCTV CAMERA MODULES 46X70X29mm, 30 grams,12v 100mA. auto electronic shutter, 3.6mm F2 lens, CCIR,512)(492 pixels, video output is 1v p -p (75 ohm). Works directlyinto a scart or video input on a tv or video. IR sensitive. £79.95ref EF137.IR LAMP KIT Suitable for the above camera enables thecamera to be used in total darkness! £5.99 ref E F138PASTELACCOUNTS SOFTWARE, does everything forall sizes of businesses, includes wordprocessor, report writer,windowing, networkable up to 10stations, multiple cash booksetc. 200 page comprehensive manual. 90 days free technicalsupport (0345-326009 try before you buy!) Cu front retail priceis E129, SALE PRICE £9.95 ref SA12. SAVE £120!!!MINI MICRO FANS 12V 1.5" sq SALE PRICE E2 RefSA13.C ITOH PRINTERS 80 col, 9 pin matrix, serial/parallel,NLQ/draft, 3 mth warranty, good condition, SALE PRICE £39ref SA14.REUSEABLE HEAT PACKS. Ideal for fishermen, outdoorenthusiasts eklerly orinfirm, warmingfood, drinks etc, defrostingpipes etc.reuseable up to 10 times, lasts for up to 8 hours pergo, 2,000wh energy, gets up to 90 degC. SALE PRICE £9.95REF SA29A4 DTP MONITORS Brand new, 300 DPI. Com plate withdiagram but no interface detaile.(eo you will have to workit outl) Bargain at just E7.99 0.0111111 Ref EF18512V2AMPLAPTOPpsu's110x55x4Omm(includes standardIEC socket) and 2m lead with plug. 100-240v IP. SALE PRICEE6.99 REF SA15.PC CONTROLLED 4 CHANNEL TIMER Control (on/offtimes etc) up to 4 items (8A 240v each) with this kit. Completewith Software, relays, PCB etc. £25.99 Ref 95/26COMPLETE PC 300 WATT UPS SYSTEM Top of therange UPS system providing protection for your computersystem and va luable software against mains power fluctuationsand cuts. New and boxed, UK made Provides up to 5 minsrunning time in the event of complete power failure to allow youto run your system down correctly. SALE PRICE just £69.00.SOLAR PATH LIGHTS Lowenergywalklights powered byth sun! builtin PIR so they work when you walk past. Includessolar panel & rechargeable bat. SALE PRICE E19.9REF EP62

BIG BROTHER PSU Cased PSU, 6v 2A output,2m o/p lead, 1.5m input lead, UK made,220v. SALE PRICEE4.99 REF EP7WANT TO MAKE SOME MONEY? STUCK FOR ANIDEA? We have collated 140 business manuals that give youinformation on setting up different businesses, you perusethese at your leisure using the text editor on your PC. Alsoincluded is a certificate enablingyou to reproduce the manuals as much as you like! SALEPRICE £14 REF EP74RACAL MODEM BONANZA! 1 Racal MPS12231200/75modem, telephone lead, mains lead, manual and commssoftware, the cheapest way onto the net! all this for just £13 refDEC13HOW LOW ARE YOUR FLOPPIES? 3.5'. (1.44)unbranded. We have sold 100,000+ so ok! Pack of 50 £24.99ref DEC165mw LASER POINTER. Supplied in kit form, complete withpower adjuster, 1-5mw, and beam divergence adjuster. Runson 2 AAA batteries. Producesthin red beam ideal for levels, gunsights, experiments etc Cheapest in the UK! just £39 95 refDEC49RADIO PAGERSBrand new, UK made pocket pagersclearance price is just £4.99 each 100x40x 15mm packed withbits! Ref SEP5.BULL TENS UNIT Fully built and tested TENS(Transcutaneous Electrical Nerve Stimulation) unit, completewith electrodes and full instructions. TENS is used for the reliefof pain etc in up to 70% of sufferers. Drug true pain relief, safeand easy to use, can be used in conjunction with analgesics etc.£49 Ref T EN/1

COMPUTER RS232 TERMINALS. (LIBERTY)Excellentquality modern units,(like wyse 50,$) 2x RS232, 20 functionkeys, 50 thro to 38,400 baud, menu driven port, screen, cursor,and keyboard setup menus (18 menu's). £29 REF NOV4.PC PAL VGA TOTV CONVERTER Converts a colour TVinto a basic VGA screen. Complete with built in psu, lead ands/ware.. Ideal for laptops or a cheap upgrade. Supplied in kitform for home assembly. SALE PRICE £25 REF SA34EMERGENCY LIGHTING UNIT Complete unit with 2double bulb floodlights, built in charger and auto switch. Fullycased. 6v 8A H lead acid req'd. (secondhand)E4 ref MAG4P11.SWINGFIRE GUIDED MISSILE WIRE. 4,200 metre reelof ultra thin 4 core insulated cable, 281bs breaking strain, lessthan 1mm thick! Ideal alarms, intercoms, fishing, dolls house'setc. SALE PRICE £13.99 ref EP51ELECTRIC CAR WINDOW DE-ICERS Complete withcable, plug etc SALE PRICE JUST £4.99 REF SA28ASTEC SWITCHED MODE PSU BM41012 Gives +5 @3.75A, +12@1 5A, -12@.4A.230/110, cased, 9M41012. £5.99ref A UG6P3.

A UTO SU NCHA RGER 155x300mm solar panel with diodeand 3 metre lead fitted with a cigar plug. 12v 2watt. SALEPRICE £8.99 REF SA25.TOP QUALITY CENTRIFUGAL MAINS MOTORSSALE PRICE2 FOR JUST £2.60 REF SA38ECLATRON FLASH TUBE As used in police car flashinglights etc, full spec supplied, 60-100 flashes a min. SALEPRICE £6.99 REF SA15.24v AC 96WATT Cased power supply. New. SALE PRICEJUST £9.99 REF SA40MILITARY SPEC GEIGER COUNTERS Unusedanstraightfrom Her majestys forces. SALE PRICE £44 REFSA16MICRODRIVE STRIPPERS Small cased tape drives idealfor stripping, lots of useful goodies including a smart case, andlots of components. SALE PRICE JUST £4.99 FOR FIVE REFSA26SOLAR POWER LAB SPECIAL You get TWO 6"x6" 6v130mA solar cells, 4 LED's, wire, buzzer, switch plus 1 relay ormotor.Superb value kit SALE PRICE JUST £4.99 REF SA27RGB/CGA/EGA/TTL COLOUR MONITORS 12" in goodcondition. Back anodised metal case. SALE PRICE £49 REFSA16SWITCHED MODE PSU ex equip, 80w +5v@5A, -5v@.5A,+12v@2A,-12v@. 5A 120/220vcased 245x88x55mm I ECi nputsocket £6.99 REF MAG7P1PLUG IN ACORN PSU 19v AC 14w , £2.99 REF MAG3P10POWER SUPPLY fully cased with mains and o/p leads 17vDC 900mA output. Bargain price £5.99 ref MAG6P9

'SOME OF OUR PRODUCTS MAT BE UNLICENSABLB IN THE UK

ps*.4.V.OMMA.VOOMPICattit.

11 El,: 0127110350oFAX 01273 323077

ACORN ARCHIMEDES PSU +5v4.4A. on/off swuncased, selectable mains input, 145x100x45mmSALE PRICE £4.99 REF SA113.8V 1.9A psu cased with leads. Just £9.99 REF MAGI OP3PPC MODEM CARDS These are high spec plug in cardsmade for the Amstrad laptop computers. 2400 baud dial up unitcomplete with leads. Clearance price is £5 REF: MASSP1200 WATT INVERTER Converts 10-15v DC into either 110vor 240v AC. Fully cased 115x36x156mm, complete with heavyduty power lead, cigar plug, AC outlet socket. Auto overloadshutdown, auto short circuit shut down, auto input over voltageshutdown, auto input under voltage shut down (with audiblealarm), auto temp control, unit shuts down if overheated andsounds aud ible alarm. Fused reversed polarity protected. outputfrequency within 2%, voltage within 10%. A well built unit at ankeen price. Just £64.99 ref AUG65.UNIVERSAL SPEED CONTROLLER KIT Designed byus for the C5 motor but ok for any 12v motor up to 30AComplete with PCB etc. A heat sink may be required. £17.00REF: MAG17COMPUTER COMMUNICATIONS PACK Kit contains100m of 6 core cable, 100 cable clips, 2 line drivers with RS232interfacesand all connectors etc. Ideal low cost method of communicatingbetween PC's over a long distance. Complete kit £8.99.ELECTRIC MOTOR KIT Comprehensive educational kitincludes all you need to build an electric motor £9.99 refMAR10P4VIEWDATA SYSTEMS made by Phillips, complete withinternal1200/75 modem, keyboard, psu etc RGB and compositeoutputs, menu driven, autodialler etc. SALE PRICE £12.99REF SA18AIR RIFLES .22 As used by the Chinese army for trainingpuposes, so there is a lot about! £39.95 Ref EF78. 500 pellets£4.50 ref EF80.PLUG IN POWER SUPPLY SALE FROM £1.60 f igsin to 13A socket with output lead. three types available, 9vdc150mA £1.50 ref SA19, 9vdc 200mA £2.00 ref SA20, 6.5vdc500mA £2 ref SA21.VIDEO SENDER UNIT. Transmits both audio and videosignals from either a video camera, video recorder, TV orComputer etc to any standard TV set in a 100' range! (tune TVto a spare channel) 12v DC op. Price is £15 REF: MAG15 12vpsu is £5 extra REF: MAG5P2FM CORDLESS MICROPHONE Small hand held unitwith a 500' range! 2 transmit power levels. Reqs PP3 9v battery.Tuneable to any FM receiver. Price is £15 REF: MAG15P1MINATURE RADIO TRANSCEIVERS A pair of walkietalkies with a range up to 2 km in open country. Units measure22x52x155mm. Including cases and earp'ces. 2x PP3 req'd.£30.00 pr. REF: MAG30FUTURE PC POWER SUPPLIES These are295x 135x 60mm, 4 drive connectors 1 mother board connector.150watt, 12vfan, iec inlet and on/off switch. SAL EPRICE £7.99REF SA 22FMTRANSMITTER KIT housed in a standard working 13Aadapter!! the bug runs directly off the mains so lasts forever!why pay £700? or price is £15 REF: EF62 Transmits to any FMradio. (this is in kit form with full instructions.)"FM BUG BUILT AND TESTED superior design to kit.Supplied to detective agencies. 9v battery req'd. £14 REF:MAGI 4TALKING COINBOX STRIPPER COMPLETE WITHCOINSLOT MECHANISMS originally made to retail at £79each, these units are designed to convert an ordinary phoneinto a payphone. The units have the locks missing andsometimes broken hinges. However they can be adapted fortheir original use or used for something else?? SALE PRICEJUST E2.50 REF SA23GAT AIR PISTOL PACK Complete with pistol, darts andpellets £12.95 Ref EF82 extra pellets (500) £4.50 ref EF80.6"x12-AmoRPHoussoLARPANEL12v155x310mn,130mA SALE PRICE E4.99 REF SA24FIBRE OPTIC CABLE BUMPER PACK 10 metres for£4.99 ref MA G5P13 idea! for experimenters! 30 m for £12.99 refMAGI 3P1

WE BUY SURPLUS STOCK FOR CASHFREE CATALOGUE

1995 100 PAGE CATALOGUE NOWAVAILABLE, 45P STAMP OR FREE

WITH ORDER.PORTABLE RADIATION DETECTOR

WITH NEW COMPUTER INTERFACE £59A Hand held personal Gamma and X Ray defec-tor. This unit contains two Geiger Tubes, has a 4digit LCD display with a Piezo speaker, giving anaudio visual indication. The unit detects highenergy electromagnetic quanta with an energyfrom 30K eV to over 1.2M eV and a measuringrange of 5-9999 UR/h or 10-99990 Nr/h. ref NOV18

(IN(11 \(). I MON REPLY CARD

642 ELECTRONICS WORLD+WIRELESS WORLD August 1995

DSP

Discrete -timekey to dsp

Real-time digital signalprocessing calls for anunderstanding of theprinciples of discrete -timelinear systems. HowardHutchings explains thetheory, and then offers apractical way to try outthe results.

Interfacing to a pc and real-time program-ming undoubtedly call for engineeringingenuity.

But successful real-time digital signal pro-cessing requires something more - an under-standing of the principles of discrete -time lin-ear systems.

The fundamental mechanism of sampleddata manipulation is time -domain convolution,or z -domain multiplication. These particulartopics are well -understood and have beenextensively documented, typically with theassistance of mathematics.

But with only a small investment of time itis possible to demonstrate the principles of dspin action in a dramatic way.

The approach is to use a pc to examine thetime- and spectral -performance of a sampledsinusoid detailed as a rational z -function, to besubsequently developed as a particular case ofa general discrete -time linear system.

Convolution is not needed as any real-timenumerical manipulation uses recursive meth-ods, while engineering design and perfor-mance of the discrete -time linear system isintroduced using the z -transform of a sampledsinusoid.

As a result there is no requirement for syn-chronised data transfer between the a -to -d andnumerical processor, and engineering princi-ples are not compromised.

Equi-spaced samples generated by the sinu-soidal digital generator are written to the realworld via an 8 -bit d -to -a, while the resonantfrequency can be adjusted by selective scaling.

Advantage of the method is that it demon-strates several concepts in a visual way, usinga worked example. Sampled time -domain per-formance is visualised on an oscilloscope, andthe frequency -domain behaviour of poles isvisualised on the z -plane and displayed usingcomputer graphics. Other topics discussedinclude discrete Fourier transforms, the audi-ble and visible effects of aliasing in time andfrequency, unit -pulse response of an UR sys-

tem, and the real-time realisation of a pc -baseddigital filter programmed using C.

Digital oscillatorFirst step is to examine how to use a numeri-cal system to generate sine waves, exploitinga real-time pc -based digital oscillator, inter-faced to the real world through an 8 -bit d -to -aconverter.

Typically, such a system would compute therequired output samples ahead of time andstore them in a wave -form look -up table tospeed up the process of real-time wave -formgeneration. But rather than follow such a well -trodden path, we are going to look at a recur-sive real-time realisation that is more relevantto the characteristics of a discrete -time linearsystem.

It is developed from the z -transform of asampled sinusoid:

zH(z)- sinS220

z - 2z cos Do +1To understand the behaviour of this transformdetailed as a linear system, we should firstundertake a brief review of the properties oflinear systems, and then follow this with a dis-cussion of discrete summation to assist thenotion of open -and closed -forms. Then, theeffects of the sampling process can be con-sidered, and real-time performance demon-strated visually and audibly using computer -managed instruction.

Frequency preservationMany signal processors do not possess mem-ory. Frequently the purpose is simply that ofsignal amplification (A > 1) or attenuation (A< 1). The output signal should be a faithfulreproduction of the input, represented by thescalar product: y(t) = Ax(t). Impulse responseh(t) of such linear systems would ideally con-sist of a single weighted impulse h(t) = A6(t)(Fig. la).

Instantaneous output of this system is an

August 1995 ELECTRONICS WORLD + WIRELESS WORLD 643

DSP

Fig. 1.Consideration of theimpulse response ofthe spectralperformance, froma time -domainperspective,improvesunderstanding ofthe effect ofmemory onfrequency -domainfiltering.la. Memory lesssystemcharacterised by asingle scaledimpulse.1b. System withmemory,characterised by atime -extendedimpulse response.

R

attenuated version of the input, and does notdepend on past or future inputs.

Practical analogue systems seldom meet thisrequirement. Typically, capacitance, induc-tance and resistance modify the intendedresponse at certain frequencies. A testament tothe frequency -domain performance is inferredby examination of the characteristic of thetime -domain impulse response. Systemparameters such as cut-off frequency, Q -factorand undamped natural frequency can all bedetermined directly from the historical recordcontained in the impulse response. A first -order response is detailed in Fig. 1 b.

All linear signal processors exhibit frequen-cy preservation so that no new frequencies aregenerated within the system. Any signal rep-resented in terms of its component frequencieswill be processed in a very simple way, withonly the amplitude and phase of individualcomponents being modified.

This is a key factor in relation to amplitudescaling and time delay - the parameters of adiscrete -time linear system.

Filtering -a time domain perspectiveSelectively manipulating input data, or filter-ing the signal in such a way that certain fre-quencies are especially favoured, requiresmemory. Numerous practical examples ofanalogue systems exhibiting this effect can befound in the technological world around us.For example, in a simple first -order system, amercury -in -glass thermometer retains a histo-ry of the input step -function, long after thestimulus has been removed. More evocatively,striking a cathedral bell -a highly resonantsecond -order system with a Q -factor typicallyof the order of 1000s - will give rise to a pro-longed response, audible long after theimpulse has been removed.

Unwanted second -order effects in the pass -band of video amplifiers also give rise to ring-ing, an undesirable, but clearly visible effect.

Time -domain convolution and frequency -domain filtering can be thought of as comple-mentary perspectives of the same processingoperation. Here we will see how it can be

h(t) h(t)=A8(t)

0

R2

R1A =

+R2

(a)

t

h(t) (b)

h (t) = ae-at

a= 1

CR

desirable to present the characteristics of a lin-ear system as a frequency -selective filter,specified either by the frequency response,transfer function, or by the impulse response.

Although convolution is a significant con-cept in many diverse scientific fields, the con-volution integral plays a mainly theoreticalrole in analogue linear system theory. Discreteconvolution is inherently practical. The con-volution sum is frequently a direct realisationof a linear discrete -time system. It is the nat-ural mechanism for describing the perfor-mance of processing devices operating onsampled signals, whether such systems arepurpose-built electronic circuits or real-timeprograms implemented on a digital computer.

Open and closed discrete summationThe two principal types of digital filter algo-rithm are non -recursive, described by a finiteimpulse response (FIR), or recursive, charac-terised by an infmite impulse response (IIR).

A non -recursive filter calculates the currentvalue of the output by combining the presentvalue of the input, with scaled past values of

Practical adviceAim of this article is to develop a time -domain perspective on frequency -domainfiltering, with the practical result being acomputer -based account of the real-timeperformance of a digital resonator.

Engineering design and performance ofthe discrete -time linear system is intro-duced using the z -transform of a sampledsinusoid. This avoids the need for synchro-nised data transfer between the a -to -d andnumerical processor - but not at theexpense of engineering principles.

Equi-spaced samples generated by thesinusoidal digital generator are written tothe real world via an 8 -bit d -to -a and theresonant frequency is adjusted by selectivescaling.

Principles can be developed into applica-ns using computer -managed instruction.There is no need to attempt any Fourier

analysis or pole -zero plotting. The softwarewill do it all for you.

the input.But in a recursive filter, the current output

depends on the present input together withcombinations of scaled values of previous out-puts and inputs.

Computational economy in real-time signalprocessing frequently involves minimising thenumber of calculations per sample, often byexpressing the algorithm in closed form.

The sum of the infinite geometric seriescan illustrate the technique. In the equa-tion S + r + r2 + + ... we could sim-ply summate all the terms on the right-handside of the equal sign, and infer the sum as alimiting process. But, providing that I r I < 1 -a condition that applies to all the closed formswe are going to meet - the calculation can besimplified by taking advantage of the enu-meration:

1 =Il+r+r2+r3...1-rThis is an example of a discrete summationformula, where the left-hand side of theexpression is said to be a closed form of thesum. Expressions of this form are so commonin dealing with sampled -data sequences thatwe introduce a new symbol z -I to representunit time delays (for reasons that will becomeapparent in a later section).

Consider the sampled -data sequence u(n) =1, 1, 1, 1 ...

To model delays algebraically, U(z) can beexpressed as a power series in z-1 as U(z) = 1+ z-1 + z-2 + z-3 +

Each sample in the sequence can be clearlyidentified and its appropriate position in timeidentified. In this case r = z-1 so the series maybe summed as:

U(z)=1-

1

+ + z' + z 3...

Multiplying numerator and denominator by zgives:

U(z)=z

z -1

Physically, this may be clarified as the closedform of the sampled unit -step, the first sampleoccurring at n= 0.

How to use delay operator z-1 may be bemade clearer by analysing the sequence ui (n),describing the sampled unit step delayed byone sampling interval, so that ui(n)=0, 1, 1, 1,1 ... The sampled data sequence may be mod-elled as U1(z)=z-l+z-2+z-3+z-4... and summedas:

Ui(z) = =z

-11_1(z)

If the sequence is delayed by one samplinginterval, then its closed form (or transform) ismultiplied by z -I. The delay property of z-1can be expressed as a formal operation whichfulfils the following requirements. Each numerical sample must be identified insome way, by reference to its particular timeframe; Multiplication by z-1 should represent a time

644 ELECTRONICS WORLD + WIRELESS WORLD August 1995

DSP

delay of one sampling interval - moving asample value from one time frame to the next.In general the z -transform of the samplex(n-k) is X(z)z-k.

Sampling complex exponentialsThe kth sample value of a sampled sinusoidcan be written as f(k) = Asin(dc + 0), where kis an integer. The signal is characterised bythree parameters: amplitude of the sine waveA, angular frequency co, and angular startingpoint of the cycle in relation to the origin 0.

Euler's formula is a convenient way todescribe F(k) as the real part of a complexexponential F(k) = Real{ Ae(01+ 01.

The continuous phasor Acan be interpretedas a point that moves around the circumfer-ence of a circle of radius A in the complexplane. Sine wave F(k) is basically one-dimen-sional, and can be modelled as the projectionof the point on the Y-axis, rather than its posi-tion in two dimensional space.

A digital phasor can be visualised as theprocess of sampling a continuously varyingphasor, represented by exp(jcot), at equally -spaced time intervals, represented by t = kT.Behaviour of a complex digital phasor sam-pling various signals is shown in Fig. 2.

Programs listingsThe three C listings of programs referred toin the article, and written by HowardHutchings, show dsp theory in action. Fora hard copy of these listings, send an saemarked dsp to EW + WW's editorial offices(address on Comment page).

A disk containing the C program code isalso available - for £10 to cover the cost ofdisc, copying, postage and packaging -from the same address.

Or we can include the three listings, free,on the Interfacing with C listings disk,obtainable from EW + WVI/for £15.

Listing 1: encourages the user to enter theparameter fq,dic/fsampie. The associatedcomplex conjugate pole -pair is plotted onthe circumference of the unit circle withthe assistance of the computer graphics.The parameter input from the keyboardcontrols the frequency of the digitaloscillator, the output of which is madeavailable via the Blue Chip data acquisitioncard ACM -44, using an 8 -bit d -to -a(AD7226).

Base address is identified in the program.Listing 2: provides a graphicalrepresentation of the amplitude and phaseresponse of the rational function H(z). Toavoid exceeding the dynamic range of themonitor graphics the maximum value isnormalised to unity. For best visual results,it is recommended that a samplingfrequency of 640 be selected. Thismaximises the horizontal, relativefrequency axis.Listing 3: requests the user to specify asampling frequency F and an incrementAf in Hz. The program then prints theamplitude ratio and phase angle atfrequency intervals of Af over the range 0to FJ2.

All the programs are written in MicrosoftC, version 5.1.

Fig. 2a. Complex digitalphasor, and theprojection of the realpart, a digital sinusoid,onto the vertical axislabelled F(k)2b. Complex digitalphasor of frequencyzero radians per sampleinterval (dc sampling).2c. Complex digitalphasor of frequency7C radians per sample,sampling at Nyquistfrequency.2d. Complex digitalphasor of frequency(1+5) radianspersample interval;aliasing due toundersampling.

(a)

(b)

(c)

(d)

Complex plane

3

MP'

Complex plane

0,1,2,3..

Complex plane

Complex plane

4

Sampling is analogous to the stroboscopiceffect noticeable in motion picture films ofrotating objects, such as stage -coach wheels.Cine film consists of a series of still picturescaptured at 24 frames a second. When the filmis projected we interpret any displacementfrom one frame to the next as motion.

If you take a picture of a wheel with aspoke, in the 12 o'clock position and rotatingclockwise, and then another a 24th of a secondlater, the wheel will have rotated and thespoke may well be in the 11 o'clock position.Another 24th of a second the spoke will pointto 10 o'clock and so on. Our brain wronglyconcludes that the wheel is travelling anti-clockwise.

A negative frequency means that the phasoris rotating in the clockwise rather than thecounter -clockwise direction. Beware, by inter-preting the sine wave as a projection on the Y-axis, the image will rise and fall sinusoidally,exactly the same whether the wheel is turningclockwise or anti -clockwise.

To visualise the performance, and limita-tions, of the sampling process, imagine awhite rotating disc with a black dot paintednear the rim, illuminated by a stroboscope.

F (k)

1

0 2

03

F (k)0 1 2 30 0 0

F (k)

o204

0301

The revolving dot represents the fixed fre-quency phasor, while the sequence of illumi-nated dot positions represents the discrete -timesampled data. If the dot moves slightly morethan 180° between flashes, it will appear to bemoving backwards at a rate slightly less thanone-half a revolution per flash; what is more,the dot will never appear to be rotating morethan It radians per flash.

Our conclusion must be that to represent thespeed of revolution uniquely, we must sampleat least twice per period of rotation.

Sampled sinusoidIn the z -plane, the frequency -selective perfor-mance is characterised by the complex conju-gate pole -pair, on the circumference of theunit circle, together with a single zero at theorigin.

Location of the poles of this digital res-onator, given by the characteristic equation z2- 2zcosS20 + 1 = 0, will determine the fre-quency of oscillation.

Clearly, by varying S20, the linear systemcan be made to resonate in the range dc to halfthe sampling frequency.

August 1995 ELECTRONICS WORLD + WIRELESS WORLD 645

DSP

Frequency of oscillation is related to thesampling frequency by,

ircidk,

2z Ampkr

The consequence of varying this parameter,

z sin slosinn szo u [n

z2_2 zcosS20+1

z plane

(a)

f ---- -- -

141

-- _

--- --- -J

(b)

Fig. 3a. The pole -zero diagram of thesinusoid, visualised with the assistance ofListing 1. The frequency of the processedoutput is 434.78Hz using a pc clocked at25MHz.3b. Oscillogram of the d -to -a output. Q0=1E/4radians. Sensitivity 1V per division, time -base0.5ms/division.3c. The pole -zero diagram of the sampledsinusoid, visualised with Listing 1. Thefrequency of the processed output is434.78Hz.3d. Spectral response of the sinusoidal output,obtained with the assistance of Listing 2,demonstrates the unique, single -frequencyperformance of a second -order systemcharacterised by an infinite Q -factor.

and the effect on spectral and time -domainperformance is detailed in Fig. 3, which showstime and spectral response at fo=0.125fs (45°).

First, notice how in the time -domain, O.corresponds to a sinusoid with eight samplesper period. It is interpreted as the required fre-quency in fractions of the sampling frequency,so that the angular displacement S20 is

fcyclicifsample multiplied by 27t.Secondly, the frequency -domain model

would ideally consist of a single ordinate, thespectral response of a sinusoid.

Computer -based software written in C pro-vides a useful opportunity to investigate theperformance of the variable frequency, dis-crete -time, linear system. On converting fromtransforms to sequences, the relationshipbetween the input and output samples, (Fig. 4)may be expressed by the recurrence relation-ship

y(n) = 2cosiloy(n - 1) - y(n - 2) + sinDox(n -1)

The unit -pulse response of this resonator iseternal, and once stimulated, the processedoutput will continue indefinitely with no fur-ther inputs. Of course, the position of theoscillator's complex poles, precisely locatedon the circumference of the unit circle willcharacterise a conditionally -stable system. Forthis reason, the multiplier coefficients are care-fully declared in floating point format, withsix digits of precision.

Practical implicationsPractical implications of time -domain sam-pling and the effect on frequency -domain per-formance are important considerations in real-time numerical signal processing.Mathematical details are well -understood andhave been extensively documented by manyauthors. But a more contemporary approach isto employ a practical pc -based investigation ofthe sampling theorem and to explore the rela-tionship with sampled -data models or z -trans-forms.

To demonstrate the stroboscopic effects ofsampling, an interesting computer -based studyis to vary the location of the system poles, andto monitor the sampled -data output of the d -to -a, using an oscilloscope. An audio poweramplifier and loudspeaker connected follow-ing d -to -a conversion, produces an audibleoutput. With the amplifier connected to theoutput, List 1 (see note at end of article) is run.

The designed output frequency is varied bychanging the location of the system poles. Onpassing through the Nyquist frequency twotones, sounding the same, are obtained.Clearly, the Nyquist frequency "mirrors" the

unique wanted signal and unwanted alias.Performance of a sampled -data system,

which visualises the dynamic position of thesystem poles plotted on the z -plane, togetherwith the audible, variable frequency output,detailed in the panel entitled 'Poles and zerosin action'.

When the software is run the computer -based text will initially outline a statement ofthe problem, before interactively encouragingthe user to enter parameter S21) to control thefrequency of oscillation.

Output from the digital oscillator is availablethrough an 8 -bit d -to -a.

Computer graphics display the unit circledrawn in the z -plane and indicate the positionof the selected poles.

Principles into applicationsTo develop a more realistic understanding ofthe properties of sampled data, we should for-mulate the z -transform more rigorously.

Expressed simply, the z -transform formu-lates a set of sequences or a difference equa-tion into an algebraic structure, allowing muchof the manipulation to be carried out accord-ing to a few very simple rules. To design andanalyse numerical signal processing systemssuccessfully we must understand the rules.

Stated formally the z -transform of asequence x(n) is given by:

744= E -400e*

Conceptually, the transform may be visualisedas a power series in z -I, with coefficientsequal to successive samples of the signal x(n):

X(0) X(1) X(2)

This expansion is a refined perspective of themore primitive embodiment of z-1 as the unit -delay operator. Interestingly, any digital trans-fer function can be expressed as a rationalfunction (a ratio of polynomials) in z -I:

H(z). - so+ aur-4 Ihoz;e1*---44/aAr)1 dkr41

Rational z -functions of this form figure promi-nently in the analytical description of sam-pled -data systems - consult any table of z -transforms for details.

Previous use of the operator z-1 to modeltime delays placed no restriction on the shapeof the time shifted waveform. Evidently thecomplex variable s = a + jco in the expressionexp(sT) took care of this.

We will concentrate on how a digital filterwill process sine waves. Relaxing the original

y [n ] Fig. 4. Systemdiagram of adigital resonator.The frequency ofoscillation iscontrolled by theparameter s20.

646 ELECTRONICS WORLD + WIRELESS WORLD August 1995

DSP

Fig. 5. Testingfor linearity. Aninput signalformed by theweightedcomponentsafi(04-bf1(t-T)will generate theproportionaloutputaf2(04-bf2(t-T),without need toreanalyse theresponse.

Fig. 6. Scalingin the x -domain. Toevaluate thez -transform ofanf(n), trace thetop right-handpath giving F(z)followed bysubstitutionz=za--1- Orfollow the left -had path toobtain anf(n)and thenperform thetransformation.Both routes areequivalent.

1.0

e

1.0

af, (t)

>nT

Discretetime

linear system

T2.0bf -T )

I )nT

Discretetime

linear system

afi(t)+bli (t -T Discrete ) timenT

linear system I a(2(04-bf2(t-T)

1.00.5

af 2(t)0.25

.0.125' '

nT

bf2(t -T )

1.0

2.0I 1.0

0.T50.25

nT

2.5

1.25

0.625.25

z -transformsinn S20 u (n )

ansinn520u(n ) ZT

x[n]

0

x[n]

0

zsin520

(z2 -2z cosS20+1)

z = za-1

az 5 n S20

(z 2- 2a z cos flo+a 2 )

nT

n

Poles and zeros in actionTo generate a variable -frequency sampled -out-put, the digital oscillator is designed using the z -transform of a sampled sinewave

H(z) =sin S2oz-I

1- 2 cos ,S2 + z-2

Behaviour of this transform detailed as a linearsystem is easier to understand if we considerhow the general digital function H(z) can beexpressed as the ratio of two polynomials, of thegeneral form

H(z)Y (z) as + a z-1 + a2z-2

X(z) b, + + kz-2

By inspection, the coefficients of the sinusoidalgenerator are given by al = sinik bo = 1, bt =-2cosS20 and b2 = 1.The numerator and denominator polynomialscan always be factorised to give the pole -zeroplot. Characteristics of a particular datasequence are specified by the roots of the twopolynomials - numerator N(z) anddenominator D(z) typically plotted on anArgand diagram. A unit circle is generallydrawn to indicate all values of z for which I z I=1

Poles and zeros can be plotted graphically,and for a sampled -data system the unit circle isa reference from which the frequency responseof the filter can be measured geometrically.

Coordinates of the upper, unit semi -circle,traced out in an anti -clockwise fashionrepresent frequencies from dc to half thesampling frequency; the operating range. Torepresent frequencies from half the samplingfrequency to the sampling frequency, the'walk' around the circumference of the unitcircle is continued. The amplitude ratio isdetermined by the position of the poles andzeros, relative to the circumference of the unitcircle.

A pole close to the circle will cause a peak,a zero a dip in the spectral response; the closerthey are to the unit circle the more extreme istheir effect. Thus, the complex poles of thesinusoidal generator detailed previously willmodel a second -order system characterised byan infinite Q -factor.

The term zero can be misleading. Located atthe origin of the z -plane (0,0) a zero representsa time advance of one sampling interval, thiswill modify the phase response only. Anyradial displacement towards the unit circleprogressively increases the attenuation, until,upon reaching the circumference theattenuation is a maximum and the amplituderatio is zero.

The frequency of oscillation is controlled bythe parameter L20.

August 1995 ELECTRONICS WORLD + WIRELESS WORLD 647

DSP

definition of s and discarding the exponent a,

(by making a = 0) means thatz may beviewed as a phasor defined by z = exp(jcor).Of course a complex signal or system will becomposed of several frequencies and may berepresented as the sum, or superposition, ofmany such phasors. This model fits naturallywith the signal processing characteristics oflinear systems.

Any signal represented in terms of its com-ponent frequencies will be processed by thelinear system in a very simple way. Only theamplitude and phase will be modified.

But how can we be certain a system is lin-ear? To test for linearity we must apply theprinciple of superposition (Fig. 5). An inputsignal formed by the weighted componentsafi(t) + bfi(t - 7) will generate the propor-tional output af2(t) + bf2(t - 7') without need tore -analyse the response.

Z -transforms in time and frequencyMagnitude and phase of the frequencyresponse of the general sampled -data systemH(z) can be determined by replacing z by pha-sor exp(jcoT). Employing this substitution,H(exp(jall")) may be regarded as a complexnumber, which characterises the frequency -selective properties of the rational transform interms of the amplitude ratio and phase angleover the range of interest.

Viewed as a sinusoidal signal processor thetransfer function of the transform may beexpressed as:

as + aleim +azie."++ameiwirbi, + be -Jiff + kern +.....+be446r

Rational z -transforms play a central role in thedevelopment of sampled -data systems. A rel-atively modest table of transforms will now beselectively explored using pencil -and -paperanalysis assisted by computer managedinstruction. Program Lists 2 and 3 are avail-able to demonstrate this.

There is considerable merit in developingthe z -transform of the decaying exponentialsignal from first principles, as a foundationfrom which to obtain other commonly usedtransforms and to develop a real comprehen-sion of pole -zero models -a delicate topic thatmust be thoroughly mastered and understood.

10'1=

Example 1. x(n) = cos(nS10) for n 0:Consider how the sinusoidal response nor-mally associated with complex poles can beusefully developed from the decaying expo-nential x(t) = cat.

Using Euler's formula, it follows that theperiodic function x(t) = Acos(ax) can beexpressed in complex exponential form as:

(elIg4 +e -*4Aeosnoo= A

Converting to a - transforms:

X(:)= A2 +

2

2 z-e144 z

cos4z-1= A1- 2cos1)011 +

ii

..%1:1411"

13

11al

u.

11

Ij

Ir hl

Hit any ke9 to return, x to exit

li

IIii

iii

Ilit II

1,.gill II

41

,

ff

it

A

Att,I(.=ain

t ;5 s,rnile

Gai,1 r

":

r.1

1.1

Hit an4 keu to return, x to exit

: .

Fig. 7. Variations in the spectral response of I -1(z), obtained by varying the radial position of thepoles, graphically demonstrate how the Q -factor or sharpness of the peak in the amplitude ratiois related to the positions of poles relative to the unit circle. Values are flo = it/3, a = 0.9. Thenumerical response demonstrates performance for F5=1000Hz, Sf=25Hz.

Evidently, the concept of complex poles hasarisen as a natural consequence of the z -trans-form of the cosine function. Not surprisinglythe characteristics of under -damped second -order systems and frequency selective filterscan be effectively developed from complexpole -zero models.

To investigate the frequency domain prop-erties of this transform, the software can beused (Listings 2 and 3) to vary parameter Cloover the range -7C It.

Example 2. h(n) = ansin(n120): Let us investi-gate the damped sinusoidal sequence h(n) =ansin(a2.). -

Clearly the z -transform has been developedfrom the time -domain multiplication of thesequences fln) = a" and g(n) = sin(nO), orequivalently the frequency -domain convolu-tion of F(z) and G(z).

The tedious algebra associated with thisoperation is avoided by taking advantage ofthe multiplication by a" property of z -trans-forms, to demonstrate scaling in the z -domain

(Fig. 6). The effect on the poles will be a radi-al displacement along the same frequency vec-tor (Fig. 6b).

(To examine the effects of varying theparameter a, for a particular value of S20, (say

= It/3), Listing 2 could be be run, using forexample, 0.6, 0.9 as values of a. The spectralresponse is shown in. Fig. 7.

For a numerical response of the amplituderatio and phase angle then Listing 3 can berun.

ReferencesOppenheim A V and Schafer R W. (1975),Digital Signal Processing. Prentice Hall.Gabel R A and Roberts R A. (1987), Signalsand Linear Systems. John Wiley.Lynn P A. (1989), An Introduction to theAnalysis and Processing of Signals. Macmillan.(Third edition).Chamberlin H. (1977), A Sampling ofTechniques for Computer Performance ofMusic. Byte, Vol. 2, No. 9.Ziemer R. E. Tranter W. H. & Fannin D. R.(1989), Signals and Systems Continuous andDiscrete. Macmillan.

648 ELECTRONICS WORLD + WIRELESS WORLD August 1995

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49

CIRCUIT IDEAS SEND YOUR CIRCUIT IDEAS TO THE EDITOR, ELECTRONICS WORLD,

QUADRANT HOUSE, THE QUADRANT, SUTTON, SURREY SM2 SAS

Do you have an original circuit idea for publication? We are giving £100 cash for the month'stop design. Additional authors will receive cash for each circuit idea published. We arelooking for ingenuity in the use of modern components.

Backup source using resonant inverterFor

equipment that can tolerate non -sinusoidal ac supplies, this source of

backup power is simple and efficient. Itsefficiency arises from its use of an RLCresonator driving output transistors fromsaturation to cut-off, a further benefit of thisarrangement being that the circuit is lesssensitive to transformer performance than themore common Class -A push-pull inverter.Capacitive loads do introduce losses.

555Timer

3

2, 6

R7

1k2

VR2470R

ZDI1N5349B

0

24Vac

R5

10kL1

22mH

R6 CI47k 10µ

R4

10kC21µ

A 555 oscillates at 1kHz and feeds theresonator circuit R4,5, L1,C1,VRI,R2, incombination with the input loading of thetransistors, which are protected againstreverse breakdown by diodes. If mains powerfails, the normally open contacts of RLA,supplied by a step-down transformer andbridge rectifier diode pack, close and enablethe inverter. Voltage from the bridge rectifieralso maintains a charge on the battery pack

R,220R 1W 2

WAe--0- 0

D3

1N5401

RLA

R3

330R5W

through the diode and current limiter R3.Diodes D5,6 remove spikes at the output;

VR1 varies resonator frequency to match theoutput load; and VR2 determines maximumpower for a given load.Sode-shinni N RumalaFederal University of TechnologyMinnaNiger StateNigeria

Lo

7

R.OROS

20W

) Tr,

1N5401

o Outputr. D5

1 N5404

D61N5404

Tro 2N3055Tr1 2SC1848

24V

Simple and efficientinverter provides abackup source forwaveform -tolerantequipment and maintainsa charge on the batterypack.

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Recognising the importance of good design, TTI willbe giving away one of these excellent instrumentsevery six months to the best circuit idea published inthe preceding period until further notice. This incentivewill be in addition to our £100 monthly star author'sfee, together with £25 for all other ideas published.

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630 ELECTRONICS WORLD + WIRELESS WORLD August 1995

CIRCUIT IDEAS

Video amplifier with sync stripper and dc restore

R1 k1K

VINO -1

Opt

To SyncSeparator

A

!Cie

This circuit transmits 220MHz, -3dBbandwidth, video signals while stripping

off the sync pulse and performing dcrestoration. It is configured for a typicalvideo cable driver application feeding adouble -terminated 75Q load. The HFA1103,IC3, is configured for a gain of +2 to ensureunity gain overall.

Stripping syncSync is often combined with one or moreof the red, green, and blue video signals incomponent video distribution amplifiers.This is done to decrease the number ofinput and output channels required. Also,as the video signals exit the switchingnetwork, the sync pulse must often beremoved.

Other applications benefiting from syncremoval are video digitising circuits andhdtv systems. Consider a typical 1V peak -to -peak rgb video signal with a -300mVsync pulse and +700mV video data. Bystripping off the unwanted sync pulse anddigitising only the active video, designerscan use the full dynamic range of the a -to -dconverter for the +700mV video data. Thisresults in a 30% increase in resolution usingthe same a -to -d converter.

The HFA1103 video op amp is speciallydesigned to perform sync stripping. Its openemitter n -p -n output forms an emitter -follower with the load resistor, and passesthe active video signal while virtuallyeliminating the negative sync pulse.

R1175

R1075

R86.8k

+5VDC

GEM

Residual sync of the HFA1103, defined asthe remainder of the original -300mV syncpulse, referenced to ground, is only 8mV atthe cable output.

A particular advantage of sync strippingwith the HFA1103 is the resultant larger -by 0.7V - output voltage swing, comparedto simply using a wideband video op -ampwith an external emitter follower.

Because the HFA1103 contains no activepull -down, output linearity degrades as thesignal approaches zero volts. To deal withthis a 6.81d2 pull up resistor, R8, and a 7552pull -down resistor, R10, on the output ensurea fixed positive voltage offset, in this case+50mV. This offset was arbitrarily chosenas a good compromise between linearitynear the dc level and minimum residualsync. Increasing Rs decreases residual sync,at the expense of linearity. Conversely,decreasing Rs decreases linearity error, butincreases residual sync.

Dc restorationAnother common video function is dcrestoration, used when ac coupled signalshave lost their dc reference and must have itreset line -by-line in order to retainbrightness information.

The circuit accomplishes dc restorationusing a CA5260 dual op amp (/Ci,b)coupled with a sample -and -hold circuitbased on the 74HC4053 switch /C2). Vin,consisting of the input video signal and a dcoffset (Vdc), is connected to the non -

Water leak detector/stop valveAs a means of avoiding total disaster in the presence of unlooked-forquantities of flood water, this very simple circuit gives early warning

and is extendable to turn the water off, given that an electrically operatedvalve is installed.

If water bridges the two SCR electrodes the device conducts and continuesto do so until reset, sounding the buzzer. The SCR drives relay 1, which inturn drives another relay capable of operating the solenoid water valve.Shin'ichiro AsaiResearch Centre of Denkikagaku Kogyo KKTokyo

75

One of the benfits ofthis circuit is that bystripping off the syncfrom a video signal anddigitising only theactive information,better use is made ofthe a -to -d converter'sresolution.

inverting input of the HFA1103 (IC3). TheHFA1103 is configured in a gain of +2,which would result in an output of2x17b,=(2xvideo+2xVdc), were it not for thedc -restore circuit.

Vb, also travels through half of the dualCA5260 amplifier to the sample -and -holdcircuit, where the 0.1pF capacitor (C1) is thehold capacitor. (The sample -and -holdcontrol is triggered by a back -porch pulsefrom a sync separator or by horizontal videoblanking) This dc signal is then amplifiedby a gain of +2 by the second op amp (ICIb).The gain of +2 is required because the dcoffset is input to the HFAI I03's invertinginput, which provides only a gain of -1.Thus 2xVdc is summed into the invertinginput of the HFAII03 and is subtractedfrom the output signal.

Because the output impedance of /Cib ishigh, and would affect the gain at the non -inverting input of the HFA1103, a 47µFcapacitor (C2) is used to provide an acground and to maintain good high -frequencygain accuracy.

A potentiometer (R3) is used prior to /Cibto null out any offset voltage contributed bythe dc -restore circuitry.

The resulting output is a 220MHz, dcrestored video signal in which the sync pulsehas been stripped to a residual level of nomore than 8mV.Jeff Lies, Chris Henningsen and Mike PressHarris SemiconductorMelbourne, USA

RESET SWITCH

ROWER y

SUPPL

DETECTOR-

If the washing machine leaks, this circuit will buzz andoperate an electrical stop valve.

SCREVY1

BUZZER Da

NORMAL

CLOSE

WATER OUT

NORMAL OPEN

RELAY2

NORMAL CLOSE

SOLENOID WATER VALVE

WATER IN

AC LINE

August1995 ELECTRONICS WORLD + WIRELESS WORLD 651

CIRCUIT IDEAS

R/2R analogue -to -digital converterThis 4 -bit a -to -d converter tracks the input and was

I originally meant to drive the mouse input of anAmiga. It is easily extended to eight bits or more.

Under the control of the op -amp, which drives the`direction' pin, the 191 up/down counter counts until theR/2R ladder output on the non -inverting op -amp inputequals the analogue input, at which point the counter staterepresents the digital equivalent of the input.

If another 191 is to be added, connect pin 13 of the newone to pin 4 of the existing counter, point A on the laddergoing to Q3 of the new one.John HenningsenCopenhagenDenmark

Analog input

Up/down counter tracks analogue input to give a 4 -bit a -to -d converter,convertible to give more bits.

Process monitorAccepting an input of 0-5Vdc, thiscircuit monitors an industrial process

and provides out -of -limits alarms.Input goes to the two comparators,

which have their references set high andlow respectively and adjusted by R2 andR6. If the input reaches either of the tworeference voltages, one of the comparatoroutputs goes low and a led is illuminated,the low at either comparator outputcausing the buzzer driver to trigger theaudio alarm. In normal conditions, whilethe input stays between the two input

PROCESS SIGNAL

0

cd-vo

0-

RI1K

R2

RS10

R6

516100K

517SDK

d 51950K

R19100K

UlK

LM339

U1B

R35.1K

R7S. 1K

reference voltages, the buzzer driveroutput is low and the "normal" ledilluminated.

Input voltage is displayed by the digitalpanel meter, which is switchable to showthe set limits, the calibration method beingto set the inputs at half -scale and to adjustR17,19,21 to make the dpm indicate half -scale.P Bhanu Prasad and R S MahajanCentral Electronics EngineeringResearch InstitutePilani

DI3K HIGH

11

R41K

R968K

R1068K

V

D2LOW

Re1K

R111K

LM339

0S+11

R20100K

52150K

51239K

R131K

D3ir NORMAL

R141K

U1C

14

LM339

R155.1K

+15V

BUZZER

Simple processmonitor indicatesinput voltage on adpm and provides

both audio andvisual alarm

signals for normalworking and

when input limitsare exceeded.

Hf buffer withzero -offsetA high -frequency, low -impedance

ildrive to a fet switch uses an emitterfollower, the dc offset being removed byfeedback.

At switch -on, the transistor is off andthe integrator output ramps in a positivedirection, but slowly, given the 1pF and1MQ timing components. Feedback tothe transistor base turns it on, its emitterrising towards the OV on pin 3 of theintegrator. When settled, the integratoroutput is enough to maintain conductionin the transistor, its emitter being at OV,except for a possible slight offset causedby the input offset voltage of the op -amp. The LF351 has an adjustment toremove this offset.

With the components shown, thecircuit buffers frequencies up to 40MHz.G W VathUniversity of NatalDurban

With no offset to cause a pedestal in afollowing fet switch and no unity -gain op -amp buffer, this clamped emitter followerbuffers 40MHz signals.

0.1uF

INPUT

R.0102

0.1uP

+IN to 12V

1uF

111

220 WWI

1011

OUIPUT

o IVbp IN

652 ELECTRONICS WORLD + WIRELESS WORLD August 1995

CIRCUIT IDEAS

Cross -point switch controller stores inputCross -point switch AD75019 fromAnalog Devices keeps switching data in

a shift register formed from dynamicmemory and requires input to be at aminimum 20kb/s. This circuit idea allowsthe device to be used in the presence ofinterrupts.

A main processor uses a PIC 16C84 as alocal controller, providing 36 bytes for 256bits to control the 256 switches in the arrayand 4byte extra for other purposes. Either aserial or parallel interface to the mainprocessor is possible; in this case, an 8 -bitparallel port was used for speed. An on-board 64 -byte eeprom will hold two sets ofswitch data for frequently usedconfigurations.

Data to the AD75019 is clocked seriallyinto a 256 -bit register, as Sin goes high, andcontrol starts with the Y15/X15 cross point,going down to Y15/X0, proceeding to Y14and finishing with Y0/X0. Data is latchedinto the device as PCK is pulsed low, whereit remains while power is applied.

From the main processor, data is four bitsfor the X address, four for Y, one to indicaterequired switch status and four for thecommand.

We implemented six commands:RESET to clear the ram image and update

the cross -point switch to all open;

SETSW to set the ram image for switchX,Y open or closed and then to update thecross -point;

SAVE -A saves the current ram image toeeprom area A;

RECALL -A recalls the ram image andupdates the cross point;

SAVE -B saves the current ram image toeeprom area B;

RECALL -B recalls ram image and updatesthe cross point.At an 8MHz clock rate, update takes 1.2msMichael J V WatsonBasingstokeHampshire

31211

10987

RB7 CKINCKOUT

MCLR

RA7XP18C84

RBO

RAO

8MHz

Vcc

3

31

3814

18

PIC used as a local controller for theAD75019 cross -point switch allowscontrol by a main processor which isunable to comply with the minimum20kb/s transfer rate.

44

+12-12

4

YO

AD75019

Y15

SINSCKPCKSOUT

VDDVSS

XO

X153

Single -wire, duplex communications linkThis two-way link could hardly be

I simpler. It carries bi-directionalsignal simultaneously, as in a telephonelink, the household earth being used forthe return path.

Channel A 10k 33k -= 9V

100nInput Bo

Conflict is avoided by making channel 9V 100k

BC327A drive the voltage source and channel100n

B the current source.Long wire

100n

o Output AInput A oAndrew M WilkesWokingham BC327 100k

BerkshireOutput

100n

Very simple circuit providessimultaneous two-way communication,using one wire. If noise is a problem,coaxial cable will improve performance.

100k 10k

Channel B

August 1995 ELECTRONICS WORLD + WIRELESS WORLD 653

CIRCUIT IDEAS

Video image inserterX1 4MHz

1/4 IC1

680R

101

Horizontalsync. pulse

-Ur °

Verticalsync. pulse

1/6 IC2 1/6 IC2> >680R

E1/2 1C8

1/6 IC2

IC1 74LS00

IC2 74LSO4IC3, IC4 74LS393IC5 2716IC6, IC7 7495IC8 74LS20

Synchronised with a videosignal, this circuit inserts auser -definable image in thepicture at a user -definablepoint.

1/2 IC8

Using an eprom, this circuit inserts amessage at a user -definable point on the

screen. Oscillator /C1,2 provides 4MHzpulses outside the horizontal sync pulse.These pulses clock counter IC3 and registers/C6,7. Write and shift signals for the registersare provided by parts of /C2,3,8.

Adderss-selection for the eprom is carried

+5V

14

1/6 IC2

8C Vcc

2R IC3 C

3 01

13 AO12

4Q2 01

11 7 DoAl

5Q3 Q2

0 6IC5

A26 9 5

ID2

A37

GND4 A4

14

+5V

1 C V2

IC4 C3

3 4112

4Q2 01

11

503 a2

10 I 2A6

041 A7

9

A10

CS

7GND 23

+5V

4k7

2

4k7

19

18

20PGM

CE GND

+5V

9

10 3

4

13 5

4

6

7

+5V

14

13DI

IC6

Ve,

0

D11

12

11D2

D,

2

310

V C29

8GND C1

15 3

16 4

5

6

+5V

24 T2

7

Di1C7

Voc

0, 0

Di

V

GND

2

3

C2

1/6 IC2

out by /C3,4. Via address lines A0_4, the romcan store 32x8 horizontal points and 16 linesvertically via A5.8. Address bit A9,10 can beused to select one of four pictures.

Pins 3-6 of counter IC4, driving part of/C8, are used to determine the position of thepicture on the screen. Inserting invertersbetween these ICs exchanges the position of

Single op -amp full -wave rectifierMost full -wave rectifiers using op -amps need two amplifiers; this one

uses only one.On positive half -cycles, the diode

conducts and the circuit becomes a voltagefollower, and on negative half -cycles aunity -gain inverting amplifier, so that theoutput is about the same in both halves.

22k

D

22k

Since, however, the diode is not in thefeedback loop, its forward voltage drop isnot reduced and must be cancelled by the0.7V.Uday S TandiRaichurKarnatakaIndia

10k -10V

Vo

This full -wave rectifier is unusual in its use of a single op -amp, paying theprice for simplicity by its need for a bias voltage.

+5V

14

13

12

11

10

9

8

/4 IC7n

1k0Video

1N4448 out

the picture.Output of the circuit connects to the video

input. The horizontal and vertical syncpulses must be at ttl levels.Vasily FyodorovLeo TolstoyRussia

Subtracting currentswhen it is simpler to regard signals ascurrents, rather than voltages, in

signal processing, two current conveyors canbe used to produce the difference function.

Input /A is inverted in IC1 and added to 18at the X input of IC2 to give /B-/A, theoutput then being -(/B-/A) or /A-/B. Abonus is the comparatively wide bandwidthof current conveyors.L SzymanskiStamford Lincolnshire

If the signal is to behandled as a current,this circuit provides thedifference function at awider bandwidth thanthe op -amp variety.

/OUT

654 ELECTRONICS WORLD + WIRELESS WORLD August 1995

MIXED -MODE SIMULATION.THE POWER OF VERSION 4.

Analog, Digital &Mixed CircuitsElectronics Workbench®Version 4 is a fully integratedschematic capture, simulatorand graphical waveformgenerator. It is simple tomix analog and digital partsin any combination.

Design and VerifyCircuits... Fast!Electronics Workbench'ssimple, direct interfacehelps you build circuitsin a fraction of the time.Try 'what if scenarios andfine tune your designspainlessly.

Electronicsorkbench

The electronicslab in a computer -

More PowerSimi iate bigger and morecomplex circuits. Faster.On average, ElectronicsWorkbench Version 4 ismore than 5 times fasterthan Version 3.

More PartsMultiple parts binscontain over twice thecomponents ofVersion 3.

More ModelsOver 350 real world analogand digital models areinduded free withElectronics Workbench.And, if you need more, anadditional 2,000 modelsare available.

Incredibly Powerful. Incredibly Affordable.If you need mixed -mode power at a price youcan afford, take a look at this simulator andgraphical waveform generator that mixes analogand digital with ease.

Firth JJJJ No

Chwilloanias

GROUND

TINE BABE TRIGGER19 EDGE R '

,4 1.08 7,,,, LEVEL 10.. 18,1. 01/8 8 O El,

CHANNEL A CHANNEL 8

Y P08 i 140 Y P08 i Em A8 /E1., P

True mixed -mode simulation: Simultaneous AM transmission,digitization and pulse -code modulation of a signal.

With over 20,000 users world-wide, ElectronicsWorkbench has already been tried, tested and acceptedas an invaluable tool to design and verify analog anddigital circuits. With Version 4 true mixed -modesimulation is now a reality with incredible simplicity.

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Australia: 2-519-3933 Brazil: 11-453-5588 Cyptus: 2-62-1068 Derunark: 33-25-0017 Finland: 0-297-5033 France: 14-908-9000 Germany: 711-62-7740 Greece: 1-524-9981

Hungary: 1-215-0082 India: 11-544-1343 Israel: 3-647-5613 Italy: 11-437-5549 *Japan: 3-3382-3136* Malaysia: 603-7778945 Mexico: 5-396-3075 Netherlands: 18-031-7666

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VISAIN=ter:Cai3

INTERACTIVE

111111101111121ZEZIERII Off

PC ENGINEERING

AF analysisvia the pc

A relatively low-costvirtual instrumentoriginally intendedfor loudspeakeranalysis has nowexpanded into acomprehensive Ifmeasurement suite.Richard Lee has beenlooking at how thisanalyser - Clio -performs.

With virtual instruments - i.e. instru-mentation simulated on a pc screen- signal generation and analysis are

carried out by hardware, under the control ofuser-friendly software. So far, virtual instru-mentation has been expensive, but low-costsystems are starting to appear.

Clio - from Italian recording studio equip-ment manufacturer Audiomatica - offers sev-eral virtual audio instruments in one, at a basicprice of £799. It was originally designed forloudspeaker system engineers, but hasexpanded into a suite of instruments with awide number of other uses involving audiofrequencies.

Although Clio's software will not run underWindows, it does have a mouse controlledgraphical user interface. Combined with a lap-top, it forms a portable measuring systemneeding only a power amplifier for on siteloudspeaker or room acoustics measurements.No additional amplifier is required forimpedance measurements, or testing electricalor electronic circuits.

Virtual instruments included are a swept -

MLS_14.SIGPINK13.SIGPULSENEG.SIGPULSEPOS.SIGSENO.SIGSIN1000.SIGWHITE.SIGWHITE13.SIGWHITE9.SIGOURST1K.SIG

E-1131111

GENERATOR & LEVEL METER

Out -

90.1

00000-210 dBm

a dEo)

,

63

Nuts,'(luta:lanes'

LUNN Milli

3.1111a;a1

Fig. 1. The generator/voltmeter front panel window allows input/outputconditions to be set and then dropped down over most instrument

displays. The Clio board has two inputs and two outputs, but currentsoftware commons both outputs but uses only one input. Being able to use

both sets independently would simplify stereo testing.

sine frequency response analyser,10Hz-20kHz storage oscilloscope with 20kHzbandwidth and a fast Fourier transform, FFT,analyser. Spectrum analysis to 20kHz is pos-sible, and the system can measure total har-monic distortion, ac millivolts, Vrms, dBV,dBm and dB relative, fast and slow reading.Sensitivity is up to +30dBV and down to-40dBV. An LC meter is also built in.

The signal generator is programmable andcomes with a library of signals including sinewaves, with a claimed thd of 0.015%, pinknoise, white noise, square waves and pulsedsine waves, Fig. 1.

For acoustic measurements, the Clio boardincludes a preamp with switchable dc phan-tom powering and microphone sensitivity cal-ibration. The optional microphone plugsstraight into the board's input. Instrumentsdedicated to sound measurements include athird -octave real-time analyser, rta, with inter-nal pink noise source and A -weighted soundlevel meter, Fig. 2. Also for acoustics engi-neers is the RT 60 analyser, which carries outroom reverberation time measurements.

Maximum length sequence, mis, time -domain measurement and FFT analysis allowsloudspeaker frequency/phase responses to bemeasured in -situ. This avoids the need for a

656 ELECTRONICS WORLD + WIRELESS WORLD August 1995

PC ENGINEERING

RequirementsPC compatible with an 8/16bit ISA slot.286 processor or higherEga display640KB of ram or more.

two -channel FFT analyser because the mis is arecognised signal. Reflections from surfacescan be removed by post -measurement trunca-tion of the time -domain signal, Fig. 3.

Additionally, mis allows 3D sound ampli-tude/frequency versus time 'waterfall' plots tobe generated, and energy time curves whichshow how sound decays over time, Fig. 4.

Clio uses two direct memory access chan-nels, dma, one for signal generation and theother for data acquisition. The board alsomakes use of three i/o lines. This might berestrictive if your pc already has a few occu-pied slots. Clio uses the same dma and i/o asDRALABS maximum length sequence signalanalyser, so if your pc will run mlssa it shouldrun Clio.

The mis measuring system samples at 51.2,12.8 and 3.2kHz. Set to 51.2kHz for a 20kHzbandwidth, it is very fast and displays do notautoscale irritatingly. If set to 3.2kHz sam-pling frequency, it will measure down to0.125Hz.

Filing dataClio will export frequency responses to harddisk for use with cad loudspeaker design pack-ages such as Leap and Calsod. Ascii time -domain files cannot be exported, butAudiomatica can supply a Pascal structuredescribing the file format needed to do this.

Swept sine -wave measurements comprisetone -bursts at discrete frequencies, with inter-polation to create smooth curves, Fig. 5.Connecting input to output produced an over-all response flatness within 0.5dB. Frequencyresponse files may be loaded as a referenceand new measurements displayed as a differ-ence curve. This is ideal for comparing pro-duction items to standards. Files can also beimported from outside the sine wave environ-ment, displayed and post processed. Curvesfor instance, can be averaged.

Another facility takes the measured in -boxsound pressure level, spl, and simulates anoutside -of -the box spl. Text files can be editedto splice two separate sets of readings, forexample mis mid -to -high response and near -field low -frequency response, to give a com-plete anechoic frequency response.

Theile/Small loudspeaker characterisation isautomatic, very quick and simple. Theanalyser hunts for the impedance curve reso-nance peak and half points to an accuracy of1/24 octave, a worst case frequency error of2.9%. Accuracy of Theile/Small parameterswas found to be about as good as you can getwithout measuring the BL factor directly.

Hardware in the Clio package includes mea-suring cables and a half-length pc card holding

Fig. 4. This waterfall plot was taken in room.These plots can help pinpoint sources ofcolourations in loudspeakers caused by

energy storage and reflections.

et_ 1 0 -- Tti1 RD OCTAVE" ANAL 'y'S 1 S

REFERENCE

It s Ir Il

Fig. 2. Clio rta plot. The internal pseudo -random pink noise is very accurately distributed infrequency. Because its energy content is known, the analyser doesn't have to wait as long toaverage at ow frequencies - thus making it faster than a normal real time analyser usingordinary random pink noise

Lu

1

a [

1oo

so

so

70

60,20 30 100 200 300 1K 2K IK 10K 231

sP

1

V

eg

36

108

180

Fig. 3. Clio mis loudspeaker measurement taken in an anechoic room but truncated to 100ms.As with any truncated measurement, this results in losing low -frequency information, (thelonger the sample time, Ts, the better the low -frequency performance), but it does allow theroom to be taken out of the measurement frame completely. Indeed, a truncated responseexcluding reflections is more anechoic down to the Os frequency (100Hz in this case) thanthe usual swept measurement in even the best chambers. In room one could expect anechoicaccuracy down to 250Hz or so. Setting the time 'window' is particularly easy and the displayshows the 1/T, frequency.

August 1995 ELECTRONICS WORLD + WIRELESS WORLD 657

PC ENGINEERING

Fig. 5. Loudspeaker sine -wave responsemeasured with Clio in an anechoic room dB

(compare to Fig. 3 mls plot taken with sameloudspeaker). The previous ten curves can be

stored and shown as overlays, the oldest beingerased for each new acquisition.

signal processing circuits and 16 -bit sigma -delta a -to -d and d -to -a converters for per-forming analogue i/o.

Listening inAt an extra £150, the optional 8mm diametermicrophone is an electret capsule. It comeswith no curve but it does have a specificationwindow. Tested in Celestion's anechoic roomwith a known loudspeaker against a B&Kmicrophone, the frequency response wasfound to be flat except for a slight rise at highfrequencies of about +1dB from 5kHz-15kHz.Sensitivity as measured via a B&K calibratorwas probably within 0.5dB. This is typical ofa good, electret insert.

The storage oscilloscope worked well, withexcellent triggering. At some settings, wherethe screen is frequently updated, mouse oper-ation became jerky due to the fact that thepointer cannot move while the screen is updat-ing. This is easily overcome by using hot -keysto operate the buttons.

Testing the FFT spectrum analyser with theinternal sine oscillator at 1kHz, Clio's thdmeter measured down to a minimum readingof 0.01% - slightly better than the claimed0.015% thd of the generator alone, Fig. 6. Allone can be certain of from these tests is thatthe thd and 1-1,1 analyser easily meet theirrespective specifications. With intelligent useof input sensitivity and 14F1 scaling, Clio pro-vides a handy check on distortion spectra andnoise in electronic circuits.

OverviewClio is an easy to operate, fast, user-friendlypackage, combining several instrumentsgeared to acoustic and electronic testing ataudio frequencies. From a speaker engineer'sviewpoint, it is ideal for use as a professionaldesign and development tool, and could evenfmd its way from the laboratory to the factoryfloor as an inexpensive and easy to operateon-line tester.

Acoustics and speaker installation engineerswill find the real-time spectrum and RT60analysers invaluable.

Electronic engineers should fmd the elec-tronics measurements equally useful, espe-cially considering that here is a complete workbench all in one package - and well suited tocompanies on a tight budget.

Fig. 6. Distortion spectra of Clio generator looped into inputand set at -3dBm (-5.25dBV), showing second and third

harmonic both at 83dB down on the fundamental. The thdmeter reads 0.01%. Drop the input lower and the thd

reading rises. Level can rise to +1.5dBm (-0.77dBV) withchange to spectra but thd reading stays at 0.01%. Distortionspectra could be bettered by 10dB or so by using an externallow -distortion oscillator carefully set in level and frequency,

with windowing, indicating that most distortion is from theinternal sine generator. Though clearly meeting its

specification, with 16 bits available, distortion could possiblybe bettered. Muting the generator (input set to -40dBV)

produced a noise floor of around -105dBV - not at all bad

110

spl

100

90

80

70

60

Clicr

10 Frequency 200 2K Hz

180

Deg

108

36

36

20K

108

180

CLIO SpecificationsGeneratorType:Frequency range:Frequency resolution:Output Impedance:Max. output level (sine):Attenuation:Thd+noise (sine)AnalyserType:Input range:Input impedance:Phantom power:MiscellaneousSample frequency:Card type:Card connections:Adaptor cables:Microphone Mic-01 (Mic--02)Type:Accuracy:

Max. levelDimensions:MIC-01:MIC-02:Accessories:Preamp 3381/AType:

A -weighting filter:Level range:Attenuator:Accessories:

Two channels 16 bit sigma -delta d -to -a converter1 Hz -22 kHz (+0/-1dB)0.01Hz1005212dBm (3.1V rms)64x1.5dB steps plus mute0.015%

2 -channel 16bit sigma -delta a -to -d converter+30 to -40dBV64k) (2.7kS2 mic. input)8.2V

51.2kHz, 12.8kHz, 3.2kHz14cm 8bit pc slot cardfour RCA plugsfor speaker, LC tester

Condenser electret±1 dB 20Hz-1 OkHz,±2dB 10Hz-20kHz(±2dB 10Hz-20kHz direct field)120dB spl

8mm dia. 25cm longAs MIC-01 but 12cm long3m cable, stand adaptor

Rechargeable battery,individually calibrated forMIC-01 or MIC-02IEC651 - Type 170-120dB spl10dB step, 0.1dB accuracyAC mains adaptor

658 ELECTRONICS WORLD + WIRELESS WORLD August 1995

POWER SUPPLIES

Switc hersfor the masses

Highly -integratedchips and easy -to -use software bringdesigning aswitch -mode psuwithin the reach ofall electronicsengineers - as AlKelsch and WandaGarrett show.

*Al Kelsch Wanda Garrett arewith National SemiconductorCorp. in Santa Clara, CA

INV VA

NI

OSC EB

,CL CB

-CL LM3524 GA

AT EA

CT SD

GND COMP

In many applications, on -board dc -dc conversion -sometimes called point -of -load conversion - isdesirable and practical. National Semiconductor's

Simple Switcher power converter family conceptwas created to occupy a position between complex,design -intensive circuitry of a fully -custom switch-ing converter, and the simplicity of plug-in powerconversion modules.

Advantages are lower cost, compared to modules,and reduced design expense relative to discrete solu-tions.

This article reviews the principles and viewpointwhich led to the the Simple Switcher converter fam-ily, and highlights ease -of -use aspects of the con-cept.

Henry David Thoreau, the iconoclastic Americanwriter of the nineteenth century, stated the case forsimplicity in 1846 while searching for truth atWalden Pond:

Design equations

Vo

RF= 5k ( 1)

2.5

Rd-200mV

/0 (max)

1F.= -R.

2.5 Vo( V3)

VinFosc

vn- v.) v. T2co -

8 Volii,L1GND

Fig. 1. Even though early switch -mode ICs integrated a fair number of controlfunctions, power supplies incorporating them were still complex in design andcomponent hungry.

Table I. DC converters compared.*

Parameter

# of componentsDesign timeParts inventoryParts priceLabourEfficiencyOfferings

LM352-based Module1A, 5V converterlA, 5V converter16 1

months minuteshigh lowest$2.10 $9.00-$13.00high lowest80% 65%one device, broad linemany designs

*source National Semiconductor.

Simple switcherdesign5<I hourlow$3.50medium80%broad line

"Simplicity, simplicity, simplicity!, I say, let youraffairs be as two or three, and not a hundred or athousand."

William of Occam, the Medieval English philoso-pher, dealt with the subject of simplicity in the meta-physical realm before expiring in 1349. He is bestremembered for what has become known asOccam's Razor. William's famous razor says that ifmore than one theory is advanced to explain thesame set of facts, the theory that is overall the sim-plest and needs the fewest assumptions is the trueone.

Occam's Razor applies to integrated circuits, too.If two integrated circuits do basically the same job,the one that is overall the simpler and requires theleast design time and external aids is the superiorproduct.

In the not -too -distant past, it was common todesign a voltage regulator as a part of designing theend equipment. Whether it was a simple zener dioderegulator or a real series voltage regulator, on -boardvoltage stability was considered to be a part ofequipment design. This all changed with the adventof the first three -terminal linear regulator - theLM109.

From the time these devices were available, equip-ment designers everywhere ceased designing theregulator part of their circuits from the transistorlevel. They found themselves free to spend more oftheir engineering energy on the performance of theequipment or chassis itself.

Prior to 1978, the task of efficiently converting adc voltage to another dc voltage using switchingtechniques was done with discrete transistors, diodesand passive components. At that time, there weretwo possibilities open to electronic equipmentdesigners that had made the decision to enjoy thebenefits of switchers - namely smaller size andincreased efficiency. They either made use of an in-house power supply design capability, or opted foroff -the -shelf dc/dc converters.

The first integrated circuit for switching powerconversion - the SG3524 - was introduced bySilicon General in 1978. This type of design wasvery complex, compared to a linear voltage -con-version solution, Fig. 1. However, it did represent anadvance compared to bottom -up discrete switchingdesigns.

At the same time, an industry for solving the com-plexity problem associated with switchers wasemerging. The on -board conversion of one voltageto another, such as +24V to +5V, could be accom-

August 1995 ELECTRONICS WORLD + WIRELESS WORLD 659

POWER SUPPLIES

Fig. 2. Allowing designers to reap the benefits of switch -mode powersupplies without incurring all of the associated design time and costpenalties, standard modules have become a viable alternative todiscrete circuitry.

plished in minutes by the decision to purchase a self-contained dc -to -dc converter in the form of a potted module or hybrid assembly, Fig. 2.

Opposite ends of the on -board dc/dc converter spectrum in the early1980s were represented by the self-contained power component on theone hand, and the LM3524-based IC design on the other. These arecompared in the left-hand columns of Table 1.

Thoreau's simplicity of viewpoint, William's logical efficiency, andthe need for a counterpart to the three -terminal linear regulator cametogether in 1985 to spark an idea for a new class of on -board dc/dc con-verters. This five -terminal integrated switching converter becameknown at its introduction as the Simple Switcher. This new class ofconverter took up a position between the one component $10.00 solu-tion and the 16 -component $2.25 solution, with a five -component $3.50solution. This intermediate market approach is compared to the com-peting solutions in the fourth column of Table 1.

There were four elements in the creation of an intermediate positionof switching converters that appealed to non -expert digital and micro-processor equipment designer; the sum of these became the 'simple'family approach. First, the 16 component dc/dc converter had to bereduced to the absolute minimum number of components possible inthe context of an IC solution. Second, the procuring of the non -IC com-ponents had to be straightforward, foolproof, and well -supported.Thirdly, any design that was required had to be ultra -simple and had tobe supported with friendly software. Finally, the overall convener per-formance had to be guaranteed with system -level specifications.

Reduced component countTable 2 summarises the system decisions that led to the paucity ofexternal components seen in the Simple Switcher type converter.

Bringing the lA transistor on board eliminated three external com-ponents. On -board trimming to standard voltages such as 3.3V, 5V, and12V eliminates two components. Fixing the frequency at a standardvalue of 52kHz eliminates a capacitor. Fixing the current limit inter-nally and offering a range of current values, such as 0.5A, 1A, and 3Aeliminated a current -sense resistor. Eliminating a Bode compensatingnetwork in favour of on -board compensation reduces the count by twomore. Removing a resistive level setting network in the feedback path

From To

eliminated two more components. In this manner, a sixteen -componentdesign becomes a five -component converter, Fig. 3.

The five -lead minimum design converter uses two electrolytic capac-itors, one inductor, one Schottky diode and one integrated circuit. Thedesign value of the on -off switch - something not actually offered inthe 16 -component design - dictated its inclusion as the fifth active pin

Readily available componentsThe four non -IC external components that remained also had to be rel-atively free of the fear factor when viewed by non -expert designers,with regard to the design and the actual procuring of parts.

Aluminum electrolytic capacitors were specified for the input andoutput capacitors. These are readily available and popular. TheSchottky is slightly more challenging, but these devices are likewisereadily available and easily specified.

By far the most important challenge in guaranteeing ease of use wasdesigning and procuring the power inductor or transformer that is at theheart of switching converters.

Here the fear factor plays a dominant role. Gauss, B -H curves, mag-netising inductance, core materials, custom magnetics - all of thesewords and the practices associated with them have the potential toaffect design time and difficulty level.

To remedy this, we took several actions. First, the design procedurehad to be simple and unambiguous; second, there had to be pre -speci-fied, industry standard inductors, suitable to the converter application.Third, the standard inductors had to be supported by magnetics vendorsthat could offer stocked values and instant support.

Calculating an inductance value is just the start of the problem. Givensimple assumptions, the calculation is straightforward. The challengewas to reduce the solution space for all combinations of input/outputvoltages and load currents, to a small number of well-defined inductors.

Figure 4 illustrates the type of mapping needed to fully define con-verter solution space in terms that are meaningful to inductor manu-facturers. The vertical axis on the graph turns out to be calibratable inE -T, or the volt -second product needed for full specification of theinductor in magnetic terms.

Knowing maximum load current, and E -T values as dictated by inputand output voltages, the solution space is divided up into standardinductance regions. These are then specified in inductor terms. Thislead to a well -specified series of inductors that covered the convertersolution space.

With this set of basic inductor specifications, we then approachedseveral magnetics manufacturers that had the capability and interest to

Table 2. Comparison of external components required fortypical 1A step-down switching regulator design.

Function

1A o/p currentVout setting

foscCurrent limitCompensationVref levelNet componentreduction

LM3524-baseddesignTransistor, 2 Rs2 Rs

1C1R1 R, 1 C2 Rs

0

Simple SwitcherdesignOn -board >1.3A transistorInternally -set, fixed outputvoltage optionsInternal, 52kHzInternal, fixed (several options)internalInternal

11

Fig. 3. Freely available design software and a switch -mode designed for ease ofuse and low component count should make the switch -mode technologyaccessible to far larger variety of circuit designers.

FB

+7 to 40V +VILM2575T-5.0 330 pH

OUT(

+5VInputCSTO 0

ON/OFF Gnd (A) 330 pFD1100 pF 1N5819 Load

_L.

660 ELECTRONICS WORLD + WIRELESS WORLD August 1995

POWER SUPPLIES

Customising the designAlthough a successful power supply design can be generated by using the default orstandard options in the program, there are opportunities for customisation.Alterations can be made to a design that has been previously saved, or during thedesign of a new regulator.

It is a good idea to have a 'baseline' design to start from, using the default choic-es for components. Modifying the inductor selection For the buck and boost con-verters, the standard inductor selection is based on an assumption that the inductorripple current will be 30% of the average inductor current at fill load. This gives con-tinuous operation, striking a balance between inductor size and output power capa-bility.

Output power is for a given regulator is limited by the average inductor current;inductor ripple current is determined by the inductor value, the input and outputvoltages, and the switching frequency; the sum of the average and ripple inductorcurrents is limited by the regulator IC current limit threshold, as the IC must conductthis peak current when its switch is on.

For low output power applications, the inductor can afford to have a greater rip-ple current since its average current is low. This allows its value to be lower than thenormal standard value that would be chosen automatically. As the inductor selec-tion is made immediately after the input parameters are entered, you can take theoption to not take the standard default inductor. The user can then customise theinductor selection by either entering the desired inductor ripple current or a desiredinductor value, and the remaining components will be chosen accordingly.

If the choice of inductor value or current causes the peak current to exceed thelimit available from the regulator IC, an error message instructs the user to makeanother choice between lower current or greater inductance.

When the choice is accepted, the user should check the peak switch current,shown in the middle column on -screen, to see how close it is to the current limit ofthe regulator IC chosen for the final circuit.

The output capacitor value and ESR can be modified after the preliminary calcu-lations and component choices have been made. Recommended ranges for thosevalues are given in the 'limit values' column. These ranges assure the stability of theregulator, and a reasonable limit for output ripple voltages. Modifying databasesused or component selection 'Switchers Made Simple' selects the recommendedcomponents from a set of databases associated with the program. These are Asciifiles, containing component values, characteristics and ratings, and vendors' partnumbers for components including the output capacitors, inductors, and diodes. Theuser can extend the databases to include other components, if they are specified foruse in switching regulators.

The database format is shown in a header for each file. In addition, the header alsocontains the strategy for component selection, for example which parameter islooked for first.

Create new or recall old design? (N/O)

This program supports four types of power supplies.

Boost:Used to step up the input voltage, e.g. Vin = 5V, Vout = 12V

Flyback:Used for multiple output voltages, positive or negative, with thepossibility of isolation. Both step up and step down are possible.High output voltages are achievable. A transformer is neededinstead of an inductor.E.g. Vin = 5V, Vout1 = 15V, Vout2 = -15V, or

Vin = 5V, Vout1 = 15V, Vout2 = 12V, orVin = 20V, Vout = 100V

Buck: Used for stepping down a voltage, e.g. Vin = 10V, Vout = 5V

Buck -Boost:Used for generating a negative voltage from a positive onewithout isolation, e.g. Vin = 5V, Vout = -5V

For HELP, press <F1> now.

Fig. 5. Sample help screen from the Switchers Made Simple designpackage.

6040

25

20

15

12

10

9

8

7

H1500

0

Lseo

70

20

50

.2 .3 .4 .5 .6 .7 .8 .9 1.0

MAXIMUM LOAD CURRENT (A)

Fig. 4. With the Simple Switcher concept, choosingan inductor is simplified by focussing on a range ofreadily available standard parts.

Standard inductors and sources.

Inductor Inductor AIE Pulse Eng. Rencocode valueL150 150pH 415-0953 PE53113 RL1954L220 220p H 415-0922 PE52626 RL1953L330 3301j H 415-0926 PE52627 RL1952

support this effort at standardisation. Thislevel of interdependence had not been attempt-ed before between the semiconductor and themagnetics industry.

When choosing inductor suppliers, weattempted to offer a range of styles and pricesfrom the stick inductor, to the popular toroids,to low -EMI pot cores. Once on -board, themagnetics industry has done a fine job of sup-porting first-time converter designers. Thisincluded no custom charges - or any talk ofcharges - stocking of all values, overnightresponse and attractive prices.

Perform thermal check? (Y/N)

Input parametersVinmin = 8.00 VVinmax = 30.00 VTamax = 40.00 CTamin = 0.00 CVout = 5.00 VIlmax = 0.30 ADiode = Schottky

Limit valuesL > 382.00 pHMode = ContinuousIswpeak = 0.40 ACout > 330.00 pFESRmax < 0.15 OhmESRmin > 75.17 mOhmCin > 22.00 pFVripple = 50.34 mV

Component valuesCout = 330.00 pFCin = 22.00 pFL= 470.00 pFD1 = 1.00 A

Crossover 7.43 kHzPhase margin 31.15 Deg

Fig. 6. Regulator design summary screen from the Switchers Made Simpledesign tool.

August 1995 ELECTRONICS WORLD + WIRELESS WORLD 661

POWER SUPPLIES

Guaranteed system specificationsAnother key aspect of creating successful dc/dc converter designsinvolved the use of system specifications. Hence, the ICs in the SimpleSwitcher family include guaranteed system specifications when usedwith the external components recommended by NS. The basic param-eter guaranteed for the overall converter is liciut - the output voltage. Asa system specification, Vout is guaranteed over a full range of load, line,and temperature variations.

Ease of designTo convince first-time designers and analogue non -experts that a real-isable dc -to -dc converter could be designed efficiently, a simple step-by-step procedure was needed. Also, the design procedure had to beexecutable either manually, or using a pc with the aid of an expert sys-tem provided by National.

For the manual designs we created a one page, three step procedurefor the selection of the capacitors, the catch diode, and the inductor.Sources for each of these were provided in the data sheets, togetherwith the corresponding vendor part numbers.

The second support method, aimed specifically at terminal -baseddesigners, was the software called `Switchers Made Simple.' This is asoftware tool, designed from the viewpoint of the user, that createsdc/dc converter designs using the Simple Switcher integrated circuitsand standard external components. The software runs under dos and isfree so sharing is encouraged.

The following section explains the use of the `Switchers MadeSimple' software in designing onboard dc/dc power converters. Thecurrent version is 3.3, and supports all available Simple Switcher prod-ucts and their voltage options - including 3.3V for the step-down andinverting regulators.

Vin>8V<30V

J Vin(n., 131

Output

Li

470pH Vout5.00V0.300A

Cin 522.0pF

LM2574N-5 FeedbackV1 1

2.4 3

12round ..12N/OFF

CoutT330pF

7.7

Fig. 7. Switch -mode power supply example incorporating the LM2574Simple Switcher demonstrates how few external components thedevice needs.

Fig. 8. Parts list for design example, Fig. 7.

BUCK CONVERTER

Circuit Parameters

Vinmin : 8.00 VVinmnx : 30.00 VTamax : 40.00 CTamin : 0.00 CVout : 5.00 VIlmax : 0.30Diode : Schottky

Misc calculated information

Mode : ContinuousPeak switch current : 0.40 AESRmax : 0.15 OhmsESRmIn : 75.17 mOhmsVripple : 50.34 mVCrossover Freq : 7.43 kHzPhase margin : 31.15 Deg

Component List

Cout : 330.00 pF

ESR : 0.10 OhmVmax : 20.00 V

678D337M020CG4D : SpragueCin : 22.00 pF

Vmax : 43.00 VL : 470.00 pH

415-0927 : AIEPE -5311C : PulseRL1951 : Renco

D1 : 1.00 AVmax : 40.00 V1N5819 : MotorolaMBR140P : Motorola11D004 :

U1 :

L2574N-5 : NationalSemiconductor

Beginning the designThe only information a novice power supply designer may have onwhich to base a design may be the system parameters - input voltagerange, output voltage desired, load current range, and ambient operat-ing temperature range. This is the way a linear regulator or module isspecified. This is also the way a Simple Switcher design is started.

On the first screen of `Switchers Made Simple,' Fig. 5, following theintroductory screens, the user is prompted for regulator type from achoice of step-up, step-down, invert, or multiple -output. If, at this point,the user wants more information, a help file is available via the Fl key.

Once the regulator type is chosen, a screen appears on which the sys-tem parameters are entered. Pressing the 'end' key, after entering theparameters, begins the process of doing calculations and choosing com-ponents for the circuit.

Component selectionThe software asks the user if the standard inductor selection is to bemade, and if this is confirmed the software makes calculations for limitvalues. The results of these calculations are shown in the middle col-umn of the screen. They include values used to select the componentsused in the final circuit, such as minimum inductor value, peak switchcurrent, and values for the output capacitor and its equivalent seriesresistance, esr, range.

Recommended component values are then immediately shown in theright-hand column of the screen, and include all external componentsneeded in the design apart from the regulator IC. The user is then giventhe opportunity to modify the component values.

When the user is satisfied with the component choices, the frequen-cy response of the circuit is estimated, and a window displays the cir-cuit bandwidth, 'crossover', and its phase margin Fig. 6.

Thermal calculationsThe next step in the design is to determine how much - if any - heatsinking will be needed to keep the internal temperature of the regulatorIC within its ratings during its operation over the specified temperaturerange. The user is asked if thermal calculations are to be done. If so theuser is asked to choose the package type from a list of regulator ICpackages that fit the application.

If a dual -in -line or surface -mount package is chosen, the pc -boardcopper will be used for heat sinking, so the user is requested to enter thethickness and type of copper that will be used. The software calculatesthe minimum copper area required to provide any necessary heat sink-ing, and allows the user to enter the actual board area that will be used.Finally, the internal junction temperature of the IC and its thermal resis-tance are displayed in a window.

The design is now finished. The user is given an option to modify theinput parameters. If this option is not taken, the user may save the filefor further reference. The user can view the schematic on -screen Fig. 7,as well as the listing of calculation results and recommended circuitcomponents by part number, Fig. 8.

Both the schematic and parts list can be then printed, on either anEpson -compatible dot-matrix or an HP -compatible laser printer. As alast step, the user may return to the beginning of the program to doanother design, or end the program.

In most cases, the power supply design can be done in a matter of afew minutes, from specifying the circuit parameters all the way to thefinal schematic and parts list. This simplicity and speed of design hasmade the Simple Switchers the choice of many novices and power sup-ply designers alike. In addition, `Switchers Made Simple' offers expe-rienced power supply designers the flexibility to customise the design,as described in the panel.

SummaryThe 'Simple' approach to on -card dc/dc power conversion has taken upits market position between plug-in, pre -manufactured modules, andcomplex multi -component IC -based converters. Simple Switcher powerconverters provide a solution that has five or seven total componentsguarantees overall converter performance, and is well supported byreadily available components and design software.

662 ELECTRONICS WORLD + WIRELESS WORLD August 1995

STABILIZER 5

In any public address system where microphones and loudspeakers are inthe same vicinity, acoustic feedback (howlround) occurs if the amplificationexceeds a critical value. By shifting the audio spectrum fed to the speakersby a few Hertz, the tendency to howl at room resonance frequencies isdestroyed and increased gain is available before the onset of feedback.

* Broadcast Monitor Receiver 150kHz-30MHz * Advanced Active Aerial4kHz-30MHz * Stereo Variable Emphasis Limiter 3 * 10 -Outlet AudioDistribution Amplifier 4 * PPM10 In -vision PPM and chart recorder * TwinTwin PPM Rack and Box Units * PPM5 hybrid, PPM9 microprocessor andPPM8 IEC/DIN -50/+6dB drives and movements * Broadcast StereoCoders * Stereo Disc Amplifiers * Peak Deviation Meter for FM broadcasting

SURREY ELECTRONICS LTDThe Forge, Lucks Green, Cranleigh GU6 7BG

Telephone: 01483 275997 Fax: 276477

HEWLETT PACKARD HP71BAs easy to use as a calculator but a,powerful as a computer

A powerful set of basic functions,statements and operators - over 230 in all- many larger computers don't have a setof basic instructions in this complete.

Advanced statistics functions enablingcomputations on up to 15 independentvariables.

Recursive subprograms and user definedfunctions.

An advanced internal file system forstoring programs and data - the HP71 hascontinuous memory - when you turn thecomputer off it retains programs and data.

A keyboard that can be easily customisedfor your specific application.

HP -1L Interface pre -installed to create asystem that can print, plot, store, retrieveand display information. Control or readinstruments or speak to other computers,5000 bytes/sec. Built in ROM includes 46separate commands. Interface to HP -1L,HP -1B, RS232C, GPIO or series 80.Includes connection cables.

BARCODE READERSmart wand

- Automatically recognisesand decodes all major

bar-code standards.

These are second user systems ex DHSSare fully tested and working but have noprogramming (THAT IS UP TO YOU)HP71B £29.95Bar-code Reader £12.95AC Power Supply £4.95(Works from batteries normally)Keyboard Overlay £1.00(Limited quantities)Unknown Program -Memory Modules £3.00(Limited quantities)Complete kit of HP71B, Bar-code Readerand power supply £39.50(Prices include VAT -delivery £3.00)(Currently selling in USA for US$500)Allow 7 days for delivery

SPECIAL OFFERBuy 2 Kits For £59.00

Other products at give-away pricesNumeric keypad for 'AT' computer

£5 + £2 Carriage (Carriage FREE if ordered with above).

INTERCONNECTIONS LTDUnit 51, InShops, Wellington Centre, Aldershot, Hants Gull 5DB

Tel: (01252) 341900 Fax: (01293) 822786

( IR( LE NO. t 12 ON REPLY CARD

COMPONENTS FORGLOBAL POSITIONING

SYSTEMS tt:Fastest GPS ReceiverRapid time to first fix, NMEA modes andlow power consumption are standardfeatures of Rockwell's newMicroTracker LP. Other key featuresinclude direct differential inputs.

PCMCIA GPS ReceiverRockwell's astounding NavCard integrates aGPS receiver and a removable antenna intoa single PCMCIA card. Free Windowsapplication demo code is included on ,Lid

request.

41tiatmwori

GPS in 10 minutesRockwell development kits includeeverything you need to receive GPS signalsthe moment you open the box. Chooseeither MicroTracker LP or NavCardversions, all connectors and softwaresupplied.

Fry

199

71_ n AGreat a I ,p4Differential made easyThe NavStar XR5M - 12 is a 12 channel basestation receiver which outputs RTCM -SC104 differential corrections for input toremote GPS receivers such as Rockwell'sMicroTracker LP or NavCard. 144

7

Antennas in stockTDC stocks the widest range of GPSantennas for vehicle mounting, marine andairborne uses, as well as active andsurveying versions for specialistapplications. We supply all cables andconnectors too!

TDC is a franchised distributor for Rockwell, NavStar and Micropulse.

TELECOM DESIGN COMMUNICATIONS LTD

Telecom Design Communications,Connect House, Stroudley Road,Basingstoke, RG24 OUG.Tel: 01256 332800.Fax: 01256 332810.BBS: 01256 57900.

51 16. 16'5, 0 1.04'W: SU 653535'46531535

CIRCLE NO. 113 ON REPLY CARD

August 1995 ELECTRONICS WORLD+WIRELESS WORLD 663

NAVIGATION

Finding GPS

GPS chip sets are stilldifficult to obtain and

use, but there is now aversatile modular receiver

system priced under£400. Simon Taylor*

describes how thismodule is applied.

*Simon is an applications engineer with TDC

Much has been written about GlobalPositioning Systems - GPS - butuntil now there has been little scope

for experimentation with the technology.Many hand-held GPS devices are available,

but few of these have any output or controlinputs apart from the standard lcd and key-pad. If you wish to create a vehicle locationsystem for example, you will need to getposition information from the device over aserial port or similar.

This article describes the construction of aGPS receiver which provides its informationover a standard serial RS232 port suitable forinput into a pc or other processors, such as amicrocontroller.

As its core, the system uses GPS receivermodule from Rockwell Telecommunicationscalled the MicroTracker LP. Rockwell is thecompany contracted by the US Departmentof Defense to build the current block of GPSsatellites, and has made GPS receivers sincethe positioning system's inception.

The first readily available receiver module- the NavCore V - became available in 1990and was fairly power-hungry requiring about1.7W in operation. This module wasreplaced by the MicroTracker in 1992, whichreduced the size and power requirements dra-matically, and latterly the MicroTracker LPin 1994.

MicroTracker LP needs only a single 5Vsupply, and consumes about 900mW, whichcan be further reduced under software con-trol. The module can supply power to activeantennas, but these are not normally needed,as the device has an extremely 'hot' if frontend.

Before continuing with the facilities of thismodule, it is worthwhile considering some ofthe relevant parameters in the construction ofa GPS receiver.

Time -to -first -fix (ttff)When a GPS receiver is switched on, it willnot be receiving any satellites. At any time,there will be a maximum of twelve satellitesin view, out of the full operational constella-tion of twenty-four. In practice about eight ornine are in the visible sky.

The receiver needs to lock -on to a satellite,and will start to search for other satelliteswhich are in the sky at the same time.

There are many ways in which this can bedone. First, a random selection can be made,from any of the twenty-four satellites.

664 ELECTRONICS WORLD + WIRELESS WORLD August 1995

NAVIGATION

100KR9

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Fig. 1. Circuit diagram of the GPS receiverserial interface board and its power supply.

However, if the receiver 'knows' which satel-lites should be in the sky at that moment, thenthe search process is much simplified, andhence much quicker.

Periodically, the satellites download an`almanac' to the receiver, describing theirorbital characteristics. This almanac goes outof date, but while still fresh, it is of use. So, ifthe receiver knows its approximate position -within 100km will not make much difference- and the approximate time, then ttff can bereduced.

Most receivers will not have moved geo-graphically very much while switched off, if atall, and it is usually relatively simple to incor-porate a real-time clock into the system.

MicroTracker LP incorporates a real-timeclock, and retains its last position in eeprom,so the ttff is quoted as about 30s. When thereceiver is completely un-initialised, for exam-ple as they are when supplied from the facto-ry, a 'cold start' algorithm can be enabled.

J.151:33

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Note for Psion Organiser usersSoftware allowing the Psion Organiser II to read NMEA data from the RockwellGPS receiver is available.

In default mode, the Psion display shows latitude, longitude, height in metres,speed in mile/h, heading, horizontal dilution of precision (an accuracy figure),time and differential indicator.

The differential indicator shows 'Diff' when differential corrections are beingused by the receiver. MicroTracker LP accepts RTCM-104 corrections directly intoan auxiliary serial port and the number of satellites being received.Key options are :EXE selects odometer mode, this replaces the height display with an 'odometer'

showing the distance covered since the program started. Distances up to half amile are displayed in feet.

SPACE Display NGR (National Grid Reference). This displays NGR, then waits fora key press before continuing.

DEL Quits program.

Example display with odometer mode, differential corrections applied;N51°16.441'W001°03.916' 37.8

1.67 Diff 13:07:49hdop=0.78

359.3°

Sats 04

In this display, 359.3 refers to the heading, 37.8 to speed in mile/h, and 1.67 is theodometer reading. The latter is replaced by a height display in the default mode.

August 1995 ELECTRONICS WORLD + WIRELESS WORLD 665

NAVIGATION

Exclusive EW+WW reader discountA complete designer's pack is available from TDC at a discount exclusive to EW+WW readers. The kitincludes the Evaluation board, MicroTracker LP receiver, Magnetic mount antenna, mains power unit,serial cable, batteries, technical manual and software. Its price - which includes a seat on one of the GPSseminars - is £379.00 exc. VAT and postage. Normally, the combined elements of package would retail at£465.14. All elements of the kit are available individually at special prices to readers quoting this article.

The complete system is tested for GPS reception before despatch. Please add carriage at £12.50 (TNTnext day), and VAT to the total.

Please send a cheque/PO or Credit Card details (VISA/Mastercard) to Telecom Design CommunicationsLtd, Connect House, Stroudley Road, Basingstoke, RG24 OUG.Tel 01256 332800, fax 332810.

Fig. 2. Screen shot of Binary mode readerprogram. PC software for this is included in

designer's pack. It convert GPS receiveroutput into user-friendly display form. Note

that display includes OSGB coordinates,bottom left.

Lat

Lon

Aft

UTC

Hdg

Spd

N51* 16.62397344'

W01* 03.7262993T

101.1405m

20:57:02hrs

0'

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* MPH 0 KMH 0 MIS

641410 Nan Dab

OSOB Co-ordinatesNorth 153577Eastings 465412NOR SU65415357

76

Fig. 3. Screen shot of industry standard NMEA reader program, also included in kit. DisplaysGPS information on a pc but also shows positions of satellites in the sky and a tracking displayshowing a history of your position.

Lat 5116.579Lon 00103.877Sets 04UTC 130617.93Hdg 004.0Spd 0.000Alt 181In view 08SV Els Azi Sn

6 47 247 4316.13 231 3717.49 328 44290 21 299 3622.45 115 4225 45 35 4628.13 69 3329 10 126 31

HDOP 1.41POOP 2.51VDOP 2.07Last message$GPVT6$GPGGA$GPVT6$GPVT6$6PVT6

IntervalsGSVGSAPlot

Jai Amor,TID:DeTa' LTD

10105

*17

.6

'16

25

'2E

22

*29

Message GSA

MinLatMaxLatMinLonMaxLonPosition log display 100

Interval[]

This will normally find a position within aboutseven minutes.

Numbers of satellites requiredOnly one satellite is needed in order to receiveaccurate time. All of the satellites transmitUTC (Universal Time Co-ordinated) which isalmost identical to GMT.

To compute a position, four satellites arerequired initially. This gives a position inthree planes - X, Y, Z or latitude/longi-tude/height - but thereafter only three arerequired to give what is called 2D navigationcomprising latitude/longitude only).

Antennae & rf characteristicsGPS signals are transmitted on 1574.42MHz,All of the satellites transmit their data on thesame carrier frequency. Sophisticated tech-niques are used to identify individual satellitesfrom the combined signal, hence the need fora search strategy as described above.

The signal is available to the whole of theworld for free use without licensing, so thereis no restriction to the use of the information.But the position information is degraded bythe US DoD so as to not be useful for militarypurposes. The accuracy is quoted as betterthan 100m for 95% of the time, but again hasbeen found to be much better in practice.

The signal is right-hand circularly polarisedto avoid distortions and errors due to reflec-tions from buildings etc., but this frequencydoes of course require a fairly sophisticatedantenna. Such antennas are commerciallyavailable, and can be obtained from aroundthirty pounds. It is not advisable to constructan antenna as the signals being dealt with areat very low levels, and adequate performancecan be difficult to realise.

Receiver detailsThere are two connector options on theMicrotracker receiver board. First is the zero -insertion -force connector, which has histori-cally been the preferred type. However, withlower volume manufacture now possible forthese systems, the 0.1in connector is becomingmore popular due to its cost, popularity andavailability.

Connections of interest are on the 0.1in con-nector are:

666 ELECTRONICS WORLD + WIRELESS WORLD August 1995

NAVIGATION

GND power supply5V power supplyBAT! backup supply for internal ram,

which contains up-to-the-minute satelliteinformation, improving ttff.

BAT2 backup supply for the receiver'sinternal real -time -clock, again, to improvettff.

TXD data output is at ttl levels and must belevel via an RS232 buffer shifted beforeconnection to an RS232 device.

Fig. 3. Photograph of the GPS receiverinterfaced to a PSION organiser also showsNMEA reader, and the Micropulse antenna.

RXD data input, again at ttl level.NMEA/BIN selection for data format output

Data formats to and froInformation on data formats is of interest tothose of you who wish to develop your ownsoftware applications for the receiver, but it ispossible to obtain position information usingsoftware packages readily available from meand on CompuServe.

There are two data formats handled by thereceiver. The first is the proprietary 'binary'mode, which consists of a number of definedmessages which allow the user to initialise andread data from the receiver.

Binary -mode messages are `packetised' witha message header, information fields and achecksum. In this way, it is easy to detect if amessage has been corrupted, and should bediscarded. Data being sent to the receiver issimilarly `packetised'.

The second data format is the universallyrecognised National Maritime ElectronicsAssociation (NMEA) message. This messageformat is compatible to many marine displaysystems, but more importantly, outputs data inan ASCII form, which can be easily readusing a terminal program.

Writing software to take this data from aserial port, and display in whichever form theuser requires, is straightforward.

Hardware detailGPS is suited to mobile use. Generally, theonly exceptions to this rule are timing appli-cations where the 1 p s accuracy of the GPSreceivers is exploited.

Taking the example of a car, then the mostconvenient power source is likely to be the carbattery, which has a very wide range of pos-sible voltages. These extend from around 11Vup to 17V in the event of a fault.

Another example of mobile use is in aportable system, where independent batteriesare desirable. As with all portable systems,battery life versus weight is the main concern.Nickel -cadmium batteries are desirable. and it

is useful to be able tocharge these whileoperating the devicefrom a car.MicroTracker

requires a regulatedpower supply of fivevolts, and activeantennas may require

If the operating specification is different,then various other types of battery can be usedto suit the application. Power requirementscan be reduced by enabling power save modeswhere a reading is provided only once everyfive seconds rather than the usual one secondupdate rate.

MicroTracker's serial interface is at ttl lev-els, so the circuit also includes RS232 levelconversion to allow connection to an externalcomputer. A second serial port is included tocater for differential GPS corrections to beinput to the receiver to improve the accuracyof the receiver to sub -10m. The primary seri-al port is in the standard 9 -pin format.

The module will bolt to the pcb using stand-off pillars. Either connector type can be used,but if the zif socket is used, then an additionalconnection cable is required.

A PCMCIA version of the MicroTracker isavailable, called the NavCard, which providesthe same functionality, but in a ready -to usePCMCIA format compatible with modernnotebook computers. This card does notinclude NMEA data formats.

SoftwareIf an existing NMEA reader program is beingused, then provided that NMEA mode isselected, this should present few problems.

I suggested that in order to confirm correctoperation of the device, you should use provensoftware. The binary mode reader illustratedis such a program. Running under Windows,the program displays position, altitude, head-ing and speed of the vehicle.

A bonus is that conversion of latitude/lon-gitude to OSGB National Grid References isperformed by the program. It is available on

GPSreceiver - or

(MicroTracker)

twelve volts - againregulated - although Powersome will operate on sourceonly five volts.

The circuit shownhas two efficientpower converters to provide both the five andtwelve volt requirements from a wide inputsupply. Battery charging with charge & low -battery indication are also provided. A dual -colour led flashes once a second while theGPS system is running. It flashes green whilethe battery level is sufficient, and red when thebattery becomes depleted. A red led indicatescharge going to the cells.

Using six 700rnAh 'AA' size cells, there isenough operating power to supply theMicroTracker LP for about five hours, and toprovide backup to the rtc and ram while thedevice is switched off. If backup is onlyrequired for short times, then a 0.1pF capaci-tor can retain this data for about an hour.

Serialinterface(Fig. 1)

PC -based systemrunning standard

GPS softwareunder GUI

Microcontroller convertingGPS data to lcd or crt

output and post -processingGPS data according

to user input

Complete system for reading and presentingGPS data. The GPS antenna, Microtracker andpc software providing the two displays shownin this article are all part of the desgner's kit.

CompuServe, or from me at the address men-tioned below. I have also developed anNMEA reader for the Psion organiser II, oper-ating through the serial interface.

The author can be contacted at TDC'saddress, mentioned in the special -offerpanel, or via E-mail100043.104@compuserve.com.

August 1995 ELECTRONICS WORLD + WIRELESS WORLD 667

TRANSISTORS + ICS + SEMICONDUCTORS

/ in the new- £30

WORTH OF

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TOOLS+TEST EQUIPMENT+BENCHWARE

& much much more (over 10,000 lines).send today for the very interesting catalogue.

Pay by PO, cheque, credit card or tape coins to paper.

Please send me copies of the 1995 Cricklewood Catalogue.I enclose £2.50 per copy (UK & Europe) £5 overseas.

NameAddress

Please charge my credit card. No Expiry Date Tel. No EWW

Cricklewood Electronics Ltd, 40-42 Cricklewood Broadway,London NW2 3ET. Tel: 0181-450 0995 Fax: 0181-208 1441

CIRCLE NO. 114 ON REPLY CARD

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CIRCLE NO. 115 ON REPLY CARD

Data Acquisitionfor your PC

PicoScope'Virtual instrument'

software.

Pico's Virtual Instrumentation enable you to use your computer as a variety ofuseful test and measurement instruments or as an advanced data logger.

Hardware and software are supplied together as a package - no moreworries about incompatibility or complex set-up procedures. Unliketraditional 'plug in' data acquisition cards, they simply plug into the PC'sparallel or serial port, making them ideal for use with portable PC's.Call for your Guide on 'Virtual Instrumentation'.

.5170- 6 /S-44-32 Logic AnalysersPocket sized 16 Channel Logic Analyser

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668NEM=

ELECTRONICS WORLD+WIRELESS WORLD August 1995

INSTRUMENTATION

With a gain of 10 and flat to130MHz this oscilloscopeprobe is a useful tool. NickWheeler has achieved thisperformance using surface -mount devices. He's alsofound an easy way ofimplementingthe design.

130MHzactive probe

Conventional passive probes, usable ateven a few megahertz, have to have acompensated divider - usually x10 - to

minimise the effect of the lead capacitance.This division is sometimes inconvenient as itlowers sensitivity to typically 20mV/div.

Much worse, however, is the effect of mis-match, resulting in a pulse of the form of thelower trace in Fig. 1 being transformed bymultiple reflections into that of the uppertrace. The lower trace was produced by trans-mitting from a 50Q source down a 5052 cableto a 500 termination immediately adjacent tothe oscilloscope terminal.

This probe, Fig. 2, has a gain of ten, flat to130MHz and an output impedance of 500. Itsinput impedance determined primarily by straycapacitance of 5pF. Note that this is half that ofa conventional probe. The 1001(52 resistor sim-ply ensures a dc reference for the fet's GI.

Fig. 1. Multiple reflections caused by a typicalprobe feeding a 100MHz oscilloscope, uppertrace, are almost entirely absent in when theactive probe is used, lower trace, in amatched 50Q system.

SMD prototyping on a shoestring parts, with one lead per land. Many other devices can beincorporated by removing a small amount of copper

Although this circuit operates to 130MHz, standard double- locally.sided glass -reinforced pcb can be used. Where a ground connection a 1mm hole

Clean both sides and coat with an etch resistant coating. in the centre of the land and solder through.Engineer's blue works well since it is designed to be scribed Assuming 1.6mm glass -reinforced pcb material, each landwith fine lines. has about 3pF relative to the ground plane. This can be

Scribe a 0.2-by-0.2in grid on one side and etch below lowered by removing copper from the ground plane behind50°C. This grid will take most 2, 3 and four -terminal smd the land, but carrying this too far may impair the grounding.

0.2":0 zi Holes 1 mm

where required

(for power,c/bore on-

0.2"

reverse) ,0.2"

Producing square lands on one side of a double -sided pcb makes an excellent rf prototyping boardfor surface -mount devices.

August 1995 ELECTRONICS WORLD + WIRELESS WORLD 669

INSTRUMENTATION

The CF739 GaAs fet, from Siemens, has atransconductance of about 30 and is specifiedup to 2GHz. Drain load is 1000 in parallelwith the 50Q input impedance of the MAR 6silicon mmic, from Minicircuits. This yieldsunity gain. The mmic has a gain of 20dB at100MHz and 19dB at 500MHz. Thus voltagegain is close to 10 down to a few megahertz,at which point the lOnF coupling capacitorsbecome significant.

The fact that this probe has gain is useful inmany cases, but it begins to distort signalsabove 10mV pk-pk and the fet will be at riskof damage at more than three times this level.By trading off some of the gain, various formsof frequency compensated front end protectioncan be applied. This needs to be done experi-mentally, as the very small capacitancesinvolved depend on layout detail.

ApplicationBecause the MAR 6 mmic has to be capaci-tively coupled, this circuit will not workdown to dc. But lower frequencies can bedealt with using ordinary probes. This circuit

II Ferrite;bead

ii1,

Ferrite I100n

1

. I bead

10n "I'' innr:1 -1- 10n

6k8

g2

100k

g1

10n

2k2 T 1OR

10n

CF739

100n

50 co -ax

All I are through pinsIrfr7 to ground plane

All parts SMD except MAR6

is intended for examining low-level rf signalsand can be used with an input capacitor assmall as 1pF. This forms a capacitive dividerleading to a gain of about two - still useful.

A suitable type coaxial cable for linking tothe oscilloscope is semi -rigid RG 402.

Fig. 2. Surface -mount componentsare ideal for an rf oscilloscopeprobe since they allow aphysically small design with shortconnection distances.

Finally an upgradeable PCB CADsystem to suit any budget ...

,-, CaptureBoardCapture - Schematic Capture

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670 ELECTRONICS WORLD + WIRELESS WORLD August 1995

PC ENGINEERING

Douglas Clarkson buildsupwards from a simpleRS232 interface foraccessing an a -to -dconverter through to amulti -drop RS232communication link.

Increasing use is being made of serialRS232 links to control equipment and readdata remotely. Devices such as the Harris

H17159A device allow a -to -d conversion to beundertaken with control and data transfer tak-ing place on a single RS232 port. This opensup a range of interesting interface possibilities.

Resolution of the device is 51/2 binary-codeddecimal digits. It is capable of typically eightconversions a second at full resolution and off-set compensation, or 60 conversions per sec-ond at 41/2 digits resolution without compen-sation. The device cannot be considered fast,but it does have the significant advantages ofbeing relatively easy to use and of providinghigh -precision data capture.

By altering the device's conversion mode,

Getting more from

RS232its speed can be increased without compro-mising accuracy. This allows a series of mea-surements to be taken on a channel with anerror -only value followed by a series ofuncompensated values and ending with anoth-er error value. Normally the error value is con-stant and can be subtracted from the uncom-pensated value.

Such a system is ideal as an environmentalmonitoring station for example, measuringtemperature, wind speed, light level and ultra-violet levels. It could also be used withload -cells to develop medium scale sensitivi-ty weighing balances.

Various options are available for data cap-ture. Serial mode 2 allows separate HI7159Asto be addressed independently, Fig. 1. In this

mode, four separateanalogue channelsrequire four HI7159As.Since the device costsaround £20, imple-menting a large num-ber of channels in thisway becomes veryexpensive.

Accessing devices in

Table 1. Control word logic of the IM6402. A wide rangeof data bits, parity and stop bits are catered for -including the specific 8 data, even parity requirement ofthe 7159.Control word Data Parity StopCL2 CLS1 PI EPE SBS bits bits bitsL L L L L 5 Odd 1

L L L L H 5 Odd 1.5L L L H L 5 Even 1

L L L H H 5 Even 1.5L L H x L 5 Disable 1

L L H x H 5 Disable 1.5L H L L L 6 Odd 1

L H L L H 6 Odd 2

L H L H L 6 Even 1

L H L H H 6 Even 2

L H H x L 6 Disable 1

L H H x H 6 Disable 2

H L L L L 7 Odd 1

H L L L H 7 Odd 2

H L L H L 7 Even 1

H L L H H 7 Even 2

H L H x L 7 Disable 1

H L H x H 7 Disable 2

H H L L L 8 Odd 1

H H L L H 8 Odd 2

H H L H L 8 Even 1

H H L H H 8 Even 2

H H H x L 8 Disable 1

H H H x H 8 Disable 2

x=Don't care

serial -mode 2 is also slower since part of theserial traffic on the connected system is need-ed for addressing specific devices. Undermode 2, the total number of HI -7191s that canbe connected together is 32.

An alternative way of increasing the numberof analogue channels is to use standard ana-logue multiplexing. The single serial link canstill be used to control multiplexing. Usingfour lines for addressing allows the system toaccommodate up to 16 separate analoguechannels. Having programmable gain in thecircuit design is also useful.

Transmitting and receivingBasically, the IM6402 converts serial ttl logicdata to parallel and vice -versa via two separate8 bit data ports, Fig. 2. While the device canbe configured for a range of data bit, paritytype and stop bit combinations, in this appli-cation it simply has to be configured for com-patibility with the HI7159A. The format iseight data bits, even parity and one stop bit.

Table 1 is a summary of the control wordlogic of the IM6402 uart and indicates the fullrange of data bits, parity and stop bit permu-tations available.

+5VUp to 3 additionalHI7159s

15

7

T XTALTxD

END

UART/µP

VCCRxD

TxD6

1+5V

20k 20kHI7159

24BRSO 20

25 BRS1 2

+5V

18

19SMO

SW

22Addressselect

23

17

VEE DGND SEL

j28

-5V

Fig. 1. Serial -mode 2 allows several 51/2 -digit 1417159 a -to -d convertersto be addressed independently.

August 1995 ELECTRONICS WORLD + WIRELESS WORLD 671

PC ENGINEERING

VDDC E

VSSRRD

RBR8 CRBR7RBR6RBR5RBR4RBR3RBR2RBR1

PE CFE C

OE CSFD

sEDRR

DR C.RRI C

10 \._.) 402 39

3 38

4 37

5 36

6 35

7 34

8 33

9 32

10 31

11 30

12 29

13 28

14 27

15 26

16 25

17 24

18 23

19 2220 21

EPE

CLS1

CLS2SBSPI

CRLTBR8TBR7TBR6TBR5TBR4TBR3TBR2TBR1

TRO THE

TBRLTBREMR

Fig. 2. Conveniently, the 6402 uart hasseparate eight bit input and output ports.

Table 2: Bit rates and correspondingreceive frequency clock of the IM6402Bit rate Clock (Hz)

300* 4800600 96001200* 192002400 384004800 768009600* 153600

* indicates frequencies appropriate for HI -

7159.

TabkO.TrutlItableoftheD3508A.A2 AI A0 EN SwitchX x x 0 none0 0 0 1 1

0 0 1 1 20 1 0 1 3

0 1 1 1 41 0 0 1 51 0 1 1 61 1 0 1 71 1 1 1 8

Serial data signal levels for the IM6402 arettl compatible. A device such as the NMC232is needed to translate the logic levels. Thisdevice also provides isolation between the±12V RS232 and ttl levels.

Clocking requirementsWhile the uart is accepting serial data, thereceive clock frequency is 16 times the bitrate. Table 2 outlines the appropriate clockfrequencies used with commonly occurring bitrates.

Options such as 1200 baud and 9600 baudare readily available from programmableclock oscillators with a base frequency of

AO C 1* 16 Al

EN C 2 15 A2

VSS 3 14 GNDS1 C 4 ADG508A 13 VDDS2 C 5 TOP VIEW 12 S5

S3 C 6(Not to scab)

11 S6

S4 C 7 10 S7

C 8 9 S8

Fig. 3. One -of -eight switch ng is provided bythis eight -way analogue multiplexer.

Listing 1. Simple routine outlining how to control the H17159A/IM7402 combinationvia a pc.

REM the set of opening DECLARE statements are reservedREM for the PDQCOMM library routinesDECLARE SUB openCom Action$)DECLARE SUB ComPrint (Work$)DECLARE SUB CloseCom ()DECLARE FUNCTION ComInput$ (Nchar%)DECLARE FUNCTION ComLoc%5 CLS: REM clear screenREM open serial port one at 1200 baud, even parity10 CALL OpenCom("COM1:1200,E,8,1,RB128,NON")REM and one stop bitREM request value of analogue channel to be selectedREM the multiplexer chip use only three activeREM address lines15 PRINT "INPUT CHANNEL VALUE TO BE READ 0 to 7"INPUT CVALREM define line on IM7402 to be used for latching dataBOF = 64: REM LATCH ENABLE VALUE connected to B6 on HI7159AACALL ComPrint(CHR$(128 + CVAL+ BOF))REM have activated latch to control analogue multiplexerFOR JJ = 1 TO 100: NEXT JJ REM delayCALL ComPrint(CHR$(128 + cval))REM have disabled latch but analogue data being readREM by multiplexer deviceREM proceed to read data, provide options for choice ofREM command byte values all single - not continuousREM 14 = 51/2 compensatedREM 12 = 51/2 uncompensatedREM 6 = 41/2 compensatedREM 4 = 41/2 uncompensatedREM 2 = error onlyREM error only is used when wish to do fast uncompensatedREM conversions20 PRINT "input command byte": INPUT sb40 CALL ComPrint(CHR$(sb))REM now send request byte to check for completion of conversion50 CALL ComPrint (CHR$(13))REM wait until data available from conversion65 GOSUB 500: REM WAIT FOR LOC(1) TO SHOW CHARACTER

a$ = ComInputS(ComLoc%)80 IF ASC(a$) < 64 THEN GOTO 50REM request another status byte to check if conversion completeREM data now available: request data byteREM SEND REQUEST FOR FIRST DIGIT PAIR100 CALL ComPrint(CHR$(1))

GOSUB 500: REM WAIT FOR LOC(1) TO SHOW data availableD1$ = ComInputS(ComLoc%)

REM reading second digit pair200 CALL ComPrint(CHR$(5))

GOSUB 500D2$ = ComInput(ComLoc%)

320 REM READING THIRD DIGIT PAIR310 CALL ComPrint(CHR$(9))330 GOSUB 500340 D3$ = ComInput$(ComLoc%)350 REM now work out value of conversion360 b0 = ASC(D1$) AND 15370 bl = (ASC(D1$) AND 240) / 16

380 b2 = ASC(D2$) AND 15390 b3 = (ASC(D2$) AND 240) / 16400 b4 = ASC(D3$) AND 15410 b5 = (ASC(D3$) AND 48) / 16

420 ovr = (ASC(D3$) AND 64) / 64 : REM overrange430 pol = (ASC(D3$) AND 128) / 128: REM polarity440 vlu = b0 + (bl * 10) + (b2 * 100)

vlu = vlu + (b3 * 1000) + (b4 * 10000) + (b5 * 100000)if pol=0 then vlu = -vlu

442 if ovr=1 then print OVERRANGE: goto 15445 PRINT USING "#######";value = ", vlu460 GOTO 15500 REM SUBROUTINE TO WAIT UNTIL DATA IN receive buffer510 DO520 LOOP WHILE ComLoc% = 0530 Nchar%=ComLoc%540 RETURN

672 ELECTRONICS WORLD + WIRELESS WORLD August 1995

PC ENGINEERING

+5V

+5V

L nks+5V

Analogue inputpin12 IC2

Vref1

0 0 0L1 L2 L3

141 2 15

IC3

Rece'verclock

+5V

SW1 Baud

+5V+5V

128 27 26 25 24 23 22 21

IC2 HI7159A

20 17 19

GND RXD TXD (RS232 in/out)

122 118 120

8

TxD (TTL)

1

15

3

Cint

02RintR3

4 6

COfC3

12V

-12V

17

4-+5V

+5V

40139138137 1;6135

9 11_4

+5V

17

18

Master reset

23 121

Serial -to -parallel device for control of multiplexerIC4

16

(Data out lines)87 B6 B5 B4 B3 B2 B1 BOj4 5 6 7 18 9 10 11 12 11628120

4

+5V

T

5

6

10

15

IC6Latch

2 3 6 17

IC7

Analogue output

14 15 16 1719 110111112

Analogue inputs

+12V

13T

1 +5V

RxD (TEL)

To serial chip

To parallel chip

IC1 NM232DDIC2 H17159A

IC3 Prog. xtal. osc.IC4 IM6402IC5 OPA121KPIC6 74HC75

IC7 ADG508A

Fig. 4. One of the 508's eight channels isselected via the uart for processing via the

-12V single serial -access a -to -d converter.

768kHz. For most systems, 1200 baud is agood compromise.

While it is always cheaper to use specificcrystals and divide counters such as the 4020cmos device, it is usually quicker to buy off -the -shelf programmable oscillators.

Controlling the IM6402Since the H17159A is a slow device, datathroughput will not be improved by using low-level language for control. An appropriate

high-level language which can set the serialport on a pc to read eight data bits, even pari-ty is required. This specific format cannot bedriven by stand alone MicroSoft QuickBasic.Routines from the PDQCOMM library haveto be linked to make this format an option(available from Grey Matter).

The minor complication of requiring to linkroutine to another library within theQuickBasic environment is more than offsetby the ease of programming provided by the

language. The interpretive mode ofQuickBasic, however, is lost. Use of PDQ-COMM, is straightforward. A simple batchfile can be constructed to compile and link ina single line instruction.

Where the H17159A shares the same serialinput as the IM6402 there is a potential prob-lem. Sending a byte to the 6402 in order, forexample, to control an analogue multiplexer,may cause the 7159A to latch up.

Where more than one serial port is available,the function of data logging and logic controlcan be separated. Most pcs which runWindows, however, will require a port for themouse. Provided that the most significant databit of command bytes sent to the IM6402 isset, the 7159 will tend to ignore such input.This effectively leaves seven bits to control ananalogue multiplexer and other posible cir-cuitry. Thus any control data sent will beignored by the 7159.

There are many devices which can be usedfor the analogue multiplexing. Figure 3 indi-cates the pin out of the DG508A and Table 3the relevant truth table.

A latch as in Fig. 4 may be added to free thecontrol line for other functions. Switch Siselects the bit rate of the 7159. Voltage Vfl isderived from standard 1.2V reference diode.Master reset on the uart is normally low butcan be reset high on power up if required. Atthe output of op -amp IC5, potentiometer VR1scales the 7159 input voltage to ±2V.Programmable crystal oscillator IC3 has its bitrate set by links 43 as indicated in Table 4 inorder to drive the receive clock at 16 times thebit rate.

There is also the option of implementingvariable gain, programmed via data commu-nicated to the IM6402. With three digital linesbeing used for the analogue multiplexer, threelines can be used to drive programmable gain.A programmable gain amplifier suitable forsuch applications is the PGA205AP.

Listing 1 is an example of using the systemfor data capture. It demonstrates how an ana-logue channel is selected via a multiplexer,and shows how a command byte is sent toactivate the a -to -d converter. The pc thenchecks for end of conversion and polls theHI7159A for the conversion data, which isheld in three separate bytes of data.Subsequently, this data is reconstructed into asigned integer format for processing by the pc.

Multiplexing serial dataIt is possible to use the 6402 for multiplexing

Table 4. Pin configurations for 768kHzprogrammable oscillator for 1200 and 9600baud.

Table 5. Serial -line switching truth table, implementedusing the the IM6402 with analogue switches.Ascii value

PI P2 P3 P4 P5 P6 fclock(L1) (L2) (L3)

1 0 0 0 0 1 19200 40

bit

1200

128-184192200

1

1

1

01

1

1 0 1 0 0 0 153600 5 9600 208 1 1

216 1 1

Note, 1 represents logic high. 224 1 1

232 1 1

240 1 1

248 1 1

B7 E36 B5 B4 B3 Modex x x local H17159AA mode0 0 0 serial device 10 0 1 serial device 20 1 0 serial device 30 1 1 serial device 41 0 0 serial device 51 0 1 serial device 61 1 0 serial device 71 1 1 serial device 8

August 1995 ELECTRONICS WORLD + WIRELESS WORLD 673

PC ENGINEERING

RXD,

RXD,

RXD3

RXD4

RXD65

RXD6

RXD7-RXDo-

SW3Out

TXD, -TXD,

TXD, -a

TXD4 -TXD5 5

TXD6 -TX!),

TXD,

Ao A, A2

I

sw4Out

GXD, -GXG,

GXD,

GXD4

GXD5

GXD,

GXD,, -

A A, A2

SW5Out

To PC

NM23200

IM64027 B6 B5 84 B3

Enable

Latch2

A3

S

HI -7159A

S

A,

0

S2

Analogueigi tt

Fig. 5. Eight -way RS232 communications switchcontrolled by the 6402 in conjunction with alatch for addressing. Each ADG508A switch unitselects a specific transmit, receive or groundline. The system can also read data from theH17159A using a separate set of analogueswitches - dual spdt - controlled via a singlelogic line.

RS232 serial lines. Where, for example, oneserial port is available at a central pc, and alink to a specific peripheral such as a data log-ger or laboratory intrument is needed, it is pos-sible to select one from several serial devicesby use of additional interfacing to the 6402.

Where serial devices are being connectedacross only three wires - transmit, receive andground -a standard analogue switch such as aDG508A powered at ±15V will be able toswitch RS232 signals between ±12V.

Figure 5 shows how three DG508A devicesare applied to select specific serial devices.Each of the three is selected via a commonaddress bus, applied via a latch. Additionally,the 7159 can be selected by including switch-es Si and S2. These may be a dual single -pole,double -throw switch such as the DG4I9DJ.

It is common for serial equipment used fordata logging to be relatively intelligent, andable to communicate data in response to`wake-up' control characters. In this way, asequence of data capture can consist of select-ing a device, sending a serial control characteror characters, receiving a data string, closingthe link and repeating with another channel.

When high, line B7 activates the latch. LineB6 when high enables external serial links 1 to8 with the addresing of the latch. This is set byB3_5, which control the address lines of thethree DG508A analogue switches.

Table 5 shows the type of control madepossible by this arrangement.

SOFTEW+WW

Soft Index

INDEX ON DISKA computerised index of Electronics World+Wireless Worldmagazine is now available. It covers the five years 1990 to 1994 -volumes 96 to 100 - and contains over 1400 references to featurearticles, circuit ideas and applications, with a synopsis for each. Thesoftware is easy to use and very quick. It runs on any IBM orcompatible PC with 512K ram and a hard disk. Each disk isscanned before shipping with the current version of Dr Solomon'sAnti -Virus Toolkit.

For the UK, the five year index is priced at £20. Please specify51/4 or 31/2in format. This price includes UK postage and VAT. Addan extra £1 for overseas EC orders or £5 for non -EC overseasorders.

Photo copies from back issues of EW+WW are available at 50pper page plus VAT (in EC) and a flat postage charge of 50p (UK),£1 (rest of EC), and £2 (rest of world). For enquiries about photocopies send an sae to Video Interface Products.

Please allow up to 28 days for delivery. Cheques should be madepayable to Video Interface Products, not EW&WW or ReedBusiness Publishing.

Please post your request to Video Interface Products Ltd, 1Vineries Close, Cheltenham GL53 ONU, UK.

674 ELECTRONICS WORLD + WIRELESS WORLD August 1995

LETTERS

GPS vulnerabilityStatements made in the letter 'Falseposition on GPS', EW&WW March1995, should be treated with caution.Information presented at the ICAOCommunications and OperationsDivision meeting in March this year,based on work performed by the UKand supported by several states,highlighted the vulnerability of C/Acode GPS receivers to interference.

I would also refer your readers testdata published in the Institute ofNavigation Proceedings, Vol 40p249, Autumn 1993, and at severalION and Royal Institute ofNavigation conferences that confirmsuch a conclusion.

DRA and NATS have tested awide range of commerciallyavailable C/A code receivers,including Naystar's XRS andequipments certified to the FAA'stechnical service order TSO-129.The results do not support MrLeisten's claims of high immunity tointerference. In fact all C/A codereceivers tested were jammed at apower level between -130dBW and-120dBW at the receiver rf input.

The result have been confirmedduring in-flight tests. They indicatea discrepancy of some 60dBbetween the experimental data andthe power levels quoted in yourcolumn. It is however very easy tobecome misled by the mathematicsof the spectrum despreading thatoccurs in a GPS receiver.

Typical receiver noisetemperatures of 290K produce anoise power of -203.9dBW/Hz or-137dBW in the C/A code receiverbandwidth. However, as the signallevel is some 20dB below the noiselevel in the predetection bandwidth,it is not until the code has beenremoved in the correlator-despreaderthat a positive s/n ratio is achieved.

The theoretical maximum carrierto noise ratio, c/no, with a minimumguaranteed GPS satellite signalpower of -160dBW, above a 5°elevation angle, is 43.9dB. Inpractice the satellites, to everyreceiver manufacturers delight, arerunning 4dB hotter than specifiedwith the result that acquisition andtracking appear considerably betterthan specified.

To ensure the tracking loopsremain locked a signal level (c/no)of approximately 30dB/Hz isrequired in the carrier loop and

22dB/Hz in the code loop. Noiselevels that prevent tracking aretherefore -160-30, or -190dBW/Hzfor carrier and -160-22, or-182dBW/Hz for code.

The correlator C/A codedespreading process provides a gainagainst interference of 63dB/Hz.Noise powers in the receiverspredetection bandwidth thatsignificantly degraded the trackingloops measurements are therefore-127dBW/Hz for the carrier and-119dBW/Hz for the code.Generally the carrier loop has a 5 or6 Hz bandwidth resulting in aninterference power at the receiver rfinput of -133dBW -A value thatagrees well with experimental data.

The problem with the use of GPSfor precision approach is that allcurrent methods use some form ofcarrier phase tracking. To accuratelytrack carrier phase and to be surethat cycle slips do not occur asignificantly higher signal to noiseratio in the carrier loop is required.

The US RTCA committee studyingthe problem are specifying-150dBW as the limit for inbandnoise. It should be noted that thispower is below the thermal noiselevel. RTCA have set thisinterference power limit due to thesidebands that exist in the C/Acode's correlation function and theresultant degradation of 10 or moredecibels in the despreading gain; aI mW source of inband power couldtherefore cause interference at40km.

The problem of the use ofpseudolites highlights theinterference problem. If powerlevels and geographic positioningare nor carefully organised they willjam the intended recipient receiver.

The situation is not significantlydifferent for Glonass receivers.Architectures published by somereceiver developers would beequally if not more susceptible tointerference due to their widepredetection bandwidth.

In comparison ILS, andparticularly MLS, have significantlyhigher immunity to interference,although there are concerns overinterference into the ILS localiserfrom fm broadcasts. However at theICAO (COM/OPS 95) meeting theproblem of interference into GPSwas identified as a major issue andone that must be solved for the

system to achieve the integrity,availability and continuity for use inprecision approach and landingoperations.

The problem of interference andGPS will be the subject of aworkshop held by the Royal Instituteof Navigation, 12/13th October inLondon.P Nisner, R FarnworthNational Air Traffic ControlServicesI I R OwenDRA Farnborough

On your bike, SteveSteve Bush, in the July 1995 letterscolumn, writes about the need forbetter bicycle dynamos. Thestandard cycle dynamo is not in facta dynamo at all, but an alternator. Tomake it operate over a wide speedrange, it is not deliberately madelossy (although they are notfabulously efficient), but is aconstant current machine. For anygiven load resistance there is a kneeabove which increased speed giveslittle increase in output. Thestandard set uses a 6V, 100mA bulb

82R

Efficient red leds would be abetter alternative for rearbicycle lamps but using anythingother than an incandescent lampis currently illegal.

at the rear, and a 6V 400mA or500mA bulb at the front, connectedin parallel. The dynamo output is500mA. This is why failure of thefront bulb, or the connection to it,always causes the back bulb to blow,since the entire output of thedynamo then finds its way to therear bulb.

Increased output power from thedynamo is entirely possible. If 12Vbulbs are used instead, the powerdelivered is doubled, but this has thedisadvantage that the knee voltage isreached at twice the speed. At lowspeeds the performance is worse,since the bulb filaments are not atfull temperature and their resistanceis low.

I have had a number or rear bulb

Early transistor responseI read Dr Wylie's letter in the June issue with interest, and totally agreethat the history and preservation of early PC transistors is an orphansubject deserving serious attention.

Over the years, I have made an effort to preserve these devices when Ifind them, so that they now form a small part of my vintage electronicglassware collection.

The most interesting device I have is an early STC PC transistor in theAVO Book (qv) outline 20 form with a paper label `LS737-crystaltriode', which I believe dates from 1950-53 when experimental deviceswere made under Bell license.

Others include the GET1, Mullard 0050 and infamous unbranded red,yellow and green spot devices in small rectangular aluminium cases.Performance of these devices was, I recall, at best erratic. I suspect thatthe production spread was such that the colour coding was given in finaltest. I think the unbranded devices may have been out of specificationdevices from AEI, who used a similar package although AEI is notlisted by AVO as PC type makers.

It's not easy to identify early PC devices, especially if they havefailed. I often use the AVO International Transistor Data Manual, whichwas published early enough to list most of the production PCtransistors, together with their manufacturers and clear outlines to helpidentification. My copy is a third edition, about 1962, (but not dated) foruse with the AVO Transistor Tester. Early editions (up to No 6) of theWireless World Valve Data book also have some PC device listings.Anthony HopwoodUpton -on -SevernWorcestershire

August 1995 ELECTRONICS WORLD + WIRELESS WORLD 675

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TRANSISTORSPart Price Part Price Part Price Part Price Part Price Part Price Part Price Part Price Part Price Part PriceAAY32 9p D265 45p BFY9O 45p MJ2501 2N2102 50p 7815 25p TIC236D 85p AN315 210p BA6209 85p LA4110 120pAC107 40p D267 45p BLY48 85p MJ2955 2N2218A 24p 7818 25p 12A/400V AN316 350p BA6304 120p LA4120 270pAC125 30p D269 45p BR100 14p MJ3000 2N2219 24p 7824 25p TIC246D 105p AN360 100p BA6305 140p LA4140 60pAC126 30p D278 50p BR103 37p MJ3001 2N2221 23p 7905 25p 160/400V AN362 140p BA6410 220p LA4160 100pAC127 30p D311 100p BR303 85p MJE29A 2N2222 23p 7906 30p TIC253D 190p AN366 150p BA6411 250p LA4182 180pAC128K 40p D314 100p BSS74 33p MJE30A 2N2369 15p 7908 30p 20A/400V AN610 160p BA6993 150p LA4190 300pAC141K 45p D315 150p BSX20 15p MJE340 2N2484 15p 7912 30p TIC263D 205p AN3312 350p BA7001 150p LA4192 140pAC176 22p D317 150p BT100A 70p MJE350 2N2646 40p 7915 30p 25A/400V AN3821K 600p BA7004 200p 054200 130pACY18ACY19AD149

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550p100p200p

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85p230p230p

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7p7p7p

D675D676D677

40p40p38p

8U326ABU406BU406D

75p60p85p

52800MTIP29TIP29A

2144401 12p2N4403 12p2145061 20p

RED 5pYELLOWGREEN Bp

AN5712AN 5722AN5730

180p140p160p

CX141CX145CX150B

750p725p325p

LA7046 300pLA7224 150pLA7505 250p

COMPUTER ICs8C184LBC212BC212LBC213

713

7p7p7p

D678D6790680D681

40p40p40p45p

BU407BU407DBU406BU408D

55p75p60p75p

TIP29CTIP29E11P30TIP30C

2N5088 20p2N5192 50p2N5241 500p2N5245 45p

280ACPU loopZ8OADMA 200pZ8OACTC 140pZ8OAS10-1 210p

AN5732AN5753AN5763AN5790

120p130p450p240p

CX175CX187CX804ACX867

325p825p775p575p

LA7507 250pLA7520 200pLA7620 500pLA7800 90p

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BC213L 7p D682 45p BU409 85p TIP31A 2N5294 30p 5mm x 2.5mm Z8OAS10-2 210p AN5791 225p CX868 525p LA7801 100pBC214 7p D705 50p BU426A 70p TIP31C 2N5296 30p RED Sp 75107 65p AN5836 450p CX877 300p LA7802 300pBC214L 7p D707 50p BU500 100p TIP32 2145448 12p YELLOW Op 75110 75p AN5900 130p HA1125 120p LA7806 260pBC237 7p D709 50p BU505 90p TIP32A 2N6107 40p GREEN Op 75113 100p AN6135 120p HA1197 130p LA7808 250pBC238BC239BC300BC301

7p7p

20p20p

D711D736D826D828

50p50p50p50p

BU505DBU505DFBU506BU506D

90p90p

100p70p

T1P32CTIP33TIP33CTIP34

2N6292 40p2N6385 120p2146403 160p

75122 110p75154 100p75162 700p75182 95p

AN6247AN6270AN6300AN6306

200p400p600p380p

HA1199HA1319HA1338HA1339A

130p200p300p350p

LA7820 100pLA7823 200pLA7910 150pLA7940 200p

OPTOCOUPLERS

RECTIFIERDIODES

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20p20p25p

D839D897D899

55p50p50p

BU506DFBU508ABU508AF

120p70pHp

TIP34CTIP35C111,36C

4N37 58p4N38 68p

75183 95p75195 185p2114 150p

AN6320AN6332AN6341

180p320p200p

HA1377HA1388HA1389

120p320p210p

LC7131 260pLC7132 400pLC7137 450p

BC327BC3288C337

7p7p7p

D977DX33DX65

50p60p80p

BU508DBU508DFBU508V

75p115p110p

TIP41ATIP41CTIP42A

BY127 OpBY133 OpBY164 40p

BRIDGE 2532 200p2716 100p2732 200p

AN6344AN6350AN6359

440p610p500p

HA1392HA1394HA1397

120p170p200p

LF347 110pLF353 48pLF355 60p

RECTIFIERSBC338 7p DW24 55p BU508VF 100p TIP42C BY179 35p W005 16p 2732A 220p AN6360 320p HA1398 240p LF357 70pBC441 28p DW93 50p BU526 75p TIP47 BY184 92p 1A/50V 2764 150p AN6362 400p HA11219 280p LF398 300pBC446 Op DW94 50p BU536 100p TI P48 6Y206 I1p WO1 18p 27C64 200p AN6371 350p HA11221 180p L M301 26pBC477 18p DY92 100p BU546 125p TIP50 BY207 Op 1A/100V 27128 150p AN6387 480p HA11225 130p LM311 35pBC516 22p F137 35p BU608 120p TIP51 BY227 19p W02 19p 27256-25 150p AN6884 200p HA11235 120p L M319 165pBC537 25p F167 30p BU626 120p TIP52 BY228 28p 1A/200V 27512 300p AN7105 170p HA11251 190p LM324 30pBC546 8p F181 18p BU705 130p TIP54 BY298 15p WO4 21p 4116 40p AN7110 75p HA11423 140p L M 335Z 120pBC547 Op F183 20p BU706DF 175p TIP105 BY299 18p 1A/400V 4164-15 80p AN7114 120p HA11724 650p LM339 35pBC548 8p F195 7p BU706F 150p TIP106 BY448 20p WO6 23p 4164-12 90p AN7115 110p HA12002 220p L M348 50pBC549 8p F199 Op B U801 70p TIP107 BYX10 15 1A/600V 41256-15 80p AN7116 90p HA12003 250p L M358 45pBC550 13p F200 18p BU806 70p TIP110 BYX55/600 25pp WO8 28p 41256-12 100p AN7120 100p HA12005 180p LM380 80pBC556 8p F225 30p BU807 60p TIP111 BYX70/500 1A/800V 41256-10 110p AN7130 75p HA12017 100p L M 381 150pBC557 7p F240 16p BU902 110p TIP112 0A47 10p BR81D 33p 41464-12 150p AN7140 170p HA13001 110p LM382 130pBC558 8p F245 25p BU903 110p TIP112H 0591 10p 2A/100V 6116 80p AN7145 195 HA13002 200p LM386 60pBC559 Op F254 15p BU920 100p TIP115 0A202 10p BR82D 33p 6264-10 210p AN7146 210pp HA13006 400p LM387 100pBC560 8p F255 12p BU922 110p TIP116 N4001 3p 2A/200V 62256-12 300p AN7154 180p HA13007 400p LM393 45p8C637 20p F256 18p BU930 130p TIP117 N4002 3p BR84D 37p 6502A 360p AN7156 240p HA13108 350p L M431 50p8C639 20p F257 18p BU2508A 130p TIP120 N4003 3p 2A/400V 65CO2 930p AN7168 200p HA13412 600p LM710 45pBC640 20p F259 18p BU2508AF 130p TIP121 N4004 3p BR86D 43p 6522 280p AN7178 180p HA13432 400p LM723 40pBCY33BCY34

200p200p

F262F270

25p18p

BU2508DBU2508DF

130p150p

TIP122TIP125

N4005 3pN4006 3p

2A/600VBR88D 43p

6800 210p6802 220p

AN7222AN7254 15075pp

HA17524ICL7106

250p650p

LM741DIL 18pLM741MET 45p

BCY70 16p F273 15p BU2520AF 225p TIP126 N4007 4p 2A/800V 680 500p AN7256 250p ICL7660 240p LM747 55pBCY71 16p F311 21p BU2520DF 225p TIP127 N4148 2p BR32 43p 36808 500p AN7310 60p KA2102 150p LM1889 300pBCY72 16p F336 20p BU2525AF 325p TIP130 N5400 9P 2A/200V 6809 500p AN7311 90p KA2130 150p LM1894N 200p8D115 30p F337 20p BUH515 200p TIP131 N5401 Op BR34 43p 6810 150p AN7410 150p KA2206 150p LM3900 40pBD124P 50p F338 20p BUT11AF 55p TIP132 N5402 Op 2A/400V 6818 380p AY3-1015 290p KA2209 125p LM3909 100pBD131 25p F362 30p BUT12 80p TIP141 N5403 Op BR36 44p 6821 130p AY3-1270 800p KA2210 230p LM3914 160pBD132 25p F367 13p BUT56A 75p TIP142 N5404 Op 2A/600V 6840 290p AY3-1350 450p KA2212 80p LM3915 160pBD133 50p F371 17p BU18 80p TIP145 N5405 11p 0062 80p 6845 200p AY3-8910 360p KA2213 130p LM3916 270p80135 20p F421 18p BU18AF 80p TIP146 N5406 12p 6A/200V 6850 90p AY3-8912 400p KA2214 150p L200 200pBD136 20p F422 21p BUX10 150p TIP147 N5407 12p BR64 72p 8085A 300p BA301 55p KA2261 100p M491BB1 500pBD137 20p F423 25p BUX11 200p TIP150 N5408 12p 6A/400V 8086 500p BA311 80p KA2263 100p M494B1 700p8D138 20p F455 12p BUX12 150p TIP151 RGP15 25p BR251 150p 8088 480p BA313 60p KA2264 100p M50115P 320pBD139 20p F458 19p BUX20 350p TIP2955 RGP30 16p 25A/100V 8156 300p BA333 80p KA2284 100p M50117P 500pBD140 20p F462 50p BUX21 450p TIP3055 SKE4F2/06 60p BR252 165p 8224 240p BA401 60p KA2401 150p M50119P 525p80144 90p F471 28p BUX22 450p TIPL760 SKE4F2/08 80p 25A/200V 8226 240p BA402 50p KA2412 350p M50784 300pBD157 38p F472 28p BUX37 220p TIPL763A SKE4F2/10 100p BR254 185p 8250 750p BA511 145p KA2912 125p M50786 500p80166 30p F479 30p BUX40 210p TIPL791A SR2M 60p 25A/400V 8251 200p BA514 160p KA2914A 300p M50790 600p130175 30p F494 16p BUX41 200p 71561 BR256 200p 8253 160p BA516 150p LA1130 240p M51161 300p

I.C. SOCKETSBD177BD179

30p32p

F495F595

16p16p

BUX42BUX47A

200p220p

TIS90TIS93

25A/600VBR258 240p

8257 220p8271 3400p

BA521BA524

100p240p

LA1150LA1I85

150p150p

M51381P 200pM51387P 800p

BD181 45p F596 16p BUX48A 150p ZTX107 8 PIN 5p 25A/800V 8279 270p BA526 180p LA1201 75p M51544 150p80182 60p F615 30p BUX80 180p ZTX108 14PIN Op BR351 185p 8283 400p BA527 95p LA1210 140p M51848 150pBD184 60p F617 30p 6UX84 50p ZTX109 16PIN 7p 35V/100V 8284 440p BA532 100p 1A1222 80p M54523P 200p80187 30p F760 40p BUX85 50p ZTX212 18PIN 10p BR352 200p 8287 260p BA534 220p LA1230 130p M54563P 200pBD201 33p F763 40p BUX86 30p ZTX300 20PIN 12p 35V/200V 8288 650p BA536 150p 1A1364 200p M58484 500pBD202 38p F870 22p BUX87 50p ZTX301 22PIN 13p BR354 220p 8748 700p BA546 160p LA1365 120p M51516 260p8D20380204

42p42p

F871F960

22p38p

BUX98ABUY69A

350p200p

ZTX302ZTX303

24PIN 14p28PIN 16p

35V/400VBR356 230p

8755 800p8726 95p

BA612BA656

121100pp

LA1368LA1385

220p170p

M51518 200pM03712 140p

BD222 31p F961 3Sp BUY71 250p ZTX304 40PIN 18p 35V/600V 8728 110p BA658 350p LA2000 150p M03713 130pBD225BD23280233802348023580236BD237BD23880239BD24000241A

31p31p30p32p28p30p21p24p30p40p40p

F964FR90FR91FT43FX29FX84FX85FX87FX88FX89FY50

38p85p99p30p20p20p20p15p15p60p14p

BUZ11BUZ71BUZ808Y448BYT11C106DIRF630J174J300MJ 900MJ 1000

200p75p

200p20p25p28p

150p38p50p

200p200p

ZTX320ZTX501ZTX502ZTX503ZTX5042N6962N6972N6982N782N9142N9302141131

BR358 260p35V/800VBY1641.5A/100V 40pBY1761.5A/800V 40p

80684BA685BA1310BA1320BA1330BA1360BA4403BA5101855102BA5204855402

400p400p160p75p

120p160p220p350p140p200p180p

LA2101LA2200LA3160LA3210LA3300LA3301LA3361LA3375LA4030LA4031LA4032

270p190p120p65p

140p110p100p300p180p140p140p

MB3714 270pM83715 250pM83722 280pM83730 160pM03731 220pMB3756 160pMI33759 200pMB8719 360pMC1455 45pMC1496 65pMC3401 45p

ZENERS400 mWatts2V7 to 39V 5p1.3 Watts2V7 to 39V 9p

LINEAR ICs

AN203 210pAN210 165AN2140 170ppAN228 280pAN252 150pAN259 250pAN262 140pAN 271 230p

TRIACS

TIC206D 60p4/4/400V

VOLTAGEREGULATORS

BD243A 50p FY51 14p MJ 1001 200p 2N1132 7805 25p TIC225D 69p AN274 250p 1305406 180p LA4051 160p NE555 20pBD244 50p FY52 14p MJ 10012 300p 2N1613 7806 2Sp 6A/400V AN301 330p 855408 1130p LA4100 85p NE556 44)pBD245 50p FY56 25p MJ 15003 250p 2141711 7808 25p TIC226D 68p AN303 250p 006104 250p LA4101 80p NE558 80p00246A 50p FY64 25p MJ15004 300p 2N1893 7812 25p 8A/400V AN304 360p BA6208 175p LA4102 100p NE565 110p

CIRCLE NO. 1180N REPLY CARD

676 ELECTRONICS WORLD+WIRELESS WORLD August 1995

LETTERS

failures in my time, and eventuallygot so exasperated with this that Iput leds in the rear. The enclosedcircuit shows what I installed.Unlike many of the pulsing batterypowered led rear lamps seen on theroads these days, the light outputfrom this circuit is visibly constant.Four leds are used in an inverseseries -parallel arrangement so thattwo of the leds are illuminated oneach half cycle of the dynamooutput. Each limb includes one ledwith a narrow viewing angle, toproject plenty of light backwards,and another with wwide viewingangle, to spread light in alldirections. In practice this workswell. The 8mm ultrabright GaAIAsleds used (RS 577-718 and 577-730)have peak efficiencies at lowcurrents, so pulsing has noadvantage in terms of average lightoutput.

The back-to-back 8.2V zeners donot normally conduct, but protectthe circuit if the front bulb blows.Two 5W devices are well able toabsorb the entire 500mA outputfrom the dynamo, clamping thevoltage to about 9V, and the ledcircuit will tolerate this, thoughperhaps not for very long periods.Since putting the circuit in I havehad a real front -bulb failure, and therear lamp was undamaged.

In normal use the circuit consumesabout 30mA - only a third of the100mA of a standard bulb, and isevery bit as bright. At about £1 each,the leds are not cheap, but were wellworth it, in my view. More ledscould be used - twelve leds wouldconsume no more power than astandard rear bulb, and produceconsiderably more light. Ledmanufacturers are understandablyvery keen to get device efficienciesup and prices down so they willeventually supersede incandescentbulbs in motor vehicle rear lamps.When this happens, we can expectfurther improvements.

Unfortunately leds are not yet anoption at the front. My ownexperience is that halogen bulbs areadequate. These are far moreefficient than ordinary bulbs, andproduce enough light to make roadmarkings and signs visible in darkcountry lanes. As a means of beingseen by other road users, I think theysuffice.

In fairness, I should point out thatleds are not legal in rear lights,because they are not incandescent.Silly, but true, especially since theyare superior and more reliable.Prosecution for the offence ofhaving leds at the back is not,however to be expected. I concludethat this is because in York - one ofthe country's foremost cycle cities -

only about half of the cycles about atnight have lights at all, and thepolice never seem too bothered.Alan RobinsonYork

Thoughts in tandemI believe that Steve Bush's need fora small efficient dynamo may besatisfied by utilising a small shuntwound electric motor and adapting itto generate current by constructingan electronic regulator to feed thefield coil. By experimenting with thedevice to understand thecharacteristics of the motor, a fairlyefficient dynamo may be built.There should be sufficient residualmagnetism in the iron of the deviceto cause it to self excite.

It may be necessary to polarise thedevice by running it as a motor froma power supply with the field inparallel with the armature to ensurethat it charges with the correctpolarity.

All of the car type alternators areconstructed as three-phase machineswith slip -ring feeds to the rotor forthe exciting current. This type ofmachine would be a good model tocopy if one had the machiningfacilities. Details may be found in

most of the Haynes car maintenancemanuals, the one for the Land Roverseries III remember as beingparticularly good on alternators.

It may be possible to find a smalldevice from a piece of war surplusequipment, such as the BendixBomb Sight computer that wasavailable from war surplus stores,(showing my age eh?). Devices suchas a magsyns or selsyns couldprobably adapted to work as Steverequires.

There is one other alternative,details of which he may find in acopy of Haynes MotorcycleMaintenance manual for the Honda400/4, circa 1974 to 78, which had aform of variable -reluctancealternator with electronic control.From this he will perhaps be able todesign smaller vr machine.

There is another idea, which mayprove too wasteful in input energyterms. There are many smallpermanent -magnet motors availablethese days. They are often used forelectronic seat movements in cars.Such a motor would give a fairlylarge output, but regulation wouldhave to be a crude zener diode. Itmay be possible however to arrangea mechanical magnetic shunt toprevent too much energy being

absorbed from the bicycle wheel.My final suggestion is to adopt and

adapt a scheme that was prevalent inmy 'teens, from a company calledMiller, if my memory serves mewell. This had a small containerstrapped to the down tube. It heldsome dry batteries which took overthe lighting when the bike wasstationary.

By adapting the scheme toincorporate a set of nickel -cadmiumcells, or circular lead -acid cells, andrectifying the existing bike dynamooutput Steve could charge hisbattery at all times while the cyclewas moving, have good lighting,and, in case he didn't get enoughdaylight cycling during the winter,he could unplug the battery pack andtrickle charge it. Cell size could becalculated for optimum dependingon journey length, charge rate, etc.Nic HouslipDallas Semiconductor Corp LtdBirmingham

Power -line reactionIn the May 1995 issue, a letter fromRoger Coghill claimed that a reviewpublished by the IEE, in June 1994,on the possible biological effects oflow -frequency electric fields was

My heart skipped a beatI read with interest and concern the article entitledMonitoring Heartbeat in the July 1995 issue.

I note your comment concerning the mains adaptorhaving to comply with medical safety requirementsHowever, I am concerned that there is no apparentisolation from ground at the patient probe inputs.

Under certain single -fault conditions, circulating(low -frequency, typically 50Hz) currents can bepresent, causing possible fibrillation risk orundesirable muscle stimulation to occur.

There are specific medical equipment safetystandards that mandate the maximum permissibleleakage currents allowed to flow between the probes.These standards are under the group forElectromedical Equipment and are designated IEC601-1 for general safety with a further Part 2 standardspecifically applying to ECG related equipment.Michael BrettWatfordHertfordshire

Finger on the pulseIt may be worth pointing out that the instrumentationamplifier in Baki Koyunku's heart rate monitor(EW+WW, July 95, pp605-7) is probably redundant inhis configuration.

Firstly, an 'instrumentation' configuration canprovide a very high input impedance. However, theIMD input resistors prevent this feature from beingused.

Secondly, the configuration can provide a very highcommon -mode rejection ratio. However, anelementary analysis will confirm that this is onlypossible if the first stage has a high gain and the

second stage has a very low common -mode rejectionratio. This is because the common -mode gain of thefirst stage is unity so the circuit relies on a highdifferential -mode gain, and good rejection of thecommon -mode component from the first stage.

Koyunku's circuit features a first stage differentialgain of only three, which is not good enough. Hissecond stage is bizarre, featuring a different gain andfrequency response from the positive and negativeinputs. There is absolutely no chance of achievinganything approaching common -mode rejection -especially as his gain control resistor (I think this whatit is) affects the gain paths differently.

Readers implementing this circuit will do muchbetter to transfer the gain to the first stage, where it canstill be adjusted by varying the single 'central' resistor.Unfortunately, no component references were given inthe circuit, so my description necessarily vague.

The second stage should be a unity gain differentialbuffer with 0.1% resistors, and with capacitors acrossboth the feedback resistor and the resistor from thepositive op -amp input to ground.

Ideally, the input potential dividers should be alteredtoo. As it is they serve to introduce a common -modecomponent, or, if you like, they cause common modeinterference to generate a differential modecomponent. Don't forget to allow provision for the biascurrents.

These modifications will turn the circuit into aninstrumentation -quality amplifier which it quite clearlyis not at the moment. A better option may be to useone of the cheap instrumentation amplifier ICs now onthe market.David GibsonMicrosystem SolutionsLeeds

August ELECTRONICS WORLD + WIRELESS WORLD 677

LETTERS

'propagandist materialmasquerading as science'. He alsoclaimed that the composition of ourworking committee was heavilyweighted with power -utility -relatedpersonnel and that we refused todisclose the references on which thereport was based.

The IEE has been aware of thepublic's concern about the possibleharmful effects of electromagneticfields for a number of years. InNovember 1992 we set up aWorking Party, comprising both IEEmembers and others with relevantexpertise in the field to monitorrelevant scientific literature. TheWorking Party has a balancedmembership, with only one memberfrom the power -utility -relatedindustry and includes an eminentepidemiologist involved in leukemiaresearch. The literature wasretrieved by searches of three majordatabases and an abstract of eachpaper was obtained.

When Mr Coghill approached theInstitution, for a list of references, hewas informed that, because of thecontractual arrangements underwhich they were obtained, we couldnot supply him with photocopies ofthe abstracts. Since he had informedus he required the references to carryout his own research, Mr Coghillwas provided with details of thedatabases interrogated, by the IEE,and the search criteria used. We alsooffered to conduct computersearches, on a commercial basis, forhim from the same databases, usingthe identical search criteria and overthe same time period.

These searches would haveprovided him with identicalinformation that the IEE WorkingParty considered. The IEE WorkingParty has continued to monitor

relevant scientific literature andthere has been no reason to changethe conclusions reached in June1994 that the studies show no firmevidence of biological effects oflow-level, low -frequencyelectromagnetic fields.J. C. Williams, Chief ExecutiveThe Institution of ElectricalEngineersLondon

Anti-aliasing filterreworkIn my article on antialiasing filtersin the June issue, an error escapedme in the preparation of thefrequency response graphs: thecurves labelled An and D werenamed A and DX in the captions, theindex 'x' indicating their relation tothe mixed -mode response M,

I would also like to thank Mr. Selffor his comments on my letter('Lend a golden ear', May '95). Imust add that by those examples Iwas not offering proof, but ratherasking questions. Yes, it is difficultto accept that some people haveextraordinary abilities of perception.But in the case of my colleague,those resistor values were the onlydifference I could find, using asimple 31/2 -digit dmm, an HPoscillator and a Tektronix 475'scope).Of course, it is possible that I was

fooled. But I also remember readingabout a woman being held in apsychiatric clinic for 14 yearsbecause she was 'hearing voices',and then, before starting a therapywith new medication, she was sentto a routine audiometry check whereit was found out that her low -frequency hearing threshold was

about 4Hz. Hopefully, claiming ofbeing able to hear something thatothers don't will not put anyoneunder medical surveillance, but thepresent trend worries me.

I agree that too many vendors takeadvantage of the situation. But howcome we engineers struggle forevery milliohm in the amplifieroutput impedance? Is it only forstability reasons?

Regarding the communicationfailure, even we engineerssometimes can not hear ourselvesshouting. I believe I have shown (inEW+WW, July 1987) one possibleway in which 'the unmeasurableavoids to be inaudible'.

For a moment let's put aside theactual phase -switching audibilitythreshold - which in my opinion ismuch lower than the crossoverspikes audibility threshold. Thetrouble is that when we use aconstant amplitude signal source andtake the amplifier input-outputsignal difference, we intentionallycompensate the amplifier phase shiftto single out crossover spikes.

When the signal amplitude islowered, the crossover spikes fade inthe noise. The remaining phase erroris interpreted as some residualdistortion, more easily so if there areother distortion mechanisms in thecircuit. However, if the phase is notcorrectly compensated, a relativelylarge phase error will appear alongwith the crossover spikes when thesignal level is raised.

I have made this error myself oncountless occasions. Interestingly,there was nobody to comment onthis. Instead, there are only negativecomments on the amplifier modelused, despite my clear statement thatthe model was simply a simulationof a typical popular amplifier.

Possible solution for isolatingSelf's amplifier's inputbootstrapping from its feedback.

It remains to be seen if thedescribed switching phasemodulation mechanism is really thecause for the majority of 'scarcedefinition' marks in subjectiveevaluations. But engineers keeptalking about distortion, so in themind of inexperienced amplifierbuyers, if there is anything audible,it must presumably be 'distortion'.

I have yet to meet a 'subjectivist'who sticks to a Heisenberg acousticuncertainty principle, which statesthat even the presence of a singlelistener modifies the sound field -obviously true, but equallyobviously nonsense.

Finally, I would like to offer Mr.Self a possible solution for isolatingthe input bootstrapping from thefeedback in his recent design, in theform of the diagram shown.Erik MarganLjubljanaSlovenia

Mosfets, Bas andpower ampsI have been following Doug Self'sarticles on power amplifier designand the subsequent flurry of

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CIRCLE NO. 122 ON REPLY CARD

" Tr' ff t

678 ELECTRONICS WORLD + WIRELESS WORLD August 1995

LETTERS

correspondence discussing poweramplifier design philosophy. As acommercial designer, I am surprisedthat so much of the debate appearsto revolve around the inherentlinearity - or non -linearity - ofbipolar junction transistors versusfets. More significant, whenconsidering the design options, isrelative price; with a mosfet outputdevice costing pounds rather thepence a bjt commands - even inrelatively large quantities.

Further, mosfets have thedisadvantage of a finite, andrelatively large, on resistance whichwastes power and necessitatesparalleled devices in order to drivelow impedance speakers. Theseconsiderations affect 'watts perdollar' calculations considerably andprobably account for the relativedearth of commercial mosfetamplifiers more than considerationsof inherent device linearity.

But it is not wholly for commercialreasons that the fet is under attack; Ido not subscribe to the current swingin intellectual fashion against mosfetamplifiers simply because of theirinherent poor crossover distortioncharacteristics within a Class -Bcircuit. The mosfet is still worthy ofconsideration from any engineerdesigning an audio power amplifierbecause they possess a number ofhighly attractive attributes.

I can wholeheartedly confirm MrSelf's empirical observations thatthe open -loop, transfer -characteristicof the crossover region in a mosfetamplifier is less 'tidy' than thecorresponding region in a bjtamplifier when the latter is adjustedfor optimum bias. This indicates thatfets must be used in an amplifierdesigned to have adequate, andcontrolled, open -loop gain toaccommodate a relatively highfeedback factor. Fashion - and that'sall it is - dictates that this is primafacie 'a bad thing'. But the same istrue of a bjt amplifier because, whileit is true that it is possible to trim ajunction transistor output -stage topossess a linear crossover region,real -life operating conditions - andthe thermal time-lag in temperaturecompensation - mean that the biasoften departs from the optimal valuefor the output stage's givenoperating conditions. Add to this themosfet characteristics of constantgain -bandwidth product and inherentprotection against thermal runawayand secondary breakdown and it isstill possible to justify the fet's placein power amplifier design. Oneexception is perhaps where cost isan overwhelming factor.Richard BriceElectric Perception Ltd

Could germaniumperform?I have been following DouglasSelf's excellent series on poweramplifier design, and the followingcorrespondence with great interest.

One point intrigues me: Mr. Selfhas made several comparisonsbetween various output topologyand devices, bipolar and mosfet -Iwas wondering how wellgermanium performs in the sametests. By comparing the /c/Vbe curvesof silicon and germanium, intuitionsuggests that the same dips in theoutput gain curve will be present,but that the slope of the dip will beless steep, suggesting that a smallerbandwidth of gain/feedback stagewould be necessary to achieve thesame thd performance.

Or I may be entirely wrong.Ian BentonIlkestonDerbyshire

Final hearing...In his letter ("Slewing from reality",Letters, pp.500-501) Douglas Selfdenies that music can involvetransient hf levels as high as theloudest bass passages, But in this heis himself slewing dangerouslyoutside his field of competence.

He appears to be misusing data onmusic's spectral composition. Thisis based on rms, or long-term Lacqmeasurements and is free frominformation on slew demands.

Conversely, my comments stemfrom colleagues who are world classproducers of music. I doubt Self hasany primary experience ofquantifying hf levels of a rock band.The experiment with a supermarket -grade keyboard cuts no ice.

Even the inferred response out to16kHz enables full level treble seventimes higher than the 2.2kHz abovewhich he claims "large" signals donot occur in music.

In fact synthesisers can have farhigher sample rates than 44kHz, andanalogue synthesisers (which maybe digital in their controls) can alsohave edges extending way aboveaudio. In both instance, increasinguse of on-stage mic splitters enableshf edges to be preserved.

I should like to address, in turn,the errors Self alleges in mytranslation of his circuit.1. The vas "flush -out" resistor (1k0)is not altogether missing. InMicroCap, there is a minimumconductance setting across activedevice terminals, used to aidconvergence. So "re -flush" is alwaysthere, just hidden inside thetransistor, though admittedly too

high in value.Yet if Self had tried simulation,

he'd have seen that stepping theflush -out between 1ML2 and 1k52has no effect on the negativeslewing, and only a small tidying -upeffect on the positive pedestal.2. Self is adamant that fast signalscan never assault an amplifier - herehe claims my 100V/p s test signal istoo slow! But faster attack has littleeffect on the slew limit of histopology, and as excess test signalspeed also increases the time for agiven simulation accuracy, it wasn'tnecessary.3. The cvas cs base resistor isdifferent precisely because somevalue stepping was tried, and it hadscant effect.4. Self mentions that all thetransistors have been changed,skillfully drawing attention awayfrom the fact that, unlike his ownsimulations, the transistor modeldata I have used is shown in itsentirety.

Moreover, I ensured that the Self -defined slew -critical bjt parametersare amongst the highest available,So either the poor negative slewperformance is true (and hissimulation accuracy isquestionable); or the circuitschematic is extraordinarilysensitive to transistor parameters.

His comment on portal filteringhas not been thought through either.All decent audio sources havesource impedances below 100012unless they are the passive preampsor valve preamps used solely by theaudiophiles. In such cases, all thatwill happen with correctly scaled RCfiltering is that hf will be rolled offprematurely. This will not degrade%thd - apparently the onlyparameter that matters.

Turning to harmonics, I havemade it clear how real sonic issuesmay be addressed without addedparts or presets, but solely throughcareful design. The resulting valueshave been very different to thoseSelf believes are perfect. Where isthe scientific evidence that supportshis assertion that vanishingly low%thd (anything below 0.01%) hasany predictable beneficial effect onsonic quality?

Self's low distortion figures maydeserve an A plus for analogueelectronics, but real audioprofessionals award them D minus.The "much increased dc offset" is anon -problem if considered earlier inthe design process.

On another topic, I note Selfadmits that mosfets can have lowdistortion. In fact he is highlightingthe nonsense of trying to comparechalk with cheese. After 17 years of

waging war on experiencedoperators in professional audio onthese pages, it is time for Douglas tolay down his weapons.

As for the other correspondents, Ithank them for their input. But MrDavis cannot have carefully read mywords. I certainly did not say thatcapacitor mics were not used 20years ago. Rather, it takes 'classical'music combined with dynamicmicrophones and other less hf-responsive technology to explainwhy Baxandall could gounchallenged for so long.

I take Davis' word on thetheoretical limits of certain classiccutting equipment. But the factremains that ultrasonic signals havebeen measured at the replay end.

I agree with Mr van den Gevelthat vhf %thd sweeps may be usedto show slew limiting. On the otherhand, steep rises that look likeslewing can also be caused byseveral other mechanisms, andamplifiers can burn out when testedin this way.

The DIM30/100 test is rather moresensitive than thd, though suchmeasurements will not reveal theimpulse time domain informationshown in my slew simulations.

Van den Gevel has also ignoredmy other points, about the reality ofrf contamination for example.

Assuming an rf free -environment,Self's asymmetric 40-50V/ps is finefor his putative 20W amplifier. Butif you need 1020W (not sooutrageous when resealed in V, andaccount taken of fidelity -aiding stuffsuch as 6dB of head -room andlistener space greater than shoe -box -sized) 50Vp s may prove mostpainful and ultimately ear -damaging.Ben DuncanTattershallLincoln

Chain letterFollowing the Self -Duncan debate -and I must admit I declare on Self'sside - how refreshing to read JeffMacaulay's comments about "thecarefully cultivated signal...beingmangled..." and "What emerges...isa distorted version of the drivingsignal, no matter how perfect theinput may be."

How about some articles on thewhole audio chain to put amplifierperformance into its properperspective? Mark PlewsHerrschingGermany

August 1995 ELECTRONICS WORLD + WIRELESS WORLD 679

680

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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.

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The TV & 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.

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681

COMMUNICATIONS

Harmony in theanSvetlana Josifovskahas been looking atthe government'srecent spectrumreview intended toprepare the way forthe introduction ofEurope -wideservices.

Land mobile radio and other radioccdrununica-tions services, and advanced technologiessuch as T -DAB - terrestrial digital audiobroadcasting - are increasing at an incredible

rate. One of the effects of these advances isincreased pressure for more radio spectrum.

Since the radio spectrum is a limited resource, alogical progression is to reorganise existing ser-vices and reallocate frequencies. But, although thismay appear simple at first glance, it is actually adelicate game of strategies and tactics. The partiesinvolved -a mixture of government, military andcivil authorities - always request more, rather thanless, of the radio spectrum.

Stage 3 Radio Spectrum Review committee wasset up in July 1992 by the Board of TradePresident Michael Heseltine. Last month it cameup with a a synopsis that covers arguably one ofthe most crowded, and hence contentionus, parts ofthe radio spectrum - the 28-470MHz range.

"The Review Committee made 28 recommen-dations, 24 of which have been accepted by the

Government without reservation. The remainingfour are accepted in principle. The recommenda-tions cover both defence and civil use of theReview spectrum and a number of them havealready been acted upon," said Heseltine.

Within this frequency range there are allocationsthat belong to the broadcasting industry and themobile industry including land, aeronautical, mar-itime and satellite. These are also space researchand operations in the range, that still belong main-ly to the MoD. Users of this spectrum range frombroadcasters and the government to utilities andemergency -services operators and the civil mobileradio community.

The Stage 3 review of the radio spectrum in the28-470MHz range completes the governmentsponsored independent reviews of the radio spec-trum over the range 28MHz to 30GHz. The rangesbelow 28MHz and above 30GHz are subject tointernal audits and the results of these are expectedto be published later in the year.

More releases between 225 and 400MHzAmongst the agreed requirements was the role ofthe MoD in this radio spectrum and its release ofmore frequencies for civil use. Although the MoDhas already released the 225MHz to 230MHz bandfor T -DAB, it was recommended that it shouldseek, through NATO, the release of some of the225MHz to 400MHz frequency band for civil sys-tems in the UK, particularly the 380-399.9MHzband in its entirety. Access to two 5MHz sectionsin the 380MHz to 400MHz band by 1997 hasalready been agreed by NATO/ARFA for use bythe emergency services and the rest of the spec-trum's release is still under review.

"Part of an existing defence frequency band hasalready been released for a new digital radio broad-casting service for the UK. Further defence spec-trum has been released in cooperation with NATOto provide the emergency services with an oppor-tunity to develop a new radio system. This in turnwill also assist with the resolution of the longstanding continental radio interference problems inthe UHF frequency bands in England and Wales,"said Heseltine.

These frequencies are of significant importancebecause it is in line with the CEPT agreement foremergency services to be harmonized acrossEurope. According to government estimates theemergency services will begin to take up use ofthis band in 1998 and complete the changeover bythe year 2003.

The committee is urging the MoD to adopt a

682 ELECTRONICS WORLD + WIRELESS WORLD August 1995

COMMUNICATIONS

leading role within NATO, through the pro-cess of specifying new equipment and throughmore economical spectrum management,towards a reduction in the total bandwidthrequired.

The government is also paying more atten-tion to the introduction of T -DAB, by arrang-ing an EU meeting in July to discuss the sub-ject. It encourages broadcasters wishing to useT -DAB to start a service soon. All vhf soundbroadcasting should be contained within BandII (88MHz to 108MHz) as soon as possibleshould the introduction of such service provefeasible.

Improvements to mobile servicesOn the subject of land mobile services, thegovernment has agreed to a programme ofimprovements to ensure better management ofthese services' radio spectrum, which will ulti-mately benefit users.

The programme would consist of improvedmethods of frequency assignment, efficientprocedures for systematic analysis of licensingdata and monitoring results, and efficientspread of frequency spectrum between exclu-sive Private Mobile Radio (PMR) and sharedPMR. The Radiocommunications Agency(RA) has been recommended to oversee theimplementation of these improvements andcoordinate some areas of planning with themobile industry. Inclusive of PMR, the othertwo areas are Common Base Station (CBS)

and Public Access Mobile Radio (PAMR) ser-vices.

The RA will also take care of the policiesand strategic plans for the future use and allo-cation of the spectrum to meet the needs of theprivate and public sectors. It will make surethat operators use the given radio spectrum tothe best national advantage. This responsibil-ity the RA may share with the MoD, an optionwhich is currently under review.

The RA will also look into deregulatinglow -power PMR services for indoor use, forexample in the area of short-range businessradio.

Other aspects of the spectrum that have beenincluded in the review are the arrival of newtechnologies and the allocation of frequenciesto them. One such example is the emergingDigital Short Range Radio (DSRR) and 5KHznarrow -band land mobile radio.

But amongst the important points that havebeen covered in the committee's proposal andthe government's response, is the role of theUK in Europe and the economical benefits itmay gain.

"Today's response and the progress whichwill be made in implementing the recommen-dations is a further example of the steps weare taking to improve the efficiency of spec-trum management and usage in the UK to pro-mote competition and choice for the benefit ofall users of the radio spectrum," saidHeseltine.

Amongst the examples for a UK lead withinthe European community is its lead in thetalks with NATO, to release some of the fre-quency ranges for civil use, and its supportingrole in harmonizing services with the rest ofEurope. These include the emergency servicessynchronization in the uhf 380-400MHz band,that was recommended by CEPT and which isexpected by 1997, and the vhf band for public -sector spectrum requirements for PMR.

Harmonization with Europe of the spectrumuse and equipment characteristics is seen asbeing essential for the UK. The governmenttakes into account that harmonisation does notnecessarily always yield efficient use of theradio spectrum, but it will ensure the limitingof allocations where it is essential for Europe -wide capabilities or for border coordination.

These issues have been addressed before inthe consultative document, The FutureManagement of the Radio Spectrum.

"Some of the Review Committee's recom-mendations addressed spectrum managementissues which were also the subject of theConsultative Document on the FutureManagement of the Radio Spectrum.Therefore it was decided to delay the com-pletion of the Government's response to theStage 3 Review until after consideration of thesubmissions to the consultative document,"said Heseltine.

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CIRCLE NO. 120 ON REPLY CARD

August 1995 ELECTRONICS WORLD + WIRELESS WORLD

AUDIO DESIGN

Audio expert JohnLinsley -Hood rarelyenters such debates, butthe claims in favour ofthe bjt over mosfets havechallenged his decades ofexperience.

012100µ

R3

47k

C21 ZD'X'10n7 10V

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R2R1 680R

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EXPERTWITNESS

On several occasions - most recently inthe May 1995 issue - Douglas Selfhas claimed that bipolar junction tran-

sistors, bjts, are more linear than power mos-fets as audio amplifier output stage devices.

I am reluctant to accept this assertion, sinceif it were true it would overturn the whole ofmy experience - in respect of the comparativeperformance of these devices in audio poweramplifiers - over the 20 -odd years since thecommercial introduction of power mosfets. Ifeel that the progress of audio design requiresthat this claim be contested.

There are of course, many other reasons -

R4 R5

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A1133 R

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better hf performance, greater stability, greaterrobustness and inherent freedom from thermalrun -away - which have encouraged a numberof manufacturers of audio amplifiers to usemosfets rather than bjts as the output stagedevices in their top range designs. But thequestion which Self raises is that of theirintrinsic linearity as an output push-pull pair.This is a quality which I feel can be related -by means of measurements - to the residualharmonic distortion characteristics of audioamplifiers incorporating one or other of thesealternative devices in its output stage.

Some years ago, I was asked by a well

RV1 R9

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Power outputdevices

Output to LS

I

Power outputdevices

* Compensation capacitor - value depends on circuit

684 ELECTRONICS WORLD + WIRELESS WORLD August 1995

AUDIO DESIGN

InputNFBetc.

+50V

Output

Bipolar

50V

NFInput

etc

+50V +50V

Output

MOSFET

50V

NFInput

etc Output

IGBT

-50V

Fig. 2. Output emitter-follower/source-followerconfigurations used in the test circuits.

known semiconductor manufacturer to explorethe use of their recently introduced insulatedgate bipolar transistors, igbts, as output -stagedevices for audio amplifiers. It appeared thatigbts should combine the practical advantagesof both bjts and mosfets. To this end, Idesigned and built a group of audio amplifiers.These used the basic voltage amplifier layoutof Fig. 1 as a gain block. The various outputdevices were inserted into these gain blocks,in the positions shown as square boxes, usingthe various emitter or source -follower config-urations of Fig. 2.

Performance of these amplifiers, operatedfrom a pair of ±50V stabilised dc power sup-plies, is shown in Fig. 3. Measurements weremade at a frequency of 1kHz with an 80water-cooled load at power output levels up tothe onset of clipping.

In all cases quiescent current of the output -stage devices was adjusted on test to give thelowest harmonic distortion figure for theamplifier. It was noted that this adjustmentwas less critical with the mosfets than witheither the bjt or the igbt devices.

Subsequently, we found that the test oscil-lator used in these measurements had a resid-ual harmonic distortion at the 1kHz test fre-quency, of 0.003%. This was mainly thirdharmonic, so, in reality, all of these measure-ments had tended somewhat to exaggerate the

THD%

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true residual distortion figure of all of theamplifiers. Nevertheless, the superiority of themosfet based design is evident in this com-parison in which the only variable was thechoice of output stage devices.

The reasons for this difference in linearitybetween the alternative output stage devicesare complex. I suspect that two main factorsmake the negative feedback loop in mosfetamplifiers more effective than in bipolarequivalents. One is the nature of the frequen-cy distribution of the distortion componentsdue to the discontinuity of the transfer char-acteristics of the output push-pull output pair.The other is the relatively lower internal phaseshifts of mosfets.

Whatever the reasons for performance dif-ferences, it is clear that they are not adequatelyrevealed by a Spice type computer simulationof the output -pair transfer characteristics. Assuch, this type of measurement fails to meetSelf's own criterion that 'if an apparent fact isrepeated many times without number... itdeserves to be looked at very carefullyindeed'.

Further readingFor those of you interested in fuller details of thecircuitry used in these experiments, see ToshibaApplication Note X3504, March 1991.

Onset of clipping

X x IGBT-e-e- Bipolar

MOSFET

I 1111111 I I I 111111 I I 1111111

1.0 10 100Power output (±50V dc stabilised supply)

(watts)

Fig. 3.Relationshipbetween powerand totalharmonicdistortion revealsinterestingresults.

THE ART OF

LINEAR

ELECTRONICS

IThe Art of LinearElectronics - 10%EW+WW reader

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While stocks last, Electronics World &Wireless World is offering John

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'The Art of Linear Electronics' order - ISBN0750608604 - contains electronic component

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waveform generators; tuned circuits;high-frequency amplifiers/oscillators; radioreceiver circuitry; power supplies; noise and

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This practical 340pp handbook gives acomplete working knowledge of the basicsand technology of linear electronics-with

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684P CIRCLE NO. 121 ON REPLY CARD

SENSORS

Temperaturebytes

Reading temperatureinto a digital systemmeans a thermalsensor, signalconditioning anda -to -d conversion.There is now aneight -pin chip thatincorporates allthis - together withparallel -to -serialconversion and threethermal alarmoutputs.

Even given an IC that produces a voltagethat directly indicates temperature, youwould need to add at least an a -to -d con-

verter in order to interface the temperature sig-nal to a digital processing system. Simplifyingthe process of reading temperature into digitalsystems, Dallas Semiconductor has devised aneight -pin chip that not only outputs a 9bit seri-al stream representing temperature, but alsoprovides three temperature threshold switches.These switches are user programmable vianon-volatile ram.

The device measures temperatures from-55°C to 125°C in 0.5°C increments, which isthe equivalent of -67°F to 257°F in 0.9°Fincrements. Conversion time, from a temper-ature reading to output of a digital word is Isand data is read from/written via a three -wireserial interface comprising clock, data i/o andreset lines.

Although highly integrated, the DS1620 isdesigned for ease of use and requires no exter-nal components.

Converting temperature to bytesTemperature readings from the DS1620 rep-resent the temperature of the actual device sono external temperature sensor is needed.Having three thermal alarm outputs, the chipcan also act as a thermostat.

Table 1. Relationship betweentemperature and the DS1620 2'scomplement output stream.Temp Output2+125°C 0 11111010+25°C 0 001100101/2°C 0 000000010°C 0 00000000-1/2°C 1 11111111-25°C 1 11001110-55°C 1 10010010

Outputis00FA00320001000001FF010E0192

Temperature Thigh is driven driven high ifthe device's temperature is greater than orequal to a user -defined temperature TH.Similarly, Tin, is driven high if the devicetemperature is less than or equal to user -defined temperature TL. Pin Tcom is drivenhigh when the temperature exceeds TH andstays high until the temperature falls belowthat of TL.

User -defined temperature settings are storedin nonvolatile memory, so parts can be pro-grammed prior to insertion in a system, aswell as used in stand alone applications, i.e.without a cpu. Temperature settings and tem-perature readings are all communicatedto/from the DS1620 over a simple three -wireinterface.

Reading temperatureThe DS1620 measures temperatures using anon board proprietary temperature measure-ment technique. Temperature readings are pro-vided in a 9bit, two's complement format.Table 1 describes the exact relationship ofoutput data to measured temperature.

Data is transmitted serially through the 3 -wire serial interface, lsb first. The chip canmeasure temperature over the range of -55°Cto +125° in 0.5°C increments. For conversionto fahrenheit, a lookup table or conversion fac-tor is needed.

Since data is transmitted over the 3 -wire buslsb first, temperature data can be writtento/read from the device as either a 9bit word,taking /RST low after the ninth bit (msb), or

August 1995 ELECTRONICS WORLD + WIRELESS WORLD 687

SENSORS

as two transfers of 8bit words, with the mostsignificant seven bits being ignored or set tozero, as illustrated in Table 1. After the msb,the device outputs zeros.

Note that temperature is represented in termsof a I/2°C, the least -significant bit yielding thefollowing 9 -bit format:

msb I s b

x xx x x x x1 1 1 0 0 1 1 1 0

Applying the thermostatThree thermally triggered outputs, Thigh T10,,and Tcom are provided to allow the device tobe used as a thermostat, Fig. 1. When thetemperature meets or exceeds the value storedin the high temperature trip register, outputThigh goes active high and remains active untilthe measured temperature becomes less thanthe stored value in the high -temperature reg-ister, TH.

The Thigh output can be used to indicate thata high -temperature tolerance boundary hasbeen met or exceeded. Alternatively, as part ofa closed loop system, it can be used to activate

+ 5 V + 1 2 V

a cooling system and to deactivate it when thesystem temperature returns to tolerance.

Output T10,, functions similarly to the Thighoutput. When the DS1620's measured tem-perature equals or falls below the value storedin the low -temperature register, output T10,becomes active, Fig. 2. It remains active untilthe temperature becomes greater than thevalue stored in the low -temperature register,TL. The T10,, output can be used to indicatethat a low temperature tolerance boundary hasbeen met or exceeded, or as part of a closed -loop systeni, can be used to activate a heatingsystem and deactivate it when the system tem-perature returns to tolerance.

Output Twin goes high when the measuredtemperature meets or exceeds TH, and stayshigh until the temperature equals or fallsbelow TL. In this way, any amount of hys-teresis can be obtained.

Operation and controlThe DS1620 must have temperature settingsresident in the TH and TL registers for ther-mostatic operation. A configuration/status reg-

12V, 100mA FAN

Fig. 1. DS1620 acting as a digitally programmable thermostat. Programming temperaturethresholds is a one-off operation since the device incorporates non-volatile memory. Either a2N7000 or ZVN2106A - both available from Zetex -is suitable for the fan -driving mosfet.

THIGH

TLOW

Tcom

TL TH T (°C)

Fig. 2. Output Teo. adds flexibility. It turns on when temperature exceeds the value set inregister TH and stays on until until temperature falls below that of TL.

DS1620 command setRead temperature [AA16] This commandreads the contents of the register containingthe last temperature conversion result. Thenext nine clock cycles output the contentsof this register.

Write TH [0116] This command writes tothe TH temperature -high register. After issu-ing this command, the next nine clockcycles clock in the 9bit temperature limit,setting the threshold for operation of theThigh output.

Write TL [0216] This command writes tothe temperature -low register. After issuingthis command, the next nine clock cyclesclock in the 9 -bit temperature limit whichwill set the threshold for operation of theTeo, output.

Read TH [A1161 This command reads thetemperature -high register. After issuing thiscommand, the next nine clock cyclesclock,out the 9bit temperature limit whichsets the threshold for operation of the Thigh

output.

Read TL [A216] This command reads thevalue of the TL register. After issuing thiscommand, the next nine clock cycles clockout the 9bit temperature limit which sets thethreshold for operation of the TL output.

Start conversion [EE16] This commandbegins a temperature conversion. No furtherdata is required. In one-shot mode the tem-perature conversion will be performed, afterwhich the chip remains idle. In continuousmode, this command initiates continuousconversions.

Stop conversion (2216] This commandstops temperature conversion. No furtherdata is required. This command may beused to halt a DS1620 in continuous con-version mode. After issuing this commandthe current temperature measurement willbe completed and then the device willremain idle until a start conversion com-mand is issued to resume continuous oper-ation.

Write config [0C16] This command writesto the configuration register. After issuingthis command the next eight clock cyclesclock in the value of the configuration reg-ister.

Read config [AC16] This command readsthe value in the configuration register. Afterissuing this command the next eight clockcycles output the value of the configurationregister.

688 ELECTRONICS WORLD + WIRELESS WORLD August 1995

SENSORS

Table 2. Pin functions of the DS1620 thermometer thermostat.

Pin Symbol Description1 DQ Data input/output for 3 -wire communication port.2 CLK/CONV Clock input for 3 -wire communication port. When the DS1620 is used in a stand-alone application

with no 3 -wire port, this pin can be used as a convert pin. Temperature conversion will in on thefalling edge of /CONV.

3 RST4 GND5 TCOM

6 TLOW7 THIGH8 VDD

Ground pin.High/low combination trigger. Goes high when temperature exceeds TH; resets low whentemperature falls below TL.Low temperature trigger. Goes high when temperature falls below TL.High temperature trigger. Goes high when temperature exceeds TH.Supply voltage, 5V input.

ister is also used to determine the method ofoperation that the DS1620 will use in a par-ticular application as well as indicating the sta-tus of the temperature conversion operation.

The configuration register is defined as fol-lows:

Configuration/status register bitsDONE THF TLF x x x CPU 1SHOT

where,xDONE

= Don't care= Conversion done bit.

1=conversion complete, 0=conversion inprogress.

THF = Temperature high flag. This bitis set to 1 when the temperature is greaterthan or equal to the value of TH. It willremain 1 until reset by writing writing 0into this location or by removing powerfrom the device. This feature provides amethod of determining if the device hasever been subjected to temperatures aboveTH while power has been applied.

TLF = Temperature low flag. This bitis set to 1 when the temperature is lessthan or equal to the value of TL. It remains1 until reset by writing 0 into this location,or by removing power from the device.This feature provides a method ofdetermining if the device has ever beensubjected to temperatures below TL whilepower has been applied.

CPU = CPU use bit. If CPU=O, theCLK/CONV pin acts as a conversion startcontrol, when /RST is low. If CPU is 1,the DS1620 will be used with a CPUcommunicating to it over the wire port,and the operation of the CLK/CONV pinis as a normal clock in concert with DQand /RST.

1SHOT = One-shot mode. If 1SHOT is 1,the device performs one temperatureconversion upon reception of the startconvert protocol. If 1SHOT is 0, the

DO

I STATUS &CONTROL LOGIC

ADDRESSAHD RESET

TEMPERATURE SENSOR

HIGH TEhf, TRIGGER, TH

LOW TEMP TRIGGER,TL

DIGITAL COMPARATOR/LOGIC

OTHIGH

EITLow

0-rcom

Fig. 3. Programmable via a simple three -wire interface, the DS1620 registers are used to settemperature thresholds and set the operating mode. Programming is non-volatile so the devicecan act as a stand-alone controller.

PC -basedsoftware - partof thedesigner's kit -allows theDS1620 to beread andprogrammedvia thekeyboard.Oncetemperaturethresholds areset, non-volatilememoryensures thatthey remain seteven when thedevice isremoved fromits socket.

About Time/Temp Settings Application Quit

HOT

CoolingSystem

40 --

35 --

30 --

25 --

20 --

15--

10--

5-

0--

Scale

Full

a Room

Temp Mode

WI Celsius

fi Fahrenheit

Trigger Settings

29.5° C

27.5' C

High TemperatureTrigger

Low TemperatureTrigger

Temperature

27.0° C

August 1995 ELECTRONICS WORLD + WIRELESS WORLD 689

SENSORS

device continuously performs temperatureconversion

For typical thermostat operation, theDS1620 operates in continuous mode.However, for applications where only onereading is needed at certain times, and to con-serve power, one-shot mode may be used.

Note that thermostat outputs Thigh, Tiow andTcOm remain in the state they were in after thelast valid temperature conversion cycle whenoperating in one-shot mode.

Stand-alone measurementsIn applications where the DS1620 is used as asimple thermostat, no cpu is required. Sincethe temperature limits are non-volatile, thedevice can be programmed prior to insertionin the system.

To facilitate operation without a cpu, theCLK/CONV pin, pin 3, can be use to initiateconversions. Note that the CPU bit must be setto 0 in the configuration register to use thismode, Fig. 3.

To use the CLK/CONV pin to initiate con-versions, /RST must be low and CLK/CONVmust be high. If CLK/CONV is driven lowand then brought high in less that 10ms, onetemperature conversion will be performed,after which the device returns to idle mode.

If CLK/CONV is driven low and remainslow, continuous conversions will take placeuntil CLK/CONV is brought high again. Withthe CPU bit set to 0, CLK/CONV overridesthe 1 -shot bit if it is equal to 1. This meansthat even if the part is set for one-shot mode,driving CLK/CONV low will initiate conver-sions.

Communicating over three wiresThe three -wire bus comprises three signals,namely the reset line /RST, clock CLK, anddata signal DQ, Table 2. All data transfers areinitiated by driving the reset input high.Driving this input low terminates communi-cation.

A clock cycle is a sequence of a falling edgefollowed by a rising edge. For data inputs, thedata must be valid during the rising edge of aclock cycle. Data bits are output on the fallingedge of the clock, and remain valid throughthe rising edge.

When reading data from the DS1620, theDQ pin goes to a high -impedance, state whilethe clock is high. Taking /RST low terminatesany communication and causes the DQ pin togo to a high impedance state.

Data over the three -wire interface is com-municated lsb first. The command set for thewire interface, as shown in the panel, is as fol-lows; only these protocols should be written tothe device, as writing other protocols mayresult in permanent damage to the part.

Other chips in the Dallas thermal manage-ment range include a two -wire thermometerand thermostat, a two -wire thermometer withmemory and a one -wire digital thermometer.Battery temperature managers and batteryidentification chips providing time/tempera-ture histograms are also available.

PRESET

SLOPE ACCUMULATOR

LOW TEMPERATURECOEFFICIENT OSCILLATOR

V

COUNTER

JUL INC-Po

HIGH TEMPERATURECOEFFICIENT OSCILLATOR

COUNTER

COMPARE

PRESET

V

SET/CLEARLSB

F

TEMPERATURE REGISTER

STOP

A

Direct -to -digital sensingDirect -to -digital temperature sensors measure temperature through the use of anon -board Dallas proprietary temperature measurement technique.

Each temperature sensor measures temperature by counting the number of clockcycles that an oscillator with a low temperature coefficient goes through during agate period. This period is determined by a high temperature coefficient oscillator.The counter is preset with a base count that corresponds to -55°C. If the counterreaches zero before the gate period end, the temperature register - also preset to-55°C - is incremented, indicating that the temperature is higher than -55°C.

At the same time, the counter is preset with a value determined by the slopeaccumulator circuitry. This circuitry is needed to compensate for the parabolicbehaviour of the oscillators over temperature. The counter is then clocked againuntil it reaches zero. If the gate period is still not finished, this process repeats.

The slope accumulator is used to compensate for the nonlinear behaviour of theoscillators over temperature, yielding a high resolution temperature measurement.This is done by changing the number of counts necessary for the counter to gothrough for each incremental degree in temperature. To obtain the desiredresolution, therefore, both the value of the counter and the number of counts per°C - the value of the slope accumulator - at a given temperature must be known.

DS1620 designer's kit - exclusive EW+WW reader special offerDallas Semiconductor produces a designer's evaluation kit-the DS1620K- comprising software, the

DS1620 chip and a programming evaluation board that plugs into the pc's printer port. Normally priced

at £52.88, this kit is being offered to EW+WW readers at the special price of £37.50.

The user-friendly software allows the chip to be programmed and read via the pc printer port from anevaluation board including lead and D -type plug.

Send coupon to Dallas Semiconductor Corporation, Unit 26, West Midlands Freeport, BirminghamB26 3QD. Tel. 0121 782 2959, fax 0121 782 2156. Details of Dallas's range of thermal management

range will also be sent with the kit. Dispatch should be prompt, but please allow 28 days for delivery.

Name

Address*

Postcode Tel.

Tick for Mastercard or Visa 0

Card No Expiry date

Or Sterling postal order/cheque payable to Dallas Semiconductor Corp. Ltd please.

*Note: when ordering by card, above address must be that of the cardholder.

690 ELECTRONICS WORLD + WIRELESS WORLD August 1995

DESIGN BRIEF

Give asp a chanceWhile digital signalprocessing will do almostanything, Ian Hickmanpoints out that theanalogue kind hasconsiderable life left in itand has definiteadvantages - not leastthat of lower cost.

(a)

vum+

(c)

Vum+

M

0

v;

Digital signal processing can be as pow-erful as one wants, or as one's skill inwriting algorithms permits, at a price.

But very often, analogue circuitry will accom-plish any necessary signal processing.

By using analogue signal processing, youavoid the use of adcs and dacs, dsp chips,memory - and the expense of writing algo-rithms, achieving a much lower power budget.Eliminating clock signals can also be a bene-fit where small signals are being handled in aphysically small enclosure. Analogue signal -processing techniques come in a wider rangethan many people realise, and this article illus-trates some of them.

Bounding, limiting and clippingIt is often necessary to limit the maximumexcursion of a signal, for example when itcontains large interference spikes, or when thelower amplitude parts of it need to be ampli-fied for more detailed measurements.

Figure 1(a) shows the traditional way ofdoing this. If Rs is the slope resistance of the

++

Fig. 1. Circuit providing symmetrical limitingin an inverting amplifier at (a), while at (b)two circuits provide separately adjustablepositive and negative limiting levels - thoughthe inverting version is not recommended.Transistors in (c) provide very effectivelimiting in an inverting circuit.

zener diode and the bridge diodes, the gain ofthe inverting op -amp falls from R2/Ri to Rs/Riwhenever the output tries to exceed±(Vii -2V5), where Vz is the breakdown voltageof the zener diode and Vs is the forward volt-

age of the bridge diodes. For large signals, thegain falls almost to zero, or minus infinitydecibels.

Disadvantages of the circuit are possible lossof bandwidth. This is due to capacitance asso-ciated with the bridge circuit shunting R2, andthe fact that the positive and negative limitsare not easily and separately adjustable.

Figure 1(b) shows a simple non -invertingcircuit with separately adjustable positive andnegative breakpoints Viim+ and Viim_, and adistinctly more complicated inverting version.

The inverting version is not recommendedfor fast signals, since in the overdriven condi-tion the op -amp is left open -loop. This meansthat its output will fly off and hit one or otherof the supply rails. Recovery of a convention-al op -amp from overdrive is a relatively slowprocess, limiting the bandwidth of the circuit.If you can live with this, it is simpler to go fora larger gain and simply let limiting occur atthe rail voltage.

Transistors provide effective limiting in aninverting circuit, providing the output swingkeeps within the reverse Vbe ratings of thedevices. As Fig. 1(c) shows, breakpoints areseparately adjustable.

Another example of limiting is shown inFig. 2(a) -a circuit designed to measure thesettling time of an op -amp, by using a 'falsesum node'. This needs low -capacitanceSchottky diodes, with their low forward volt-age drop, to enable the 1% settling time to bemeasured.

In the case of a fast op -amp, the capacitiveloading of a conventional x10 divider probeon the false sum node may limit measurementaccuracy, so it is best to use an active probe.Measurement depends critically upon the flat-ness of the top and bottom of the test square -wave; for measurements of settling time to the0.1% or 0.01% level, more sophisticated lim-iting arrangements are called fors.

If you need a wideband amplifier with sym-metrical limiting, the Linear TechnologyLT1194, with its 35MHz -3dB bandwidth,provides a simple and convenient solution,Fig. 2(b). This ingenious device2 provides alimiting level adjustable by means of a controlvoltage Vc in the range -5V to -1V, with norequirement for any additional componentswhatever.

An additional advantage of this device isthat the gain-defming negative -feedback loop

August 1995 ELECTRONICS WORLD + WIRELESS WORLD 691

DESIGN BRIEF

is completed via a second long-tailed pair inparallel with the input pair. This means thatthe inverting and non -inverting inputs areeffectively floating and both present a highinput impedance.

Diodes in the circuit of Fig.1(b) protect theop -amp input circuit, whereas some of the oth-ers only limit the output swing. Where a cir-cuit needs protection against really largeinputs, use the arrangement of Fig. 2(c); forlarge positive inputs, D1 is reverse -biased,

0V -1-

(a)

(b)

(c)

Schottky diodes To scope Y2 input(low capacitance probe)

5k 5k

To scope Y1 input

+5V

+15V

-15V

Fig. 2. Diode limiting (a) used in a circuit tomeasure the settling time of an op -amp. At (b)the LT1194 wideband op -amp circuit withvoltage controlled symmetrical clipping level.Reproduced by courtesy of Linear TechnologyCorporation. Simple bounding circuit in (c)protects following stages from mains inputs.

Fig. 3. Diode breakpoint circuit (a), providing increasing gain with increasing outputvoltage. Transistor breakpoint circuit in (b), provides decreasing gain with increasing outputvoltage. Circuit at (c) gives sharp, temperature independent breakpoints and (d) an outputvoltage proportional to the logarithm of input voltage or current.

(a)

(b)

(c)

(d)

n

in

R2A R2

VBP2etc.

R2

VBp2 V.

0

(Vgpi + 0.6V)

R4

(R 1A+ Ai o)(Vopi + 0.6V)

R1 A

vo

vo

Slope R7

FT4

R7 R7 R7

R4 Re Re

R7 R7

R4 R5

0

R7

R0 .15 R0 .15 R0 .15

FT1 R2 A3

692 ELECTRONICS WORLD + WIRELESS WORLD August 1995

DESIGN BRIEF

R2

(i)

(a)

while for large negative inputs D2 is reverse -biased, the output voltage being limited toabout ±5V.

Given suitable reverse voltage ratings forD1,2 and a large enough dissipation rating forRI, the arrangement will protect any followingcircuitry from connection - accidental or oth-erwise - to 230Vac. In the linear range, forinputs between +5V and -5V, Vo follows V,.

If RI were only equal to R2/2, it could onlyjust succeed in raising the output to +5V. Thiswould leave no spare current to charge theinevitable stray capacitance up rapidly. Alower value avoids a poor frequency response,albeit increasing the dissipation in R, for largenegative input voltages.

If the circuit is turned upside down and thediodes all reversed, an n -channel mosfet witha 600V drain voltage rating, operating as aconstant -current generator, can be substitutedfor R1; the dissipation in this 'active R1' witha large input voltage is only proportional tothe input voltage v,, not to v,n squared.

Breakpoints and non-linear gainWhile Figure 1(a) illustrates an extreme exam-ple of a circuit with non-linear gain, there isoften a requirement for the gain of a circuit tovary over a range of finite values as the outputlevel varies, rather than suddenly falling tozero. Figure 3(a) shows a circuit that providesincreasing gain as the input increases in thenegative direction. This is because initially,the RI, R2 networks are in parallel with RB,their effect being successively removed aseach breakpoint is exceeded.

In Fig. 3(b), gain decreases as the outputvoltage exceeds each successive breakpoint,additional feedback resistors being added inparallel with RB. With reversed diodes orn -p -n transistors and negative breakpoint volt-ages, operation is extended to negative -goingoutputs for both circuits. Both types of break-point may be used together to give more com-

Fig. 5(a). This slew -rate limiter is animprovement on the leaky integrator of Fig.4, providing a constant maximum slewrate

limit, regardless of the signal amplitude. Setfor the fastest slewrate (wiper of R4 at Al's

output) and with the largest signal it canhandle linearly, (b) shows that the circuit

rapidly settles exponentially. With the sameinput, but kt's wiper now at the junction

with R5, (c) shows the circuit settling with alinear ramp, topped off with a slower

exponential tail.

2

a

Fig. 4(a) 'Leaky integrator' forms a simpleslew -rate limiting circuit (i), and afunctionally identical circuit at (ii). Addingadjustable gain in the second op -amp stage(iii) provides a variable slew -rate limit, asillustrated in (b). As the gain in the secondstage is increased, the required voltageexcursion across the capacitance is reduced.This is equivalent to reducing its capacitance,increasing the slew rate shown at (c). Thisarrangement is effectively a linear amplifierwith a high frequency roll -off. Consequently,for a fixed setting of the potentiometer,increasing signal amplitude results inincreased slew rate. The circuit can set anydesired limit to the maximum slew rate of thelargest signal but, as the signal gets smaller, sodoes the slew rate. (d) This limiter circuit canbe used to define the maximum size signalinput to the slewrate limiter.

Vi

TIME BASE = 500pSCHI V/DIV = 10VCH2 V/DIV = OZV

I

..

1 I

......... .

. ! ,WAVEFORM.c.................t..

TIME BASE = 1MSCH1 V/DIV = 0.2VCH2 V/DIV = 0.2V

I !

,1 ,

.-

.

;

1! !

......i I

(b)

TIME BASE = 1MSCH1 V/DIV = 0.2VCH2 V/DIV = 0.2V

! ,

I ...... 7 .. .. ..

TIME BASE = 500pSCH1 V/DIV = 10yCH2 V/DIV = 0.5V

(b)

...

(c)

August 1995 ELECTRONICS WORLD + WIRELESS WORLD 693

DESIGN BRIEF

+15V

10k

Bias

-1 5VFig. 6(a) This circuit is a true slew -rate limiter. Output in (b) follows the sinewave input fromthe peak (where the slope dV/dt is zero) up to the preset slew -rate limit. Thereafter, the setslew rate applies until the loop is again closed, where the output rejoins the ideal waveform,just before the next peak. As the amplitude of a squarewave input in (c) decreases, the slew rateremains constant. Unlike the circuits of Figs 4 and 5, for any given slew -rate limit setting, theslew rate at (d) remains constant until the output rejoins the input squarewave. During theslewrate limited section of the output waveform in (e), the amplifier is open loop. Thus the otainverting input (point A) during this period is not a virtual earth.

plicated shaping3.Circuits Figs 3(a) and (b) provide a gentle

transition from one slope to the next, extend-ing over a range of around 100mV or so, asthe diodes or base/emitter junctions movefrom cut-off to conducting. Despite some con-sequent variation in breakpoint with tempera-ture, this rounding is often beneficial.

Where sharply defined breakpoints freefrom temperature variations are needed, usethe circuit of Fig. 3(c). Here, the diode dropsare all within the loop and do not affect circuitperformance. When this circuit first appeared,the use of one op -amp per breakpoint wasconsidered almost profligate, but high-perfor-mance quad op -amps are now commonplacecomponents.

With jfets, either as elements in feedbacknetworks, or to vary the control voltage of avoltage -controlled amplifier, you can achievesmoothly varying gain without discrete break-points. Figure 3(d) is an example of a smooth-ly varying function of a very specific nature. Itexploits the law governing p -n junctions toprovide an output voltage proportional to thelogarithm of the input voltage or current overa wide range - up to nine decades with suit-able devices.

An op -amp with high open -loop gain isneeded to keep the base/collector voltage closeto zero, or collector leakage current ruins thelog. law at the lowest input levels. Parasiticparameters of the transistor cause the circuit tobecome very slow at very low input levels.

Slew -rate limitingCircuits for limiting slew rate prevent the rateof change of a signal exceeding some designmaximum - whatever the amplitude of thesignal. This is often necessary in electronical-ly controlled mechanical systems with largeinertia to prevent excessive forces beingapplied to moving parts.

A `leaky integrator' can form a simple slew -

rate limiting circuit, as shown in Fig. 4(a).Here, circuit (ii) is obviously functionallyidentical to that in (i). In both cases, the slewrate is limited by feedback via the capacitor.

If now a degree of gain is incorporated inthe second op -amp stage, as in full outputswing is obtained with only a reduced swingappearing across the capacitor. This is equiv-alent to reducing the value of the capacitor,changing the frequency at which the stage'sfrequency response starts to roll off, withoutchanging the low -frequency gain.

So varying the amount of gain in the secondop -amp stage provides a variable slew -ratelimit, as illustrated in Fig. 4(b). This is simplya linear amplifier with a high -frequency roll -off. Consequently, for a fixed setting of thepotentiometer, increasing signal amplituderesults in increased slew rate. Thus the circuitcan set any desired limit to the maximum slewrate of the largest signal, but as the signal getssmaller, so does the slew rate; see Fig. 4(c).

Set the largest signal input by means of alimiter, such as that shown in Fig. 4(d); thisprovides unity gain for small signals but if thepotentiometer is set midway, maximum outputswing will be limited to half the op -amp's rail -to -rail capability and progressively less as thewiper of the potentiometer approaches ground.

If the integrator of Fig. 4(a) is placed secondinstead of first and a few other changes made,an improved slew -rate limiter results; see Fig.5(a). To understand how the circuit works,imagine that the wiper of the potiometer is atthe top of its travel. Now, R2,3 are in parallel,defining the gain of Al as x18, inverting.

Figure 5(b) shows the output of A1, uppertrace, and of A2, lower trace, when a 300Hzsquarewave is applied, of just sufficient ampli-tude to provide the maximum outut swing ofwhich Al is capable. Initially, Al works as aninverting amplifier, because the voltage acrossC cannot change instantaneously. So the neg-ative -going edge of the input causes the posi-

TIME BASE = 200pSCH1 V/DIV = 5VCH2 V/DIV = 0.5V

TIME BASE = 200pSCH1 V/DIV = 5VCH2 V/DIV = 5V

T r

1 -I

t t

TIME BASE = 200p5CH1 V/DIV = 5VCH2 V/DIV = 5V

I

t

. ..

(b)

I

I I '

, ;

I

.1

1 1

I i! i I 1

(c)

lo .. i ....'

.

! f 11,

\t, i 14.

11ii.........1._........1 i I

TIME BASE = 500pSCH1 V/DIV = 1 VCH2 V/DIV = IV

I

1

(d)

(e)

Vo

tive output at A1, which in turn is applied viaR6 to the integrator, making its output slewnegatively.

The circuit settles with Al output at zero,otherwise the integrator output would still bechanging, and with the output voltage andA1 's non -inverting input at almost the inputvoltage. Output voltage vo is given by

694 ELECTRONICS WORLD + WIRELESS WORLD August 1995

DESIGN BRIEF

vinR/(R+10k0), where R is A1's effectivefeedback resistor - in this case, R2 and R3 inparallel. As Fig. 5(b) shows, the output settlesexponentially to the peak value of the square -wave input.

When the wiper of R4 is wound down to theR5 end of its travel, the action is very differentand is illustrated in Fig. 5(c). Now, only onetwentieth of A1's output is applied to R3,whose effective value as a feedback resistor istherefore not 2201(0, but 4.4MO. In conjunc-tion with R2, this gives a demanded Al gain ofx81.

With the same input amplitude as before, Alis now heavily overdriven and, moreover, thevoltage driving the integrator stage is alsoreduced to one twentieth. So Al remains over-driven while the integrator output slews at aconstant rate. It does this until voltage at Al 'snon -inverting input is so near that at its invert-ing input that Al re-enters the linear range.Thereafter, the circuit settles exponentially asin (b), but on a longer time constant - so long,in fact, that in (c) at this frequency and ampli-tude the output never quite reaches the peakvalue before the next edge of the squarewave.

Whatever the frequency, amplitude or wave -shape of the input, the slew rate set by theposition of R4 is never exceeded. As long asAl is overdriven, the first part of the settlingwill be at the maximum slew rate - howeversmall the input signal. This is a big advanceon the Fig. 4, but the exponential tail to thesettling time, visible in Fig. 5(c), remains adisadvantage.

A substantial improvement in this respect, atthe cost of a reduced range of slew -rate adjust-ment, is obtained by connecting a 1 MU resis-tor between the output of Al and the invertinginput of A2. Although this speeds up the expo-nential end of the settling tail, it can never beentirely eliminated. An ideal slew -rate limiterwould at all times slew at the same rate as theinput signal, or at the maximum rate, whichev-er was the lower.

Figure 6(a) shows the circuit of such a trueslew -rate limiter. You can see in 6(b) how theoutput follows the sinewave input from thepeak - where the slope dv/dt is zero - up tothe preset slew -rate limit. Thereafter, the setslew rate applies until the loop is again closed.At this point the output rejoins the ideal wave-form, just before the next peak.

If either the frequency or the amplitude isreduced (decreasing the maximum slew rate ofthe signal) or the control voltage lie isincreased (increasing the ota's maximumtransconductance), the sinewave is undistort-ed. On the other hand, if the amplitude or fre-quency are sufficiently increased (or liereduced) the sinewave is permanently in slew -rate limit - it becomes a triangular wave.

Figure 6(c) shows how, as the amplitude ofa squarewave input decreases, the slew rateremains constant - unlike the effect of the cir-cuit of Fig. 4. Also, the slew rate remains con-stant until the output rejoins the input square -wave, as in Fig. 6(d). During the slew -ratelimited section of the output waveform, theamplifier is open -loop and the ota inverting

10k

Set dVdT

-5V

100k 100k

BC107

R3

R2 R4

10 = V1 -V2 independent of VAR1

dVdT

OV

(a)

(b)

OV

Fig. 7(a). Howland current pump provides an accurate, linear, bipolar, voltage -controlled currentsource. Non -inverting integrator at (b) is arranged as a linear timebase circuit.

input is not a virtual earth during this period,exhibiting the waveform shown in Fig. 6(e).Note the pull -down resistor at the operationaltransconductance amplifier's Darlington out-put buffer stage. This is recommended if usingthe LM13600, since the internal biasing of thebuffer in this ota is varied in sympathy withthe control voltage Vc: the LM13700, with itsfixed buffer current, might be a better choicein this application.

Integrating and differentiatingBasic op -amp circuits for integrating and dif-ferentiating are so well known that I won'tspend any time on them here. But theHowland current pump4 in Fig. 7(a) is perhapsa circuit that deserves to be better known. It isa voltage -controlled current generator with(ideally) infinite output impedance, and caus-es a current (V2-V1)/R1 to flow in a load.

If the load is a capacitor and V1 is tied toground, then the circuit forms an integrator.As such, it possesses two advantages over themore usual op -amp integrator: firstly, it is anon -inverting integrator, and secondly, oneend of the integrator capacitor is grounded.Figure 7(b) shows a linear ramp or timebasegenerator based on the circuit of Ref. 3.

Some of the circuit techniques mentionedearlier can usefully be combined with inte-grators and differentiators. For instance, if aband -limited signal is differentiated, clippedand then integrated, the result is slew -rate lim-ited. If, instead of clipping, the differentiatedsignal is slew -rate limited and then integrated,then its second derivative d2v/dt2 is limited.

References1. Methods for measuring op -amp settling time.AN10-1, July 1985, reproduced in the 1990Linear Applications Handbook from LinearTechnology Corporation.2. Hickman, I., Four op -amp inputs are better thantwo. EW+WW, pp399 - 401, May, 1992,reproduced in the Analog Circuits Cookbook,Butterworth -Heinemann, 1995, ISBN No. 0 75062002 1.3. Hickman, I. Add on a spectrum analyser.EW+WW, pp982 - 989, December, 1993, also inthe Analog Circuits Cookbook.4. Pease, R A. Improve circuit performance with aI -op -amp current pump. EDN, January, 20 1983,pp85-90.

August 1995 ELECTRONICS WORLD + WIRELESS WORLD 695

:isi PjftIMI KUM :VIVO :1IJ

RADIO

ENGINEER'S

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Covers all aspects of radio andcommunications engineering fromvery low frequencies tomicrowaves, with particular emphasison mobile communications. Waveprinciples and the decibel scale,instrumentation and power supplies,equipment types and encryptionmethods, connectors and interfaces,are all included in this book.

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Circuit Designer'sCompanionby T Williams, 320pp, paperbackOrder -0 7506 1756 XPrice £15.99

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Valued by linear and digital designersalike, this guide explains and outlinessolutions that take into account theimperfect behaviour of realcomponents, interconnections andcircuits.

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SERVICINGPERSONALCOMPUTERS

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Presents an extensive treatment ofapplications and a practically oriented,unified theory of operational circuits.Provides the reader with practicalknowledge necessary to select anduse operational amplifier devices.

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Written for students and peopleinvolved with vcr servicing, this bookis an invaluable guide and referencecovering all aspects of modern vcrs.Contains new material on basicmagnetic theory to C&G 224

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Easy -to -read, but nonethelessthorough, this book on digital circuits isfor use by students and engineers, andis a readily accessible source of data ondevices in the ttl and cmos families.

694D

um num :io1.0J MIN MO :181'4111 74I1 MO :1.)The Art of DigitalAudioJohn Watkinson, 490pp, hardbackOrder -0 240 51320 7Price £49.50

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As a bench -side companion andguide, this work has no equal. Itspurpose is to ease and speed up theprocesses of fault diagnosis, repairand testing of all classes of homeaudio equipment: receivers,amplifiers, recorders and playbackmachines.

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EMCFOR

PRODUCTDESIGNERS

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M & B RADIO (LEEDS)THE NORTH'S LEADING USED TEST EQUIPMENT DEALER

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CIRCLE NO. 12'2 ON REPLY CARD

COMPONENTSSYSTEMS FROM IOSIS

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CIRCLE NO. 126 ON REPLY LARDCIRCLE NO. 127 ON REPLY C -1R1

RF DESIGN

0

High-performance

ANTENNAUnable to find a 24cm antenna combiningthe features of wide beam, wide bandwidthand useful gain, John Cronk set aboutdesigning his own.

This antenna design has fewer criticaldimensions then most other configura-tions, and can be easily customised. It

comprises a lightweight parabolic shapedplane reflector which is illuminated with a hor-izontally polarised dipole and reflector feed.Size of the reflector suggested is about theminimum worthwhile for 1.3GHz operation.

Design considerationsBoth electrical and mechanical factors have to

0

18 SWGAluminiumcentre support

TV type elect clamp

Fig. 1. Using wing nutsfor securing the boom onits centre supportreduces assembly time toaround half a minute.

Fig. 2. Horizontal test pattern of the 24cmparabolic antenna. Frequency 1255MHz, swr1:1.2 and power 1W.

be considered when deciding on the reflectorsize and shape. One aspect taken into accountin this design was to keep the structure light,and small enough to move around in a familycar. The feed boom is removable for trans-portation. If two wing nuts are used on themast clamp, it is possible to assemble theantenna in about half a minute and withouttools, Fig. 1.

The distance of 20in from the reflector to thefocus was chosen mainly for mechanical rea-sons. It was arrived at through the use of fullsize drawings. Performance tests on the anten-na show the choice to be acceptable.

The reflector should be formed as accurate-ly as possible, but departures from the meanshape of up to one -tenth of a wavelength aregenerally tolerable. This is 2.3cm at 1.3GHz -an easily achievable tolerance.

Mesh for the reflector can be seen as a largenumber of reflecting elements spaced one -thir-tieth of a wavelength over most of the reflectorsurface and one -sixtieth of a wavelength in thearea of the overlap at the centre. No figure foractual reflectivity is available. Wind resistanceis considerably less for this material than forexpanded aluminium mesh.

Test conditionsGain of the antenna comes from concentratingthe radiation in the vertical plane. Claims forantenna gain are notoriously controversial. Myantenna was tested in a coastal car park withthe sea behind at 1W transmitter power.

The receiving station was about 2.4kminland and used a multi -element yagi antennacombined with a commercial receiver with anS -meter driven from the automatic gain con-trol line. The S -meter was calibrated usingexternal attenuators in the antenna feeder.During the tests, the attenuators were also usedto extend the dynamic range of the receivingsystem.

The centre of the test antenna was about2.4m above ground and the mast was equippedwith a scale marked with 15° divisions. Adipole antenna was used to establish the OdBdreference. The horizontal radiation pattern ofthe test aerial, Fig. 2, was remarkably smoothcompared to those of several other aerials test-ed. An honest attempt to obtain an accurate

for 24cm

Featuring wide beam, wide bandwidth anduseful gain, the 24cm antenna is easilydisassembled for transportation.

gain figure yielded a result of 15dBd(powerx31.6) or, say, 17dBi. The degree ofexperimental error was not determined.

Feed designWide bandwidth was necessary so that theantenna could be used over as much of the1.3GHz band as possible. This use includesamateur television.

The feed design satisfies the requirementthrough the use of few tuned elements and thetype of balun chosen. The dipole element islarge in diameter relative to the operatingwavelength, the size being chosen to bring thecentre impedance close to 50g.

Dipole to reflector spacing is approximately0.2 of a wavelength but the actual distance canbe varied to allow fine adjustment of the feedimpedance. Length of the dipole elements can

August 1995 ELECTRONICS WORLD + WIRELESS WORLD 699

RF DESIGN

X7 X6 X X X2 X

-1 Itklk 1111111190"'''' 90"`

F

20"

6

A

460in

Fig. 3. Antenna's parabola profile can becalculated then plotted, but it can also bedrawn without resorting to mathematics byusing a pin and string.

be trimmed so that the dipole becomes reso-nant at the design centre frequency, providinga resistive match at the frequency.

The centre frequency chosen for the antennais 1.255GHz. Bandwidth of the feedimpedance is further increased by making thebalun slightly longer than a quarter wave-length electrically. This adds inductive shuntreactance at frequencies below the centre fre-quency of the design and capacitive shuntreactance at higher frequencies. In this way, itis possible to extend the matching over awider bandwidth.

Constructional notesBoth imperial and metric dimensions are usedin the following description, as the materialsused are produced variously in both size units.

A full-size drawing of the parabola profile isneeded. Several methods of doing this areshown in handbooks. The beauty of the stringand pin method described here is that itrequires no mathematics, Fig. 3.

First draw line AB, and then at its centredraw line PFX, at right angles to AB. Nexteither draw line XY parallel to AB, or use along rule or tape parallel to AB, this must bemarked off with regular divisions - X1, X2 etc:

Now fix one end of a piece of string at pointF using a pin. Take the string around anotherpin at P1, and then up to point X1, and markthis length with a knot. Now plot the curve bymoving the knot to X2, and keeping the stringat right angles to XY, prick a mark at P2, andso on, until half the curve is marked out.Repeat for the other half of the curve. Draw aline smoothly rough the pin pricks to showthe shape of the reflector surface.

This graphical method illustrates the actionof the reflector. If XY is a wavefront, thelength of string show lines of constant phaseto the focus.

Next the reflector former has to be shapedto fit the drawn profile, Fig. 4. The formeruses 60in of I/2in square aluminium tubestock, as commonly used for tv yagi antennabooms.

Use a simple bending machine as shown inFig. 5 to avoid crumpling. This consists of ablock of hardwood, cut in two by a curved cutwith a radius slightly less than the curve at thecentre of the required profile. A small scrap ofplywood tacked to the underside of one of thetwo pieces will help to keep things in line.

Shaping of the former is carried out by mak-ing a sandwich of the blocks and the tubing inthe jaws of a vice. Starting from the centre,squeeze the former gently to shape, movingthe metal along an inch or so at a time. Whencorrectly shaped, it can be used to mark outthe 18swg aluminium centre support.

Rigidity of the former can be considerablyimproved by shaping the straight edges rounda suitable mandrel of, say, half -inch diameterrod, with a mallet to produce a rolled edge.

A 3-by-2ft sheet of wire mesh called HandyMesh was obtained from a local hardwarestore to provide the material for the reflectorsurface. The mesh consists of half -inchsquares formed by 22swg tinned wire. Thesheet was cut in half along its length and thepieces overlapped to form a strip 60 incheslong. The overlapped section was strengthenedby binding some of the coincident wires with22swg tinned copper wire, then soldering.

A small, off-centre hole will be required toclear the boom, as shown in the drawing. Themesh is fixed to the square tube former by

Main reflectorWire mesh 0.5in2 22 SWG tinned wire{2x3ft sheet, cut in half and overlapped at centralte 0556S S S SS S 5000 e

0.5in2 section

4 BA self -tappingscrews

4.5in

60in

o Ref.

Dipole

18SWG.

Rolled edge

Mast 1.25x1.5in

4 holes 1.5in dia.

TV type clamp

Fig. 4. Reflector detail. Mesh is a commercially -available type comprising half -inch squaresformed from 22SWG tinned wire.

-6in

Vice jaws

Jaw

Fig. 5. To avoid having the tube crumpleduring curve shaping, it is advisable to makeyourself a bending fixture.

PTFE plug tospace elements

2mmt

To fit inside dipole elements

80cm

Coax. to N typein line connector

Dipole Ref

Solder50 Coax.

Solder 110mm

Balun 64-1.mrnsx7oom2Ol in PVC flex

mm ube

42mm

Ref

1.5cm2

Enlarged view lookingOn end of boom

Fig. 6. Plan of antenna boom with feed dipoleand reflector. The boom is electrical conduitwith a removable lid.

gripping between a strip of three-quarter inchwide 22swg aluminium, with four BA size selftapping screws or one eighth inch pop -rivets.

Feed boom detailsDimensions and construction of the feed boomand elements are shown in Fig. 6. The boomis an 80cm length of 1.5cm square plasticelectrical conduit. This conduit has a press -oncapping and is a tight fit in the tv-type squareboom mast clamp.

The elements were made from 6mm diame-ter aluminium tubes, the dipole connectionsbeing made with special aluminium solder.Thin -walled brass or copper tube could also beused. The small plug in the centre of thedipole keeps the halves under control duringassembly. Each element is held in place withepoxy resin filler. This same material is usedto weatherproof the end of the co -axial cable.

The balun uses a length of common 32strand of 0.0076in PVC -covered flex, joinedbetween the outer and inner of the co -axialfeeder cable. To obtain maximum bandwidth,the length of 64mm was arrived at experi-mentally.

Finishing touches can include replacing theU -bolt clamp fixing nuts with wing nuts,weather-proofmg the ends of the square tubeswith plastic plugs and varnishing overall.

700 ELECTRONICS WORLD + WIRELESS WORLD August 1995

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Custom designs from IOVA to 3kVA

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100% Final test approved to ISO 9003

All transformers manufactured at UK factory

Designs to most international standards

70V or 100V Line & low noise audio designs

fori

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Rapid quotation, design and prototype service

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4:e;

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CIRCLE NO. 123 ON REPLY CARD

`OFF -AIR' FREQUENCY STANDARD

* Provides 10MHz, 5MHz & 1MHz* Use it for calibrating equipment that relies on quartz crystals,

TCXOs, VXCOs, oven crystalsPhase locks to DROITWICH (rubidium controlled andtraceable to NPL)For ADDED VALUE also phase locks to ALLOUIS (cesiumcontrolled and traceable to OP - French eq to NPL)

* British designed and British manufactured* Options available include enhanced receiver, sine wave

outputs and 13MHz output for GSM. Prices on application.

a

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£195-0,,Output frequencies -10MHz, 5MHz, 1MHzShort term stability - betterthan 1x10 (1 sec)Typical -4x10-9 (1 sec)Long term - tends to20102 (1000 sec)Call for 'ON -Air' Standard list112=

TEST EQUIPMENTWe are well known for our quality, new and used Test Equipment. Our list is

extensive, the following will give some idea of our range and prices:

TIME 404S Precision mV source £95 FEEDBACK SS0603 1MHz sine/square oscillator £125

TIME 2003N DCV Pol/Cal, 0-10V, null, etc £249 FEEDBACK DPM609 10Hz-100kHz phase meter £125

TIME 2004 DC Volt standard 0.005% £945 TEKTRONIX 2215 60MHz dual trace, dual delay T/B £450

TRACOR 890A 60kHz/75kHz trackingRx £95 TEKTRONIX 2455 300MHz 4 trace, dual delay T/B £1950

FLUKE 8012A 3.5 digit lcd, addc/V/1/ £149 GOULD 0S3000A 40MHz dual trace, dual delay T/B £249

FLUKE 8600A 3.5 digit led, ac/d0/1/0 £59 HITACHI V222 20MHz dual trace, N trig £249

KEITHLEY 197A 4.5 digit led, ac/dc to lkV £149 MARCONI TF2370 100MHz spectrum analyser £995

ADVANCE VM78 ac lmV to 300V, up to 1MHz £25 ADRET 740A 01 MHz-1.2GHz sig. gen. AM/FM/PM £1450

MARCONI TF2600B video urn 300V, to 10MHz £75 FLUKE 9318 AC rms/differential voltmeter, 0-1kV ac £95

MARCONI TF2163 DC to 1GHz attenuator £195 BRYANS BS272 2 pen 10cm/min to 1 Ornm/hr £95

E.V. EV4020A NTSC V/scope £395 GOULD 2400 6 pen 5mm/sec to 200mmimin £125

LEADER LG396 NTSC pattern generator £395 VIGILANT SR532 10KHz-30MHz, AM/CW/SSB, PLL £1250

PHILIPS 5509 PAL pattern generator £195 VIGILANT SR510 10KHz-30MHz, AM/CW/SSB, PLL £750

PHILIPS PM5716 pulse generator £495 EDDYSTONE ECI 0 150kHz to 30MHz, AM/CW/SSB £125

PHILIPS PM5134 function generator £1495 RACAL RA17 0.0 to 30MHz AMJCW/SSEVIIL £149

MARCONI TF2700 universal LCR bridge £195 DRAKE MN2700 ATU/PSU £380

AVO CZ457/5 component comparator £95 DIGITAL LNO3 Serial Laser Printer £249

PHILIPS 8833 Mk 2 RBG, comp, sound £99 DIGITAL MicroVAX II 9 VT220 terminals, Hubs, SAN£P0A

Call for Equipment list CIRCLE NO. 125 ON REP.( 1 f skit

SPECIAL OFFERWe have obtained an IMTEC 300 film/aperture card reader/printer which has had verylittle use. Output on plain paper from paper trays, sizes A5 to A3, including the 'B' sizes,

and variable. This is high quality equipment, serious offers are invited.

[A1,1 HALCYON ELECTRONICS423, KINGSTON ROAD, WIMBLEDON CHASE, LONDON SW20 8JRSHOP HOURS 9-5.30 MON-SAT. TEL 0181-542 6383. FAX 0181-542 0340

LOW COST DEVELOPMENT SYSTEMECAL comprises a versatile relocatable assembler withintegral editor which runs about ten times faster than

16 & 32 bittypical assemblers. Support includes 4, 8,processor families including75X, 6502, 6809, 68HC05/11,8031/51, H8-300, 78K, PICs, ST6& Z80/180, 68000, 80C196, H8-500 & Z280.

ECAL is either available for asingle processor family or allfamilies.

Single processor version £295Multiprocessor version.... £395

Overseasdistributors

required

OEMA Ltd.,7 & 711Brook Lane,Warsash,Southampton 5031 9111Tel: 01489 571300Fax: 01489 885853

The PC based ECAL hardware emulator is fullyintegrated with thethe target through the

assembler. Connection is made toeprom socket so a single pod

can support all processors.Facilities include windows forthe inspection or change ofregisters or memory. You caneven watch your programexecuting at source level!

Download time is about twoseconds!

Pods can be daisy -chained for16/32 bit systems.

Applications include softwaredevelopment, hardwaredebug, test and, finally,teaching about micro -controllers in education.

ECAL emulator £475

Quantity discounts ofup to 50% make ECALsoftware ideal foreducation.

IRCLE NO. 128 ON REPLY CARD

August 1995 ELECTRONICS WORLD+WIRELESS WORLD 701

Electronic Designs Right First Time?Affordable Electronics CAD

EASY -PC: Entry level PCB and Sch. CAD. $195.00 £98.00EASY -PC Professional: SchematicCapture and PCB CAD. Links directly toANALYSER Ill, LAYAN and PULSAR.

$375.00 £195.00

PULSAR: Digital Circuit Simulator- 1500 gate capacity.

$195.00 £98.00

ANALYSER Ill: Linear Analogue CircuitSimulator - 130 node capability

$195.00 £98.00

LAYAN: New Electro-magnetic layoutSimulator. Include board parasitics in yourAnalogue simulations.

$950.00 £495.00

Z -MATCH for Windows: Wndows basedSmith -Chart program for RF Engineers.

$475.00 £245.00

FILTECH: Active and Passive Filter Design $275.00 £145.00We operate a no penalty upgrade policy.Technical support is FREE FOR LIFE.Special prices for Education

US$ pricesincludePost andPacking

StellingPricesexcludeP&P andVAT.

Number One SystemsRef WW, Harding Way, St. Ives,

Huntin 'don, Cambs. PE17 4WR,For Full Information Please Write, Phone

Tel: +44 (0) 1480 461778Fax: +44 0 1480 494042

UK.or Fax.

Schematic Design

It.^..951122498

It..983138E8

Create your schematics quickly andefficiently using EASY -PC Professional.Areas of the circuit can be highlighted onscreen and simulated automatically usingPULSAR, ANALYSER III and Z -MATCHour simulation and design programs.

Digital and Analogue SimulationModify theconfigurationand changecomponentvalues until therequiredperformance isachieved.

PCB DesignThe design, complete with connectivity, canthen be translated into the PCB. Theconnectivity and design rules can be checkedautomatically to ensure that the PCB matchesthe schematic. And with LAYAN the Parasiticeffects of the PCB canbe included in theAnalogue Simulation MC

IttCLE NO. 129 ON REPLY CAR°

When Performance is more important than size:-

two new re -programmable BASIC Stamp Computers.

04544,1,s

4v 440,

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up to 100 program lines2,000 lines/sec

Comms to 2400 baudf29 single price

BS2-IC16 I/O lines

up to 600 program lines10,000 lines/sec

Comms to 9600 baud149 single price

Programming package £66

Milford Instruments Tel 01977 683665 Fax 01977 681465

702

=ffliffinTIMELECTRONICS WORLD +WIRELESS WORLD August 1995

NEW PRODUCTS C_ASSIFIEDPlease quote "Electronics World + Wireless World"when seeking further information

ACTIVEA -to -d and d -to -aconvertersLow -power, low-cost a -to -d.Analog's AD876 joins the range oflower -power analogue -to -digitalconverters, delivering a 20Msample/sconversion rate at a cost of $9.95 inquantity. It possesses a differentialtrack -and -hold amplifier to eliminatethe need for an external buffer anddigital error correction allowsimmediate sampling without the needfor internal calibration. Power is160mW at 5V. Analog Devices Ltd.Tel, 01932 266000; fax, 01932247401.

Discrete active devicesPower mosfets. Two 30V SOICpower mosfets from Siliconix, the

Low -leakage diodes. Precisiondiodes by Zetex in the FLLD200series of dual devices featurereverse currents of up to 800%better than standard types.Three models are available: theFLLD263 common -anode type;the 258 common -cathodeversion and the series -connected 261. Leakagecurrents are of the order of3-5nA/100V, with a typicaldiffusion capacitance of 0.9pF at1V. Average rectified forwardcurrent is 250mA. Zetex plc.Tel., 0161-627 5105; fax, 0161-627 5467.

Si4410DY and Si4435DY, possesshalf the on resistance of any other onthe market, says the company. 4410is an n -channel device giving 13.5m0at 10V gate voltage and 20m0 at4.5V, while the 4435 has 20m0 at10V and 35m0 at 4.5V. Both use thecompany's Trench technique toprovide transistor densities of 12million cells per square inch.Siliconix/Temic Marketing. Tel., 01344485757; fax, 01344 427371.

Digital signalprocessorsSilicon delay lines. Data DelayDevices all -silicon delay lines, inSOIC or 14 -pin dips, offer five and tenequally spaced taps and give delaysfrom 5ns to 500ns. Operatingfrequency is 100MHz and groundbounce is said to be low. The devicesare compatible with ttl and cmos. BFIIBEXSA Electronics Ltd. Tel., 01622882467; fax, 01622 882469.

Linear integratedcircuitsDual amplifiers. Current -mode dualamplifiers by Elantec, the EL2280 andEL2270 operate from 3V or 12V(±1.5V, ±6V) supplies at low powerand with good video performance.Bandwidth at -3dB is 250MHz(70MHz), supply current 3mA (1mA),and slew rate is 1200v/ps (800V/Ns)and differential phase and gain of0.05° (0.15°) and 0.05% (0.15%).Elantec. Tel., 0171-482 4596; fax,0171- 267 1026.

Video op -amp. Having a 300MHzbandwidth at a 1 mA supply currentfrom 5V, the AD8011 op -amp byAnalog Devices is for use in theprocessing of high-speed video,

giving 0.1dB gain flatness up to25MHz, 0.02% differential gain and0.06° differential phase error. Worst -case thd is -62dB at 20MHz into1500 and the amplifier slews at3500V/ps, settling to within 0.1% in25ns. Analog Devices Ltd. Tel, 01932266000; fax, 01932 247401.

Memory chips1Mbit synchronous srams. Sincethe pPD431232LGF-A8 1Mbitsynchronous static ram has a dataaccess time from the clock of 8ns, it issuitable for use with 66MHzprocessors and, being organised as32 by 32, will form a 256K cachememory using two devices. Thesedevices have a burst counter andproduce either an interleavedaddressing sequence to suit the IntelPentium PE54C and 8046 processorsor a linear sequence for MIPS types.NEC Electronics (UK) Ltd. Tel., 01908691133; fax, 01908 670290.

PCMCIA memory cards. Centonsram cards are available with storagecapacities from 64Kb to 2Mb, with orwithout attribute and in flash memory,in 5V/5V or 5V/12V versions, from256Kb to 32Mb capacity. Alsoavailable are ATA flash, Ethernet andfax/modem cards. METL. Tel., 01844278781; fax, 01844 278746.

Microprocessors andcontrollersFilter/codec. MT9160 is a 5Vfilter/codec from Mitel that hashandset transducer interfaces andprogrammable sidetone path, withdigital gain control, anti-aliasing filtersand reference and bias voltagesources. It supports both A -law andp -law requirements and offersprogrammable CCITT (G.711)/sign-magnitude coding. There is adifferential interface to handsettransducers, including a 3000receiver driver. Register access is viaa serial microport compatible withstandard microcontrollers. MitelSemiconductor. Tel., 01291 430000;fax, 01291 436389.

0.9p PICs. Microchip has two newPIC risc cpus in a 0.9pnm process.PIC16C58A has 2048 by 12byte ofprogram storage and 73 by 8byte ofsram for data. With 12 i/o linesindividually direction controlled andthree timers, the device is fullycompatible with other versions. Itworks on 2.5-5.5V and draws under2mA. PIC16C54A replaces the C54and is suitable for lithium battery

'Fastest' a -to -d. Claimed by itsmakers. Signal ProcessingTechnology, to have theindustry's highest samplingrate at 1GHz, the 8 -bit SPT7760is a full parallel flash designgiving a bandwidth of over900MHz. Because of the widebandwidth and inputcapacitance of only 15pF,external track hold amplifiersare unnecessary in mostapplications. A proprietarydecoding method reducesmetastable error to under llsbof the Gray code output. Eachof the 256 comparators has itsown input preamplifier to actas a buffer and to stabilise thecapacitance with input voltagerange and with frequency. Thedevice is thereby easier todrive than previous designs. Allclock inputs, controls and dataoutputs are ECL-compatible.Signal Processing Technology.Tel. (USA), 001 719 2300: fax.001 719 2370.

power. Hawke Components Ltd. Tel.,01256 880800; fax, 01256 880325.

Mixed -signal ICsLogic power interface. Devices inTI's Power+Array family drive three-phase, dc and stepper motors directlyfrom 5V logic -level input. Currentratings are 0.75-1A/channel at up to60V, and there are low -side and high -side drivers and bridges. PolarElectronics. Tel., 01525 377093; fax,01525 378367.

PASSIVEPassive componentsResistor networks. Thick -film resistornetworks from BI Technologies aremeant mainly for use in inrushlimitation, snubber circuits and upsequipment. Four standard types, BPC-3/5/7/10, are rated at 3,5,7 and 10W,resistance range being 10 to 200k52at tolerances between ±0.5% and±10%. Operating voltages are 300Vacand 500V dc and the networks canhandle peak currents of twenty timesrated current for 8ms. Temperaturecoefficient is 100ppm/°C. BITechnologies Ltd. Tel., 01384 442393;fax, 01384 440252.

August 1995 ELECTRONICS WORLD + WIRELESS WORLD 703

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Encoder interfaces. MBMElectrodynamics isproducing custom interfacesfor its range of shaftencoders and scanningmotors, thereby presentingthe user with a 'ready-to-wear' output at a lower costthan usual. MBMElectrodynamics. Tel., 01273413981; fax, 01273 425256.

Connectors and cablingBoard/board connectors. On a 2mmpitch, Robinson Nugent Pak -2 board -to -board connectors have pinsdesigned for through -hole or surface -mounting, vertical and right-angle, in4-100 ways; optional flangesaccommodate various mountingrequirements. A variety of stackingpossibilities is offered. RobinsonNugent (Europe) Ltd. Tel., 01256842626; fax, 01256 842673.

Cut flat cable. Sumitomo flat cable isnow available cut to length in 1mmand 0.5mm pitch in 100mm and150mm lengths in short runs at theprice normally associated with longproduction runs, with a next -daydelivery. Stripping and reinforcementcan be done to order and mating FFCconnectors from either JAE or Molexfitted. Flint Distribution. Tel., 01530510333; fax, 01530 510275.

2mm jumper socket. At the sameheight above board as a typical ICpackage, 3Ms 2mm jumper socket forreconfiguring boards offers analternative to dil switches andpossesses the advantage of easyaccess for testing. 3M UnitedKingdom plc. Tel., 01344 858000; fax,01344 858758.

DisplaysActive -matrix module. Citizen hasits first active -matrix video module,which uses a new two -mask TFTtechnique and a four -level drive. It isbased on the use of higher -thresholdpixels, which are thereby unaffected

ProductionequipmentElectric screwdrivers. Eliza20V Electric screwdrivers madeby Atlas Copco have a patentedmechanical clutch for enhancedaccuracy. Screws from 1.2mm-4mm can be tightened totorques of 0.05-3.4Nm and thetools have a very light triggerand reverse switch. Accessoriesinclude pistol -grip attachments,vacuum pickup adaptors, ascribe and various insert bits.Hunter AP, Tel., 01934 876028;fax, 01934 876928.

by stray signal from nearby lines orpixels. Additionally, the small size ofthe diodes allows a 480 by 230resolution in the 3in diagonal module,with a contrast ratio of 200:1 and a40ms response time. Citizen EuropeLtd. Tel., 01753 584111; fax, 01753582442.

FiltersControl -line filters. BLPComponents's SCF range of rf filtersare designed to protect linescontrolling fire and intruder alarms,emergency lighting, elevator controlsand the like. They conform to MIL -STD -220A and are suited to Tempest -rated equipment. Both ac and deversions handle up to 2A and comewith two, four or ten -line stand-aloneform and 10 -line modules for cabinetmounting. BLP Components Ltd. Tel.,01638 665161; fax, 01638 660718.

HardwareBobbins. BFI IBEXSA has a range ofSMD, EFD, EP, RM and EE coilbobbins and bases for high -volumeproduction. As well as customdesigns, the bobbins are available ina low -profile range in vertical andhorizontal form. Materials are AmocoLVP, Sumitomo LCP and phenolic, allUL approved. BFI IBEXSA ElectronicsLtd. Tel., 01622 882467; fax, 01622882469.

InstrumentationESD generator. A low-costelectrostatic discharge generator, thepQT from picoQ Corporation, testsequipment for immunity to esd andemi. It produces a controlled airdischarge through direct contact,needing no ground wire, powersource, internal contact -mode relay orpolarity switch. E -field and H -fieldprobes are available and theinstrument is calibrated to abroadband or human -body model.Lyons Instruments Ltd. Tel., 01992768888; fax, 01992 788000.

Tv spectrum analyser. Mainly fortelevision work, the U4341 spectrumanalyser in the R&S Advantest rangeis light and portable and yet highlysensitive, having a built-indemodulator to allow programmes tobe shown on the tft screen. Level andfrequency measurements may bemade, selection being by storedchannel frequency, which can beedited for more channels at up to2.2GHz. Two slots take PCMCIAcards to store data and settings. Allnational television standards aresupported. Rohde & Schwarz UK Ltd.Tel., 01252 811377; fax, 01252811447.

Electrostatic fieldmeter. Hand-E-Stat is an instrument made by theDutch company Simco to measurethe potentials associated with staticcharges. It is a pocket -sizedinstrument, offering sample and holdmodes, with a light -ranging method ofachieving repeatable results. Its caseis conductive and there is a ground

Energy conservation.Schuter's power managementmodule switches off a pc'smonitor when it is idle,bringing it back to life if themouse moves or someonetouches the keyboard. It is asnap -in mounting inlet outletplug and socket with thenecessary control circuitryand is meant to offer energysaving when large numbers ofpcs in an organisation arenormally left running all day,being used infrequently.Radiatron Components Ltd.Tel., 01784 439393; fax, 01784477333.

clip. Autoranging covers ±20kV at adistance of 2.5cm and, as well as thedigital display, an analogue output isprovided. Accurate measurementscan be made in areas using airionisation. Simco (Nederland) BV.Tel., 0031 5730 88333; fax, 00315730 57319.

Lcd panel meter. Needing noexternal power supply, bypasscapacitors or trimmers, the DMS-30LCD-4/20S panel meter by Datel ispowered by a 4-20mA current loopand measures 2.2in by 0.93in, with a0.4in high display. An eight -positiondip switch selects range, offset anddecimal point placing, no jumpersbeing needed. Datel (UK) Ltd. Tel.,01256 880444; fax, 01256 880706.

InterfacesGPIB controller/analyser. Twointerface boards from National turnexisting National interface boards, theAT-GPIB/TNT and the PCMCIA-GPIBcard, into GPIB analysers, controllingGPIB instruments as well as sortingout difficulties such as addressinginconsistency, protocol violation andothers. AT-GPIB/TNT+ and PCMCIA-GP/B+ also capture HS488 activity.National Instruments UK. Tel., 01635572400; fax, 01635 523154.

Infrared data link. Conforming to theInfrared Data Association (IrDA) serialinfrared comms standard, H -P's

704 ELECTRONICS WORLD + WIRELESS WORLD August 1995

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HSDL-1000 provides a link effectiveup to lm for communication betweenmobile computers and devices. Itworks at 870nm and 115.2kb/s over±15°, the package consisting of a ledand detector, led driver, photodiodetransimpedance amplifier, comparatorand bias network. Communication iseffective in 10klux of sunlight and upto 1klux of incandescent orfluorescent lighting. Hewlett-PackardLtd. Tel., 01344 366666; fax, 01344362269.

Sample -rate converter. Analog'sAD1893 SamplePort is a -16 -bit stereoasynchronous sample -rate converterthat accepts a digital input samplestream at an arbitrary or varying rateand outputs the stream at the user'schosen rate, thereby also minimisingthe effect of clock jitter. It is based onthe AD1890, but also offers anoscillator, single 3-5V operation, a -

power -down mode and right -justifiedserial interface format. Thd+n is 96dBminimum, as the dynamic range witha 0-20kHz, -60dB input. AnalogDevices Ltd. Tel., 01932 266000; fax,01932 247401.

LiteraturePower mosfets. Several kilograms ofpaper in the form of InternationalRectifier's Hexfet designer's manualis available free. In 2500 pages, thebook contains product data andapplication notes on the use of Hexfetpower mosfets. Solid State SuppliesLtd. Tel., 01892 836836; fax, 01892837837.

Keyboard. Model G81-3100keyboard by Cherry is described in anew brochure. This unit is completewith a magnetic card reader, whichwill read all the data on all popularcards, and/or a bar decoder that iscompatible with common readingdevices. Cherry Electrical ProductsLtd. Tel., 01582 763100; fax, 01582768883.

MaterialsStickier sticky labels. New from 3Mis a pressure -sensitive labellingmaterial that sticks to virtuallyanything, including the 'difficult'plastics and powder -coated finish.Both ScotchMark 7871/2 have apolyester face, 7871 in gloss and7872 in matt platinum, and both areprintable by thermal transfer. 3MUnited Kingdom plc. Tel., 01344858000; fax, 01344 858758.

Navigation systemsRange of GPS. Naystar Systems hasa range of global positioning systemequipment, being the only Britishmaker of course acquisition GPSreceivers with particular experience inprofessional and defence work.Telecom Design Communicationsannounces that it has concluded analliance with Naystar. The rangeincludes 2m -resolution, 12 -channeldifferential base stations, six -channelreceivers, post -processing softwareand remote surveying/loggingsoftware. Telecom Design

Please quote "Electronics World + Wireless World"when seeking further information

Communications Ltd. Tel., 01256332800; fax, 01256 332810.

Small, low -power GPS receiver.Power -saving facilities in the RockwellMicro Tracker LP five -channel receiverengine will, according to TDC, doublebattery life. More complete integrationhas reduced component count fromearlier Rockwell designs, butcompatibility is retained. The boardmeasures about 2in by 3in anddelivers differential GPS accuracy towithin 5m most of the time, with atime to first fix of 30s from a warm

Mini-otdr. Tektronix'sTekRanger TFS3031 isminiature optical time -domain reflectometercapable of both single -modeand multi -mode testing ofoptical -fibre cable in the oneinstrument. A feature torecommend the instrumentfor field work is IntelliTrace,which adjusts parameterssuch as pulse width andnumber of averages as theinstrument automaticallyanalyses a fibre link, therebymeasuring small and closelyspaced events accuratelyeven over long distances.Since the dead zone issmaller than in previousinstruments, events down to5m and up to 100m aretestable, results beingdisplayed on a large, backlitIc display. Up to 200waveforms may be storedand recalled for comparisonor analysis and an optionalhard disk can be used forarchiving anddocumentation. A powermanagement system isincluded, battery life beingeight hours. Tektronix UKLtd. Tel., 01628 486000; fax,01628 474799.

start. CityTracker software facilitatesuse on the move in cities with steadiertracking than before. Although thereceiver is optimised for static work, itis able to work at altitudes up to40,000ft under 4g acceleration.Telecom Design Communications Ltd.Tel., 01256 332800; fax 01256332810.

Power suppliesMulti -output smps. A range of verylow-cost convection -cooled power unitsby Coutant Lambda, the SW seriesincludes 30W, 40W, 65W and 100Wmodels having one to four outputs from5V to 24V. The units meet UL, CSA andIEC requirements. Coutant Lambda Ltd.Tel., 01271 865656; fax, 01271 864894.

Small dc -to -dc converters. FromDatel, the XWR series of 5W convertersare in 1 in by 1 in by 0.45in metal casesand conform to the pinout used bymuch larger types. They are designedfor use in systems with distributedsupplies, where the converter can beplaced at the load to reduce losses,poor regulation and slow transientresponse. Outputs are 5V, 12V and 15Vunipolar or bipolar and the inputshandle 18-36V or 36-72V. Protection isprovided. Datel (UK) Ltd. Tel., 01256880444; fax, 01256 880706.

Safe 20MHz oscilloscope.OX801, a 20MHz analogueinstrument by Metrix, has doubleinsulation to IEC 1010-1 Class 2.While offering the usual facilitiesof an oscilloscope at this level, italso possesses amicroprocessor bus systemwhich, among other functions,removes the need for high -frequency signals to be near thefront panel. More unusually, thebus has allowed automatic modeindication and remote controland also linking to a computerwith software to simulate theoscilloscope screen on that ofthe computer. Controls areanalogue in feel, though digitalin operation. Metrix UK Ltd. Tel.,01256 311877; fax, 0125623659.

Apd supplies. Gardners has a newtype of dc -to -dc converter, theGR84907, designed to providevariable high -voltage supplies foravalanche photo diodes used in wide -band digital optical communicationreceivers, as an alternative to the useof fixed supplies and high -valueresistors. Output (20V-100Vdc at 0-1.6mA) is isolated and contains only50mV ripple and noise, voltage beingregulated by a control voltage. Thereis no internal stabilising feedback,since the unit is designed for systemuse with an external loop, althoughclosed -loop models can be supplied.Gardners Ltd. Tel., 01202 482284;fax, 01202 470805.

UPS batteries. SmartCell XR batterypacks for Vero's 3kVA and 5kVAMatrix ups range reduce cost ofownership, since they replace four ofthe earlier modules, one XR unitgiving 45 minutes hold-up time at3kVA at only 60% of the cost. Theunits are in 11U high 19in rackmodules. Computer monitoring ineach SmartCell tests its condition andindicates the need for replacement tothe front panel and to the monitorsoftware, also providing a log ofperiodic checks made by theprocessor and an accurate indicationof run time when the battery is in use.Vero Electronics Ltd. Tel., 01703266300; fax, 01703 265126.

August 1995 ELECTRONICS WORLD + WIRELESS WORLD 705

NEW PRODUCTS CLASSIFIED

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Production testequipmentTransformer tester. Voltech'sAT3600 is a comprehensiveautomatic tester for transformers andother wound components. It is fullyprogrammable to allow an all -in -onetest, providing all the functions thatnormally require up to sevenindividual instruments, all resultsbeing presented either in a single testreport or as a simple pass/failindication. The measuring process isof a closed -loop nature for accuracy,giving a basic 0.2% accuracy onwinding resistance from Int/ to100k.Q, turns ratio 10-10-4 andinductance 100nH-100kH. Windows -based software is supplied to carryout 21 tests, with a further 16 to comelater in the year, for which thesoftware is to be supplied free. Theuser simply enters a schematicdiagram of the transformer, creates a'virtual fixture' by connecting its pinsto any of the unit's nodes and selectsthe tests to be run from menus.Fixtures can be made from kits orbuilt by Voltech. Voltech InstrumentsLtd. tel., 01235 861173; fax, 01235861174.

Pcb test. CITS200 is a bench -topprinted board tester by Polar whichverifies the characteristic impedanceof tracks, including balanced -lineconnections using time -domainreflectometry to single -ended ordifferential measurements. Agraphical user interface makes foreasy operation and flexibility. Astandard pc is linked to a two -channeltest system that automates allimpedance tests, set-up being carriedout by a Windows -based package. Inoperation, the test file is selected bythe operator, who positions the probeand presses a switch. Next the testsare carried out in succession withprompts to the operator to repositionthe probe as needed. Results areprocessed to give a graphical view ofimpedance, printed and saved to disk.Polar Instruments Ltd. Tel., 0148153081; fax, 01481 52476.

Switches and relays3GHz miniature relay. Teledyne'sRF300/303 series of ultraminiaturerelays provide ±0.1dB rf signalrepeatability over the 0-3GHzfrequency range. They are meant forlow-level rf and dc switching inattenuators, tuning, filters, etc., in whichthe features of wide bandwidth, goodshielding and grounding and highcontrol -to -signal isolation are required.These relays are in TO -5 cans.Teledyne Electronic Technologies. Tel.,0181-571 9596; fax, 0181-571 9637.

Resettable cut-outs. Bi-metallic,resettable cut-outs by Steatite protectagainst over -temperatures. Ratingsare 4A, 6.3A and 10A, the 4A typebeing BEAB-approved to C0652 andparticularly suitable for use in woundcomponents. Contacts are normallyclosed and are rated at 250Vac at50Hz. Accuracy of the cut-off is within±5°C. Steatite Power Ltd. Tel., 0181-778 6611; fax, 0181-778 7722.

Timer switch. Amerace announcesthe 48mm DIN Agastat ElectronicTimer, designed for a standard 48mm

panel cut-out and to be rail -socket orpanel mounted. It has up to eightuser -selected timing modes, sixtiming ranges from 0.1s to 10h at arepeat accuracy of ±0.5%±10ms. Allmodels have 10A dpdt contacts.Amerace Ltd. Tel., 01635 49191; fax,01635 521641.

Reed switch. Switching 250Vac at1A, Gentech's GR19 miniature reedswitch has Dimet contacts to give it alife of 100,000 operations. It isavailable with sensitivities of 20-50AT,an initial contact resistance of 20m0,insulation resistance of 10120 and awithstand of 700Vdc. Under extremeconditions, the GR19 handles 5A at20Vdc for a short time. GentechInternational Ltd. Tel., 01465 713581;fax, 01465 714974.

Thin, high -voltage relays.Matsushita's photo-MOS opticallycoupled relays control a 400V, 130mAload from a 5mA led input, but areonly 2mm high off the board. Twomodels of this type, the AQV212Sand AQV214S have on resistances of0.830 and 300 respectively withleakage current of 100pA at 400V, theled drawing 5mA and dropping 1.14V.The 212 is for load voltages to 60V at0.35A, the 214 for 400V at 0.1A, bothbeing normally open. In a largerpackage standing 3.4mm high, theAQV212A and AQV214A are identicalcomponents. Model AQV614A hasone normally open and one normallyclosed contact in the 3.4mm package.Flint Distribution. Tel., 01530 510333;fax, 01530 510275.

Rotary switches. New features onthe Grayhill range of rotary switchesare a spring return facility forapplications such as 'hold -to -test',and isolated positions in which theshaft must be pulled before rotation toprovide a standby or emergencyposition. To maintain contact in the'hold' positions, a rotary force must beheld, the switch returning to its normaldetent position when the force isreleased. Models having up to sixdecks are available, with up to sixpoles per deck. Ratings are 200mA-1A. EAO-Highland Electronics Ltd.Tel., 01444 236000; fax, 01444236641.

Signal re-routeing on a pcb. LatticeSemiconductor's ispGDS is aprogrammable digital switch IC thatallows signals to be re-routed on a pcboard under software control,eliminating jumpers, dil switches and

added bits of wire. Control is by afour -wire, 5V serial interface. MicroCall Ltd. Tel., 01844 261939; fax,01844 261678.

Transducers andsensorsOptical -fibre sensor. FromHoneywell comes the HPX series ofsensors, which the company claims isin the slimmest (10 by 28 by 60mm)package available. There are threemodels for use in paper and objectsensing, in machinery to detect jamsand to count, in electronic gear tocount small components and inpharmaceuticals to count pills. Unitshave a three -turn pot. to adjustsensitivity and an alarm is given if thedevice needs cleaning. HoneywellLtd. Tel., 01344 826000; fax, 01344826240.

Custom load cells. CorinTech cannow supply thick -film load cells tocustomers' specification, usingtechniques developed at theUniversity of Southampton.Piezoresistive thick -film resistors onone-piece metal substrates providerobustness and low cost and the tri-beam design exhibits linear andrepeatable output and invulnerabilityto eccentric loads. CorinTech Ltd.Tel., 01425 655655; fax, 01425652756.

Displacement controller. D1displacement indicators by ControlTransducers connect directly to linearsensors to act as a 3.5 -digit readoutand to pass signal to a pc.Transducers may be rectilinearpotentiometers, amplified sensors orcurrent -loop transmitters and the D1provides the sensor's power supply.Readout is supplied in the requiredunits, with specified set -points andtype of signal output. ControlTransducers. Tel., 01234 217704; fax,01234 217083.

Liquid gas level. ControlTransducers's NGTT gas level sensorreduces the problems of adaptingnatural gas to power machines byproviding an accurate method ofdetermining the level of liquid in thetank. A constant -resistance pressuregauge is also used to measuretemperature, both quantities beingneeded to calculate level. Output issupplied directly to an analogue ordigital voltmeter. Control Transducers.Tel., 01234 217704; fax, 01234217083.

Vision systemsDigital video encoder. IBM hasannounced the first chip to compressor encode the data to transmit andstore digital video, frame by frame.MPEG-2 I -Frame Encoder, the 'I -Frame' referring to the intermittentframe used in high-speedcompression and decompression, andan enhanced version of the MPEG-2Decoder for the pc and televisionconsumer market. Blue MicroElectronics. Tel., 01604 603310; fax,01604 603320.

Video disk recorder. H -P's HP 4:2:2VDR now has double its previous

capacity - 24 minutes. The instrumentis for workstation use in computergraphics and animation; the newspecification allows a half-hour tvprogramme - the bit between the ads- to be recorded to a hard -disk arrayfor playback, with digital audio. Thereis a full set of Ethernet commands forfile transfer and a SCSI set. The unitis supported by major animation andgraphics developers. Hewlett-PackardLtd. Tel., 01344 366666; fax, 01344362269.

Windows data acquisition.Windspeed software fromWindmill provides notebookcomputers with the facility tolog and display data. Thepackage runs under Windows,continuously logging data todisk and charting it in real timeso that users can remove andsave parts of the record in achoice of formats. Sincenotebooks do not oftenpossess expansion slots,Windspeed uses Microlink dataacquisition hardware thatconnect to a COM port on thecomputer or to a PCMCIAnetwork adaptor. The systemwill stream analogue data to ahard disk at 700sample/s via theCOM port or at 36,000 sample/sthrough Ethernet. Hardware isconfigured from the software bymeans of set-up files from alibrary saved by the user.Different channels may besampled at different intervalswithin one scan or somechannels may be sampled everyscan and others every nth scan.Windmill Software Ltd. Tel.,0161- 833 2782; fax, 0161- 8332190.

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COMPUTERComputer board -levelproductsPC -104 modules. Pro -Active Controlhas a range of microprocessor mini -modules based on the PC -104 for theembedded -systems market. The unitsrun dos software and only need dosand interfaces to work. Top of therange is PAC -486, based on a CyrixCx486SLC2 50MHz processor andincluding 2Mbyte of dram, with a4Mbyte option, battery -backed sramup to 512K, clock/timer, serial andparallel ports, keyboard i/o, disksupport and power management.Secondly, there is the PAC -86, whichuses the Chips & Technologies8680A pc chip running at 14MHz.This is an 8 -bit PC XT computer withfull i/o facilities and PCMCIA support,full CGA graphics with crt/lcd drive,1Mbyte mapped dram, 512Kbytesram, 512Kbyte eprom, an RS -232port and a PCMCIA slot.The third module is the PAC V-25,using the NEC V-25 chip to makeone of the lowest -cost pc -compatibleprocessor modules available,

optimised for embedded applications.Pro -Active Control Ltd. Tel., 01223300801; fax, 01223 300979.

Optical bus expansion. PCX-797 isan expansion kit by Fairchild to allowadditional ISAbus slots to be linked toa pc using an optical -fibre link. Thekit has two cards: a master for the pcand a slave for the remotes passivebackplane, with up to 100m of opticalfibre between the two. Multiple cardscan be used to obtain hundreds of i/oslots for a standard pc. Datathroughput is 1.6Mb/s and the 96Mb/soptical transmission avoids bus timingproblems. Fairchild Ltd. Tel., 01703559090; fax, 01703 5559100.

68030 VME card. Syntel's new68030 -based card, the SYN-VME203,is a 3U single -board computer for theVMEbus offering good powereconomy. Facilities on board includea 68882 float co -processor, 1Mbyte or4Mbyte of 32 -bit -wide dram and up to1Mbyte of eprom. Two RS232asynchronous serial channels areavailable with one 16 -bit interrupttimer and there is a watchdog timer.The dram subsystem supports fast16 -byte cache burst filling andcacheing is included for all VMEbus

operations. Both 8 -bit and 16 -bitVMEbus transfers are carried out.Auto bus sizing converts 24 -bit and32 -bit cpu operations to consecutive8 -bit and 16 -bit transfers. SyntelMicrosystems. Tel., 01484535101/2/3; fax, 01484 519363.

Data acquisitionPC measurement modules. KyleData Services offers the MM -232family of data acquisition modules forcomputers with RS -232 ports. Unitsfor the measurement of voltage,frequency, digital signals and eventsare currently available, each with fourinput channels, two further digitalinputs and two digital outputs. Specialsoftware is not need and all modulesare easily accessible from Basic,Pascal, C and other languages.Modules either plug directly to a25 -pin port or may be remote; theyare powered either by the RS -232 lineor by external supply. Kyle DataService Ltd. Tel., 01292 311169; fax,01292 318005.

SoftwareSignature analysis. Since'compatible' ics from different

manufacturers can possessmarginally differing signatureanalyses, the technique sometimesproduces invalid results. PolarInstruments can now offer AVR,which is Advanced VendorRecognition, to detect the slightdifferences automatically, avoidingunnecessary fault repair. PolarInstruments Ltd. Tel., 01481 53081;fax, 01481 52476.

Application generator. VisualDesigner application generatorsoftware from IntelligentInstrumentation now supports theKeithley DAS 16 family of boards,giving access to any analogue ordigital i/o functions from the boardsincluding dma, counter and rate -generator functions. The software isWindows -based and allows people todevelop application software bydrawing block diagrams, with noprogramming. Virtual sliders, switchesand instrument panels appear onscreen and control the application.Intelligent Instrumentation. Tel.,01923 896989; fax 01923 896671. IIII

TELFORD ELECTRONICSOSCILLOSCOPES

Gould 0S250A 15MHz Dual Trace ...SE labs 111 18MHz Dual Trace

Telequipment DIOIIR 10MHz Dual Trace ........Telequipment DM63 50MHz 4 Trace storageTrio CS1566A 20MHz Dual TraceCossor C00150 35MHz Dual Trace .2222_2._HP1740A 100MHz Dual Trace/storage

HPI80A + 1801A + 1821A 50MHzHPI742A 100Mitz Dual Trace/storage

Tektronik 465 100Mlit Delay sweep/Dual TraceTeldronik 7854 c'w 7511 plug-in/7111 fitted with S1 sampling head IGHzTektronik 7834 c'w 7826 e2 + 11392A x2 200MHz ....OTHER SCOPES MIME

SIGNAL GENERATORS

£120 CALIBRATION EQUIPMENT

Haven temperature calibrator 0105 oil/water bath £500

0150lime CD millivot pot source Model 404110v DC comet soma Moder 505 .............................. £250

150Leader LOC705 Scoper calibrator AS NEW E1,200

4115Casella WBGT . . ..............

PPM 411F Current reference £250

nxn Cropico resistance standards various in stock from . E75

£900

£400HP8654A 10-520MHz £350HP8614A 0.8-2.4GIO signal generator £300HP8616A 1.8-4.5GH, signal generator .. 6400

Marconi TF2019 AWFM 10Hz-11061Hz . E170

Racal 9081 520MHz synthesized £490Racal 9082 I 5-520MHz synthesized £480Wavetek 3000 1-520MHz £300

LF OSCILLATORS

Gould 138 101-1z-100101, sine/square wave metered: very low distortion ............. ........HP42134A 10Hz-1MHz

HP3200B VHF Oscillator'

HP85111 Test Oscillator

HP203A Variable phase IF generabx .

Radford 1.004 Low distortion Oscillator' .

Radioed IOM52/2 Low distortion measuring setGlobal Specialities 20MHz pulse/LF generator Type 8201 diePhilips PM5I32 function generator 0.111z-2MHz AS NEW ...

Rhode & Schwarz Type, W2

POWER SUPPLIES

HP6111A DC 0-20V 0-1A . .

£15001 50

£200[115£125

£50

£300£300£P0A

£350

£150E250

E200 REEL TO REEL RECORDERS

Hagra T instrumentation tape recorder

Bradley lf generator digital type 235 .... £250

Bradley DC calibrater type; 1238 04w 1268 E150

Keithley Picoamrneter typo 417 £250

Wallace & Tiernan precision pnuematic calibrator . £P111/1

Schwarzbeck HF Interference measuring receiver 85101z 3061Hz .. £300

Microdine telemetry receiver c/w spectrum display unit 2.2 2.30112 ............................................ £100

DIGITAL & ANALOGUE MULTI METERSAno 8 MIL5 i 6 cm case, leads, prods etc., (cAir Cal cert. NPL)....Solartron 7045 4.5 digit bench multimeter battuy/mains ...............

Fluke 80008

FREQUENCY COUNTERS

HP5342A Microwave 18CHz ..........HP5308A 75MHz counter/Omer ..

Marconi TF2431 200MHz digital frequency counter

E200

£250

£100£700

HP60028 0-504 0-108 2008 EPOli

HP6209B DC 0-3208 0-0.18Lambda LP114226 FM regulated; DC 0-40V/1A 82 E100

Heiden Toe; 1108/16 0-16V 0-208 £P0A

VARIOUS SWIM MODE MAR SUPPLIES & HTIRMISFORMERS IN STOCK- PLEASE PHONE

Marconi TF2440 20GiirEIP Type 331 Microwave 251.111z -18G14

Racal 9904IM) 50MHz

Racal 9913 10112-200MHz Fitted FX standard

Racal 9914 10H2-520MHz. Fitted FX standard

Racal 9915IM) 10Hz-520MHz. Fitted FX standard

Racal 9917511 10Hz-560MHz. Fitted FX standard . .

Racal 1992 1300MHz .

Dictaphone 2x tape decks .

Racal ICR recorder

SE Labs eight four

Uher 42011/4400 in stock from £125

£45

£1.400

L100£275

£150£250

. £1,300

£650

£100

.E125.. £125

E125

... £125E195

E700

£650

E1,200

. £350

. E500

........£600... £500

. E700

EPOA

EPOA

EPOli

EFYIA

TRANSMITTING EQUIPMENT

Racal TA1885 Auto tuned HF transmitter freq. 1.6-3061Hz 1101/ output ................ EPOA

Racal TA1800 HF linear amplifier inch 2-30MHz 101041 output ALL MODE GPO',

Pye T300AM 68.174MHz 300W output _.Rediton GA484 400W solid state amplifier c/vo IKW aerial filter uniUdrive unit,Hams ATU type, 601A I-30MHz 1141 AS NEW

MISCELLANEOUSDatalab 010080 programmable transient recorder E300

Tektronix T912 10MHz Storage scope £175

Racal 9084 Synthesized generator tiler GF1B Interlace 9934A (As new rendition) E700

Matsu SS -5416A Synchroscope DC-40MHz C350

Roland drafting plotter A2. DPX-2200 Various interlaces. 8 pen £1200Roland DG X -Y plotter Al 000-980A Various interfaces. 8 pen. £375

Krohn -Hite filter Model 3202R E150

Cabletron Systems MR -9000C civi Lanview Multiport EthemetAEEE 802.3 Repeater EPOA

Cabletron Systems FR -30011 c.w Lanview FibreopticAEEE 802.3 Repeater Und . EPOA

Anritsil Channel Selector MS 120A .......... ............ CP00

Bniel & Meer Vibration programmer 7H0100 . EPOA

£350

£350L650

Watkins & Johnson Demodulator DM112.5 . ................. £450

Watkins & Johnson ICED Frequency Extender Und FE1.4.5A 0.95-2CHz + 2-4.501it ........... £500

Watkins & Johnson Signal Monitor SM9403A _ .......................................................... CADO

Sullivan Automatic Component Analyzer X5555 £P0A

new Digital AC Power Meter 2503 EPOA

Aillech Noise Monitor . £P0/1

£1250Phoenix Telecommunicabons Analyzer 5500AInd Unit; Phoenix 5500-MSU 5500-200

5500-555 55006-8283rd Unit, Phoenix Control Module 55002200 + 550111-828The above 3 items come as one unit

Racal Dana 1898 Frequency Counter 101tz 1.301z ..................Racal Dana 9303 True RMS Level Meter claw Sensing Head 2Gliz

Bird Tenuline Coaoal Alternator 30dB 500W 50ohm Model 8325Brand New Boxed £200 VARIOUS OTHERS IN STOCK - PI ELSE ASK

MICROWAVE COAXIAL SWITCHES"N" Type connectors. R.LC. Model S-2799

£45

Teledyne. SMA connectors. Model C5385.15£40

EPOA

£1200E3000

£1100£900

E650

£1250

EPoA

FIDIVIELL COAXIAL CABLECu2Y size 158th" 50 ohm approx. 120018 available (NEW)

SPECIAL OFFER WHILE STOCKS LASTHP1110 50MHz Dual Trace/Delay timebase with probes £150

AN EXTENSIVE RANGE OF TEST EQUIPMENT IS AVAILABLE. PLEASE SEND FOR OUR NEW CATALOGUEPostage and packing must be added. Please phone for price. VAT @ 171/2% to be added to all orders. Please send large SAE for details.

Telford Electronics, Old Officers Mess, Hoo Farm, Humbers Lane, Horton, Telford TF6 6DJTel: 01952 605451 Fax: 01952 677978

( IRCLE NO. 120 ON REPLY CARD

August 1995 ELECTRONICS WORLD + WIRELESS WORLD 707

Field Electric Ltd.Tel: 01438-353781 Fax: 01438 359397 6roli

Mobile: 0836-640328/0860-213370Unit 2, Marymead Workshops,

Willows Link, Stevenage, Herts, SG2 8AB.102 key at IBM compatible keyboard terminated to6 pin din mini plug £8 c/p £3.75Conrac 7211 C19EK. 18" RGB/Video inputbroadcast quality monitors 240 VAC £100360/720K 5.25" TEAC BBC compat. disk drives

£9.50 C/P £3.50Yuasa NP 10-6: 6v 10ah sealed lead acidbattery NEW £7.95 C/P £3.50PC PSU 200watt square type NEW £15 C/P £5NEC CMV 123NE 12" colour monitor will work onPC VGNAMIGA/ATARI/BBC. Supplied with leadfor PC VGA. Cased 240vac £85 C/P £12Sony 9" colour monitor Trinitron super fine pitchmodel KTM 1000ub Cased with data for RGB £50Intel flash memory cards 1Mb to 4Mb from £80Test equipment: please ring for C/P detailsHP 7475A, RS232C/CCITT V.22 graphics/CAD pro:plotter A3/A4 IEEE 488 £150HP 427A voltmeter £145HP 79595 £50HP 431C power meter cable and head £195HP X532B frequency meter £165HP 1332 X -Y display with options 215/300/315/570/631 £150HP 10013A probe £24.50 C/P £3.50HP 331A distortion analyser £150HP 415E SWR meter £195HP 9872A 4 pen plotter £225HP 3550B test set £275HP 3551A transmission test set £725HP 16108 Logic State Analyzer with Pods £135HP 1611A Logic State Analyzer £125TEK:7A15A amp plug in £175TEK: 7CT1 N curve tracer plug in £450TEK: 06 7-502 standard amplitude calibrator £100TEK: swept frequency converter 015-0107-00 £59TEK: 7D12 A/D converter plug in £150TEK: TM504 mainframe £125TEK: 184 time mark generator £95TEK: D10 o'scope mainframe £95TEK: DAS9100 digital analysis system £295

TEK: 067 0508 00. 50 ohm amplitude cal. £95TEK: 7S11 sampling unit £180TEK: 453 o'scope 50MHz dual beam £200Laser drive inc. Model 134 HE -NE gas laser input10-14v output DC 1250v new & boxed £125Sony video cassette player VP5040 NTSC/PALJSECAM £325Stag Prom eraser SE100 £150Philips Universal sync & patt. gen £14512" Mono VGA chassis paper white enclosed 240VAC £35 c/p 12-5012 VDC fans 90mm x 25mm £4 c/p 1-50DATA I/O Romulator Data I/O Ram -Pak £95DATA VO 29A Universal Programmer c/withUnipak 2 £225Racal 835 Universal counter £145Philips PM 8154 6 pen plotter IEEE 488 £280Calcomp 81 8 pen plotter (digitising) £400Marconi inst= multiplex tester 2830 £600Wendel & Goltermar LDE-2 measureing set forgroup delay & attenuation: receiver £150Wayne -Kerr 022D video oscillator £95Spectra brightness spot meter 1514-UB £125Bio-Tec Mst Model 501 £125Greibach Inst. AC/DC microamp meter £35Pirelli Focum muitiport repeater 5709 £140Singer Gertsch phase angle voltmeter c/w 400Hzmodule £125Paratronics inc System 5000 P1-540 logic analyzer

£190Optimation inc Model AC125 calibrator £90Calrec ZN1232 Desk PSU £85Systron Donner pulse gen: 100C £95Hydrostatic stability indicator £425Hughes Model 639 scan conversion memory £300Philips PM 8940 isolation amp etc £85DLi delay gen: DG100 £80Marconi TF 2602 diff: DC voltmeter £65Bromma LKB 2210 recorder 1 -channel £60Fluke 893A AC.DC dill voltmeter £250General Radio 1433-H decade resistor £135Borg-Warner SWR Ind: M401 £120

PLEASE ADD 17.5% VAT. TO ORDER: RING FOR C/P PRICES NOT SHOWN:OFFICIAL ORDERS AND OVERSEAS ENQUIRIES WELCOME

TO ALL SMALL BUSINESSES AND COMPANIES. WE WOULD LIKE TO BUYYOUR SURPLUS OR REDUNDANT COMPUTER HARDWARE/GOOD TEST

EQUIPMENT ETC.

CIRCLE NO. 131 ON REPLY CARD

KESTRELELECTRONIC

COMPONENTS LTD* All items guaranteed to manufacturers' spec.* Many other items available.

'Exclusive of V.A.T. and post and package'

1+ 100+ 1+ 100+27C64-15 2.00 1.45 628128LP-85 8.30 7.2027C128-15 2.40 1.80 62256LP10 3.00 2.6027C256-15 2.20 1.70 6264LP-10 2.10 1.4527C512-15 2.20 1.70 MM58274CN 4.90 3.75270010-15 3.60 2.30 ULN2003A 0.43 0.3027CO20-15 6.00 3.99 7805 0.32 0.2527C040-15 8.60 6.45 MAX232 1.35 0.8880C31-12 2.10 1.65 7406 0.35 0.238255AC-2 2.00 1.50 7407 0.35 0.23Z80A CPU 1.80 1.00 74HC244 0.35 0.24LM386N-3 0.50 0.35 74HC245 0.35 0.2475176BP 1.35 0.85 74HC373 0.35 0.2568w PLCC skt 0.90 0.70 74HC374 0.32 0.25

74LS, 74HC, 74HCT Series availablePhone for full price list

All memory prices are fluctuating daily, please phone toconfirm prices

178 Brighton Road,Purley, Surrey CR8 4HA

Tel: 0181-668 7522. Fax: 0181-668 4190.

C1R( LE NO. 132 ON REPLY CARD

T8 CAVANS WAY,BINLEY INDUSTRIAL ESTATE,COVENTRY CV3 2SFTel: 01203 650702Fax: 01203 650773

MEM Mobile: 0860 400683(Premises situated close to Eastern -by-pass in Coventry with easyaccess to M1, M6, M40, M42, M45 and M69)

OSCILLOSCOPES

Gould 0S4000, OS4200,054100, 051000B from £125Gould 033000 -40MHz, dual ch. £250Gould 4035 -20MHz digital storage £600Gould 4050 -35MHz digital storage £750Gould 5110 -100MHz intelligent oscilloscope £950Hewlett Packard 1707A, 1707111- 75MHz dual ch. from £275Hewlett Packard 17408,1741A, 1744A, 100MHz dual ch..... ........... from £350Hewlett Packard 54201A- 300MHz digitizing £1750Hewlett Packard 54504-400MHz digitizing (As new) £3500Hitachi V-212 -20MHz dual trace ................................. .... ..£175Nicolet 3091- Low freq D.S.O. £1100Philips 3315- 60MFiz D.S.O £750Tektronix 468 -100MHz D.S.O. £800Tektronix 2213-60MHz dual ch £425Tektronix 2215-60MHz dual ch £450Tektronix 2225 - 50MHz dual trace £450Tektronix 2235 -100MHz dual oh. (portable) £800Tektronix 2335 -100MHz dual ch. (portable) £750Tektronix 24658 400MHz 4 channel £3950Tektronix 464/466 - 100MHz, storage from £350Tektronix 465/4658 -100MHz dual ch. from £350Tektronix 7313, 7603, 7613, 7623,7633,100MHz 4 ch from £300Tektronix 7704 -250MHz 4 ch. from £650Tektronix 7834 with 7842,7880,71385 -Plug -Ins (Storage 400MHz) 11500Tektronix 7904 -500MHz from £950Telequipment D68 - 50MHz dual ch. £200Philips 3206, 3211, 3212, 3217,3226, 3240, 3243,3244, 3261, 3262 (2ch + 4 ch.)Philips PM3295A -400MHz dual channel £1950Hewlett Packard 54501A- 100MHz Digitising -4 channel £1950Tektronix 2236 -100MHz Dual Trace with Counter/Timer/Dmm .£995lwatau TS 8123 - 100MHz Dig. Storage .£850

Other II le too

from £125 to £350

MIIIIMINE=111111111.=Hewlett Packard 3580A 5Hz 50KHz £995Hewlett Packard 3582A - 25KHz analyser, dual channel £2500Hewlett Packard 182T with 8559A (10MHz -21GHz) £3750Marconi 2370- 110MHz £995Marconi 2371 - 30Hz-200MHz £1250Rohde & Schwarz - SWOB 5 Polyskop 0.1 -1300MHz £2500Schlumberger 1250- Frequency response analyser £2500Alltech 727 -22.4GHzAlltech 70727 - Traceng Generator for 727 (10KHz- 12.4GHz) .......... } £2000Truman AL51A - 1GHz £850Tektronix 7L14 with 7603- Mainframe (1.8GHz) £2000Tektronix 7L12 with 7603 mainframe (1.8GHz) £1500Tektronix 7L18 with 7603 mainframe (18GHz) 2950Polrad 641-1 10MHz - 18GHz £1500Hewlett Packard 35601A- Spectrum Analyser interlace £1000Hewlett Packard 8754A Network Analyser -4 -1300MHz £3250Hewlett Packard 3709B Constellation Analyser with 15709A HighImpedance Interface (as new) £6750

TELNET11M1211111:123311=MINIAnritsu MG642A Pulse pattern generator £1500Balla ntl ne 323 True RMS voltmeter £350Datalab DL 1080 - Programmable Transient Recorder £350Datron 1061 - precision multimeter £650Dynepert TP20 - Intelliplace tape peel tester, immaculate condition

£1950E.I.P. 331 18GHz frequency counter £850E.I.P. 54138 -frequency counter (26.5GHz) £3500Farnell 2081 FVF Power meter £350Farnell TSV70 Mkll - Power Supply (70V -5A or 35V -10A) £225Ferrograph RTS2 Audio test set with ATU1 £500Fluke 5101A - Calibrator AC/DC £3500Fluke 5101B Calibrator AC/DC £6500Fluke 5220A- Transconductance Amplifier (20A) £3000Heiden 1107 - 30v -10A Programmable power supply (IEEE) £650Gould K1000 - 100MHz Logic Analyser with PODS £350Hewlett Packard 3325A -21MHz synthesiser/function gen £1500Hewlett Packard 3437A System voltmeter £350Hewlett Packard 3438A Digital multimeter £200Hewlett Packard 3490A Digital multimeter £250Hewlett Packard 3586A - Selective level meter £1750Hewlett Packard 3702B/3705A/3710A/3716A Microwave link analyser

£1500Hewlett Packard 3711A/3712A/3791B/3793B Microwave link analyser

£3500Hewlett Packard 3760/3761 Data gen + error detector each £300Hewlett Packard 3762/3763 Data gen + error detector each £350Hewlett Packard 3764A Opt.002 - Digital Trans. Analyser £2250Hewlett Packard 3777A Channel selector £250Hewlett Packard 3779A/3779C Primary mule analyser ... ...... £600/£1000Hewlett Packard 5150A Thermal printer £275Hewlett Packard 5316A - Universal counter liPIB £550Hewlett Packard 53168 Universal counter HPIB £750Hewlett Packard 5385A - Frequency counter 1GHz (HP1B) with Opts001/003/004/005 £995Hewlett Packard 595018 HP 1B isolated D/A power supplyprogrammer

£150Hewlett Packard 6181C D.C. current source £150

Hewlett Packard 6261B Power supply 20V -50A £500

DISCOUNT FOR QUANTITIES

Hewlett Packard 7402 Recorder with 17401A x 2 plug -ins £300Hewlett Packard 8005B Pulse generator £250Hewlett Packard 8011A Pulse gen. 0.1Hz -20MHz £500Hewlett Packard 8152A optical average power meter £1250Hewlett Packard 81588 - optical attenuator with opt's 002 +001 £1100Hewlett Packard 8443A Tracking gen/counter with IEEE £300/£400Hewlett Packard 8620C Sweep oscillator mainframe £400Hewlett Packard 8750A Storage normaliser £375Hewlett Packard 3456A Digital voltmeter £750Hewlett Packard 8684A- 5.4GHz to 12.5GHz Sig Gen £3000Hewlett Packard 6632A - System Power Supply (HPIB) £500Hewlett Packard 864013 - ANI/FM Signal Gen. (512MHz) £850Hewlett Packard 5340A 18GHz Frequency Counter £900Hewlett Packard 5356A -18GHz Frequency Converter Head £450Hewlett Packard 432A - Power Meter (with 478A Sensor) £275Hewlett Packard 435A ore - Power Meter (with 8481A/8484A)

from £750Hewlett Packard 8662A - (10KHz - 1280MHz) synthesised signalgenerator £7950Hewlett Packard 4953A- protocol analyser £3500Hewlett Packard 1630G- logic analyser- 65 channels £850

Hewlett Packard 5359A -time synthesiser £P,O.A.Hewlett Packard 5505A - laser display £P.O.A.International Light - IL 1700 research radiometer with Erythemalsensor headLyons PG73N/PG75/PG2B/PG Pulse generator from £225Marconi 2306 Programmable interface £500Marconi 2337A Automatic dist. meter £150Marconi 2356 20MHz level oscillator £300Marconi 2432A 500MHz digital freq. meter £200Marconi 2830 Multiplex tester £850Marconi 2831 Channel access switch £250Marconi 8938 NF power meter £295Marconi 2019A 80KHz - 1040MHz synthesised sig. gen £1950Multi core "Vapourette" bench top vapour phase SMD solderingmachine (new and unused) (E1100+ new) £650Philips PM 5167 10MHz function gen. £400Philips PM 5190 LF synthesizer w/th GPIB £800Philips 3551A- logic analyser £P.O.A.Phoenix 5500A - telecom ms analyser with venous interface options

£2500Racal 9301A True RMS FVF millivoltmeter £300Racal Dana 1992 - 1300MHz frequency counter opts 4B+55 £800Racal Dana 3100 40-130MHz synthesiser £750Racal Dana 5002 VVideband level meter £650Racal Dana 5003 Digital m/meter £150Racal Dana 9000 Microprocessing timer/count. 52MHz £250Racal Dana 9081 Synth. sig. gen. 520MHz £550Racal Dana 9084 Synth. sig. gen. 104MHz £450Racal Dana 9242D Programmable PSU 25V -2A £300Racal Dana 92465 Programmable PSU 25V -10A £400Racal Dana 9303 True RMS/RF level mete £650Racal Dana 9341 LCR databridge £250Racal Dana 9500 Universal timer/counter 100MHz £200Racal Dana 9921 3GHz frequency counter £450Rohde & Schwarz BN36711 Digital 0 meter £400Rohde & Schwarz LFM2 Sweep generator 0.02-60MHz £1500Rohde & Schwarz SCUD Radio code test set £1500Rotek 39808 - AC/DC Precision Calibrator with Rotek 350A HighCurrent Adaptor £1,0ASchlumberger Si 4040- Stabilock, high accuracy 1GHz radio test set

£5950Schlumberger 4923- Radio Code Test Set £1500Schlumberger 2720 - 1250MHz Freq. Counter £600Systems Video 1258 Waveform analyser + 1255 vector monitor +1407 differential phase & gain module + 1270 remote control panel

£2250Syatron Donner 60548 or D-18GHz or 24GHz Freq. Counter

from £800Tektronix DA59100Senes Logic Analyser £500Tektronix - Plug -ins -Many available such as PG508, FG504, SC504,SW503, SG 502 etc.Tektronix Th15003 + AFG5101 Abritrary Function Gen £1750Tektronix 1240 Logic Analyser £750Time 9811 Programmable resistance £600Time 9814 Voltage calibrator £750Watanabe WTR211 3 pen plotter £250Weller 0900 Desoldeing station £150Wilton 352 Low freq. differential input phase meter £350Wiltron 560 Scalar Network analyser £800

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

708 ELECTRONICS WORLD+WIRELESS WORLD August 1995

CLASSIFIEDTEL 0181 652 3620 FAX 0181 652 8956

ARTICLES WANTED

WANTED!!Top prices paid for your test equipment made by HEWLETT-PACKARD,MARCONI, FLUKE, TEKTRONIX, BOONTON, ROHDE & SCHWARZ etc.

From Europe's No. 1 Test Equipment LeaderROSENKRANZ-ELEKTRONIK, AXEL ROSENKRANZ

GROSS GERAUER WEG 55, 64295 DARMSTADT/GERMANYPhone: 0049-6151-3998-0 Fax: 0049-6151-3998-18

CONTACT US NOW!You are looking for test equipment? More than 10,000 units in stock forimmediate delivery. Call or fax for our new 100 page catalogue

-- today ---

** WHAT WE DON'T HAVE YOU DON'T NEED **

FREE CLASSIFIED

TEKTRONIX MODULES 7A26,7A18, 7B85, 7B80, 7B50A: Fullytested. Sensible offers please. Ian Stirl-ing, Cottaracre Star. Fife KY7 6LA.01592 757384.WANTED: pre-war television. JacJanssen, Hogeham 117D, NL-5104JDDongen, Netherlands. Tel: (eves)01031 1623 18158. Fax (office): 0103113 624664.

WANTED: TEKTRONIX Plug in mod-ule, Type AA501 Distortion analyser.Also SG505 oscillator. Phone: G. E.Gillard 0115 9846116.

WANTED: Agent/spy radio sets. Allperiods. SOE/SAS/SSTR-SOVJET etc.German W.W.2 radios. OZ8RO. R.Otterstad, HOsterkObvej 10, DK-3460Birkerod, Denmark. Tel: 4281 5205.

WANTED: TUBE for SolartronCD1400 oscilloscope, type SE5/2A.Poole 01202 602722.FOR SALE: Dranetz phase meter, 2Hz- 700 KHz, 0.01 degrees resolution,good for filters, crossovers etc. £350ono. Tel: Mike 01483 487189 (eves).SALE OR SWOP for CD -Rom drive.Perkin Elmer, infra -red specs poto-meter, infragraph H1200, working.Phone 01273 553505.

FOR SALE: EWWW 1980 to 1994,Offers. Phone: Tony - 01276 66155 -evenings.WANTED: pre-war television. JacJanssen, Hogeham 117D, NL-5104JDDongen, Netherlands. Tel: 01031 162318158. Fax (office): 01031 13 624664.Thanks!

ADD VALUE AND CREDIBILITY WITH

RE PRINTSMultiple copies of your articles and advertisements published in this magazine make ideal

promotional material for sales literature, exhibition handouts, direct mail, new product launches,distributor promotions, Public Relations etc.

You can add your own artwork and copy, utilise the front cover of this magazine, include your list ofdistributors, and/or your latest advertisement/s. Reasonably priced reprints can be tailor-made to your

own specific requirements or simply reprinted in their original form. (Minimum order number 250)For a FREE quotation please telephone Jan Crowther now on: 0181-652 8229 or fax: 0181-652 3978

Reprint Services, Reed Business Publishing,Room 1006, Quadrant House, The Quadrant, Sutton, Surrey SM2 5AS, England

INDEX TO ADVERTISERSPAGE PAGE

Anchor Supplies 632 MB Radio (Leeds) 698Antrim Transformers Ltd 698 Millford Instruments 702Bull Electrical 642 Number One Systems 702Cricklewood ElectronicsCrossware Products

668701 OEMA Ltd 701

Dataman OBC Pico Technology 668Display Electronics Ltd 686 Quickroute Systems Ltd 626ERT IBCField Electric Ltd 708 Ralfe Electronics

Research Communications712630

Grandata Ltd 676 Robinson Marshall (Europe) Ltd 655Halcyon Electrics 698 Seetrax Ltd 630ICE Technology Ltd IFC Stewart of Reading 668Interconnections 663 Surrey Electronics 663IOSIS 701 System Enclosures 678John Morrison (Micros) 626 TDC 663Johns Radio 641 Telford Electronics 683JPG Electronics 626 Telnet 708Kestral Electronic Components 708 Tsien Ltd 670

CLASSIFIEDTEL 0181 652 3620 FAX 0181 652 8956

DISTRIBUTORS

AN5521 1.35 STK4352 6.20 STRD6008 10.00 TE42026C 4.50AN5732 1.40 STK4372 5.65 TA7227 1.85 7E45170 1.40AN6327 9.85 STK4803 7.05 TA7271 2.50 TUA2000-4 4.25AN6677 8.50 STK4843 7.05 TA7280 2.25 U8840 2.35BA5114 1.55 STK5315 5.85 TA7281 2.20 U4606B 5.50BA6218 1.85 STK5332 1.80 TA7698 5.00 UAA1008 3.00BA6219 1.20 STK5338 3.25 TA8200 3.50 UPC1178 1.05HA11423 1.65 STK5361 4.15 TA8210 3.00 UPC1182H 5.15HA13119 2.50 STK5372 2.85 TA8214 3.00 UPC1278H 2.20KA6210 4.99 STK5372H 4.15 TA8215 3.00 UPC1420 4.50LA3220 0.60 STK5412 3.75 TA8205 3.95 UPD1937 3.00LA4183 1.35 STK5471 3.85 TA8659 13.00 25A814 0.71LA4445 1.90 STK5490 4.95 TA75339 0.75 25A839 1.40LA4495 1.40 STK6732 14.00 TDA1908A 2.00 25A1062 1.00LA4588 2.55 STK7226 7.50 TDA2170 3.00 0 U4264 1.10LA7835 2.35 STK7308 4.05 TDA2270 2.50 BU500 2.45LB1416 2.25 STK7348 4.05 TDA3562A-TFK 3.25 BU506D 1.50LM301 0.25 STK7356 4.75 TDA3562A-SG 3.00 8U508AIPHILI 0.80LM317T 1.50 STK7404 6.50 TDA3645 8.00 BU508AFIPHII 1.00M4911381 4.75 STK73410 5.15 TDA3650 8.99 BU508DFIPHII 1.25M494BB1 6.75 STK73410/2 5.95 TDA3850 18.99 B U8064 1.40M51393 5.95 STK73605 4.50 TDA4400 1.75 0U807 0.85M58655 3.30 STR441 14.75 TDA45054 4.10 0U908 1.15MB3730 1.70 STR451 25.00 TDA4505B 4.10 BU932 1.50MB3756 8.00 STR3125 5.50 TDA4505E 4.00 BUK444/500 2.15STK078 6.00 STR4211 5.50 TDA4505M 6.80 BUK454/600 1.95STK435 4.00 STR4090 11.15 TDA4505K 6.15 BUT11A 0.70STK461 6.00 STR20005 5.00 TDA4660 4.50 BUT11AFIPHII 1.20STK2250 7.45 STR40090 4.00 TDA4950 1.40 BUT11F 1.20STK4121/2 7.00 STR50103A 3.85 TDA5660P 2.50 BUT12A 1.10STK4141/2 5.50 STR54041 3.75 TDA7072 3.99 BUT12AF 1.10STK4142/2 6.50 STR58041 3.75 TDA8370 14.00 8UT564 0.80STK4162/2 6.25 STR80001 6.00 TDA8405 8.00 BUT76A 1.05STK4171/2 8.10 STR1706 4.75 TDA8732 5.95 BUV48C 3.10STK4191/2 8.50 STRD1806 4.50 TE420184 1.50 BUW13 1.50

When you have been let down by the restcome and try us for fast friendly service.

Ask for our full, comprehensive catalogue,FREE OF CHARGE

Please phone us for the types not listed. Please add 60ppost & packing and then add 17.5% VAT to the total.

Callers by appointment only.

J.J. COMPONENTS63 THE CHASE, EDGWARE,

MIDDX. HA8 5DN, ENGLANDHotline No: 081-381 1700/081-952 4641Free fax orderline ONLY: 0800 318498

General Fax: 081-381 1700

RECRUITMENT

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enthusiastic editorial assistant.

No experience needed.

Hard work but rewarding -a unique

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publishing with Britain's best.

Based in Sutton, Surrey

Ring 0181 652 8638 for more details.

ARTICLES FOR SALE

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 542457

IEC21111191111=1

ADVERTISERSPLEASE NOTEFor all your future enquiries

on advertising rates

Please contactMalcolm Wells on

Tel: 0181-652 3620Fax: 0181-652 8956

-(10

CLASSIFIEDTEL 0781 652 3620 FAX 0181 652 8956

ARTICLES FOR SALE

Cooke InternationalSUPPLIER OF QUALITY USED

TEST INSTRUMENTSANALYSERS, BRIDGES, CALIBRATORS,

VOLTMETERS, GENERATORS, OSCILLOSCOPES,POWER METERS, ETC. ALWAYS AVAILABLE

ORIGINAL SERVICE MANUALS FOR SALECOPIES ALSO AVAILABLE

EXPORT, TRADE AND U.K. ENQUIRIES WELCOME,SEND FOR LISTS OF EQUIPMENT AND MANUALS.

ALL PRICES EXCLUDE VAT AND CARRIAGEDISCOUNT FOR BULK ORDERS SHIPPING ARRANGED

OPEN MONDAY -FRIDAY 9AM-5PM

Cooke InternationalELECTRONIC TEST & MEASURING INSTRUMENTSUnit Four, Fordingbridge Site, Main Road, Barnham,

Bognor Regis, West Sussex, P022 OEB

Tel: (+44) 01243 545111/2 Fax: (+44) 01243 542457

EQUIPMENT & ACCESSORIES PURCHASED

CIRCLE NO. 135 ON REPLY CARD

TOPPRICES

PAIDFor all your

valves, tubes,semi conductors

and IC's.

Langrex SuppliesLimited

1, Mayo Road,Croydon,

Surrey CR0 2QP

TEL:0181-684 1166

FAX:0181-684 3056

VALVES

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

ARTICLES WANTED

.1)

WE WANT TO BUY !!

IN VIEW OF THE EXREMELYRAPID CHANGE TAKING PLACE

IN THE ELECTRONICSINDUSTRY, LARGE QUANTITIES

OF 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.

TELEPHONE081-445-2713/0749FAX 081-445-5702.

VALVES WANTEDFOR CASH: KT88, PX4, PX25 C45;DA100 £75; EL34, FL37 £10; ECC81/CV4024, CV4003, CV4004, ECC83 E3.Valves must be Mullard/GEC, West

European to achieve the price.Ask for our free wanted list.Prompt & courteous service.

Visitors by appointment only (we area very busy Export Warehouse).

Billington Export Ltd,Tel: 01403 784961 Fax: 01403 783519

TO ADVERTISEHERE PLEASE CALLMALCOLM WELLS

ON

0181 652 3620

WANTEDHigh -end Test Equipment, only

brand names as Hewlett-Packard,Tektronix, Rhode & Schwarz,Marconi etc. Top prices paid.

Please send or fax your offer to:

HTB ELEKTRONIKAlter Apeler Weg 5,

27619 Schiffdorf, West GermanyTEL: 01049 4706 7044FAX: 01049 4706 7049

WANTEDTest equipment, receivers, valves,transmitters, components, cable

and electronic scrap and quantity.Prompt service and cash.

M & B RADIO86 Bishopgate Street,

Leeds LS1 4BBTel: 0113 2435649Fax: 0113 2426881 9956

711

SPECTRUM ANALYSERS HEWLETT PACKARD

IFR MODEL A-7550 1GHz portable with inbuilt tracking gen & IEEE ops

HP141T 18GHz system (8552B, 8555A)

HP3580A 5Hz -50kHz audio frequency spectrum analyser

HP3582A audio frequency fit analyser dual -channel

HP8557A 350MHz Opt 01 750) (requires mainframe)

HP8559A 21 GHz spec an in 853A digital mainframe HPIB

HP8568A high -specification 1.5GHz spectrum analyser

MARCONI 2386 100Hz-26.5GHz (in tHz steps!)

TEKTRONIX 492 21GHz spectrum analyser

RALFE ELECTRONICS36 EASTCOTE LANE, S. HARROW, MIDDLESEX HA2 8DB

TEL: 0181-422 3593. FAX 0181-423 4009

NOWIN

40thYEAR

£5000

£2000

£1500

£2500

£1000

£4500

f7500

£15000

£5000

MARCONI INSTRUMENTS

2305 modulation analyser 50kHz - 2.3GHz

2828N2629 digital simulator/analyser

2955 mobile radio test set ALL SOLD

2386 spectrum analyser, superb specification, 100Hz-26.5GHz

6460/6421 power meter & sensor 10MHz-12.4GHz

605X -series signal sources, all in range

6500 amplitude analyser c/w 2c 6514 waveguide detectors

6960 microwave power meter with 6910 power sensor 10MHz-20GHz

0A2805A pcm regenerator test set

TF2910/4 non-linear distortion (video) test set

TF2910 N interval timer

DISTRIBUZIONE EASSISTENZA, ITALY: TLC RADIO, ROMA (06) 871 90254

TEST EQUIPMENTANRISU ME518A portable error rate test setBRUEL & KJAER 2511 vibration meter (file set 1621 Mier)BRUEL & KJAER 2317 portable level recorderBRUEL & KJAER 2635 charge amplifierBRUEL & KJAER 2610 measuring amplifierBRUEL & KJAER 2318 graphics printerBRUEL & KJAER 2308 analogue X -Y pen recorderBRUEL & KJAER 2639 preamplifierDATRON 1065 digital multimeterFARNELL 2081/100 RF power meter to 100W & 1GHzFLUKE PM97 scopemeterFOTEK M200 fibre optic lcd power meter & test sourceHITACHI 0509 50MHz portable battery powered osdloseope (ncludee butts)

£2000£2000£1500£950

£1250£750£750£275£500£250

£500

£250£550

ralfe electronics /). professional T&M

** HP8673D Synthesized Signal Generator **SOMHz-26GHz full HPIB control. £9999.

** Schlumberger Stabilock 4015 Communications **Test Set £4000

** Marconi 2386 Spectrum Analyser **100Hz-26.5GHz, Hi -specification. £10000.

2019 synthesized ANUFM signal generator 80kHz -1040MHz

£2000

£3250

£1000

£3000

£15000

£350

£500

£2500

£1000

£750

£500

£250

KIKUSUI 8520 frequency response analyser 20Hz-200KHzNARDA bi-directional coaxial coupler 1-4GHzRACAL -DANA 1992 frequency counter 1.3GHz IEEE optionSCHLUMBERGER 1250 frequency response analyserSCHLUMBERGER 4040 communications test set, many options included

SYSTRON-DONNER 60548 frequency counter 20Hz-24GHz GPIBTEKTRONIX P6303 o'secpe probes NEW 250MHz X10(10 with readout pin

TEKTRONIX transistor curve tracer type 577 with standard test fixtureTEKTRONIX PG502 250MHz pulse generator (/agues TM -series mainframe)

UHER report 4200 portable tape recorderWAYNE KERR SR268 source & detector

£750£250£600

£3000£5000

£1250£50ea

£1500

£750

£250

£350

16406 serial data analyser

334A distortion meter

3325A function generator

3400A voltmeter, analogue 10Hz-10MHz

3456A digital multimeter

3580A audio frequency spectrum analyser

3581C selective voltmeter

3586A selective level meter

3762A/3763A data generator/error detector, pair4140B pNmeter, DC voltage source

415E swr meter

4275A multi -frequency la meter

432NR486A uWave power meter waveguide 26-40GHz

4356 microwave power meter (analogue) (requires sensor)

436A microwave power meter cJw 8481A detector HPIB opt

4951C protocol analyser with 18179A pod

5335A 200MHz frequency counter w ops 20 & 40

6012A power supply 0-60V 0-50A 1000W

6033A system power supply 0-20V 0-30A

6038A system power supply 0-60V 0-10A

6253A dual power supply 0-20V 0-1A twice

64436 power supply 0-120V 0-2.5A

6825A bipolar power supply/amplifier-20V to +20V, 0-1A

8011A pulse generator 0.1Hz-20MHz

816A slotted line 1.8-18GHz with carriage 809C and 447B

8444A tracking generator with option 059

8505A 500KHz-1.3GHz RF network analyser

8671A synthesized signal generator 2-6.2GHz

8568A spectrum analyser 100Hz-1.5GHz

86568 synthesized signal generator 0.1-990MHz AM/FM

8901A modulation analyser with option 02/010

£500

£300

£1600

£250

£750

£1500

£1250

£2000

£1000

£3250

£200

£4000

£500

£500

£1000

£1250

£2000

£650

£1250

£1250

£250

£400

£350

£500

£500

£1500

£4500

£2500

£7500

£2950

£400

URGENTLY REQUIRED - HIGHEST CASH PRICES PAID FOR 8566A/I/C, Spectrum/network

analysers. 8590/1/2/3 portable analysers. Please call us if you have high -end capital

equipment being under-utilised.

PLEASE NOTE: ALL OUR EQUIPMENT IS NOW OPERATION -VERIFICATION

TESTED BEFORE DESPAK71 BY INDEPENDENT LABORATORY

We would be pleased to handle all grades of calibration or NAMAS certification

by same laboratory at cost price. All items covered by our 90 -day parts and

labour guarantee and 7 -day 'Right to Refuse' (money back) warranty.

ELECTRONIC UPDATEContact Malcolm Wells on

0181-652 3620

I DON'T BELIEVE IT!This new 264 page Guide toSMDs now includes 64 pages ofSM Connector Systems fromAMP, JAE, Molex, Hirose, Oxley,Cinch and Sumitomo andmainly from stock as well.Not only that but it's bulgingwith new SMDs from over 30franchises which now includePanasonic. What an incrediblyuseful publication.

I had better ring01530 510333 for my copy

before they run out!MIZIEClig=1=

1 995 MASTER PRODUCT CATALOGUE1995 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) * DIO " Timer/Counters * RS232 *RS422/485 * A/D * D/A " plus OptoIsolated versions. New ParalleUSerialRS232, Opto Dual RS232, Motion Control,Converter and Repeater for 1995!ISO 9001 Quality guarantee /UK design and manufacture36 month no -quibble warrantyTelephone hotline supportCompetitive pricing on the pageIntelligent solutions - friendly service

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VXI - EASY -TO -USEINSTRUMENTATION

Four page, colour brochure designedto teach users about VXI plug & playtechnology. Explains how standardframeworks, instrument drivers, softfront panels, and technical supportcan help end users buildmultivendor, VXIbus-basedinstrumentation systems. Givesinformation on the VXI plug & playvendor members, guidingprinciples, and how end -users canjoin the Alliance User Group.

NATIONAL INSTRUMENTSFOR FURTHER INFORMATION

CALL 01635 523545

CIRCLL NO. 139ON REPLY CARD

PC ADH24

24 Channal 12.131t Analog Input Cardwith DMA & Interrupts

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DATA ACQUISITION &CONTROL FOR PCs

Bede Technology provide a wide range of productsfor PC/XT/AT Compatibles:

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* ParallellSerial Interfaces.Products offer: *Excellent Quality *Three YearWarranty *Made in the UK *Free Technical Support.For a free catalogue and demo disks call (0191)4280353 or fax (0191) 4282904.

Bede TechnologyTel: (0191) 4280353. Fax (0191) 4282904

CIRCLE NO. 140 ON REPLY CARD

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ILI TVACIRCLE NO. 102 ON REPLY CARD

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CIRCLE NO. 103 ON REPLY CARD

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