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ELECTRONICS IWORLD

INCORPORATING WIRELESS WORLDMarch 1996 £2.25

Low -noiseantennaamplifier

1 AccessingInternet

'Non-slewing'audio power

Chargingcircuits

Applyingavalanchetransistors

Transmissionlines explained

Austria Asch. 65.00Denmark DKr. 66.00Germany DM 15.00

Greece Dra.1000.00Holland Dfl. 14.50

Italy L. 8500 00Malta Lm. 1.45

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Contents 190 DESIGNING VALVE

PREAMPSMorgan Jones details how to get the bestfrom valves in hi-fi preamplifiers.

196 FRACTIONAL -NSYNTHESISERSCosmo Little discusses implementing thefractional -N synthesiser and shows howadding a second accumulator reduceslow -frequency spurs.

202 SPEED CONTROL WITHSERVO OPTIONDesigned for use with a 12V motor,Matthew Hall's pwm speed controller isadaptable for use with a servo arm.

205 GATES CONVERTDC TO DCIan Forster has found that 74AC logicgates - with their high switching speed andlow output impedance - help make simpleand cheap low -power dc -dc converters.

208 LOW NOISEANTENNA PREAMPIn D Conway's low -noise, narrow bandmasthead amplifier, dual mosfets eliminatethe balun, enhance overload capability andreduce harmonics.

212 TRANSMISSION -LINEPRINCIPLESBill Russell shows how transmission linescan be explained clearly and simply viabasic measurement equipment and anartificial delay line.

216 HANDS-ON INTERNETUsing a working yet almost free demoversion of PSpice as an example, CyrilBateman runs through the practicalities ofdown loading software from the Net.

219 AVALANCHINGTRANSISTORSIan Hickman has been looking at howordinary transistors avalanche and at acouple of extremely rare devices specifiedfor avalanche operation.

223 PUTTING THEPOWER BACK INDesign criteria for battery charger circuitsare dictated by cell type, the applicationand operating conditions. John Lenkexamines popular IC charger designs.

229 BUILDING BLOCKSOF TIMETraditionally, Radio -Code time signalreceivers have been expensive, self-contained units, but now there are low-costmodules providing access to the raw timesignal for well under £30.

244 COAXIAL CABLECHOICESNick Wheeler discusses choosing the rightcombination of cable and connector.

256 NON-SLEWINGAUDIO POWERGiovanni Stochino shows how his`non-slewing' technique can be applied toaudio power with excellent results.

Regulars 179 COMMENT

A computerised confidence trick.

180 NEWSGovernment rejects electronics advice,Quarter -size PCMCIA, Road -toll trials,New semiconductor, Molecular diode.

185 RESEARCH NOTESSingle -electron switch, War robots, Bose-Einstein condensate, Hearing mechanisms,Scientists rethink superconductivity.

234 CIRCUIT IDEASInductance on a capacitance meter,Remote resistance measurement, Short andcontinuity test for coax, Measuringconductivity, RS232-to-RS485 PC -powered converter, Dual rail regulator,High -power, isolated switch,Programmable voltage -to -time converter

247 NEW PRODUCTSPick of the month - classified forconvenience.

252 LETTERSCable simulation response, Valveamplifiers, Internet integrity, EMC.

Cover - Hashim Akib

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Radio -Codemodule offerGalleon is offering EWreaders discounts on modulesdesigned for a variety ofRadio Code receivingrequirements. See page 232.

APRIL ISSUEON SALE MARCH 28

EW reader discountRepresenting a very comprehensive guide to switching andlinear power supply design, John Lenk's set of books isavailable to EW readers at a 10% discount. See page 226.

March 1996 ELECTRONICS WORLD 177

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178 ELECTRONICS WORLD+WIRELESS WORLD March 1996

COMMENT

EDITOR

Martin Eccles0181 652 3128

CONSULTANTS

Jonathan CampbellPhilip DarringtonFrank Ogden

DESIGN

Alan Kerr

EDITORIALADMINISTRATION

Jackie Lowe0181-652 3614

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NEWSTRADEDISTRIBUTION

David G. Sanders0181 652 8171

ISSN 0959-8332

.40-4ft. REED

PUBLISHING

A computerised confidence trickAlthough I'm not particularly.ancient I can remember quite

clearly what one kilobit of programram and a large helping ofingenuity could produce from theoriginal Sinclair ZX81 computer. Itprovided an object lesson inefficient programming. Workingwith such limited resourcesrequired absolute focus on theintended application for theprogram.

I also remember equally clearlythat, as a former components editoron our sister publicationElectronics Weekly, I wrote withsome awe about the power of theMIPS R3000 risc architecture. Thiscache equipped microprocessor hadbeen designed to run multitaskingUnix at the heart of a high endgraphics workstation.

Much has happened over the last10 to 15 years, six of which I spentas editor of this magazine. But I amnot sure that the progress I seearound me is always in a forwarddirection. Having marvelled at thelatest generation of gameshardware and its astonishingpolygon animation, it should havebeen no surprise to learn that theparticular one that I was looking atused as its main processor the sameworkstation architecture in itsR4000 incarnation. There is noproblem here. The games machinecompanies always said that theywould eventually lead the way inthe use of raw processing powerand, being totally focussed on thetrivial, we pundits never reallybelieved them or paid muchattention.

It is amazing what a single-minded application feeding into amass market can achieve.Comparing the performance ofSony's Playstation with that early2X81, it is easy to see what theextra megaflops and megabits haveachieved.

Not so with the Intel/Microsoft

personal computer market. Thecombine regularly doubles thepower of its offerings but without acommensurate doubling of utility.Microsoft continues to turn outsloppily programmed, convolutedand memory intensive software.Intel matches this with increasinglypowerful general purposemicroprocessors to make theinefficient software architecture runat halfway decent speed.

It is not even as though we needthe dubious sophistication of theduopoly's latest offerings. Themajority of business applicationsshould require relatively modestmemory and processorrequirements; spreadsheets,wordprocessors, presentationgraphics and networking involverelatively little data computation andmanipulation. It shouldn't take16Mbits of ram, 133MHzprocessors and a Gbyte of hard diskto run the things that you or I wantto do - unless we are working inprofessional graphics.

Yet the Intel/Microsoft axis haspumped so much marketing moneyinto persuading us all that computergear more than a couple of years oldis fit for nothing but scrap that italmost amounts to a confidencetrick. It causes people andbusinesses to spend needlessly onupgrades while at the same timecreating chronic inefficiency byforever trapping users on a perpetuallearning curve.

Even the computer manufacturersare not immune from the effects ofthe duopoly's cavalier marketing.One household name PC makerfound that it was unable to pay forthe massive shipment ofmicroprocessors and other chipswhich it had bought from Intel.

Being loaded with your moneyand mine, Intel simply turned thedebt into a loan. The reason that thebill went unpaid in the first placewas that the PC maker had gambled

that the hot PCs for the seasonwould be 75MHz Pentiums andgeared up production accordingly.In the event, duopoly marketingensured that the punters weredemanding 100MHz and 133MHzmachines. The loan allowed the PCmaker to unload the 75MHzmachines at bargain prices, causingall sorts of people to lose out in theprocess.

And then there is the Internet.While much of the purpose which issupposed to drive this technolgoicalhula -hoop verges on insanity, useswill emerge which make sense -and virtually none will requireintensive local processing. Thus

Games machines have advancedphenomenally - buthave pcs made the same progress?

may be born the PC Killer, anInternet access appliance whichallows users to do all the genuinelyuseful things of which the net issupposed to be capable, but withouthaving to invest thousands ofpounds in the latest Intel/Microsoftconfidence crisis. A simplecomputer, fitted out with justenough memory and processingpower to make sense of the Internet,may induce a change of thinking.

It is about time that we ignoredthe advertising and started toreconsider what we actually dowith the machines which wepurchase.Frank Ogden

Electronics World is published monthly. By post, current issue £2.35, backissues (if available £2.50.) Orders, payments and general correspondenceto L333, Electronics World, Quadrant House, The Quadrant, Sutton, SurreySM2 5AS. TIx:892984 REED BP G. Cheques should be made payable toReed Business Publishing GroupNewstrade: Distributed by Marketforce (UK) Ltd, 247 Tottenham Court RoadLondon W1P OAU 0171 261-5108.Subscriptions: Quadrant Subscription Services, Oakfield House PerrymountRoad, Haywards Heath, Sussex RH16 3DH. Telephone 01444 445566.Please notify change of address. Subscription rates 1 year £30 UK 2, years£48.00 3 years £70.00. Surface mail 1 year £35.00 2 years £56 00 3years £80.00 Air mail Europe/Eu 1 year £43.00 2 years £68.00 ROW 1year £52.00 2 years £83.00

USA: $52.00 airmail. Reed Business Publishing (USA), Subscriptions Office205 E. 42nd Street, NY 10117.Overseas advertising agents: France and Belgium: Pierre Mussard, 18-20Place de la Madeleine, Paris 75008. United States of America: Ray Barnes,Reed Business Publishing Ltd,205 E. 42nd Street, NY 10117. Telephone (212) 867-2080. Tlx 23827.USA mailing agents: Mercury Airfreight International Ltd Inc, 10(b)Englehard Ave, Avenel NJ 07001. 2nd class postage paid at Rahway NJPostmaster. Send address changes to above. Printed by BPCC Magazines(Carlisle) Ltd, Newtown Trading Estate Carlisle. Cumbria, CA2 7NRTypeset by Wace Publication Imaging 2-4 Powerscrott Road, Sidcup, KentDAt 4 SDT ,

Reed Business Publishing Ltd 1995 ISSN 0959 8332


UP DATEGovernment rejectsmicroelectronics advice

The recommendations of theGovernment's high technology

advisory panel highlighting the needfor a microelectronics R&D centrehave fallen on deaf ears.

The first 63 projects bidding forfunding under the TechnologyForesight initiative were named lastweek and the proposal to set up auniversity -based microelectronicscentre providing R&D and trainingsupport was not among them.

Although the strong emphasis onmultimedia and broadcasttechnologies in the IT projects iswelcome, there is some surprise atthe omission of the microelectronicsbid.

According to Neil Downie atsemiconductor manufacturing

equipment and materials tradeassociation JEMI (UK) there is a needfor technology development andtraining support and companies wereprepared to fund it. "Inward investorsdon't do R&D here and we need toencourage them," said Downie.

One of the Government's ITadvisors on the Foresight programmeIan Barron, founder of Inmos, saidthere was a need for amicroelectronics R&D house tosupport the high levels of inwardinvestment by semiconductormanufacturers. "We need to maintaina source of expertise for inwardinvestors to call on and use," saidBarron.

The shortlisted projects wereselected from over 500 involving

Road toll trials: "No problem"Department of Transport (DoT)has denied its motorway tolling

trials, due to start in July, are injeopardy following the decision of asecond consortium to withdraw lastweek. The Tollway group, led by USfirm Amtech and including Serco andWS Atkins, has pulled out just oneweek after Siemens announced itswithdrawal citing lack of governmentcommitment to a commercial system.

But the DoT says it expects apreliminary shake -out. "We arebasically in discussion with manycompanies which want to participatein the trials and these discussions willgo on for another six weeks. We'llknow which companies willdefinitely participate in the trials insix weeks time," said a DoTspokeswoman.

However, the departures of

Small format memory -card imminentA miniature memory card a quarter the

rl size of the PC Card (PCMCIA) formatwill appear in the summer as part of aninitiative by electronics firms in Europe,the US and Japan.

Small format memory cards, due forsummer appearance, will be a quarterthe size of their PCMCIA predecessors.

The standard format, dubbed theMiniature Card, is expected to be smallenough for use in cameras and audioequipment as well as notebook PCs. Detailsof the format, including interfacespecifications, will be released duringFebruary, with first products using the cardexpected in July.

Bill Howe, general manager for memorycomponents at Intel, a leading member ofthe Miniature Card Implementers Forum,said: "We believe flash memory is the idealstorage medium for hand-held consumerdevices and for bringing that data back tothe PC for further use. We have severaldesign wins for Miniature Card in hand andwill ship product in the second quarter ofthis year".

Internal memory of up to 64Mbytes ofeither flash, DRAM or ROM will enablethe cards to store image, text and voicedata. Data transfer to the PC will probablybe via a standard PCMCIA adaptor. The

collaborations between industry anduniversity research groups. Theaverage size of the projects is £4m,ranging from £500,000 funding forthe smallest up to £15m for thelargest. The winning groups will benamed at the end of May.

There were just six projects namedunder the heading of InformationTechnology, Electronics andCommunications (ITEC), theyincluded the setting up of four UKcentres of excellence in mobilecommunications, microsystems at theRutherford Laboratory, broadcast anddata mining at the University ofUlster. There were also projectslooking at multimedia at LancasterUniversity and display technology atThorn EMI's CRL.

Siemens and Tollway could befollowed by others if the UK trials donot begin on time. A number of thesix remaining consortia preferinvolvement in trials for a SouthKorean system, scheduled to beginthis Spring.

But Tony Kellett, the technicaldirector of Peek, the company leadingthe Tollstar consortium, believescompetition will remain intense.

ruggedised package with a pinlessconnector, at 38 x 33 x 3.5mm, is a quarterthe size of PCMCIA cards.

The small format memory cards areexpected to have applications in digitalcameras, audio recorders, mobile phonesand other consumer equipment.

Companies supplying the coresemiconductor technology includeAdvanced Micro Devices, Fujitsu, Intel andSharp. End user system support includesCompaq Computer Corporation, HewlettPackard, Konica Corporation, NokiaMobile Phones and Olympus OpticalCompany.

The Miniature Cards will competeagainst Compact Flash from SanDisk andthe as yet unannounced Solid State FloppyDisk Card from Toshiba. Compact Flashhowever only offers flash memory and usesconnector pins less suited for consumersystems.Richard Ball, Electronics Weekly

1 80 ELECTRONICS WORLD March 1996

UPDATE

Circuit board designers

unprepared for EMCPCB designers have a lack of

knowledge concerning the newEMC Directive, according to a surveyby Zuken-Redac, the pcb and multi -chip module CAD/CAM softwarecompany.

The survey of 135 UK printedcircuit board designers showed that94 per cent were unprepared for theEMC Directive even though 84 percent were fully aware of the newregulations.

Zuken-Redac said most companieshad not taken the opportunity toimprove their designs with respect toemc in advance of January 1996, thestarting date for complying with theEMC Directive.

Another worrying point is that 80per cent of all pcb designs are carriedout on pcs. However, there are fewpc -based pcb CAD design tools withintegrated emc design rules. Supplierssuch as Zuken-Redac, VeriBest andMentor Graphics are only nowintroducing the required tools.

Even though pcb designers do notnecessarily have to make theirproducts comply, they may besupplying to original equipmentmanufacturers, designing without emcin mind during the early stages canlead to rework and time -to -marketdelays later. In most cases this willcost a significant amount of time andhence money until emc design at thepcb level is more fully appreciated.Layout designers with no emcknowledge have no way of knowingwhether their design is helping orhindering the final system in terms ofemc.

Currently available design tools foremc can be roughly classified intopredictive and analysis types. Toolsusing predictive and analysistechniques, such as Ultimate's EMCExpert or Zuken-Redac's EMCAdviser, now released for the pc,compare the design with a set ofstandard emc rules giving aqualitative rather than quantitativeresult, at the expense of someaccuracy.

Modelling the emc characteristicsof individual components on the pcb,such as carried out with Mentor'sQuad Quiet, has the potential to givethe most accurate results, but thisdepends on the accurate modelling ofeach device. The disadvantage here isthe heavy processing overhead andonly the fastest pcs can handle thework load. It may be that accurateemc analysis cannot be carried out onpc based systems.

Emitter

Gate Source CollectorField plate

New combined bipolar/fet switching device

Zetexhas produced a novel device

for high side switching from lowside control signals.

The ZHD100 `treeswitch' wasoriginally designed for a specificautomotive application but is nowbeing offered for general sale.

The equivalent circuit is a p -n -ptransistor with its base connected tothe drain of an n -channel mosfet.This is very similar to an igbt, wherethe collector and source are alsoconnected. Dave Casey, co -developerof the device said: "There is aparasitic igbt in the structure whichwe have suppressed."

The advantage of separating thecollector and source is that the lowsaturation voltage of the transistorcan be fully exploited. In saturation,the igbt becomes a diode with avoltage drop of about a volt. Thesource of the treeswitch can be takenmore negative than the collectorwhich allows the transistor to fullysaturate down to a few millivolts.

The p -n -p transistor is made bydiffusing n, then p structures into ap -type substrate.

The fet is diffused as a p -well,similar to the emitter, with an n -typeisland in it. The gate metallisation forthe fet overlaps the n -island and the

main base n -type diffusion. It isinsulated from the substrate by anoxide layer.

Pulling the gate positive withrespect to the source attractselectrons into the p -type materialbelow it which forms an n -channelbetween the base and source. Thisallows base current to flow and turnsthe transistor on.

The transistor has Zetex's matrixarchitecture which results in a lowsaturation voltage. The fet sits in themiddle of it and is small incomparison, limiting the amount ofcurrent it can pass. This makes the fetapproximate a constant currentdevice, removing the need for adrain -base current limiting resistor.

The ZHD100 is rated to switch halfan amp at 80V. At high voltages thedevice dissipation is predominantlyfrom the 10mA base current. If thefull output current of the device is notrequired this can be reduced byadding a series resistor between thesource and ground.

There are other high side switcheson the market. Casey said: "Thematrix architecture results in a verysmall chip compared with itscompetitors. The small chip leads toa low device cost."

Similar to an igbt,the new high -sidetree switch hasseparate source andcollector terminals.Small relative to thebit, the fetapproximates aconstant -currentdevice, removingthe need fora drain -base resistor.

Pentium P7 slips backc ources close to Intel report that theJforthcoming P7 microprocessor, thesuccessor to the Pentium Pro, will be delayedby as much as year and will not involveHewlett-Packard to the same extent as waspreviously believed.

The P7, now code named the Merced, islikely to be launched in 1998, not 1997 as hasbeen indicated earlier by Intel. Also Hewlett-Packard's involvement in Merced now seems tobe to define the 64 -bit instruction set andsoftware interfaces. Originally, Hewlett-Packard and Intel said they would both be

involved in the design of the chip.The Merced will feature a new 64 -bit

instruction set but it will also run x86instructions in native mode rather than relyingon emulation technologies. Hewlett-Packard isbelieved to be working on its ownmicroprocessor design to support the samemicrocode.

The P7 delay could be a deliberate Intel ployto give it more time to establish Pentium Pro inthe marketplace. There is less pressure on Intelto bring out new microprocessor architecturessince its competition is struggling.


UPDATE

Cellular phone speech and noise areimproved by superconductors

Superconducting technology isbeing used in the US to improve

the noise performance and voicequality of cellular phones.

Ameritech Cellular Servicesreported excellent results from theuse of a cellular system radio -frequency filter incorporatingsuperconducting devices fromIllinois Superconductor. Ameritechsaid that use of the filter at the cellsite, improved voice signals by more

than a third and was 10,000 timesmore effective at eliminatinginterference and signal noise.

The SpectrumMaster filter alsoallowed more cellular phone users toaccess the system and increased thereceive path range. There were alsofewer dropped calls and an increasein the number of usable channels.Ameritech said that the filter isespecially effective at cell sites thathave problems from interference,

Poor demand for video games hits 3D0Wide() games console designerV 3DO, said that its third quarter

results will be worse than expecteddue to poor demand for videogames systems during the recentChristmas season. 3D0 said that it

Conventionalcurrent flow

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Syntheticproteins

Scientists in Japan have fabricated a diode only 2.5nm acrossusing a synthetic protein molecule. The molecule has beenmade by Mitsubishi Electric and is a combination of the naturalprotein cytochrome C552 and the vitamin flavin. Under anelectric field an iron atom in the cytochrome can be persuadedto release an electron to the flavin. Conversely, a similarelectric field in the other direction cannot push an electron tothe cytochrome. Forward voltage drop is reported to be900mV at 70pA and 10,000 of these devices would fit onto adiode made with leading edge 0.25pm semiconductortechnology. Like most of the current wave of molecularelectronics, it is still in development and requires severalhundred kilos of specialist equipment to make it work. Tooperate the molecule a scanning tunnelling microscope is usedto select one of a number of the molecules that has been laiddown on a metal substrate. The substrate is then the cathodeand the microscope the anode.

will be forced to establish reservesagainst large inventories and a fivemillion dollar charge due tochanges in its business model whichincludes a focus on Internet relatedproducts. The troubled company

either from buildings or from otherradio signals. If other cellularphone system providers adopt thefilter, it could open a major newmarket for superconducting materialsand help drive the development ofother superconductor basedtechnologies.

High temperature ceramicsuperconductors continue to operateabove the boiling point of nitrogen(77K).

continues to struggle to establish itsvideo game hardware in anincreasingly competitive marketthat includes Nintendo, Sega andnewcomer Sony with itsPlayStation.

Speech secure enough for banking?r'ambridge-based speechk...recognition technology firmVocalis, is to develop a speakerverification system for secure bankingover telephone lines as part of the EU-funded CAVE (CAller VErification inbanking and telecommunications)project.

The project's primary objective isto prove that speaker verification canbe applied to financial transactionservices, providing an initial level ofprotection.

"It is a pilot scheme acting as ademonstrator for the feasibility and

applicability of this technology. Bankshave been very cagey and we have toprove that this technology is feasible,"said Richard Winsky, senior researchscientist at Vocalis.

CAVE is expected to last two years,after which the technology and thesecurity provided by it will beupgraded. First field trials areexpected within the year.

The actual deployment of speakerverification technology will await theoutcome of the R&D work in CAVE.The resulting system is to complementother security mechanisms.

Modem makers boosted byInternet connections

pward spiralling numbers ofIfInternet connections in the US,

with consumers linking their pcs toonline services, is good news formodem suppliers.

More than 18.6 million modemswere shipped last year, generatingrevenues of about $5.8bn, exceedingearlier expectations, said US marketresearch firm International DataCorporation (IDC). The market grew82 percent compared with 1994shipments of 10.2 million.

The increased shipments, however,came at the expense of falling pricesfor almost all modem speedcategories except in sales of top speedV.34 (28.8kbit/s) equipped modems

which held their sales value. Thesales boom was led by U.S. Robotics,GVC and Hayes MicrocomputerProducts. IDC foresees continuingboom times for the modem industryfor at least the next few years as thepopularity of the Internet and onlineservices continues to attract millionsof new users and as modem ownersupgrade to faster modems.

US Robotics, the Illinois -basedmodem maker is reported to beplanning a move into the market forconsumer telephone hand sets, tooffset falling prices which issqueezing margins in its core modembusiness.

182 ELECTRONICS WORLD March 1996

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RESEARCH \OTES

Single electron switches presagequantum computing

Many obstacles have to beovercome before we can make

practical use of single -electrondevices, and fundamental research isfeverishly being carried out to thisend around the world. But theultimate goal, of developing deviceswhose principles of operation arequantum mechanical - progressingelectronics far beyond the scalabilityand performance limits ofconventional circuits - means thefield is hot one for science.

The work of one team in the USgives a good indication of where weare in development of real singleelectron devices - and also gives aglimpse of what could be achieved.

M G Ancona and colleagues at theNaval Research Laboratory in the USnoted that comparatively littleattention has so far been paid to thedevelopment of circuit architecturescapable of exploiting single -electrondevice performance at circuit level. Sohe has devised a set of principles forsingle -electron digital circuits (sedc)and then used these rules to designsome circuits ('Design ofcomputationally useful single -electrondigital circuits', J App Phys, Vol 79,No 1, pp. 526-538).

For computational use, circuitsrequire non-linear rather than linearoperation, which means mixingcontrol and data circuits. Since thedata now are single electrons, someportion of the control must alsooperate on this level. To achieve thisAncona has devised a single electronswitch (ses).

Physical basis for the the ses isdirect electron -electron repulsion. Theswitch is composed of two circuits, aswitching circuit and control circuit,made up of a number of islands. Thecircuits interact through a capacitor,and the principle is that repulsionmakes it energetically unfavourablefor islands 3 and 6 (see figure) to beoccupied.

When the 'switching island', 2, isoccupied by an electron, the gatebiases must cause this electron totransition, in a fully Coulomb -

blockaded manner, to island 4 ifisland 6 is occupied, and to island 3 ifisland 6 is unoccupied. In this way,the electron in the switching circuitwould be under the control of theelectron in the control circuit.

Ancona says he has discovered anumber of capacitance and bias valuesthat allow this switch to operate,though have not discovered theoptimum as yet.

Ancona also shows how theswitches could be linked together tomake And/Or and Xor circuits, and 1bit memories.

M G Ancona is at the Naval ResearchLaboratory, Washington, DC 20375,email [email protected]

Cc70_17(!)21_08 Switching

island

Controlcircuit

Electron -level switching. This SEScomprises two circuit interactingthrough coupling capacitor C. Basis ofoperation is electron repulsion whichinhibits the simultaneous occupancy ofislands 3 and 6.

Sun set: We will not be around to see it but what will our Sun look like at its death?Images produced by Nasa's Hubble Space Telescope of planetary nebula NGC 7027show remarkable new details of the process by which a star dies. Features captured byHubble include faint, blue, concentric shells surrounding the nebula; an extensivenetwork of red dust clouds throughout the bright inner region; and the hot central whitedwarf, visible as a white dot at the centre.

The nebula is a record of a star's final death throes. Initially the ejection of the star'souter layers, when it was at its red giant stage of evolution, occurred at a low rate andwas spherical. The photo reveals that the initial ejections occurred episodically toproduce the concentric shells.


RESEARCH NOTES

Hearing in two different waysGeorge Zweig at Los AlamosNational Laboratory has spent a

lot of time looking into ears. As aresult he has shown that how we hearloud sounds is quite different fromhow we hear soft ones. Now histheories of the mechanics of hearingare opening new directions inacoustic research that could lead tobetter hearing aids, improvements inthe technology of cochlear implantsand further development of speech -recognition machines.

Cross-section of the human earshows the inner ear and the cochlea,where sensory hair cells respond tovibrations and send impulses to thebrain. Travelling waves, amplified bythe hair cells, can be reflected backand forth in the cochlea, causing theear to ring or whistle. (Graphic byEdwin Vigil)

For loud sounds, the textbookunderstanding of hearing isessentially correct: sound waves enterthe ear canal and vibrate the eardrum,whose oscillations are transmitted bythe tiny bones of the middle ear to theinner ear, creating waves in the fluid -filled tubes of the cochlea. Sensoryhair cells in the cochlea respond tomotion of the fluid, generatingelectrical impulses that are interpretedby the brain as sensations of tone.Low -frequency tones excite hair cellsfurther from the middle ear than dotones of higher frequency. Deafness isoften associated with the destructionof hair cells.

For very quiet sounds, however, theear is not just a passive receiver ofsense impressions. Instead, the earresponds to and amplifies faint wavesgenerated by soft noises.

Zweig, a physicist in Los Alamos'Theoretical Division, has recogniseda symmetry governing behaviour ofthese waves in the cochlea and hasdeveloped an equation that describeswhat happens to these subtletravelling waves within the ear.

"Understanding how the earfunctions has important implicationsfor signal processing, for how you goabout extracting information frommany kinds of signals, not just speechand not just signals in the frequencyrange of hearing," says Zweig.

Back in the 70s his work led to the

discovery of the continuous wavelettransform, a way of displaying andextracting time and frequencyinformation in a signal. Now,continuous wavelet transforms areused by other researchers inmathematics and engineering, withimplications for a broad range ofendeavours from music production toseismic testing to submarinesurveillance.

Zweig hopes a clear picture of howthe ear works also can help buildbetter speech recognition systems."When you look at how the earresponds to speech, what you see in itare the acoustic signatures or theresonant modes of the mouth,including how the vocal folds aremoving in the throat. This is the kindof information you would need if youwanted to identify electronicallywhether one thing was being saidrather than another, or who said it,"says Zweig.

Zweig can also use his waveequation to explain common ringingin the ear. He shows that wave energynot transferred to the middle ear isreflected again and amplified again,combining with the original wave.This backward and forward waveamplification and reflection can setup a standing wave or resonance inthe cochlea. If the process runs awaywith itself, the ear begins to whistlespontaneously.

Scientists rethink superconductivityCould a new type of electron behaviour beresponsible for 'high -temperature'

superconductivity?A team at IBM has conducted an experiment to

suggest that this could be the case, opening the door tothe production of new high temperaturesuperconductors with predictable properties.Eventually, scientists hope they will be able to to findsuperconductors that don't need to be cooled at all.

Superconductivity is believed to result from theability of electrons to overcome their mutual repulsionand pair up in ways that enable them to pass unimpededthrough the host material.

In recent years, two different types of electronbehaviour have received significant support fromtheoretical physicists as possible keys to the mechanismof high -temperature superconductivity:`s-wave'electron pairing where charge -induced vibrations in the

material hold the pairs together, and 'd -wave' where theelectron magnetic spins are critical.

Conventional low -temperature superconductivity iscaused by a well -understood form of s -wave pairing.But some scientists have been sceptical that this shouldbe the starting point for theoretical explanations of thehigher -temperature phenomena.

Unfortunately, past experiments to distinguishbetween s -wave and d -wave have given mixed results.Now Chang Tsuei, John Kirtley and co-workers atIBM's TJ Watson Research Center and at StateUniversity of New York campuses in Buffalo andStony Brook have come up with the most convincingevidence yet for d -wave electron pairing. The result isexpected to be a shift in research that could spawnsuperconductors designed to exploit d -wave pairing,and perhaps nearing the goal of room temperatureoperation.


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RESEARCH NOTES

Bose-Einstein postulate is condensedA US group looks to have made ar\breakthrough in the decades -longeffort to understand the rare state ofmatter known as the Bose-Einsteincondensate (BEC). BEC, amysterious quantum -mechanical statein which matter is coherent and haslaser -like' properties, was firstpostulated more than 70 years ago by

Indian physicist Satyendra Nath Boseand Albert Einstein. It has beenobserved in liquid helium andsuperconductors, and more recentlyin semiconductors.

Now work of professor WolfgangKetterle and his colleagues in theResearch Laboratory of Electronics(RLE) and the Department of Physicsat Massachusets MIT is expected toallow scientists to move beyonddemonstrating BEC to using it tostudy little -understood quantummechanical effects.

BEC is achieved by chilling a gasof atoms to such a low temperaturethat the normal motion of the atoms issuddenly halted and they loseindividual identity and displayuniform behaviour as required by therules of quantum mechanics. Becauseof this, scientists believe they may beable to study quantum effects on therather large scale of several

Bose-Einstein condensation is a phenomenon in which a macroscopic number of atoms end up in the groundstate of the trap. This means that we can produce a macroscopic system that exhibits quantum behaviour. Thiscoherent state of matter is to 'normal' matter what laser light is to 'normal' light. The three images show theoptical density of a dilute sodium gas as a function of position after the gas has been allowed to freely expandfor several milliseconds. The images were taken at three different temperatures: one just above the transitiontemperature, one just below the transition temperature, and one well below the transition temperature. These'time of flight' images show us the velocity distribution of our atoms. Above the transition temperature, asexpected, the velocity distribution is a spherical gaussian. But as we cross the transition line, we see a suddenchange. The distribution becomes bimodal, with two separate contributions from the ground state and from allother states. In the third picture, the temperature has been lowered enough so that most of the atoms are inthe ground state, and the distribution looks gaussian again.

War machine that won't stopYou might think "It doesn't get tired, itdoesn't get hungry, it doesn't get sleepy

- and it's expendable" sounds like a quotefrom Research Notes' favourite film TheTerminator. In fact you wouldn't be farwrong. Because it is actually a projectmanager's chilling description of aprototype robot soldier that is currentlybeing tested in the US.

`Sarge', being developed at SandiaNational Laboratories, could well becomestandard battlefield equipment, serving as a`force multiplier,' to increase soldier/Marineeffectiveness and survivability. Its primeaim is to engage in remote surveillance, asevidenced by its full name - surveillanceand reconnaissance ground equipment.

The final, complete tugv (teleoperatedunmanned ground vehicle or 'tug-vee' toyou, me and Norman Schwarzkopf) will beproduced by the hundreds and put into thearmed forces inventory. Individual ormultiple robots will be assigned to infantryunits and battalions.

Unlike the walking, talking, metalhumanoid Hollywood robots with lasers foreyes, Sarge is a much simpler machine, andthe latest in a long line of prototype

battlefield robots.Its base platform is a commercial

recreational lour -wheeler,' a YamahaBreeze, with the addition of a roll cage andfour video cameras - two for surveillanceand two for driving - on a pan/tilt platform.

Everything - steering, throttle, cameras -can be remotely operated from a suitcase -size operational control unit miles away.

Sarge's predecessor, Dixie, had to beteleoperated via a 1200 -baud radio link.Coupled with the slow speed of itsprocessor, that caused a 75ms delay betweenuser command and machine response.Operators had to drive ahead, or plan forwhat was coming up to compensate.

With Sarge, the lag time has been muchreduced. Its command/response delay isapproximately 20ms, thanks to its muchfaster modem processors andcommunications equipment.

The developers hope that Sarge will makeit unnecessary for a contingent of soldiers tohave to go out on reconnaissance duringcombat, to determine the enemy's positionand assess the situation.

Instead, the robot could be sent ahead, andimages captured by its video cameras would

hundredths of a millimetre (atoms are10,000 times smaller).

The MIT advance has been toobtain Bose -condensed atoms with avery much higher production ratethan previously, and reaching thislevel in 9s, compared with the severalminutes required by devices used inthe other experiments.

Keys to the achievement were aspecial arrangement of laser beams tocollect and cool the atoms and aunique magnetic trap that kept theatoms from escaping.

The result: a Bose condensate withabout 500,000 sodium atoms

BEC is a ubiquitous phenomenonwhich plays significant roles incondensed matter, atomic, nuclearand elementary particle physics, aswell as in astrophysics.

According to the MIT team: "Thestudy of BEC in weakly interactingsystems holds the promise ofrevealing new macroscopic quantumphenomena that can be understoodfrom first principles, and may alsoadvance our understanding ofsuperconductivity and superfluidity inmore complex systems."

For more information please contactprofessor Ketterle at MIT [email protected]

be relayed back. If there is an enemyambush, the number of casualties would beless than one.

"Obviously, using a robot for surveillanceis different from using a person," saysproject manager Bryan Pletta. "It's not goingto be as good at some things as a personwould be, with eyes and ears and a brain".

Gaining acceptance of the use of roboticsamong infantry soldiers may be a challengetoo.

"Right now, using robotics is a prettyradical departure from the way theycurrently do things," Pletta says.

The next critical part of the project is themanufacture of eight to ten Sarge units to begiven to infantry battalions, getting theminvolved in development up -front.

"The program will actually give them toinfantry battalions and say, 'This is yours,keep it. Take it home, learn how to use it.Try and figure out what you could do with itif you had one,"'

Take it home??

Bryan Pletta can be contacted at Sandia NationalLaboratories, Albuquerque, USA.


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AUDIO

Desisnin9valve preampsMorgan Jonesdetails how to getthe best fromvalves in hi-fipreamplifiers, buthis article shouldprove equallyuseful to designersopting fortransistors.

preamplifiers receive a variety of signals at dif-ferent levels, process them, and pass them tothe power amplifier. They should do this with-

out adding noticeable noise or distortion and theyshould be convenient to use.

Figure 1 is a block diagram of a typical pre -ampli-fier. Working back from the output, there is a linestage providing a limited amount of gain. This stagemay be designed to drive long cables. It is precededby the volume control and input selector; associatedwith this will probably be some form of switching toprovide facilities for tape machines, which may, ormay not, be buffered.

One of the sources to the selector switch will be anRIAA equalised disc stage, although many modempre -amplifiers neglect this stage because it is so dif-ficult to design. The excuse for this is that the long-playing record is obsolete. This may be so, but thereare still many treasured collections of LPs that need

to be played, so a proper pre -ampli-fier should include a disc stage.

The pre -amplifier only has to pro-vide a very limited output voltage tothe power amplifier; even the mostinsensitive power amplifiers will notrequire more than 4 or 5V rms todrive them into clipping. This meansthat the line stage may be optimisedfor linearity, rather than headroom,but it will have to drive the capaci-tance of the output cable without lossof high frequencies. It may need tobe able to drive power amplifiers oflower input impedance, such as tran-sistor amplifiers.

Since the stage will be preceded bythe volume control, the power ampli-fier will amplify all of its self -gener-ated input noise, so we will need toensure that this noise is minimised,the stage also requires a low outputimpedance, coupled with low gainwhich ought to be quantified.

Low capacitance screened cablehas a capacitance of around 100pF per metre. Toavoid inducing hum from the power amplifier mainstransformers into the pre -amplifier, it will probablybe necessary to separate them by one metre. By thetime the routing of the cable between the line stageand the input connector of the power amplifier hasbeen allowed for, about 1.5m of cable will have beenused. This is equivalent to 150pF. A valve amplifierwill typically have input capacitance around 20pF,

so it should be possible to drive 170pF.In combination with the shunt capacitance of the

cable, the source impedance forms a low-pass filterwhose -3dB cut-off we can calculate from;

1

f-3dB2710?

It would be useful, however, to have the high fre-quency roll -off within the audio band to be far lessthan 3dB. As a result, it is necessary to fmd out whatf_3(ig corresponds to a given amount of loss at agiven frequency,. This can be found from,

f(dB

1

f_3dB

-I3 1

107

As an example of using this equation, we fmd thatfor 0.1dB roll -off at 20kHz, we requiref_3dB=1311cHz. It should be noted that this formula isonly valid for a single high -frequency CR or LR net-work. We can now determine that for 0.1dB loss at20kHz, driving 170pF of capacitance, we need anoutput impedance of 7k0, and preferably less.

For a single low -frequency CR or LR network,

1

f-3dB = f(dB dB I107

Using this formula, 0.1dB roll -off at 20Hz corre-sponds to anf_3dg of 3Hz.

Once stages are cascaded, both high and low -fre-quency cut-offs begin to move towards the mid -band. For 'n' stages, each with identical low -fre-quency cut-off, the cut-off frequency of eachindividual stage is related to the cut-off of the com-posite amplifier by,

f-3dB(individual) = -3d13(composite)

Applying this formula to a three -stage (n=3) capac-itor coupled amplifier, you will now find that the3Hz cut-off for the entire amplifier requires eachstage to have a 1.5Hz cut-off. The traditional valueof 0.1pF coupling capacitor into 1Mi2 grid -leakgives a cut-off of 1.6Hz.

Traditional power amplifiers had inputimpedances of MU or more; this is a usefulimpedance, because it allows a low value of cou-pling capacitor from the pre -amplifier. A value of47nF almost meets our 20Hz 0.1dB criterion, but100nF is better. Note that many modem valveamplifiers have an input impedance of 100k0,


AUDIO

requiring a 1pF coupling capacitor.A power amplifier input stage using a triode

with a sensitivity of 2V rms has excellentnoise performance. But the higher gain of apentode not only results in increased sensitiv-ity - 125mV rms is common - but the intrin-sically noisier pentode further worsens thealready compromised signal to noise ratio.

Because of the previous low -frequency cut-off and noise considerations, valve pre -ampli-fiers should be designed to drive 2V into 1MS2- even if it means modifying the power ampli-fier to achieve this match.

Typically, a sensitivity of around 250mVrms is needed at the input of the line stage.This results in an it of 8 for the line stage, butit may be useful to have 3dB to 6dB morethan this, to allow for unusually low recordinglevels. As a result, maximum allowable gain

is 16, so an Ay of 12 would be fine.This stage will be preceded by the volume

control, which is discussed later. For themoment, it will suffices to simply state that itwill probably be a 100k0 potentiometer,whose maximum output resistance will be25ki/.

The question of potentiometer output resis-tance is crucial, because it forms a low-passfilter in conjunction with the input capacitanceof the line stage. Using the earlier argument of0.1dB high -frequency loss at 20kHz (-3dB at131kHz), you can see that the maximumallowable input capacitance of the line stage isaround 50pF.

If the input sensitivity of the stage is around170mV, i.e. 2V/12, and a signal to noise ratioof 100dB or more is needed, then the self -gen-erated noise of the stage referred to the inputwould be 170mV-100dB, which is 1.7pV.This is certainly achievable with triodes.

Together with the previous arguments, thisresults in a table of requirements asfollows.

A, 12Zt 71d2 max.Cin 50pF max.Vnoise 1.70pVmax.Output coupling 100nF

A good design is a simpledesign, so you should check tosee whether the common cath-ode triode such as the ECC82, alow p triode will suffice Fig. 2.

A, 15.5Zout 77k0qn 30pF

Gain is certainly satisfactory, asis the input capacitance due toMiller effect and strays. The out-put impedance however is a littleover the required value.Although the output impedanceis higher than the ideal, inputcapacitance is considerably lessthan the allowable maximum.

Reduced roll -off at this pointcompensates for the slightly

CDLINE -TAPE -

SELECTOR

LINE

T.4.PE OUT

increased high -frequency roll -off at the output.Provided that great care is taken with thecapacitive loading of the output cable, or thestage is converted to a p -follower, this wouldbe a satisfactory solution.

Sadly, the ECC82's octal predecessor, the6SN7, would have an input capacitance ofaround 70pF, because Gag is 3.9pF, and wouldtherefore only be suitable if a 501d2 volumecontrol could be tolerated.

Controlling volumeThe volume control is an essential part of apre -amplifier and should be treated with thesame care as any other part of the design.

Human ears have a logarithmic response tosound pressure level, so if you want a volumecontrol that has a uniform perceived responseto adjustment throughout its range, you needto use a logarithmic potentiometer. This is theroot cause of all our problems.

It is not a problem to make a linear poten-tiometer; all you need do is to deposit a stripof carbon of uniform width and thickness ontoan insulator, put terminals at each end, andarrange for a contact to scrape its way round.

In an attempt to produce a logarithmic law,the coating thickness is made variable; in def-erence to audio sensibilities, a pressed metalscreening can is fitted, and two potentiometersare ganged together on one shaft. Making thecoating thickness continuously variable wouldbe expensive, so the logarithmic law is approx-imated by a series of straight lines, Fig. 3.

It is surprising how good a fit to the ideal

Fig. 1. A typical pre -amplifierselects input signals at differentlevels, processes them, andpasses them to the poweramplifier.

+285V

IM

ECC82

E. CC

EAR

147.5V

22K

I OW

IM5108

2JV

470µ

IOM

Fig. 2. Common cathode ECC82 triode stagesuitable for preamplifier output use.

logarithmic curve can be made using only fourdifferent resistance tracks, but it will come asno surprise to you that this still results in stepsin the response as the knob is rotated.

You would also expect the mechanicallylinked potentiometers to produce identical lev-els of attenuation all the way from 0dB to60dB. Some of them are remarkably good, butthe carbon track potentiometer's natural habi-tat is buried in the undergrowth of a television.

If quality is paramount, and a control that isnot continuously variable is acceptable, a

°fisting: QBasic fort ulating potelIMILM resistors.CLS

A = 0

B = 0

N = 0

PRINT

PRINTPRINT

INPUTPRINTINPUT

PRINTINPUT

PRINT

INPUT

"This

"taps

"How many switch positionsS

"What step size (dB)";D

"What value of load will be across the output of the potentiometer";L

"What value of potentiometer is required";R

program calculates individual values of resistors between"of a potential divider string."

can you use";

DO UNTIL N = S - 1

Y = ((R - L /C =R -Y- BPRINT A; "dBB = B + C

A = A + D

N = N + 1

LOOP

PRINT A;

10 ^ (-A / 20)) + SQR((L / 10

"; C; "ohms"

"; R - B; "ohms."

(-A / 20) - R) ^ 2 + 4 * R * L) ) / 2


AUDIO

switched attenuator can be used. Such anattenuator has conventional resistors connect-ed to a switch in order to control volume.Adherence to the logarithmic law can now beperfect, as can channel balance. Commerciallymade switched attenuators are available withresistors fabricated directly onto the ceramicsubstrate of the switch wafer. Their perfor-mance is excellent.

The practical disadvantage of the switchedattenuator is that you can only have as manydifferent volume levels as switch positions.Although rotary switches are available with 30positions - as opposed to the more usual 12 -this still limits us to 26 or 27 positions once anend stop is fitted.

For a normal volume control, it is oftendesirable to have a mute position, followed by

a -60dB position, then uniform steps all theway up to OdB. Already 6 of the 30 positionshave been used, so 60dB divided by 24 stepsgives 2.5dB per step. This is too coarse, andcommercial attenuators coarsen the lower lev-els to allow finer control at the upper levels,but this still only brings the basic step sizedown to 2dB.

If you don't mind wiring individual resistors

This panel defines the requirements for a high-performance RIAAequalisation circuit.

Low noise and no hum. It has to be admitted that valves arenot as quiet as the latest generation of low -noise IC op -amps, butthey can be made quiet if you use dc heater supplies. Pentodesare too noisy, and care is needed when using triodes.

Constant input impedance. This might seem obvious, but manydesigns have failed to appreciate this requirement. Cartridgemanufacturers design for a specific loading of resistance andcapacitance. They use this to equalise mechanical deficiencies ofthe generator system. This is particularly noticeable for movingmagnet designs such as the older Shure and Ortofon models.

Accurate RIAA. It is unbelievable how many designs haveincorrect RIAA equalisation - ancient and modern. This is eitherdown to a failure to use the correct equations, or to appreciatethe loading conditions.

Low sensitivity to component variation. Valves age, and as theydo so, their anode resistance rises. When a valve is replaced, nei-ther the new value of ra, or Cag, may be the same as the oldvalve. Neither of these effects should noticeably affect the accu-racy of RIAA equalisation.

Good overload capability. But what capability is necessary?Using a Tektronix TDS420 digital storage oscilloscope, thedynamic range of LPs was investigated in conjunction with ahigh quality record playing system. The TDS420 was first used in'envelope' mode to find maximum output of the cartridge, andmonitored an entire day of listening to music. The largest musi-cal peaks were found while playing a Mobile Fidelity pressing of

Beethoven's 9th Symphony. Before equalisation these peaks roseto +16dB above the nominal 5cm/sec level, but clicks due todust or scratches rose to about twice this level at +22dB, Fig. 6.

Individual clicks were then captured, and it was found that thevinyl/cartridge tip mass resonance was being excited, producingan oscillation at 56kHz for this particular moving coil cartridge,Fig. 7. If these ultrasonic signals were to overload the pre -ampli-fier, they would generate intermodulation products that wouldcome back down into the audio band, and make the clicks muchmore noticeable.

You should now allow for variable cartridge sensitivity of about6dB; if you need more than this, the disc stage should be recon-figured. A good design should not operate permanently at its lim-its, so a further 6dB margin is desirable. This gives a total of 28dBin the audio band, rising to 34dB or more at ultrasonic frequen-cies. Very few pre -amplifiers of any age achieve this requirementsimultaneously with low noise.

Worn/old discs generate more ultrasonic energy than a newdisc. This may be due to dirt ground into the groove walls, orbecause they were played by a cartridge that mistracked, caus-ing wall damage as the stylus flailed from side to side of thegroove. Inadequate ultrasonic overload margin is the reason whysome pre -amplifiers will make worn records sound unplayable,but a good pre -amplifier is able to extract the best from the disc.

Low distortion. This is an obvious requirement, and is linked tooverload capability.

Low output impedance. Ideally, the stage should be able todrive cable capacitance, so that it can drive a tape machine, orbe sited within the plinth of the turntable.

Tok Run: JUKta Envelope

A: Pawl?9: loturod

Talk Run: 2SOkSirs

SO.Onsv 2asjii

Fig. 6. Unequalised enveloped music output from cartridge.Peaks are dust/clicks. The rest is Beethoven's 9th.

Fig. 7. Unequalised output from cartridge showing excitationof vinyl/tip-mass resonance.

Enveicipe

Redi i:ox Vert Cox' koiz

1.1.111 3,00mV 20.0ms

53.19kHee: 192.3kFl3

1dfii d


AUDIO

Rna tam cc

Mix*. togroucsa)

Fig. 3. Making thecoating thickness of alogarithmicpotentiometercontinuously variable isexpensive, so the loglaw is approximated bya series of straightlines.

100

90

eo

70

60

50

40

30

20

I0

00 80 120 180 220 21190 300

Angle of retain= (degrees)

onto switches yourself, you can do rather bet-ter than 2dB steps. It is necessary to designyour pre -amplifier so well that all incomingsignals arriving at the volume control are atprecisely the same level. Additionally, the out-put of the pre -amplifier is perfectly matched tothe power amplifier, and is only able to over-load the amplifier on the last few steps of thevolume control. This is feasible, and willallow you to use 1 dB steps.

Usually, you will also need a separate muteswitch in addition to the volume control. Thistype of arrangement is surprisingly conve-nient, and a matched, truly logarithmic volumecontrol is a pleasure to use.

Assuming that you have a pair of 30 -way,switches available to make a volume control,you need to calculate the values of resistorsrequired. You could do this by hand, but aprogrammable calculator or computer makeslife so much easier.

One form of switched attenuator is similar tothe conventional potentiometer. It has a stringof resistors from which you can take the appro-priate tapping. The Qbasic Listing shown gen-erates the resistor values for this attenuator; itis not a miracle of programming, but is quickand easy to use, and can easily be modified fordifferent versions of Basic. It could also bemade to run on a programmable calculator.

The program asks for the load resistanceacross the wiper. This is the grid -leak resistor ofthe following valve. It is tempting to try to usethe potentiometer as the grid -leak, but this ispoor practice, and can cause noise problems. Itis also unnecessary, since the program accountsfor its loading in designing the attenuator.

The final value given by this program isconnected between the last useable switchcontact and ground; it is often convenient touse one of the spare contacts on the switch asa ground terminal.

Ideally, an earthed metal screen should befitted between the individual switch wafers inorder to eliminate capacitive crosstalk betweenthe stereo channels.

Selecting inputsIt is quite likely that you will have a numberof alternative sources to the pre -amplifier, forexample 1p, cd, digital tv and radio. These willneed to be selected to the volume control. Youmay also want to be able to record them ontotape, in which case you will need a tape loop,Fig. 4.

Fig. 4. Input selectors with switchable tape output.Attenuators and an RIAA equaliser preprocess the inputsto bring them to similar levels.

You will see that the arrangement is verysimple. Incoming signals are routed throughthe input selector to the volume control via thetape monitor switch. This allows off -tape orsource monitoring. The tape monitor switchshould be of the on/off/on type in order to pro-vide a centre mute position.

An unusual feature is the inclusion of aswitch in the output to tape. All of the sourcesto the selector will be low impedance, and per-fectly capable of driving the cable capacitanceto a powered -up tape machine. As a result, atape buffer is not required.

An unpowered tape machine, however, pre-sents a non-linear load to the source. This loadis in the form of unbiased transistor junctions,and may cause distortion. Most of the time,you will not be recording the source, so thetape output is switched off.

As the circuit stands, the rotary selectorswitch could suffer from crosstalk due tocapacitance between adjacent contacts. Onhigh -quality traditional pre -amplifiers, thisproblem was solved by having two switches.One selected the source, and the other dese-lected the short-circuit to ground on thatsource. Unfortunately, such wafer switches areno longer available, but a method that worksalmost as well is to use alternate contacts asinputs on a standard wafer switch, and connectthe unused contacts to ground, which thenguards the signal contacts.

A further advantage of the alternatelygrounded contacts is that if a tape loop is notrequired, the combined source/mute/tapeswitch may be dispensed with, since alternatepositions of the selector switch provide themute function, Fig. 5.

Criteria for RIAA equalisationRIAA is the abbreviation for 'RecordingIndustry Association of America'. It is theworldwide standard for equalisation of`microgroove' records, as opposed to thenumerous standards for 78s. The Europeanstandard is known as IEC, and has an addi-tional -3dB point at 20Hz (7950µs) on replayonly in order to reduce rumble.

Most manufacturers of quality pre -ampli-fiers assume that their products will be com-plemented by equally good turntables, and thatrumble will not be a problem, so they ignorethe IEC recommendation. Their equalisation istherefore RIAA.

If power amplifiers were let down by their

Fig. 5. Capacitive crosstalk on the inputselector is reduced by guarding. A furtheradvantage of this is that if a tape loop is notrequired, the combined source/mute/tapeswitch may be dispensed with.

phase splitters, then the Achilles heel of the pre-amplifier must surely be the RIAA disc stage.The stage has to satisfy so many contradictoryrequirements at the same time that its designand execution is fraught

The 'Golden Age' of valves producedpower amplifier designs that became classics.There are no classic RIAA stages; they varyfrom mediocre to plain awful.

Requirements for an RIAA stage are shownin the panel. The next stage is to consider asuitable topology. Constant input impedanceand low noise requirements eliminate shuntfeedback. Low noise also rules out the pen-tode. You are therefore left with a combina-tion of triode stages having active equalisationdetermined by series feedback, or with passiveequalisation. Each of these contenders may befurther broken down into performing theequalisation all in one go, or splitting it over anumber of stages.

To tackle the problem of RIAA equalisation,

Ri

R2

2

Fig. 8. Passive RIAA de -emphasis network.This is the only feasible network for a valvepre -amplifier.


AUDIO

it is necessary to define RIAA equalisation.The equalisation is specified in terms of timeconstants; 75ps, 318ps, and 3180ps. TheRIAA equation plus some spot results aregiven below.

s=21rf

318x106 xsGs=

(1+3.18x10-3 xs)(1+75x10-6 xs)

Frequency(Hz)

Gain(dB ref. 1kHz)

10 +18.80220 +17.59230 +16.55840 +15.65750 +14.86270 +13.509100 +11.899200 +8.418300 +6.289400 +4.778500 +3.612700 +1.8621000 0

2000 -3.7893000 -6.2044000 -8.0345000 -9.5227000 -11.87610000 -14.50220000 -19.91530000 -23.21840000 -25.60550000 -27.474

From the table we see that considerable gain isneeded at low frequencies, while high -fre-quency attenuation must continue indefinitely.

Because the high -frequency attenuation con-tinues indefinitely, you can now exclude theseries feedback 'all -in -one -go' topology. Thisis because the gain of this topology can onlyfall to unity. Although this failing can beexactly compensated after the feedback ampli-fier, it does mean that the response beforecompensation is rising. In turn, this means thatultrasonic overload capability within theamplifier is being compromised.

Because the 1 kHz level is around 20dBbelow the maximum level at low frequencies,any 'all -in -one -go' passive network must havea minimum of 20dB of loss, and probablymore. This is because the network will havethe grid -leak resistor of the following valve inparallel with it, which will cause additionalattenuation. You will fmd that it is extremelydifficult to design a pre -amplifier of acceptablenoise and overload capability using such a net-work, so this topology can also be excluded.

If you decide to use either of the two previ-ous topologies, the relevant formulae are givenin the definitive paper by Stanley P. Lipshitz,`On RIAA equalisation Networks', Journal ofthe Audio Engineering Society, 1979 June,Vol. 27, No 6, pp. 458-481.

Of the four possible networks that Lipshitzgives, these reduce to two for passive equali-sation. Of these two, only one has a capacitor

in parallel with the lower arm of the network.This feature is important because it allowsstray and Miller capacitance to be taken intoaccount. It is therefore the only feasible net-work for a valve pre -amplifier. Fig. 8. Relevantequations for this passive network are,

R1C1 2187psR1C2 750psR2C1 318psC1/C2 2.916

These numbers have not been rounded.Remember that any grid -leak resistor in par-

allel with the lower arm of the network, or

75µs

TFig. 9. Split RIAA de -emphasis. It is usual toperform the 75ps time constant passivelyfollowing the input stage. This has theadvantage of ensuring that the impedanceseen by the cartridge is constant withfrequency, apart from input capacitance.

3180/3181/

0 Fig. 10. Outline of an RIAApreamplifer involving a passive

Imo 75ps stage, followed by passivepaired 3180ps, 318ps constantsover several stages.

non -zero output impedance of the drivingstage, changes the effective value of R1 asseen by the network. Therefore, the values forthe network must be calculated using theThevenin impedance seen by that network.Likewise, any stray or Miller capacitance willneed to be subtracted from the calculatedvalue of C2.

For any 'all -in -one -go' topology other thanthe above network, it is essential to refer to theLipshitz paper, and read it thoroughly beforeembarking on design.

You are now left with only two possibilitiesfor equalisation - split active, and split pas-sive. The first job is to define how to split theequalisation. Fortunately, there is only onerational way to split the equalisation, and thatis to pair the 3180ps with the 318ps, but toperform the 75ps separately.

The 75ps time constant defines a low passfilter whose -3dB point is at around 2122Hzand rolls off at 6dB/octave thereafter. This isan ideal filter for use early in the pre -amplifi-er since it allows high -frequency overloadcapability after that stage to rise at 6dB/octaveabove cut-off. This is exactly what is needed.

It is usual to perform the 75µs time constantpassively following the input stage. This hasthe advantage of ensuring that the impedanceseen by the cartridge is constant with fre-quency, apart from input capacitance, forwhich a value is usually specified by the car-tridge manufacturer, Fig. 9.

The reason for choosing a passive network isthat a series feedback amplifier cannot achievean of less than unity, and a shunt feedbackamplifier would have noise problems.

Additionally, although it was not noted ear-lier, a feedback amplifier attempting thisresponse would fmd its output stage facedwith a heavy capacitive load. This capacitive

load demands a large current at high frequen-cies, and would be equivalent to changing theac loadline to a far lower value of load resis-tance. The result would be additional distor-tion before the feedback loop was closed.

Note that all of the previous observations areequally relevant to discrete semiconductor orIC based pre -amplifiers.

The 3180ps, 318µs pairing defines a shelfresponse with a level variation of exactly20dB. Using IC op -amps it is equally conve-nient to perform this actively or passively, butwith valves it is more convenient to use pas-sive equalisation.

The preceding description allows you todefine the optimum way of achieving RIAAequalisation in a valve pre -amplifier. Assumea passive 75ps stage, followed by passivepaired 3180µs, 318ps over several stages oftriodes. All you need now do is to define thetopology and operating conditions of eachstage, and calculate component values.

It is now possible to draw a block diagram ofthe pre -amplifier, Fig. 10. Note that the blockdiagram has completely ignored practicalitiessuch as coupling, or decoupling, capacitors andgrid -leak resistors. Nevertheless, it represents asimplicity of design to which we should aspire,i.e. dc coupling throughout. This ideal isachievable, but it is not ideal for the novicedesigner, you will need to be a little more cau-tious in your first attempt.

Morgan will discuss implementing the valve RIAA stage,

psrr and balanced preamplifiers in a second article.

Further readingLipshitz, S P, 'On RIAA equalisation Networks',Journal of the Audio Engineering Society, 1979June, Vol. 27, No 6, pp. 458-481.Wright, A, 'The tube pre -amp cookbook' 1994.


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RF DESIGN

Fractional I\synthesisers

Cosmo Little discusses implementing the fractional -nsynthesiser, and shows how adding a second accumulator tothe basic synthesiser system described last month reduces low -frequency spurs.

In my first article, I discussed the basic frac-tional -N synthesiser with a single accumu-lator, and provided a simulation of its per-

formance. In this article, I examine anmodification to the method which uses a sec-ond accumulator to generate a differentsequence of divisors. This important enhance-ment reduces the low frequency spurs seen inthe previous simulation.

In addition, I discuss here some methods ofimplementing the fractional -N synthesisers inhardware and software.

Two -accumulator fractional -N loopInvented by Racal, this modification to thefractional -N loop is based on the idea that it ispossible to change the frequency spectrum ofthe error waveform. This avoids the large dis-crete spurs that appear at low frequencieswhen generating a small fractional increment.This could be possible by dividing by agreater range of numbers based on N.

Obviously, it is feasible to divide by anynumber, provided that the average over a fullcycle of accumulator additions - a maximumof the accumulator modulus - equals therequired fractional divider.

Numbers are selected on the following basis.The loop filter is an integrator at low fre-quencies and as a result integrates the errorvoltage which builds up as a ramp asdescribed last month. If a large negative errorvoltage is generated at the right intervals, theintegrator can be reset to zero. This negativeerror voltage could be produced by dividingby N+1, and then immediately by N-1 at thenext reference cycle.

Provided that a division by N+1 always hasa corresponding division by N-1, the meanloop divisor has not been altered. As the nor-mal control mechanism requires periodic divi-sion by N+1, the combination of the two con-trols results in divisions by N-1, N, N+1, andN+2.

I have never found this argument - ref 2,p201 - convincing as the error voltage is mod-ified by the loop forward transfer response,not the loop filter. Forward transfer response isa constant multiplication by N at low fre-quencies. However the above algorithm cer-tainly works, as will be seen later.

The second control may be implemented bymeans of a second accumulator, which accu-mulates the contents of the normal accumula-tor. These will be referred to as accumulatorsA and B. As an accumulator is an integrator,overflow of accumulator B can be used to ini-tiate a correction cycle of division by N+1 andN-1.

A simple combinational logic function canbe designed to combine the overflow state ofboth accumulators and the previous overflowstate of accumulator B which must be storedin a latch.

Operation of accumulator B is shown in thedocument Program 1, as is the effect on thetime error waveform. This waveform still hasabout the same peak to peak amplitude as thatfor the single accumulator fractional -N loop,but the peaks are only reached on pulses.These pulses contain less energy at low fre-quencies. If you make a mental averagethrough the area of pulses, you will find thatthe main low frequency waveform is a trianglewave of much lower amplitude.

A correction waveform may be constructedfor the two -accumulator fractional -N loop, butthe relationship to the contents of accumulatorA is more complicated. The rule is that if Bhas overflowed in the previous referencecycle, then the value in accumulator A mustbe complemented - i.e. subtracted from themodulus.

A 5% accuracy of the correction voltage hasbeen assumed in the document, and all otherparameters are the same as for the right-handMathCad document in the last issue of EW.This allows the Fourier transforms of the error

voltages to be directly compared. But note dif-ferent Y axis) The improvement is dramatic.The frequency range in both graphs extends tofref/2, so a typical natural loop frequencywould be 5kHz. Frequency components high-er than this are progressively filtered out.

Automatic correction of the correction volt-age by synchronously rectifying the error volt-age is possible for the two -accumulator loop.This turns out not to depend upon accumulatorA at all, but only upon the overflow state ofaccumulator B. The graph in the documentshows that the function does work.

There is a possibility that other algorithmscould result in even lower low frequency spu-rious content to the error voltage. You coulddivide by a larger set of integers, for example.Alternatively, there might be a better sequenceof the set of four integers than that generatedby the two accumulator implementation.

Implementation the fractional -N loopThe lack of widespread use of the fractional -Ntechnique may partly be due to the lack of anycommercial large -scale -integration digital chipfor implementing the accumulators and cor-rection circuits required. This contrasts withthe large number of single -loop synthesiserchips available, most with provision for con-trolling dual modulus prescalers, and havingmicroprocessor interfaces for setting up thevarious internal dividers.

Figure 1 gives a possible block diagram fora single chip implementation of the two accu-mulator loop. Everything is included exceptthe d -to -a converters for generating the cor-rection voltage. Because of the difficulty ofimplementing the inverse scaling of the cor-rection voltage with change of vco frequency,a simple latch is provided for controlling ad -to -a converter. It is assumed that the con-trolling microprocessor will calculate the scal-ing factor.

For many applications binary accumulators


RF DESIGN

0

0-> >

R

0.Latch

1Phase/frequencydetector

Data o

Moduluscontrol

Cycleclock-.

Latch

Updatelogic

0'N

Adder

o,1

Latch

Accumulator B

0A

Accumulator A

,o,Latch

0'M

R N A M F

0 0 0 0 0'Clock o

Shift register

Latch o-> ,To all latches

A A

Next Nlogic

Note: optional direct cancellation of time errors shown in dotted area

Moduluscontrol

4

1

Cycleclock

S/H

7 phase detector_c,

Fig. 1. This block diagramsuggesting how the dual -accumulator fractional -Nsynthesiser could be implementedon a single chip includes everythingexcept the d -to -a converters forproducing the correction voltage.

CycleI ---clock

Complementlogic

FE>

L

atch

I

>CorrectionDAC output

Mainprocessor

INT

Slave processor

Digitaldelay

Z\

I>.

>Correctionscaling DAC

Phase/freq

0 f REF

S/H

1

DAC

Toloopfilter

Fig. 2. It is possible to use aprocessor to calculate thedual -accumulator algorithmin real time if the referencefrequency is not too high.


RF DESIGN

VCO

are adequate. This means that the output canonly be an approximation to a decimal fre-quency. For some applications such as signalgenerators, binary -coded -decimal accumula-tors will be needed.

It is important that the phase detector usedshould have very good linearity at small phaseoffsets. Otherwise the error voltage from thephase detector will not match the correctionvoltage. Digital tristate phase/frequency detec-tors are very poor in this respect, and shouldonly be used for initial acquisition. A sam-pling phase detector should be used for track-ing. This approach is used in the GEC/Plesseyrange of chips.

Until a manufacturer decides to make asuitable lsi chip, low budget designers mustlook for other ways to implement the synthe-siser. Single chip microprocessors are cheap,and are powerful general purpose logicmachines. It is feasible to use a processor tocalculate the two accumulator algorithm inreal time provided that the reference frequen-cy is not too high.

A possible block diagram is shown in Fig. 2.The processor must be synchronised to theoverflow of the loop divider, either by aninterrupt or by polling a port. The processormay take most of a reference cycle to calculatethe next value of N and the appropriate errorvoltage does not appear at the phase detectoroutput until the loop divider has finished acycle. As a result, the correction voltage willneed to be delayed internally to the processor

P/P + 1MC 4-,

fREF

MCOUT

GEC/Plessey PDA

NJ88C22

LogicMCIN

N

1T/INT

Processor

Start of cyclecounters reloaded

to keep it synchronised to the error voltage.It is also assumed in Fig. 2 that the proces-

sor will scale the correction voltage output tothe correction d -to -a converter, either by cal-culation of lookup table.

I constructed a prototype fractional -N syn-thesiser for an high -frequency receiver designabout a decade ago. It was based on the twoaccumulator algorithm and used an 8041 slaveprocessor to calculate the algorithm in realtime. The reference frequency was 10kHz, andthe processor used double precision arithmeticto give 16 -bit accumulators.

The processor ran at 6MHz, and the algo-rithm just fitted into the 100ps available. Thecorrection did not use d -to -a converters, butcorrected the time errors before the phasedetector by the use of binary increments ofdelay.

I used a miniature analogue delay line withfour sections of 80, 40, 20, and lOns. Thesesections were switched in and out of circuitusing bipolar transistors. The prototypeworked reasonably well, but it proved difficultto get the delays accurate. This method ofdirectly correcting the time errors is worthconsidering as an alternative to the usual sys-tem of generating a correction voltage. A chipsuch as the Analogue Devices AD950I whichprovides 8 -bit resolution of delay with subnanosecond resolution would seem ideal forthe purpose. This correction system is shownin Fig. 2.

Microprocessors have advanced consider -

Correction

VCO

Fig. 3. Low-costimplementation of thefractional -Nsynthesiser using anoff -the -shelfsynthesiser IC.

Note: MCOUT is extended by 0, 1, 2 or 3 cycles of FIN accordingto value N supplied by processor

P + 1

P + 1

FIN

p MCIN

p MCOUT

ably over the past decade, and it is likely thata 16 -bit digital signal processor could calcu-late the algorithm in lOps, making possible a100kHz reference frequency. For even fasterimplementations, the processor could calculatethe algorithm in advance, and store all the val-ues of N and the correction in ram. The pro-cessor could then respond to an interrupt andoutput the next values in less than 1µs.

A low-cost implementation is possible byusing a single chip synthesiser with dual mod-ulus prescaler control, and adding logic todelay the change of modulus from P+1 to Pby up to three input cycles. This will changethe overall division ratio. This idea is outlinedin Fig. 3.

Programming of the 'N' and 'A' countersmust be altered from the usual arrangement toensure that the four divisors are availablewithout requiring the 'A' counter to be zero,as otherwise the logic would not work. A littlethought will show that provided the 'A'counter has a higher modulus than theprescaler, P, then programming for any fouradjacent integers will always be possible.

This implementation would require only 1x2bit and 1x8 bit port on the processor, and onespare interrupt. If sufficient ram was availableto store the divisors and corrections, then themain system processor might have sufficientcapacity to run the synthesiser as well.

One advantage of the ram storage techniqueis that decimal accumulators can be as easilyprogrammed as binary. As the algorithm iscalculated once only for each frequencychange, the extra time required to calculate fordecimal accumulators would not matter.

Predicting vco spuriiOne final MathsCAD document is offered,Program 2. This 'document' calculates thelevel of the vco sidebands due to the fraction-al -N mechanism. It communicates with eitherPrograms 1 or the right-hand MathCad docu-ment in the last issue of EW using a data file,so the appropriate program should be run first.It is also necessary to design a sensible phase -locked loop using the phase -locked -loopMathCad document presented last month.

Loop time constants are copied across man-ually to Program 2. The document then cal-culates the voltage -controlled oscillator spu-rious sideband levels. The simplification ismade that the voltage -controlled oscillatorphase modulation index is small, so each com-ponent of the phase modulation of the voltage -controlled oscillator only results in one pair ofsidebands.

Cosmo is head of the rf design, prototyping andconsultancy company, RF Solutions, Penryn.

Further readingDigital PLL Frequency Synthesisers, Ulrich L.Rhode, Prentice Hall.Frequency Synthesis by Phase Lock ,William F.Edan Wiley.Frequency Synthesisers, Theory and DesignVadim Manassewitsch, Wiley.Phase Locked Loops. Application to coherentreceiver design, Main Blanchard, Wiley.


RF DESIGN

Program 1. This MathCad document is for evaluating operation ofthe fractional -N synthesiser's second accumulator, designated B. Italso shows how the time error waveform is affected.Phase lock loop companson frequency, f l& Integer part of loop divider, N =10

Fractional part of loop Owder, M .7. Accumulator modulus, Modulo =24.

Correction DAC modulus, DAC re.

fvco =fmr (N, 0)

f VCO =1002734.375

1- f o(Modulo.8 - I) A,,,=0 ND.:=N4-1 T,,m;

The next two statements form thevectors of values in the two accumulators. A,, ..mod(A+M,Modulo)

Special vector function definition. returns 1 if next entry in vectorless than current entry. Serves to mark accumulator overflows.If index is <0 returns 0

B,, :=rood(13,..A,Modulo)

OVFILV,j) .if(3.40,0,d(Vio<),I,O))

Logic section to create vector of divisors based on overflow of the two accumulators.Order of statements is important.

ND :=N

ND,+, it(OVFL(B.i).1.N Nr+t Di, ,)

ND, ,rif(OVFL(B,i- 1,ND+tt,o)ND,+, ..if(OVFL(A.1).1.NDi,i+ I .N Di eteso(ND) .10.027818

Graphs of accumulator content and loop divisor

rpi 10

Create vector of time errors due to non exact &Avon.T =Tee + T

f VCO

Create correction voltage from accumulator A. Note that Accumulator la truncated to no of DAC bits.

Corr. mfii OWL( B,1 - 1).1. (DAC floor(modwol DAC)).1locr(m.b.a% DAC) ( ) 2 1.59

f VCCOAC

Create error voltage vector at output of phase detector.Phase detector constant assumed equal to 1 59 tsar .) 2 .1 59 93.Corr,Note that correction is assumed to be accurate to 5% (TraRemove DC component from error voltage .(v MV)

Graphs of time error, correction. and voltage error

0 01

za

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

G - 2.81.1,V ,mor; Icingth V ena- 1048. I it' 'engin( G - 1.023.101

j 0..1000(0) - I WRITE( freqincl ) .Ha WRITEPRN(freq l) :41

lvlength V

Spodrum of error voltage (y axis in volts eqty to peak voltage of a transformed sine wave)

032

Automatic adjustment of error voitege correctionReajVCIVFMB,i - ),- V Vby synchronous rectification of V.error

mean(Rect) =0.0167

Program 2. MathCad routine worksheet for calculating vcosidebands due to the fractional -N synthesiser's mechanism.

Loop fixed parameters:

op amp low frequency pole and open loop gain: f 0 := 10 AO -=100000

loop filter component values, RI =4700 R2 =10000 Cl := 10.104 C2 := .5.109

Phase detector gain constant ( volts per radian) Kp 1.59

VCO gain constant (radians per volt second) Kv =50.103

VCO modulation pole(Hz) f mod = 30.103

Loop division ratio N .= 10

Additional low pass pole(Hz): f e20000

Data from previous fractional N calculations:

READ(frequicl ) SPUR =READPRN(freql) i := 0.. last(SPUR)

I. 4 Hz last(SPUR) =1.024.103 length(SPUR) 1.025.103

calculated values

t 3 =C2.14.2

F(s)

`°=

t mod

t t 2 -.R2.(C1+ C2)

t polo I :=2.xj2xf polo

A0. (1+ 842)

s340414 3 +33.(A0.1143+t 143+to4 + tot 2)+a(Aot +t +t 2+to)+ (1+ s.tmod 1 +atook

Kp.K.F(s) 0(s).21(s) B(s) -

1 1,3(s).11

14,1t mod =5.30516.10' t0=0.01592 t -4.7.10 5

o03 v (13(a) )1--!KP t polo -7.95775.10-3 t 3 =5.10

This graph is peak phase deviation of the VCO

i0 VCoi

0.004

0.002

12=105.10'

W IFFT(4VCO)

VCO phase deviation in time domain

0.03

-0.0

j = O.. lest(W)

SBLEVEL '31(1.VCOI

VCO single sideband spud

tv,ti,110\14

100 150

V\k4

200 230 300 400 430


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CONTROL ELECTRONICS

Designed for usewith a 12V dcmotor, MatthewHall's pwm speedcontroller isadaptable for usewith a servo -armmechanism.

SPEEDcontrol

with servo optionThis motor speed controller evolved from a needto be able control the speed of my 12V electricdrill while drilling pcbs and the like. Having an

interest in radio control, I also wanted a design thatcould be actuated by a servo arm.

Design considerationsTo suit my needs, the motor controller needed the fol-lowing attributes.

High efficiency

Complete control via one drive shaft, i.e. fastthrough to slow forward rotation, fast through toslow reverse and stationary.

No moving parts eg. reversing relays/switchesetc. other than the drive shaft.

When the controller is being actuated by a servoarm, the +45° moved by a typical radio -controlservo will need to be mapped onto the full controlrange. Therefore provision to trim this mappingwill be required.

Performance maintained for small fluctuations inthe supply voltage.

Low cost

Regarding efficiency, it is widely accepted that pulse -width modulation control is more efficient than a sim-ple rheostat since very little power is lost in theswitching components as they are either fully on orfully off. Pulse -width modulation control also has theadvantage that higher torques can be achieved at lowmotor speeds when compared with rheostat control.

Table 1. Suitable driver mosfets - prices and sources.

Table 2. Truth table of voltages within theoutput circuit around Tr3_6.

Designation Type RDs(on) Price (each) Distributor V[13] VD 4] Tr3 Tr4 Tr5 Tr6

Tr4,5 BUZ11 0.0351 £1.44 Maplin low low off off off offTr4,6 BUZ10 0.0852 £0.80/20.65 Maplin/Grandata low high on off off onTr3,5 BUZ271 0.1552 £2.15 RS high low off on on offTr3,5 MDT2955E 0.30 £1 .97 RS high high off off off off

Fig. la). Pulse -width modulationmotor controller extendingfrom full power reverse,through stop, to full -powerforwards.

12Vo

R1

330R

Tr1

2N2646

OVo

R2 C412k 100n

[5]

[1]

b1 Z Ci100n

[2]R4

10kTC2

47n

Y 1N4001

Tr22N694VR1

22k

Relaxation oscillatorf = 800Hz

R7

4k7 R9 R10 R11100k 100k 22k

C5100n

ICi a

1/4 TL084

o C6

4[17

[7]D2

1N4001[6]

D3

1N4001

[8]

[9]

V1,13.

22k

R12100R

R13

[10] 100R

R14100R

VR3b22k

R15

100R


CONTROL ELECTRONICS

Hence, the design given here is based on pwmcontrol.

Moreover, this design can generate highduty cycles and the motor switching compo-nents have low 'on' resistances. This leads tohigh efficiency at maximum speed so thatnearly full power may be attained.

In this design, motor power is produced viaa solid state complementary bridge driver,Tr3_6 on Fig. 1.

An optional alteration to the design appearsin Fig. 1 b. This makes the circuit fully com-patible for control via a servo arm.

To keep the cost down, the only relativelyexpensive components in the design are outputmosfets Tr3_6. When choosing these transis-tors, a compromise needs to be made betweenlow RDs(06) and low price. In practice having alow RDS(on) is more important for motorsrequiring high currents. This is because what-ever the on resistance of a switching mosfet,more power is dissipated in the device as thecurrent through it increases.

With these considerations in mind, theTable 1 gives some possible types for Tr3_6along with prices and corresponding distribu-tors.

Circuit detailsResistors R1_6, together with VR1, C1_3, Di, Tr1and Tr2 form a linear sawtooth generator.Without R46, VR1, C3, Tr2, and with D1 short-ed, the circuit would function as a standard

R16

1k

[12]

R18

1k

R10 and R11 will also require adjustment

From ICI b output

From ICi, output

,-LcsL[11] 100n

IC2a

unijunction transistor relaxation oscillator witha repeating cycle as follows.

Capacitors C1,2 charge through R2,3, the volt-age at point [1] rising towards 12V accordingto a negative exponential curve.

When the voltage at [1] reaches the peakpoint voltage of the unijunction device, theemitter becomes forward biased and thedynamic resistance between the emitter andbase 1 drops dramatically to a low value.Capacitors C1,2 are then rapidly dischargedthrough the emitter.

When voltage at [1] drops below a criticalvalue - usually about half the saturated emit-ter voltage for the given circuit -the unijunc-tion transistor ceases to conduct and the cyclestarts again.

The signal at point [1] is indicated in Fig. 2.With the improved circuit, comprising all thecomponents, as the voltage at [1] rises, thevoltages at [3] and [4] fall and rise respec-tively due to the increased conduction of Tr2.

The increase in voltage at [4] is effectivelytransferred to [5], since C3 relatively is large.This rising voltage at [5] makes Ci8,2 chargeat a more constant rate, rather than progres-sively reducing which would occur if the lin-earisation components were omitted and thecharging voltage was the 12V supply.

Linearisation is further increased by the inte-grating network R1C1 which provides secondorder compensation for the nonlinearity of thewave form. By adjusting VR1, a near -linear

To inv.input of IC2b

To inv. input, of IC2a

1 b). Optional circuit extension,replacing R72_15 and VR3, adds

45° servo -arm facilities to thepwm motor controller.

1/2 747 Tr[13]

R17

1M'WA

IC2b

1/2 747

R19

1M

[14] Tr

D4

4 x 1 N4001

C9100n D6

D5

M -.

D7

Tr,

Tr

00n

fi

Time

Fig. 2. Waveform obtained using a standardunijunction transistor relaxation oscillator.

fi

5'

Time ig>

Fig. 3. Enhancing the relaxation oscillatorproduces a much more linear sawtooth.

sawtooth may be obtained, a positive rampappearing at [4] and a negative ramp at [3].

A suitable inverting amplifier, /Cia, theninverts, amplifies and shifts the voltage at [4]to a usable level, impedance and amplitude.Voltage at [6] therefore changes as per Fig. 3.

Diode -capacitor pairs D3C7 and D2C6 findthe upper and lower bounds of the voltage at[6] respectively. The upper boundary appearsat [8] and the lower at [7]. Op -amps /C168,,then act as voltage followers, lowering theimpedance of the voltages at [7] and [8]. Thevoltages appearing at [11] and [12] can there-fore be varied between the upper and lowerbounds of the sawtooth at [6].

Potentiometer VR3 is arranged such thatwhen one wiper voltage is at the upper boundthe other is at the lower and vice versa.

Op -amps /C2a,6 act as Schmitt triggers: for/C2a, when the sawtooth voltage at [6] isgreater than the voltage at [11] the output at[13] is high. The same applies for IC2b andpoints [12] and [14].

Note that since the thresholds for theseschmitt triggers are actually derived from theupper and lower bounds of the sawtoothwaveform, very high duty cycles may beachieved at their outputs. This technique offersa significant improvement over the duty cycleattainable using standard monostables. Inaddition, should the sawtooth voltage at [4]and at [6] change by a small amount in ampli-tude or level, due to fluctuations in the supplyvoltage, the performance of the circuit will bemaintained. This all helps to fulfil my first andfifth design considerations.

Note that R178,19 were introduced to providea small amount of positive feedback, andtherefore hysteresis in each schmitt trigger, toreduce any change or erratic triggering.

A simple truth table of voltages at points[13] and [14], Table 2, should help you under-stand the motor drive circuitry around Tr3_6.

Clearly when Tr3&6 conduct the motor willmove in one direction and it will move in theopposite direction when Tr4&5 conduct.

Note that D47 and C9 are included purely toprevent the mosfets being destroyed by backemf, transient spikes, etc.


CONTROL ELECTRONICS

a

b

d

a

\\\\N\N\Tr3. Tr6 Tr3, Tr6 Tr3. Tr6 Tr3. Tr6

0

REV FWD

Near full powerreverse

0

REV FWD REV

Medium powerreverse

0

Stop

A

FWD

Fig. 4. These timing relationships show howthe pwm control sweeps from full -powerreverse to full -power forward.

Tr4, Tr5 Tr4 Tr5 Tr, Tr5 Tr4 Tr5

REV FWD

Medium powerforward

REV

J

FWD

Near full powerforwards

V181 and V1101

V[121

V[11]

V171 and VLSI

V1131

V1141

Bridge drivertransistorsin conduction

Position of VR3

In order to show more detailed operation ofthe circuit, and to show that VR3 correspondsto the full control range needed, I have pro-duced a timing diagram/chart, Fig. 5. Sections

d, e, and f are particularly useful in thisrespect.

Modification for servo actuationProblems will arise when driving VR3 from aservo, since the typical angle of swing is+135° for a potentiometer, but only 45° for aservo.

Differential voltage V1101-V191 thereforeneeds to be amplified using,

V9] +V101

2

This is achieved by the modification as inFig. lb). Wiper voltages of VR3 may be variedbetween the upper and lower bounds of thesawtooth waveform at [6], without using thefull range of VR3's travel. The amount of trav-el used is dictated by the position of VR4, andthis can clearly be used to carry out the rim-ming outlined in the design considerations.

In practice the amplification introduced byIC3 may need to be so high that the outputs ofIC3 will saturate, in order to provide the cor-rect range of travel for the servo/VR3.

Under these circumstances R10 or R11 mayrequire adjustment in order to reduce the gainprovided by ICia, allowing V[9] and Km] to liebetween the maximum and minimum outputvoltages of the op -amps IC4a and IC4b.

We are makingprogress withthe new version5 of SpiceAgeRapid digital filter modellingwith links to SuperFILTER digitaland analogue filter synthesizer(optional extra)Non-linear magnetic modellingincluding ferromagnetic hysteresisExtended scope of Modelmaker(optional extra), the utility thatsynthesizes opamps, transform-ers, attenuators, bipolar, JFETand MOSFET transistor librarymodelsOther benefits from thismature product which enjoys dil-ligent maintenance and profes-

SpiceAge-c. \ spiceageInets \iir_cheb.cmp

Fie Graph Network Analyse Frequency Time Presentation Window Help

Transient

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sional support include: a newmanual; new (rationalised) pin convention; faster calculating; larger circuits;tougher convergence; helpful customer base (for mutual problem solving andmodel sharing); widening third party support with links to schematic capture andsynthesis programs (native schematic capture also available as an optional extra).Contact Those Engineers Ltd at 31 Birkbeck Road, LONDON NW7 4BP.Tel: 0181 906 0155 Fax: 0181 906 0969 Email [email protected]

-VitomEngineers 1)2,(1 6QQJ11*

CIRCLE NO. 1200N REPLY CARD'


POWER SUPPLIES

Gates convert

dc to doThe 74AC series of logicgates have a number ofunique characteristics,

including low static power con-sumption, very high speed andlow output impedance. Thismakes them an useful buildingblock for some simple and inex-pensive power conversion circuitsas described here.

These power conversion cir-cuits can be considered as highfrequency resonant impedanceconverters. Their Q is determinedby the output impedance of the74AC logic gate and the L/Cratio. This has the effect of multi-plying the input 5V swing to ahigher level, which is then recti-fied to produce a stepped up pos-itive or negative - or both - dcsupply.

Two basic circuits are shown inFig. la) and b). Components Lt,C1 and C2 are the resonant circuit,with D1 - or :Du in the voltagedoubling case - providing rectifi-cation, with C3 filtering the outputripple.

Output voltage against load cur-rent is shown for both circuits,equivalent to a 1.1142 outputimpedance for the circuit of Fig.1(a) and 4.51(51 for Fig. 1(b).Negative voltages can be gener-ated by reversing the diodes.

Ian Forster has foundthat 74AC logic gates -with their high switchingspeed and low outputimpedance - make usefulbuilding blocks forsimple and cheap low -power dc -dc converters.

2MHz clock

Vout

ControlLogic '1' high V out

Logic '0' OV out

Fig. 1. Basic dc -to -dc converter basedon a 74AC logic gate, together withload performance curves. Outputimpedance of a) is around 1.1k51,while that of b) is around 4.5141.

21

20 -

19-

18-

17 -

01413 -

12 -

11 -

10 -

9 -

2MHz clock

C4 D1

01

40out

/4 74AC08 C 35

30Control

Logic '1' high V out 8, 25Logic '0' OV out

Component values: 20

L1 10µH surface mount TOKO 43FS series5.2- 15

C1 470p ceramic 0C2 120p ceramic 10

C3 100n ceramic (see text)C4 100n ceramic 5

D1, D2IC1

BYV10-40 Schottky diode74AC08

0

11112 3 4 5 6 7 00

Load current mA10j

0 1 2 3 4 5 6 7

Load current mA

2MHz clock

ControlData '0' +5V out

Logic '1' -10V out

Fig. 2. Logic powerconversion applications. a)is useful as a serial -portdriver while b can deliverup to 96dBa from a piezo-electric sounder.

Component values:

Li 10µH surface mount TOKO 43FS seriesC1 470p ceramicC2 120p ceramicC3 1n ceramic (see text)R1 3k9D1 BYV10-40 Schottky diodeIC1 74AC00

2.7kHz drive

App7. 40v p -p

1/4 74AC00

Control

Component values:

L1 220mH TOKO axialC1 100n ceramic 100ySounder - 35mm piezo sound elementin Helmholtz resonator

Sounder

High level2.7kHz sound


POWER SUPPLIES

2MHz clock

1/4 74AC08


Logic '0' OV out

Component values:

L1

C1

C2D1

D2

RiTr1

101.tH surface mount TOKO 43FS series470p ceramic120p ceramicBAT42BZX79C1210k 1/8WIRFD110

+5V

TrFig. 3. In a) the74AC powerconverter is being

load used to drive ahigh -side switch,with a 1.27ps risetime and 3.11psfall. In b), muchhigher voltagescan be produced -up to t60V - atthe expense ofoutput impedance.

2MHz clock

/4 74AC08

L1

03

Tc2

V


Logic '0' OV out

Component values:

L1 471.1H surface mount TOKO 43FS seriesC1 68p ceramicC2 68p ceramicC3 100n ceramic 100VC4 100n ceramic 100VD1, D2 D3 D4 BYV10-40 Schottky diode

Figure 2a) shows the ideaapplied to serial data communi-cations. Here a quarter of a74AC00 nand gate is used to gen-erate either -10V by power con-version or +5V via L1 and R1.The main limitation on speed isthe value of C3, which includesline capacitance; with the loadshown the circuit was able todrive at an equivalent of 9600baud.

Figure 2b) shows another waythe high drive capability of the74AC gate can be used. Here thetuned circuit is formed by L1 andthe capacitance of the piezoelec-

tric sounder disk. Capacitor C1prevents dc being applied to thedisc. With the disc mounted in anappropriate Helmholtz resonator,a very high sound level can beproduced - in excess of 96dBa.

Delivering up to 60VFigure 3a) shows a power con-verter high -side driving an n -channel mosfet as a 5V switch.Mosfets with a p -channel struc-ture tend to have higher on resis-tance than equivalent n -channeldevices and are also more expen-sive.

In this circuit Lt, C1 and C2 are

the impedance converter with DIrectifying the signal. Diode D2limits the voltage to avoid dam-aging the gate. In this example,smoothing of the rectified signalrelies on the gate source capaci-tance, and R1 provides a dischargepath to allow modulation. Asshown, with a 10/50 load resis-tor, the on resistance of Tr) wasmeasured as 0.5411 and modula-tion with a 50kHz square wave atthe control input gave a 1.27psrise and 3.11p s fall time.

Figure 3b) shows a converterusing a much higher impedancetransformation and hence higher

output voltages. Under no-loadconditions V+ is 65V and V- is-60V. With a simultaneous 68k0load, V+ is 43V and V- is -38V.

For interest, I found that it waspossible to light a neon lamp withthis circuit.

Power conversion circuits usingthis principle have a number ofpossible advantages; they arecheap, flexible and, for use incommunications circuits, bothfrequency stable and clock syn-chronous. This avoids problemsassociated with jamming of inter-mediate frequencies.

rum

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.from £750Hewlett Packard 5328A- 100MHz universal frequency counter. C250Hewlett Packard 3325A- 21MHz synthesiser/function C1500

Hewlett Packard 3438A- Digital multimeter...... ..... ..... ..... ...... .... ..........£200Hewlett Packard 3455A - 61/2 digit multimeter (autoscal) ..... ....... ........ ..........£750Hewlett Packard 3456A- Digital voltmeter............. . ....... ..... ....... . ... .............£750Hewlett Packard 3488A- HP -113 switch/control unit (various plug -insavailable) . ............... ............C650Hewlett Packard - Dig*MdfliMetarl. ......... ..... ..... .£250Hewlett Packard 3711A/37128/379113/37938- Microwave linkanalyser £3500Hewlett Packard 3746A- selective level measuring set £1750Hewlett Packard 4192A-L.F. impedance analyser (514z-13MHz) £8995Hewlett Packard 4261A -LCR meter (digital) MOOHewlett Packard 42719- LCR meter (digital) £900Hewlett Packard 4342A- O meter £995Hewlett Packard 4948A - transmission impairment measuring set £2000Hewlett Packard 4953A - Protocol analyser £2750Hewlett Packard 4954A - Protocol analyser £2995Hewlett Packard 5314A - (new) 100MHz universal counter £250Hewlett Packard 535013- (new) microwave frequency counter(20GHz) . £2500Hewlett Packard 5359A- Time synthesiser EP.O.A.Hewlett Packard 5385A- Frequency counter 1GHz (HPIB) with Opts

Hewlett Packard 5505A- Laser displayHewlett Packard 6002A- autoranging 505-109PSU £650Hewlett Packard 6181C- D.C. current source £150

£250£150£350£650

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TE LAN ETHewlett Packard 62818 - Power supply 20V -50A . ...... .... E450

DISCOUNT FOR QUANTITIES

Hewlett Packard 7402 - Recorder with 17401A a 2 plug -ins .............Hewlett Packard 800513 - Pulse generatorHewlett Packard 8011A - Pulse gen. 0.1Hz 20MHz. ..... ... ....Hewlett Packard 8116A - Pulse/function generator (1MHz-50MHz)Hewlett Packard 8152A - Optical average power meterHewlett Packard 81586- Optical attenuator with opts 002 -) 001 .

Hewlett Packard 8165A - 50MHz programmable signal source .......Hewlett Packard 83496 - Microwave broadband Amp (as new)

Hewlett Packard 83566- Sweep oscillator mainframe (plug -ins

Hewlett Packard 3403A - modulator . .

Hewlett Packard 8601A - generator/sweeper. 110MHzHewlett Packard 8620C Sweep oscillator mainframeHewlett Packard 86600- Synthesised signal gen. 10KHz 2 6GH,Hewlett Packard 86839- Microwave signal gen. (23-6 5G HrHewlett Packard 8684A - 5.4GHz to 12.5GHz Sig GenHewlett Packard 8750A Storage nonnaliser.. ..... ......... ..........Hewlett Packard 8903A - Audio analyser (20Hz-100KHz)........ ................Hewlett Packard 8903B Audio analyser (20Hz-100KHz)Marconi 8938 A/E power meterMarconi 2019A - 80KHz-1040MHz synthesised sig. genMarconi 2305 modulation meterMarconi 2871- data communications analyserMarconi 6500- automatic amplitude analyserPhilips PM 5167- 10MHz function genPhilips PM 5190- LF synthesizer w/th GPIBPhilips PM 5565- Waveform monitorPhilips PM 5567- VectorscopePhilips PM 8226- 6 -pen recorder £550Pfxlenix 55009 -tekawrrons analyser with vatkxa klledace dp6ons £2250Racal Dana 1992 - 1300MHz frequency counter opts 4B+ 55...... ...........Racal Dana 3103 40-130MHz synthesiser ................. ......... ................. £750Racal Dana 9084 Synth. sig. gen 104MHz ................................. ............ ._ £450Racal 9301A True RMS RIF millivoltmeter ..... £300..Racal Dana 9303 True RMS/RF level meter......... ..... ................................ £650

Schaffner NSG 200E - Mainframe for NSG .... .. £1250Schaffner NSG 203A- Line voltage variation . £1250Schaffner NSG 222A- Interference simulator £850Schaffner NSG 223 - Interference generator. ..... .............£850Schlumberger 2720- 1250MHz Freq. Counter £600Schlumberger S14040 Stabilodr, high accuracy 1GHz radio test set .0950Schlumberger 4923 - Radio Com. Test Set .. . . 01500Tektronix Plug ms Many available such as PG508, F0504.

SC504. SW503, SG 502 etc.Tektronix TH5003 r AFG5101 Abritrary Function Gen £1750Tektronix 1240 Logic Analyser ........... ..... ........... ..... ........... E750Tektronix 576 Cure tracer (with test fixture)...................... E1250Textronia AM503 178501 P6302 current probe amplifier £995Textronia PG506 r TG501 + SG503 TM503 - Oscilloscope calibratorTextronix CG5001 - Programmable oscilloscope cal. generator £6995Time 9811 Programmable resistance-._. ............ £600Time 9814 Voltage calibrator

.C£1975500Wavetek 200213 - Sweep generator (0-2.5GHz)

Wiltron 560 Scalar Network analyser ......................................_.._.._._.......__£800

£300£250£500

C2500£1250£110001650

£4250

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£4500£3500£3500

C375£2250£2995

£295£1950£2500£2000£1750

£400£800£200£600

OSCILLOSCOPES

Gould 053000 -40MHz, dual ch.Gould 05330013Gov d 054000- 10MHz Digital storage

E250E250E200

Gould 5110 - 100MHz intelligent oscilloscope E750Haemeg 203/203-4/203.5'203.6- 20MHz Dual CH From £175Hewlett Packard 1800 - 100MHz 4 channel £300Hewlett Packard 182C - 100MHz 4 channel £350Hewlett Packard 17079, 1707B- 75MHz dual ch. from£275Hewlett Packard 1740A, 1741A, 1744A,- 100MHz dual ch from £350Hewlett Packard 19808- 100MHz -2 channel -HP1B programmable £750Hewlett Packard 54100D- 1GHz digitizing £3995Hewlett Packard 54201A- 300MHz digitizing £1750Hewlett Packard 54501A- 100MHz Digitising -4 channelHitachi V650F - 60MHz Dual channelKikusui COS 6100 -100MHz 5 channel 12 trace

£££1439750505

Lecroy LS 140- 100MHz 4 channel D.S.O. (As new)ES:21710050Nicolet 3091 - Low freq D.S.O

Philips 3217 - 50MHz Dual CH £350Philips 3219- 50MHz with analogue storage, Dual CH

£1500£4Philips 3295 - 350MHz dual chPhilips 3302 - 20MHz Digitalstorage £d75Philips 3315-60MHzPhilips PM3295A -400MHz dual charm& £1950Tektronix 455 - 50MHz dual channel £350Tektronix 7854 - 400MHz Waveform processing oscilloscope £1500Tektronix 464/466- 100MHz. storage from £350Tektronix 465/465B 100MHz dual ch from C350Tektronix 468- 100MHz D.S.O

£425£75°Tektronix 2213 - 60MHz dual ch.Tektronix 2215 - 60MHz dual ch.

C%45500Tektronix 2225 - 50MHz dual traceTektronix 2235 - 100MHz dual ch. (portable) £800Tektronix 2236 -100MHz Dual Trace with Counter/Timer/Dmm £995Tektronix 2335 -100MHz dual ch. (portable) £750Tektronix 7313, 7603, 7613, 7623, 7633,- 100MHz 4 ch...... .... ........ ...from 0300Tektronix 7704 - 250MHz 4 ch..... ..... .. .................... . ..... ............. ..from E650Tektronix 7904 500MHz from 0850TelequIpment D83- 50MHz dual ch.............. ..... . ... .................. ...C200

Other scopes available too

Advantest 4133A -10KHz-20tH.Advantest 41338- 10KHz-20GH- (60GHz with eat. mixers) £7995Hewlett Packard 1411 8552B + 8555A (10MHz-18GHz) £1600Hewlett Packard 1827 with 8559A (10MHz-21GHz)...... ......... ......... £3750Hewlett Packard 8535 with 8559A (0.01-216Hz).............. ................. £4250Hewlett Packard 3562A - dynamic signal analyser, dual channel ..... £7500Hewlett Packard 3580A -5Hz-50KHz........... ..... ..... ..... .......... £995Hewlett Packard 3582A- 25KHz analyser, dual channel ....... £2500Hewlett Packard 37096- Constellation Analyser with 157096 High

Impedance Interface (as new)Hewlett Packard 8505A- Network analyser (500KHz-1.3GHz).. .....

Hewlett Packard 8590A- KHz-1.5GHz - ........ ..... .......... £4250Hewlett Packard 8754A- Network Analyser - 4-1300MHz £3250....Hewlett Packard 356019 - Spectrum Analyser InterlaceMarconi 2370 -110MHz £995Marconi 2371 - 30Hz-200MHz £1250Pol rad 641-1 - 10MHz-18GHz £1500Rohde 5 Schwarz- SWOB 5 Pohiskop 0.1-1300MHz E2500Schlumberger 1250- Frequency response analyser £2500Tektronix 496P - 1KHz-1.8GHz programmable

££442500Tektronix 2710 - KHz-1 8GHz50MANY MORE ITEMS AVAILABLE - SEND

LARGE S.A.E. FOR LIST OF EQUIPMENT ALLEQUIPMENT IS USED- WITH 30 DAYS

GUARANTEE. PLEASE CHECK FOR AVAILABILITYBEFORE ORDERING - CARRIAGE

& VAT TO BE ADDED TO ALL GOODS

206


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hatever your specific interest ; radio -controlledmodels, radio -communications or general electronics,the one component you can't afford to be without isElectromail.

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RF DESIGN

Low noiseantenna preamp

In D F Conway's low -noise, narrow -band masthead amplifier, input is sharedbetween two mosfets. This eliminates the balun, enhances overload capabilityand reduces harmonic levels for high-level in -band signals.

This amplifier is specifically designed tobe connected to a balanced antennainput for reception of signals over a nar-

row band of about 2MHz. It was originallydesigned as a mast -head amplifier for receiv-ing weather satellite transmissions in the rangeof 137MHz to 138MHz. However, its centrefrequency can be varied over a wide range byselecting suitable values for the tuned circuitcomponents.

The amplifier has 28dB gain and a lownoise figure. It is powered from a 12-15V sup-ply, fed down the coaxial cable. Mast -headamplifiers are an effective method of enhanc-

Liutenant Commander D F Conway, ME(Elect),MIEE, MIPENZ, C Eng, psc, RNZN.

Fig. 1. Output signal amplitude for a signalswept from 0Hz to 1GHz. The hump at about700MHz is mainly due to self resonance ofthe dc blocking circuit used to isolate thesupply voltage from the spectrum analyserinput.

rg. 2. Output signal amplitude for a signalswept from 100MHz to 200MHz. Frequencyresponse is narrow and shows good roll off.

ing weak signals because they provide a gainstage at the antenna. Any loss that occursbetween the antenna and the first gain stageadds directly to the noise figure of the entireantenna/receiver system.

Most single transistor amplifiers have anunbalanced input which requires the insertionof a balun between a dipole antenna and theamplifier. These have insertion losses of about1dB or morel which is greater than the noisecontribution of typical low noise amplifiers.

Parallel amplifiersThis amplifier uses two low -noise mosfets asparallelfor a balun at the input and improve thedynamic input power range when compared toa single -device amplifier.

Sharing the input signal between two mos-fets means that the amplifier will accept a 3dBhigher signal before overloading, comparedwith a single device amplifier. This in turnraises the third -order intercept point by 9dB.The circuit looks similar to a long-tailed pairbut the inclusion of by-pass capacitor C1decouples the sources of both mosfets toground.

To ensure even power sharing between thedevices, it is important that both signal pathshave the same characteristics. Balance isachieved by a symmetrical circuit layout andby the input and output inductors. The trans-former action of these inductors compensatesfor any gain variations between the two mos-fets. This is so effective that varying RVI overits full range has no observable effect on theamplifier's overall performance.

Implementation detailsCorrect operation of such a high -gain ampli-fier depends on good circuit layout and prop-er shielding. I constructed the amplifier on adouble -sided pcb using surface mounteddevices to minimise parasitic reactances.

The BF981 device is obsolete and has beenrepackaged as a BF991. I used the BF981because the SOT -103 package can be mount-ed on its 'back' so that the rf signal pathsthrough both mosfets were symmetrical.

Fig 3. Output frequency spectrum for aOdBm input at 137.5MHz. Even at this highinput level, the second harmonic is down30dB while the third is down 50dB. Sweepfrequency is 0-500MHz.

Fig. 4. Output frequency spectrum for a-30dBm input at 137.5MHz. At this lowerinput level, the second harmonic is down50dB while the third is down 70dB. Sweepfrequency is 0-500MHz.

1.010 00.41.01.01 0.00101

0 01 0

otrat1.4

Fig. 5. Plot of input signal level at 137.5MHzversus the output levels of the fundamental,second and third harmonics. The 1dBcompression point occurs at about 5dBmwhile harmonic suppression is good even athigh input levels.


RF DESIGN

Shielding made of sheet steel was used to iso-late the input and output signals and preventoscillation.

Inductors are air cored, space wound using18swg enamelled wire. The centre tap is ashort piece of wire soldered to the centre turn.On the output transformer, the secondarywinding is one turn that straddles the centretap of the primary coil.

The setting up procedure consists of solder-ing a short link in place of C3 and measuringthe supply current, which should be 10 to20mA. Replace the link with C3 and adjustRV1 so that the supply current is now doublethe initial reading. Connect the antenna to theamplifier and adjust C4 and C5 to achievemaximum amplifier output at the desired inputfrequency.

Performance of the amplifier is fully record-ed in the 'plots.

To summariseThis amplifier is suitable for receiving weaksignals and is for use with a balanced antenna.Its narrow bandwidth provides good receptionin the presence of high level out -of -band inter-ference. As a bonus, using two mosfets toshare the load significantly reduces harmoniclevels for high-level in -band signals.

Reference1. Mini -Circuits ff./if Designers Handbook,'92/'93 Section 14.

R8

47R

CB

7100n

L2

RFC

E1me C9-10n

B1

Rf output

43)

_rirrrirYWYWY5_

MI

BF981

c,10n

Ri27R

/I C42 - 22p

Narrow -band low -noisepreamplifier optimised foroperation at 137.5MHz.

L1

Pri: 4turnsSec: 1 turn18swg on 6mm former

M2BF981 R4

100R

R6

100k

R7

47k

RV1

22k

C5 18swg2 - 22p 4 turns on

6mm former

C6 C72p2 2p2

B2

I I antenna

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50HP 141 0T/8552B/0553B I KHz-110 MHz spectrum ir;tlyser..... ... L450HP I 4T/8552B/8554B 100 KHz-1250 MHz + L1000HP I 41T/8552B/8555A 10 MHz -I8 GHz (1355313)... .£1700

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SIGNAL GENERATORSHP8672A 2 GHz-18 OHz synthesized signal generator (new)..................L7000HP8683D 2.3 GHz-I3 GHz OPT 001/003 solid state generator (new)

HP8620C/86290B 2 GHz-18 GHz sweeper. .L2250HP8620C/86230B 1.8 GHz-4.2 GHz sweeper..HP8620C sweeper mainframes (as new)..HP3325A frequency synthesizer I uHz-21 MHz

HP3585C 50 H,.33.5 MHz selective level meter. .£1750HP3314A 0.001 Hz -19.99 MHz funttion/waveform generator .0950

HP435A/84412AH 100 KHz-4.2 GHz RF power meter............................... 0550HP 1916 step GHzHP117 16A kit (1 x 84948 + 84968) 0-110db .13-1.0HPI I 58IA attenuator set (4x 849IA DC -1 GHz ATT) 3/6/111/20..... L500HP50117A distribution amplifier (NEW) ,. L750

HP8477A RF power meter calibrator .. L225HPI I683A power meter calibrator 095HP436A digital RF power meters (sensors available FDA) L650HP3851 C 15 Hz -SO KHz selective vohmeter... L600HP4951A protocol analyser L350HP333A distortion analyser L295HPI I 710A down converter.. L250

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HP6825A power supply/amplifier-20v to +200/0-2 amp L250HP626813 DC power supply 0-40v/0-30 amp OPT 005/010/040 ............ L500BIRD 43 OF wattmeters L100BIRD 8323 30db coaxial attentuator 100w...._L300

L250FLUKE 33308 prog constant current/voltage calibrator L450BALLANTINE 6125C pros time/amplitude test set L400BRADLEY 192 oscilloscope calibrator. L500ALTECH 5335(.1 I calibrator (1 HP355c/1 HP355D ATT) .......................[295

WAYNE KERR CT496 LCR meter battery . £75RADIOMETER TRB I 1 RLC component comparator .... L1.50AVO 215-L/2 AC/DC breakdown/ionisation tester...FARNELL RBI030/35 electronic . L495FARNELL TM. 10 KHz 1000 MHz true RMS sampling voltmeter L350SIEMENS U2233 psophometer (new). £350

SIEMENS W2100 200 KHz-30 flblz level oscillator. LISONARDA 3001 460 MHz -950 MHz directional coupler 20db.. L100NARDA 3041-20 500 MHz 1000 MHz directional coupler 20db. 025NARDA 3044B-20 3.7 GItt-8.3 OH. 20db directiona/ coupler......._....._ L150NARDA 3004-10 4 GHz-10 GHz 10db directional coupler L 175NARDA 60132 solid state amplifier 8 GHz -12 GHz ................. . 050SAYROSA AMM 1.5 MHz -2 GHz automatic modulation L195IWATSU SC7104 10 Hz -1000 MHz frequency counter............................. 075

RACAL RAI218 30 MHz receiver . L300RACAL RAI779/MA 1107 30 MHz receiver .C1700

RACAL 9008 1.5 MHz -2000 MHz automatic modulation meter L300RACAL DANA 9904M 50 MHz universal counter balerRACAL DANA 9915 10 Hz -520 MHz frequency L100RACAL DANA 9916 10 Hz -520 frequency counter L 155RACAL DANA 9919 10 Hz -1100 MHz frequency counter.................... L295RACAL DANA 9908 10 Hz -1 100 MHz universal counter L400RACAL DANA 9921 10 Hz -3000 MHz frequency L400RACAL DANA 1991 10 Hz -160 MHz universal counter L395RACAL DANA 1992 10 Hz -1300 MHz frequency counter L600RACAL DANA 6000 microprocessing digital voltmeter L250BRUEL & KJAER 2203 precision sound level meter/W80812 filter ....... L400

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86 Bishopgate Street, Leeds LS I 4613Tel: (01 13) 2435649 Fax: (01 13) 2426881



FLUKE 8506A thermal RMS voltmeter .LPOAFLUKE 5100B calibratorFLUKE 5200A programmable AC calibrator .LPOAFLUKE 5205A precision power amplifier . .LPOAFLUKE 5440B direct volts calibrator .LPOARF MICROSYSTEMS INC. ANfTRC-176 VHF/UHF K & L fikers ........ L400

SPECIAL OFFERSSOLARTRON 7045 4.5 digit bench multimeter (battery/mains)FLUKE 25 High spec digital multimeters with manual/probes (as new)SMITHS r diameter altimeters . L6SSIEMENS PDRM82 portable LCD radiation meters (new)..........................LSO

HP8640A 500 KHz-1024 MHz signal generator OPT 002 £750

HP8406A comb generator. .L250HP214A high power pulse generator 10 Hz 10 MHz OPT 001..._£500

FLUKE 6011 A 10 Hz -11 MHz synthesized signalROHDES & SCHWARTZ APN62 0.1 Hz -260 KHz LF gen (new)....- L2000FARNELL SSG2000 10 KHz-2000 MHz synthesized gen (as new) L2000FARNELL DSG2 0.001 Hz -110 KHz synthesized 12130SYSTRON DONNER 1702 100 KHz-1000 MHz synthesized gen ......... L650

GIGA GR I 10IA I TGHs-113 GHz pulse generator (as £650MARCONI TF20 15/2171 10MHz-520 MHz (with synchronizer). 0150MARCONI TF2016 10 KHz-I20 MHz (L250) TF2016A 095MARCONI 60558 850 GHz-2150 GHz signal source 025MARCONI 6060 2 GHz-4 OHz signal source.. 025PHILIPS PMS 190 LF synthesizer I uHz-2 MHz digital L375ADRET 2230A 200 Hz -1 MHz synthesized source_ 095[INSTEAD 0)000 10 Hz -10 MHz synthesized oscillator. L200THANDAR TG503 0.005 Hz -5 MHz pulse/function generator.. 025

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SYSTEMS VIDEO 2360 component video generator 41500SYSTEMS VIDEO 1152/11 SS compact IT waveform/vectorttope ..... L500PHILIPS PM5567 pal vectorscopes L500SCHLUMBERGER 7702 dip transmission analyser (new) .................... L750SCHLUMBERGER 4900SCHLUMBERGER AF405 3 tone generator/modulator.. 1150AMBER 4400A audio test set L450ROD -L M1OOBVS5 hipot tester. L250WANDEL & GOLTERMAN PSS19 level generator. 4650MARCONI TF2305 mod meter 50 KHz 2.3 GHz (46883 5270) .42750MARCONI 6950/6910 10 MHz-20GHz RF power meter.......................... 4850MARCONI 6593A VSWR indicator.._..._._L495MARCONI TK2374 zero loss probe L200MARCONI TF2432A 10 Hz -560 MHz frequency counter 1125MARCONI TF2700 LCR meter battery portable . L I 50EIP 371 18 GHz source locking microwave counter L9501-1P5328A universal frequency counter 2x 100MHz + DVM ................._...050HP5342A 500 MHz -18 GHz frequency meter OPT001/003. .11200HP5345A 1.5 MHz -26.5 Gbh counter/5355A/5356A+ 8 sensors ........... L2000HP435B/8481A/8484A/II708A 10 MHz -18 GHz (new) .L11®HP435B/8481A 10 MHz -18 GHz RF power meter 0100

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reader offer30V, 5A power supplyFor a limited period, Vann Draper is offering over 25% discount on the305 LDD - a bench power supply featuring digital display of both voltageand current. Normally, the 305 retails at £159 excluding VAT anddelivery but it is available to EW readers filling in the coupon on the rightat the 25% discount price of £139 - fully inclusive of VAT and delivery.Infinitely variable between 0 and 30V - with coarse and fine controls -and adjustable between 0 and 5A, the 305 LDD has a ripple figure oftypically 10mV. Its load regulation is also excellent, at typically ±0.2%.

Accuracy of the supply's dual 3.5 -digit liquid crystal displays is 0.1decimal digit. The output can handle a continuous short-circuit,overloading at 5.5A ±0.5A. When the overload circuit is activated, itcauses both audible and visual alarms, resettable via a push-button on thefront panel.

Dimensions of the 305 LDD are 310 by 260 by 120mm and its weight is5.5kg. Housed in a light -grey steel enclosure, the unit is built to complywith UL, CSA and TUV safety standards.

Features of the 305 LDD0-30V fine and coarse adjustments0-5A adjustable10mV rippleDigital displays for V and IContinuous short circuit protection±0.2% load regulation

Use this coupon to order your 305 LDD

Please send me 305 LDD(s) at the fullyinclusive special offer of £139

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*Overseas readers can also obtain this discount but details varyaccording to country. Please ring, write or fax to Vann DraperElectronics


I 1110

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

K1100 AUDIO DESIGN 80 WATTPOWER AMPLIFIER.

This fantastic John Linsley Hood designed amplifier is the flagship ofour range, and the ideal powerhouse for your ultimate hifi system.This kit is your way to get 0K performance at bargain basementprices. Unique design features such as fully FET stabilised powersupplies give this amplifier World Class performance with startlingclarity and transparency of sound, allied to the famous HART qualityof components and ease of construction.Useful options are a stereo LED power meter and a versatile passivefront end giving switched inputs, with ALPS precision Blue Velvetlow -noise volume and balance controls. Construction is very simpleand enjoyable with all the difficult work done for you, even the wiringis preterrninated, ready for instant use!. All versions are available withStandard components or specially selected Super Audiophile com-ponents at £29.60 extra per channel, plus 02.40 if you want to includeGold Plated speaker terminals.K1100B Complete STANDARD Amplifier Kit, £395.21A1100B Factory Assembled. £499.21K1100SC Complete SLAVE Amplifier Kit, £333.62Al 100SC Factory Assembled £422.62K1100M Complete MONOBLOC Amplifier Kit. . £261.20A1100M Factory Assembled. £329.20RLH11 Reprints of latest Amplifier articles £1.80K1100CM Construction Manual with full parts lists .. £5.50

"CHIARA" SINGLE ENDEDCLASS "A" HEADPHONE

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This unit provides a high quality headphone output for 'stand alone'use or to supplement those many power amplifiers that do not havea headphone facility. Easily installed with special link -through featurethe unit draws its power from our new Andante Ultra High Duality lin-ear toroidal supply. Housed in the neat, black finished, Hart miniboxit features the wide frequency response, low -distortion and 'musical-ity' that one associates with designs from the renowned John LinsleyHood. Pre -terminated interconnecting leads and PCB mounted sock-ets prevent supply polarity reversal and on -board diagnostics providevisual indication of supply line integrity. Volume and balance controlsare Alps "Blue Velvet" components. Very easily built, even by begin-ners, since all components fit directly on the single printed circuitboard. The kit has very detailed instructions, and even comes with acomplementary roll of Hart audiograde silver solder. It can also besupplied factory assembled and tested. Selling for less than the totalcost of all the components, if they were bought separately, this unitrepresents incredible value for money and makes anattractive and harmonious addition to any hifi system.K2100 Complete Kit £109.50K2100SA Series Audiophile version with selected audiophilecomponents.. £112.46A2100SA Series Audiophile version, factory Assembled. . . C149.46K3565 "Andante" Power Supply Kit to suit "Chiara"... . . .£85.42A3565 Power Supply, Factory Assembled £128.42CM2100 Construction Manual. £2.50SPECIAL OFFER. Both units together. Kit Form.. .....£184.92Factory Assembled and Tested. £267.88

"Andante" SERIES 20VAAUDIOPHILE POWER

SUPPLIESSpecially designed for exacting audio use requiring absolute mini-mum noise, low hum field and total freedom from mechanical noisethis unit is a logical development from our highly successful 1550series.Utilising linear technology throughout for smoothness and musicalitymakes it the perfect partner for any module requiring fully stabiliseds15v supplies.Two versions are available. K3550 has 2 z15v supplies and a single15v for relays etc. and can be used with our K1400 preamp and ourK1450 RIAA pickup preamp, as well as other useful modules soon tobe introduced. The K3565 is identical in appearance but only has the*1 5v lighter current supply for use with the K1450 RIAA pickup preamplifier or "Chiara" headphone amplifier1(3550 Full Supply with all outputs £93.75K3565 Power Supply for K1450 & K2100. £85.42

ALPS "Blue Velvet"PRECISION AUDIO

CONTROLS.

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

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

"THE ART OF LINEARELECTRONICS."

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

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"DIGITAL AUDIO AND COMPACT DISC TECHNOLOGY"0-7506-0614-2 . £17.95'INTRODUCING DIGITAL AUDIO CD, DAT AND SAMPLING. ISBN1870775 22 8 .. £7.95"THE ART OF SOLDERING" 0-85935-324-3. 0 £3.95"TOWERS' INTERNATIONAL TRANSISTOR SELECTOR"0-572-01062-1. £19.95"AUDIO" F.A.Wilson. BP111 E3 95"HOW TO USE OSCILLOSCOPES & OTHER TEST EQUIPMENT"R.A.Penfold. BP267 £3.50"THE LOUDSPEAKER DESIGN COOKBOOK" Vance Dickason.

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VALVE & EARLYCLASSIC BOOKS

THE VTL BOOK David Manley BKVT1 £17.95LOUDSPEAKERS; THE WHY AND HOW OF GOOD REPRODUC-TION. G.Briggs. 1949 0-9624-1913-3. £8.95MULLARD TUBE CIRCUITS FOR AUDIO AMPLIFIERS BKAA27

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

SPECIAL OFFERPRECISION Triple PurposeTEST CASSETTE TC1D.

Are you sure your tape recorder is set up to give its best? Our latesttriple purpose test cassette checks thethree most important tapeparameters without test equipment. Ideal when fitting new heads.A professional quality, digitally mastered test tape at a price anyonecan afford. Test Cassette TC1D. Our price only £9.99.

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

SOLDERINGThe size of modern components makes the right soldering equipmentessential for good results. Everything we offer we actually use in ourown workshops!. See our Lists for the full range. 845-820 XS240ANTEX 240v 25w Soldering Iron. This is the ideal Multi -purpose ironas the bit is designed to totally surround the element giving the bestheat transfer. This excellent design also means that although it is

small and handy enough for modern components its heating capaci-ty is better than larger irons of conventional construction. ExcellentValue £9.93845-080 ST4 Lightweight Soldering Iron Stand. This has provision forthe classic damp sponge for Olt wiping .......... £3.95

HART SUPER AUDIOGRADESILVER SOLDER.

Hart Super Audiograde Silver Solder has been specially formulated forthe serious audiophile. Not only does it give beautiful easy -to -makejoints but it is designed to melt at normal soldering temperaturesavoiding the possibility of thermal damage to components or the needfor special high temperature irons. A very low residue flux makes per-fect joints easy but eliminates the need for board cleaning afterassembly.

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

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CIRCLE NO, 124 ON REPLY CARD '4'" El PE00E5111,4

ANALOGUE DESIGN

Relayinctransmission line

principlesBill Russell showshow transmissionline principles can beexplained clearly andsimply with the aidof basicmeasurementequipment and anartificial delay line.

Fig. 3. Signals for a one -wavelength matched line.Output at the load, onewavelength from the input is inphase while at tap 5, half awavelength from the input, thesignal is 180° out of phase. Inthis and subsequent diagrams,the top waveform in each screenrepresents input voltage.

The concept of a travelling electromagnetic wave, and the acvoltage and current supporting the wave, has always been adifficult one to present in non -mathematical terms. Even in

this age of computer simulation, students remain unconvinced,and ask if there is any simple way that they can establish the basicprinciples in the laboratory.

In the past, it was usual for most teaching establishments tohave a lumped component line, with a delay of 1 ms, a Zo ofaround 6000, and often with small current -sensing resistors sothat progressive voltage and current waveforms could be dis-played on an oscilloscope. The real problem - that of simultane-ously displaying voltage and current against time and distancealong the path of the wave - is not truly solved. However, pro-gressive measurements allow the phase lag and phase velocity tobe established. Additionally, current and voltage distributionalong the line can be recorded with different terminations.

Unfortunately, the large inductors required for such lines aredifficult to accurately fabricate. They also introduce significantlosses, which result in discontinuities along the line, heavy atten-uation, and a characteristic impedance Zo. Although Z0 may havethe correct magnitude, it has a defmite reactive component, mak-ing such lines unsuitable for simple introductory experiments.

Evaluating the delay lineThe discovery of a set of early 1980s computer boards containing12 -pin encapsulated Bps, 81d1 delay lines suggested a possiblesolution. A few simple measurements showed that these linescould be operated into a resistor of 8k0 at frequencies of 100kHzto 200kHz.

These lines produce negligible standing wave or attenuation.The delay appeared to be generally about 8.4p s. Frequencies of

Fig. 4. Ignoring a smallcapacitive lead, the ratio ofinput voltage to current givesa nominal resistance equal tothat at the termination onewavelength away. This showsthat the ratio of line voltage tocurrent in a travelling wave isconstant along the length of amatched line. Load is 81(Q.

Fig. 1. Below, test set-up for the artificial lines.Simple resistive terminations of Zo, 2Zo and 0.5Z0are provided for each line.

Waveformgenerator

input100R

Lexor artificial delay line 8ps 81c.(2

Input 1 3 4 5 6 7 9 10 Gnd

(CH1) 0(t 16k

RF input8k

4 (CH2)

Line dimensions: Length - 65mm 4kWidth - 12mmdepth - 9mm

1k

8k

4k

4-0-0Line

output

0

Fig. 2. Above, this acinterface allows 5052signal generatoroutput to be matchedor mismatched to theline input. The 10052resistor in the returnline monitors inputcurrent whenrequired.


ANALOGUE DESIGN

Fig. 5. In the half -wavelengthmatched line, outputs at the loadand at tap 5 are 180° and 90° outof phase respectively.

Fig. 6. Half -wavelength matchedline outputs at the load, topscreen, and at tap 5, bottomscreen, are lagging byapproximately 90° and 45°respectively. Top waveform ineach screen represents inputvoltage.

approximately 120kHz, 60kHz, and 30kHz allowed the lines tosimulate one, half, or quarter wavelengths of uniform line. Inaddition each delay line had taps at each of the ten sections.

The initial exercise was to calculate the inductance and capac-itance per section of the delay line using the simple theory of alossless line.

Delay per section for Td=0.8ps is q(LsCs)Characteristic impedance for 4=81(51 is 4(LjC5)

Note that L5 and Cs are the inductance and capacitance per sec-tion. This gives:

Ls=Td4,=.6.4mH and Cs=Td/Z0=100pF.

A second type of nominal delay, 4p s, and 4, 41M, gave 1.6mHand 100pF. Since these values are easily practicable, discretelines could be fabricated in place of the encapsulated onesobtained so fortuitously. The simple test panel for the artificiallines is shown in Fig. 1. Simple resistive terminations of Z0, 24and 0.5Z0 are provided for each line. Open circuit and short cir-cuit options are also available.

Making measurementsMeasurements using sine waves are described first, since thesecan be carried out with a standard 0.2Hz to 2MHz function gen-erator and a 20MHz double beam oscilloscope. An ac interface,Fig. 2, allows the 500 output of the signal generator to bematched or mismatched to the input of the line. The 1000 resis-tor in the return line monitors input current when required.

Initial measurements are carried out with source and termi-nating resistors set at 8ka The waveform generator output isadjusted to give a sine wave of 8V peak on the 200 to 200kHzrange. Frequency is adjusted around 120kHz so that line inputand output voltages on channel 1 and 2 are in phase.

The line is now equivalent to a transmission line of one wave-length and the voltage at each tapping point will establish theprogressive phase lag over one wavelength, a slight indicationof a standing wave, and a small attenuation over the ten sec-tions. Figure 3 shows the output at the load end, and at thehalfway point. This means that, as was to be expected, the arti-ficial line is not entirely loss free, hence Zo will have a reactiveelement.

Channel 2 is now moved to the line end of the 1000 resistorand the sensitivity increased to display the line input current ofthe nominally matched line. The ratio Viogio gives the nominalvalue of line input impedance, and it will be noted that this isapproximately 8141 with current leading by a small angle.Figure 4 shows the input voltage and current for the matchedone wavelength line.

Readjusting frequency - so that the line behaves as one half,and one quarter wavelength - enables the simple properties ofthese line lengths to be established. This is provided measure-ments are carefully recorded and processed. For the purpose ofthis article, measurements were made using a storage oscillo-scope with plotter interface so that a hard copy of the wave-forms could be obtained. A selection of these results is shown inFig. 5 and 6.

Fig. 7. With a wavelength line, a 161d1 load results in a 2:1mismatch at the end of the line, and inspection of the voltageat successive taps shows a 2:1 voltage -standing -wave havingmaxima at each end and in the centre (half -wavelength) andminima at quarter and three-quarter wavelengths from theinput. The voltage/current at the input (8V and 0.5mA) gives anominal input resistance of 16ki2 - identical to that at the load,one wavelength away. Due to the 2:1 standing wave of current,the line voltage/current at the quarter and three-quarterwavelength points will thus be 4V and 1mA, giving a lineresistance at these points of 41d2. This is more appropriatelyshown by the measurement on a line of electrical lengthquarter -wavelength as in Fig.10.

Fig. 8. Loading of 452 also resultsin a 2:1 mismatch, with acorresponding standing wave. Thistime minima of 4V appear at eachend and in the centre (half -wavelength). Input resistance isagain equal to that at thetermination i.e. 41cS2 due to thestanding wave of voltage andcurrent. Line voltage to currentratio will be a maximum of 16k11(8V and 0.5mA) at the quarter -and three-quarter wavelengthpoints, and a minimum of 41d2(4V and 1mA) at the half -wavelength point.

Fig. 9. Due to the standing wavecaused by the 2:1 mismatch, thevoltages at input and load areminima of 4V but are in antiphase.If monitored, input current wouldbe maximum of 1mA (inputresistance 4k52). At tap 5 - thequarter -wavelength point - thevoltage is a maximum of 8V andlags by 90°. Standing wave currentat this point would be 0.5mA(16k0).


ANALOGUE DESIGN

Fig. 10. With a quarter -wave line,161c52 loading establishes 2:1voltage and current standing waveon the quarter -wave line, with avoltage maximum (8V) and acurrent minimum (0.5mA) at theload end. Voltage minimum (4V)and current maximum (1mA)occur at the input. This is aparticular example of the so called'quarter -wave transformer' inwhich the ratio of output to inputresistance is proportional to thesquare of the standing -wave ratio,in this case 4:1.

Line propertiesIn order to establish the properties of a mismatched line, the inputis readjusted to the frequency. This makes the line equivalent toone wavelength, and the line is terminated in 2Z0 or Z0/2.Monitoring the voltage outputs at successive taps will indicate a2:1 voltage standing wave on the line in each case with successivemaxima and minima spaced at quarter -wave intervals. With a16k0 load, voltage maxima occur at each end and in the middle(half -wave point ), with minima at the quarter -wave and three-quarter -wave points. With a 4k0 load, a 2:1 standing -wave ratio isagain produced but the relative positions of maxima and minimaare interchanged.

Figures 7 and 8 show conditions at the input of these lines andby inference, conditions at successive 14 wave points can bededuced. Figure 9 shows the input, output at the load, and the out-put at tap 5 for a mismatched line of half -wavelength. Figures 10and 11 are included to show examples of the traditional quarter -wave matching section.

A second delay line used had characteristics of 4ps and 4kaConnected to the main 8ki2 line and operated at a frequency whichmakes the 4ps line equivalent to quarter -wave, a 2k0 load causeda standing wave in the quarter -wave section and acts as a roughmatch for the main 8kS2 line.

Due to the wide range of measurements provided by this delayline arrangement, the whole exercise is designed to be brokendown into a progressive series of laboratory sessions. In this waypractical expertise and theoretical understanding gradually increaseand are mutually supportive. The use of artificial delay lines tomeasure the propagation of rectangular pulses will be examined ina further article.

Further reading1. Ian Hickman, `RF Reflections', EW+WW Oct 1993.2. D.C.Green, 'Radio Systems Technology', Ch. 3, Transmission Lines.

Fig. 11. Again with a quarter -wave line, 41d2 load establishesa voltage and current standingwave, with a voltage minimum(4V) and current maximum(1mA) at the load, and avoltage maximum (8V) andcurrent minimum (1mA) at theinput. In this case, output andinput resistances are in theratio 1:4.

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Analysing fm noise

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COMMUNICATIONS

Cyril Batemanruns through thepracticalities ofdown -loadingsoftware fromthe Net - using aworking yetalmost freedemonstrationversion of PSpiceas an example.

Hands-onInternet

Having followed DougSelf's amplifier series, orOwen Bishop's introduc-

tory circuit design articles, youmight have had a desire to learnPSpice hands on'. Buying therequired software can be pro-hibitively expensive. The cost ofdown loading an evaluation copyfrom Internet, however might sur-prise you.

Over the past year, in theInternet Newsgroups targeted toElectronics and this periodical,interest in using circuit simulationhas doubled. An Internet 'Gopher'search against `13Spice' produced258 'hits' compared with 143 inFebruary 1995.'

Fundamental to circuit simula-tion is the 'device model' usedwith the simulation software. Anop -amp could be described usingthe exact circuit description, butthis would result in very large filesand slow simulation, so mostsemi -conductor makers issue disksof simplified 'MacroModels'extracted using the PSpice 'Parts'software. For most users simula-tions produced in this way are suf-ficiently accurate.

Burr -Brown offer a disk - partNo AB/E-020F - for the company'sop -amp catalogue. It includes fourlevels of model topologies,`MacroModels' and three improvedlevels. These culminate in 'LevelIV: Simplified Circuit Models'describing the op -amp at the tran-sistor level for the most accuratesimulations. Disks are available onrequest from the relevant customerservice departments for most man-ufacturers.

This article demonstrates FileTransfer Protocol, FTP, using theInternet software included with

OS/2 Warp. Where possibleactions needed using Windows orthe Mac computer are also indi-cated - assuming you have accessto a local FTP host.

Carrying out the quotes asshown should enable successfultransfer of the PSpice software.The indicated costs assume BTcosts at 3.5p per minute andService Provider costs at £3 perhour, using a 14400 baud or fastermodem with off-peak transferstypically at 100kbyte/min.1

The best off-peak times areSaturday and Sunday mornings

I II' I O1 WI.11110n Ilucl

Host: ftp.netcorwcom

User: anmymua

Password: s

Account -

(a)

while America sleeps, howeverthese times are used for file main-tenance in the US (2-5am USlocal), hence the best times forlarge file transfers tend to be 10amto fpm.

Constantly updatingThe Internet is always changing, Irecently down loaded a copy ofPSpice Eval6.1 from,

'ftp.iastate.edu/pub/pc/pspice',

However on preparing this article,I found a message saying PSpice

I 1%1 CIei, 14...mtv 11081

Flost: klIngort se. iastate.erkt

User: anonymous

Password: AX.K.00001.101

Account; xxxxxxmxxxxxxxxx

C01tc01 Helpac

(b)

Fig. la) Logging on to a remote host, using anonymous ftp.Microsim.FTP(Windows only) 'ftp.netcom.com'.lb) lastate.edu(dos/Windows/Mac) Ilingon.ee.iastate.edu'. Hostsautomatically respond with the correct drive set to its root directory.

Macro -models for use withAnalog Devices.Apex Microtechnology Corp.Burr -Brown Corp.Harris Semiconductor.Linear Technology Corp.Texas Instruments Corp.

PSpiceSpice Model Library.Spice ModelsApplication Note AB/E-020FAnalog Products.Spice models.Mixed Signal Access

Useful Internet sourcesInternet Newsgroups sci.electronics

sci.electronics.designsci.electronics.cadsci.electronics.basicssci.electronics.equipmentsci.electronics.components


COMMUNICATIONS

had moved. An Archie search againstTSpice' indicated two sources, relo-cated at Ilingon.ee.iastate.edu' and thenew source at Microsim's FTP siteftp.netcom.com'.Microsim's own source at `ftp.net-

com.com' offers the latest Windowsevaluation version (6.2) of PSpice. Thisincludes schematic capture, Optimiserand Polaris, in total around 12Mbyte ofself extracting zipped files. Its transfercost is £10.20.

Address `klingon.eelastate.edu' hasa slightly older version of 6.2 split intofloppy -sized files. These might be eas-ier to down load - in total around14Mbytes - and with a transfer cost of£12.60. To use these Windows ver-sions you must have a suitablewin32s ' file. This is available from

either site. Also, a minimum of a 386with co -processor is needed, togetherwith 8Mbyte of extended memory, Dos5 and Windows 3.1.

Address `klingon.ee.iastate.edu' alsohas Mac and dos evaluation versions ofPSpice, including `pseval5.3' for doswhich does not need a co -processor.While the dos versions do not haveschematic entry, they have much small-er files, typically 2.5Mbyte costing only£2.25 to down load. This is an ideallow-cost start to circuit simulation -especially if your only access to FTP isby 'E -Mail'.

Logging on to the netHaving decided which version ofPSpice you want, start up your localFTP host and log -on to the chosen siteusing 'anonymous' FTP, Figs 1 a) and1 b).

Change to the correct 'remote' direc-tory, capture the screen or print thisdirectory for later use, transfer theappropriate text files, save to disk andlog -off, Figs 2 and 3.

Read the down -loaded text files; seeTable.

Having read the text files, choose

Table. Files on the net relating to PSpice - and where to find them.Remote hostLog -on:

Remote Directory

Text Filealso

carrell, Dlreclocy

Directories/Files

Microsim.FTP(Windows only) lastate.edu (Dos/Windows/Mac)"ftp.netcom.com" "klingon.ee.iastate.edu"

"/pub/mi/microsim"

"message.txt""wineval.txt"

Include Files

Drives/Directories

141creekte

IndICI

reeb/m1/rntereet I Include Files

/123560 so -2/0111111-571- TIESIC-ISTinTii7921066 60 2.000 Oct 5 11135 62avirte. 9223055 50 1937362 Oct 0 /I:26 62ortrer. 0123955 SO 210127 nee IS ISIS 1121212 let .23056 SO 29007 low I9 1911623966 60 2500000 Aug I7 011 , 49 0 11011. 523955 90 2352234 17 90 :49 62011009 . to223955 59 20922 1110 116,64 brochure. int23995 50 6392 Oct 25 01,17 Alf me . me23955 50 3372 Jut 17 IV 1111 ASSAMMfg IR 1611 Nov

Cutrent Director, 111AI1PII01111 lecke& Files [IIFIW DrIves/C,Ineeterlee

nelotonno00pneenadotennrnent

Current Direclere

Directories/FilesMetal IMF

Irene* F IIes

ItoItoft0ftpnoItoIto

404427 2::9 21 14417 11211141411111Ann aup 21 14:07 112034022,22e41111911 3200 21 MR 11321110./.

o

11342911111011 An 21 14:07 120101014.20044 ln 21 1447

Olen /102 21 Inn411200 An 21 InnZinn /112 31 14101 0221224,1242442513 Nue 2121 14010 11302n0.22/410010 1.4

which packages are needed and high-light these on the directory printout.Repeat the above log -on, selectTransfer Mode Binary, select therequired files and down load.

With large file sizes, if for any reasonthe transfer slows down unduly, waitfor 2-3 minutes, or longer if much ofthe file has already transferred, to see ifit restarts and/or regains speed. If notlog -off and try for a less busy time

Limitations of the Pspice evaluation package'PSpice', by Microsim Corporation, is the industry standard pcsimulator and is available in several versions These range in pricefrom £115 for the evaluation system with manuals to £4200 for thestandard package.

With the evaluation package, circuit simulation is limited tocircuits with up to 64 nodes, 10 transistors, two op -amps, or 65

digital primitive devices, or a combination thereof; 10 ideal trans-mission lines with not more than 4 non -ideal lines (lossy lines usingRLGC parameters), 4 coupled lines; device characterisation limitedto diodes; stimulus generation limited to sine waves; sample libraryof 22 analogue and 140 digital parts. Schematic capture is limited tosingle A4 page schematics, containing a maximum of 25 symbols,with a reduced symbol and package library set.

Manuals can be purchased from Microsim. Alternatively, shouldthe on -screen 'Help' not suffice and a low cost option is needed,Spice -A Guide to Circuit Simulation & Analysis Using PSpice byPW Tuinenga of Microsim Corporation might well suffice.2

"/pub/pspice"

(PC only)"pspicftp.txt"

(Mac only)"pspicmac.txt"

Fig. 2. Logged -on to'ftp.netcom.com' with remotedirectory changed toVpub/mi/microsim'. Change theremote directory by enteringVpub/mi/microsim' into currentdirectory box. Now ready totransfer the highlighted remotefile '62pldlib.zip' into thedirectory. Note the system hasbeen set to binary transfermode. To initiate transfer, clickon 'QuickTrans'.

Fig. 3. Logged -on to'klingon.ee.iastate.edu' withremote directory changed to'/pub/pspice'. Change theremote directory by entering'/pub/pspice' into the currentdirectory box. Now ready totransfer the highlighted remotefile '62wine2.exe' into the localdirectory. Note the system hasbeen set to binary transfermode. To initiate transfer, clickon 'QuickTrans'.

later. Some packages provide auto log -off after a pre -selected inactive periodfor example five minutes, Fig. 4.

File -Transfer Protocol has two modesof file transfer. Text mode is restrictedto printable characters, e.g. text onlyfiles, while binary mode transfers thefull ascii set and is essential for pro-gram or zipped files.

A word of caution. If you are downloading Windows software from theInternet, always ensure you have avalid current backup of your diskbefore installing the package. From pastexperience, some sites do not supplythe complete configuration routines.The new package works fine, but cor-rupts the system files, such that none ofthe old software works. Once more,back-up first so that you can easilyrestore if needed

Readers wanting more information onrequirements for accessing the Internetshould see reference 1.

References1. Surfing with Intent EW&WW June '95pp. 488-492.2. Spice - A Guide to Circuit Simulation& Analysis Using PSpice by PaulW.Tuinenga, Prentice Hall ISBNO 13834607 0.

002110212111/443411111,24271140Aten9 61030113344.04.-,11ain1fon.9An41204 493/73/1400414,16411 ,1notron03113.2401n110.1237241rmicsioyarrAddnn1001101113019n2D921100139,414404PaglarCommuieskoOko0104110....CennegisolfmnytIACtmemplealsonit

Fig. 4. OS/2 warpintemet 'dialler'. Notethe horizontal'speedometer' bar above'Connected through...'showing the presenttransfer rate as apercentage of the 'peak'rate attained for thissession. Numbers showactual rates in and out,quantity of datatransferred and elapsedtime 'on-line'. The datain/out rate iscontinuously updated asprior five secondsaveraged, during thissession.


INTERFACINGWITH C

HOWARD HUTCHINGS

If you have followed our series on theuse of the C programming language,then you will recognise its value to thepractising engineer.

The book is a storehouse of informationthat will be of lasting value to anyoneinvolved in the design of filters, A -to -Dconversion, convolution, fourier and manyother applications, with not a solderingiron in sight.To complement the published series,

Howard Hutchings has written additionalchapters on D -to -A and A -to -D conversion,waveform synthesis and audio specialeffects, including echo and reverberation.An apendix provides a 'getting started'introduction to the running of the manyprograms scattered throughout the book.This is a practical guide to real-time

programming. The programs having beentested and proved. It is a distillation of theteaching of computer -assisted engineeringat Humberside Polytechnic, at which DrHutchings is a senior lecturer.

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Working with

AVALANCHEtransistors

On avalanching, atransistor can be made toproduce extremely fast,high -current pulses. IanHickman has beenlooking at how ordinarytransistors avalancheand at a couple ofextremely rare devicesspecified for avalancheoperation.

1. 4 x 1011 operations without failure2. 107 operations to failure3. 103 operations to failure

I I I I I I

20 40 60 80 100 120 140 160 180

Pulse width (ns)

Fig. 1. Maximum permitted avalanche currentversus pulse width for the ZTX415, for thespecified reliability.

Ihave been fascinated by avalanche transis-tor circuits ever since I first encounteredthem in the early 1960s. They have proba-

bly been known since the earliest days of sili-con transistors. I have never heard of thembeing implemented in germanium.

One important use for avalanche transistorswas in creating extremely fast, narrow pulsesto drive the sampling gate in a sampling oscil-loscope. Such oscilloscopes provided, in thelate 1950s, the then incredible bandwidth of2GHz. At that time, other oscilloscopes werestruggling, with distributed amplifiers and spe-cial cathode ray tubes, to achieve a bandwidthof 85MHz.

Admittedly, those early sampling oscillo-scopes were plagued by aliased responses and,inconveniently, needed a separate externaltrigger. But they were steadily developed overthe years, providing, by the 1970s, a band-width of 10-14GHz.

The latest digital sampling oscilloscopesprovide bandwidths of up to 50GHz, althoughlike their analogue predecessors they are lim-ited to displaying repetitive waveforms, mak-ing them inappropriate for some of the moredifficult oscilloscope applications, such asglitch capture.

The basic avalanche transistor circuit is verysimple. A version published in the late 1970sapparently produced a 1Mpulse/s pulse trainwith a peak amplitude of 11V, a half -ampli-tude pulse width of 250ps and a 130ps risetime 1. It achieved this with a 2N2369 - anunremarkable switching transistor with a500MHz ft and a Cobo of 4pF.

The waveform, reproduced in the article,was naturally captured on a sampling oscillo-scope.

The avalanche circuit revisitedInterest in avalanche circuits seems to have

wavered a little after the 1970s. Perhaps thiswas due to the fact that the limited number ofspecialised uses for which the devices areappropriate resulted in the spotlight alwaysresting elsewhere.

A problem with designing an avalanchetransistor circuit is the absence of transistortypes specifically designed and characterisedfor this application. But this situation hasrecently changed, due to the interest in highpower laser diodes capable of producingextremely narrow pulses. Applications forsuch lasers include range finding, Pockel celldrivers and streak cameras.

Two transistors specifically characterised foravalanche pulse operation, types ZTX413 andZ7X415, have recently appeared2, togetherwith an application note3 for the latter.

The avalanche transistor depends for itsoperation on the negative resistance charac-teristic at the collector. When the collectorvoltage exceeds a certain level, somewherebetween Vice and litho, depending on the cir-cuit configuration, the voltage gradient in thecollector region exceeds the sustainable fieldstrength, and hole -electron pairs are liberated.These are accelerated by the field, liberatingothers in their turn. As a result, the current

+170 - 280V

Fig. 2. Simple high current avalanche pulsegenerator circuit, driving a laser diode.


DESIGN BRIEF

4 x 1N4007

14

2 x 47tt 500V

o6.3V

81:5).3V

o5V

o0

Fig. 3. High voltage power supply, using a mainstransformer from the days of valves.

rises rapidly, even though the voltage acrossthe device is falling.

The resultant 'plasma' of carriers results inthe device becoming almost a short circuit,and it will be destroyed if the available energyis not limited. If the current in the avalanchemode, /usB, and the time for which it isallowed to flow are controlled, then reliableoperation of the device can be ensured, asindicated in Fig. 1 for the ZTX415.

From the diagram, you can see that for 5Onswide pulses, a pulse current of 20A can bepassed for an indefinite number of pulseswithout device failure. This is provided ofcourse that the duty cycle is kept low enoughto remain well within the device's 680mWallowable average total power dissipation Ptot.

Figure 2 shows a simple high -currentavalanche pulse generator, providing positivegoing pulses to drive a laser diode. Peak cur-rent is determined by the effective resistanceof the transistor in avalanche breakdown plusthe slope resistance of the diode.

As both the preceding parameters are currentdependent, it is not easy to determine accu-rately just what the peak value of current is. Inpractice however, this is not an insuperable

M probe

10kHz3.8V p -p 68p

100R

10k

ZTX

+250V6n8

7400V

2n

difficulty. Energy dissipated in the transistorand diode is simply equal to the energy storedin the capacitor. Since, given the value of thecapacitor and the supply voltage, the storedcharge is known, the pulse width can be mea-sured and the peak current estimated.

If, in a particular circuit, the avalanche- anddiode -slope resistances are unusually low, thepeak current will be higher than otherwise, butthe pulse width correspondingly narrower.Charge passed by the transistor is limited tothat originally stored in the capacitor at theapplied supply voltage.

Implementing the avalanche deviceHaving obtained samples of the ZTX4I5, I

decided to investigate the performance in avariant of Fig. 2. This variant provides nega-tive -going pulses, but substitutes a resistiveload for the diode to allow quantitative mea-surements to be recorded.

First I produced a high -voltage source, giv-ing up to 800V off-load. A voltmeter wasincluded, and for versatility, the transformer'slow voltage windings were also brought out tothe front panel, Fig. 3.

The test set up is shown in Fig. 4a), the

415 10dB 10dB 50 CH1

47R 500 pads throughtermination L

)(10 CH2probe

Oscilloscope Tektronix 475A

Fig. 4. a) Test set-up used to view the pulse produced by an avalanche transistor.

b) Upper trace, voltage across load, effectively 50V/div (allowing for 20dB pad), OV = 1 cmdown from top of graticule, 5Ons/div; lower trace, collector voltage, effectively 50V/div(allowing for x10 probe), OV = 1cm up from bottom, 5Ons/div.

high -voltage supply being adjusted as requiredby the simple expedient of running the powersupply of Fig. 3 from a variable voltage trans-former, of the type commonly known under itstrade name of Variac.

With the low value of resistance between thebase and emitter of the avalanche transistor,the breakdown voltage will be much the sameas BVCES, the collector -emitter breakdownvoltage with the base -emitter junction shortcircuit. With no trigger pulses applied, thehigh -voltage supply was increased until puls-es were produced. With the applied high volt-age barely in excess of BycEs, the pulse -rep-etition frequency, prf, was low and and theperiod erratic, as was to be expected.

With the voltage raised further, the prfincreased, the free running rate being deter-mined by the timeconstant of the collectorresistor and the 2nF capacitor. This free run-ning mode of operation is not generally useful,there being always a certain amount of jitteron the pulses due to the statistical nature of theexact voltage at which breakdown occurs. Thehigh voltage supply was therefore reduced tothe point where the circuit did not free run,and a 10kHz squarewave trigger waveformapplied.

The pulses were now initiated by the posi-tive edges of the squarewave, differentiated bythe 68pF capacitor and the base resistor, at aprf of l0kpulse/s. On firing, the collector volt-age drops to near zero. This causes a negative -going pulse to appear across the load resistor,which consisted of a 4752 resistor in parallelwith a 5052 load. The latter comprised two10dB pads in series with a 5011 'through ter-mination' (RS type 456-150). It was mountedat the oscilloscope's Channel 1 input socketand connected to the test circuit by half ametre of low -loss 500 coaxial cable. Thecable presented a further 5052 resistive load inparallel with the 470 resistor.

Performance observationsDrop in collector voltage can be seen to bealmost the full 250V of the supply, Fig. 4 b),lower trace. However, the peak voltage acrossthe load resistor - upper trace - is only around-180V. This circuit provides a negative -goingoutput, unlike that of Fig. 2.

The lower amplitude of the output pulse wasascribed to the esr - equivalent series resis-


DESIGN BRIEF

51R

+135V

10k2.31.1H 2.3µH

7R2

Fig. 5. Circuits producing square output pulses; a), negative -going output pulses and b), positive -going pulses both using coaxial lines; c),negative -going pulses using a lumped component delay line.

tance - of the 2nF capacitor, which was a foiltype, not specifically designed for pulse oper-ation. This is confirmed by the shape of thepulse. Its decay is slower than would beexpected from the 50ns timeconstant of thecapacitor and the 2552 load, plus transistorslope resistance in avalanche breakdown. Thisemphasises the care needed in componentselection when designing fast laser diode cir-cuits.

Peak pulse voltage across load correspondsto a peak current of 7.25A and a peak powerof 1.3kW. However, the energy per pulse isonly 1/2CV2, where C is 2nF and V is 250V,namely some 630, including the losses incapacitor esr and in the transistor. This repre-sents a mean power of 630mW, most of whichwill be equally divided between the 4752 resis-tor and the first of the two 10dB pads, whichis why the prf was restricted to a modest10kHz.

In Fig. 4b), the lower trace shows the dropacross the transistor during the pulse to beabout 16V, giving an effective device resis-tance in the avalanche mode of 16/7.25 orabout 2.20. Thus, given a more suitablechoice of 2nF capacitor, over 90% of theavailable pulse energy would be delivered tothe load.

In Fig. 2, though, the laser diode slope resis-tance would probably be less than 2552, result-ing in a higher peak current, and an increasedfraction of the energy lost in the transistor.

Ringing on the lower collector trace in Fig.4b) is due to the ground lead of the x10 probe;it could be almost entirely avoided by morecareful grounding of the probe head to the cir-cuit. As it also caused some ringing on theupper output -pulse trace, the probe was dis-connected when the upper trace was recorded,Fig. 4b) being a double exposure with the twotraces recorded separately.

At present, I cannot explain the negativeunderswing of the collector voltage, starting200ns after the start of the pulse, before thecollector voltage starts to recharge towards+250V.

Squaring the outputThe shape of the output pulse from circuitssuch as Figs 2 and 4a), a step function fol-lowed immediately by an exponential decay,is not ideal: for many applications, a squarepulse would be preferred. This is simply

arranged by using an open -circuit delay line,in place of a capacitor, as the energy storageelement.

When the avalanche transistor fires, its col-lector sees a generator with an internalimpedance equal to the characteristicimpedance of the line. Energy starts to bedrawn from the line, which becomes emptyafter a period equal to twice the signal propa-gation time along the length of the line, asdescribed in Ref. 4.

Figure 5 shows three such circuits, a) andc) producing negative -going pulses and b)positive going. If a long length of line is used,

Fig. 6. a) A circuit for providing higheroutput voltage pulses.b) Circuit providing even higher outputvoltage pulses.c) Circuit for providing increased outputcurrent pulses.

to produce a wide pulse, then version b) ispreferable to a), since it has the output of thecoaxial cable earthed. In a), the pulse appearson the outer of the cable, so the capacitance toground of the outer - which could be consid-erable - appears across the load.

If a wide negative -going pulse is desired,then an artificial line using lumped compo-nents as in c) can be used. Here, the lumpeddelay line can be kept compact to minimise itscapacitance to ground.

Where exceptional pulse power is required,ZTX415 avalanche transistors can be used inseries to provide higher pulse voltages as in


DESIGN BRIEF

20kHz3.8V p -p 8p

o- I

100kHz1.8V p -p 68p

BFR51

100R

+35V

6n882k 1400V

47R

4- 97cm-m.

5052 co -ax

To 500_ _ -*through terminal

5052 co -ax at oscilloscope

BFR91

2k2

+35V

6n882k 1400V

4- 22cm-p.

L-5011Coix

47R

To through

500 co -ax-*terminal at

oscilloscope

Figs 6a) and b). Alternatively, they can beused in parallel to provide higher pulse cur-rents as in c).

A high speed versionRise time of the negative -going edge of theoutput pulse in Fig. 4b) was measured as3.5ns, or 3.2ns, corrected for the effect of the1.4ns rise time of the oscilloscope. This is aspeed of operation that might not haveexpected from a transistor with a minimum ftof 40MHz and a maximum Cob of 8pF, butthis emphasises the peculiar nature ofavalanche operation of a transistor.

An obvious question was; could a substan-tially faster pulse be obtained with a higherfrequency device? Low -power switching tran-sistors, being no longer common in these daysof logic ICs, the obvious alternative is an rftransistor, which will have a high ft and a lowvalue of Cob. I therefore decided to experi-ment with a BFR91, a device with a VcEco rat-ing of 12V and an ft of 5GHz.

I built the circuit of Fig. 7a) using a lengthof miniature 50SI coaxial cable, cut at randomfrom a large reel. It turned out to be 97cm.Given that the propagation velocity in thecable is about 2/3 the speed of light, the cablerepresents a delay of 4.85ns and so shouldprovide a pulse of twice this length or, inround figures, lOns.

In the upper trace, Fig. 7b) shows that thecircuit produced a pulse of width lOns andamplitude 5V peak, into a 25n load, deliver-ing some 200mA current. Oscilloscope set-tings were lOns/div, 2V/div with a centre lineof OV. The lower trace shows - again using adouble exposure - the collector voltage at20p s/div, 10V/div and OV at the bottom ofthe graticule. With circuit values shown, at

the 20kHz prf rate used, the line voltage hastime to recharge virtually right up to the 35Vsupply.

Effects of a shorter lineI repeated the experiment, this time with thecircuit of Fig. 8a). Line length was reduced to22cm, some other component values changedand the prf raised to 100kHz. The outputpulse is shown in 8b), at lns/div horizontaland more than 1V/div vertical, the VARiableY sensitivity control being brought into playto permit the measurement of the 10% to 90%risetime. This is indicated as 1.5ns, but themaker's risetime specification for a Tektronix475A oscilloscope, estimated from the 3dBbandwidth, is 1.4ns.

Rise times add rms-wise, so if you were toaccept these figures as gospel, it would implyan actual pulse rise time of a little over 500ps.In fact, the margin for error when an experi-mental result depends upon the difference oftwo nearly equal quantities is well known tobe large.

When the quantities must be differencedrms-wise rather than directly, the margin oferror is even greater. As a result, no quantita-tive certainty of the rise time in this case ispossible, other than that it is probably wellunder lns. Unfortunately, a sampling oscil-loscope does not feature among my collectionof test gear.

This raises the intriguing possibility that thissimple pulse generator might be suitable asthe sample pulse generator in a sampling add-on for any ordinary oscilloscope, extending itsbandwidth for repetitive signals to severalhundred megahertz, or even a gigahertz.

For this application, it is important that thesample pulse generator can be successfully

Fig. 7a) Circuit of anavalanche pulsegenerator using a BFR91transistor with a 97cmline length.b) Output of a); uppertrace, output pulse,1Ons/div, 1V/div,OV = centre line; lowertrace, collector voltage,20ps/div, 10V/div,OV = bottom line

Fig. 8a) Circuit of anavalanche pulse generatorusing a BFR91 transistorwith a 22cm line length.b) Output of a); outputpulse, at 1 ns/div, >1V/div,indicated rise time 1.5ns.

run over a range of repetition frequencies.With an exponential approach to the supplyvoltage at the firing instant, there is the posi-bility of jitter being introduced onto its tim-ing, due to just how close to the supply volt-age the collector has had time to recharge,Fig. 7b), lower trace.

The way round this is to use a lower valueof collector resistance returned to a highersupply voltage. This ensures a rapid recharge,but the midpoint of the resistor is taken to acatching diode returned to the appropriatevoltage just below the breakdown voltage. Thecollector voltage is thus clamped at a constantvoltage prior to triggering, whatever the repe-tition rate.

References1. Vandre, RH, 'An ultrafast Avalanche transistorpulser circuit', Electronic Engineering, MidOctober 1977, p. 19.2. `NPN Silicon Planar Avalanche TransistorZTX413' Provisional Data Sheet' Issue 2, March1994 and `NPN Silicon Planar AvalancheTransistor ZTX4I5 Data Sheet' Issue 4, Nov1995.3. 'The ZTX415 Avalanche Transistor', Zetex plc,Apr 1994.4. Hickman, I, 'RF Reflections', EW+WW, Oct1993, pp. 872-876.

Figures 1, 2, 5 and 6 are reproducedcourtesy of Zetex plc.


ANALOGUE DESIGN

Putting thepower

back inDesign criteria for battery charger circuits aredictated by cell type, the application and operatingconditions. In this extract from Simplified design ofmicropower and battery circuits John Lenk examinesthe characteristics of popular IC controllers.

The first step in designing charging cir-cuits must be to look in detail at an ICthat provides fast -charging for popular

NiCd/NiMH batteries. Maxim MAX712/713controllers can fast -charge batteries from a dcsource at least I V higher than the maximumbattery voltage.

One to sixteen series cells can be charged atrates between one-third of the battery capaci-ty, i.e. C/3 and four times capacity, or 4C. Avoltage -slope -detecting a -to -d converter,timer, and temperature -window comparatordetermine charge completion.

The ICs (Figs. 1, 2, 3 and 4) are poweredby an on -board +5V shunt regulator and drawa maximum of 51.1A from the battery when notcharging. A low -side current -sense resistorallows the battery -charge current to be regu-lated while still supplying power to the load.

The MAX712 terminates fast -charge by

V+

detecting zero voltage -slope while MAX 713uses a negative voltage -slope detectionscheme. Both ICs are available in sixteen pinDIP and SO packages. An external powerp -n -p transistor, blocking diode, three resis-tors, and three capacitors are the only requiredexternal components.

For high -power charging requirements, theICs can be configured as a switch -mode bat-tery charger that minimises power dissipation.

Basic operating principlesThe ICs provide charging by forcing a con-stant current into the battery in one of twooperating states: fast -charge or trickle -charge.During fast -charge, the current level is high,and once full -charge is detected, the currentreduces to the trickle -charge state. The ICsmonitor three variables to determine when thebattery reaches full charge: voltage slope, bat-

PGM2

PGM3

THI

TEMP-.ILO-.

PGM2 PGM3

TIMER

TIMED_OUTT

BATT-

+5V SHUN

REGULATO

POWER ON RESET

GND

AVDETECTION

AV_DETECTCONTROL LOGIC

FAST_CHARGE

I N

BATT-

IN REGULATIO

CURRENT

AND

VOLTAGE

REGULATOI

TEMPERATURE

COMPARATORS

HOT

COLD

MAXIMMAX712MAX713

UNDER VOLTAGE

FASTCIIG

DRV

CC

BATT-

GND

VLIMIT

BATT-

BATT+

PGMO

PGM1

WALLCUBE

tery temperature and charge time.Full -charge state are determined by the IC's

timer, voltage -slope (V) detector, and temper-ature comparators, and its voltage and currentregulator controls output voltage and current,and senses battery presence.

In a typical battery -charging sequence, Fig.5, when the batteries are already insertedbefore application of power, initially the ICdraws negligible power from the battery.

When power is applied to DC IN, thepower -on reset holds the IC in trickle -charge.Once the power -on reset signal goes high, theIC enters the fast -charge state as long as thecell voltage is above the under voltage -lockout(uvlo) voltage of 0.4V per cell. Fast -chargingcannot start until the battery voltage dividedby number of cells exceeds 0.4V.

As soon as the cell voltage -slope becomesnegative, the fast -charge is terminated and theIC reverts to the trickle -charge state. Whenpower is removed, the device draws negligiblecurrent from the battery.

Temperature may be used to control charg-ing too, Fig. 6. The ICs can be configured sothat either voltage -slope or temperature detectsfull -charge.

On a cold day, the battery pack may be toocold for fast charging. During the initial peri-

DC IN01

2N6109

R1

10µF

- Cl

R21500

THI DRV

V+ MAXIM2

VLIMITMAX71mAX713

REF BATT+

TEMP

CC

BATT- ILO GND

.01wF

1N4001

BATTERY

RSENSE

Fig. 2. Typ cal operating circuit for fast -charge controller. Thiscircuit benefits from a 22162 resistor between BATT- and TEMPand 68k between VIIMIT/REF and TEMP. A lOnF capacitor overR2 may also be necessary.

LOAD

Fig. 1. MAX712/713 used as a fast -charge controller.


ANALOGUE DESIGN

VUMIT E

BATT+ aPGMOj

PGM1 E

THI

TLO

TEMP E

FASTCHG E

MAXIMMAX712MAX713

18 REF

E v+DRV

g GND

g ahn-E ccg

PGM2

DIP/SO

Fig. 3. Pin connections for fast charging witha MAX712/713.

od the ICs will remain in the trickle -chargestate, and when the battery temperatureexceeds the limit set by THI (pin 5), the ICswill again revert to trickle -charge.

It is possible that the battery will be insertedinto an already powered -up IC (Fig. 7). Tobegin with, the charger output voltage will beregulated at the number of cells times VLIMIT(pin 1) and the IC will be in the trickle -chargestate. But on insertion of the battery, the ICwill detect current flow into the battery andswitch to fast -charge.

Once full -charge is detected, the IC willrevert to trickle -charge. If the battery isremoved, the IC will remain in trickle -charge,and the output will once again be regulated.

Powering the ICsThe ICs are inactive with the wall cubeunplugged, Fig. 2, drawing a maximum of5p A from the battery. Diode DI prevents thecollector -base junction of Tri from conducting

current into the DRV (pin 14). With the wallcube connected, R1 charges C1. When C1charges to +5V, the internal shunt regulatorsinks current to regulate V+ to 5V, and fast -charge commences. The IC remains in fast -charge until one of the three fast -charge ter-mination conditions is triggered.

If DC IN exceeds 20V, a cascode connec-tion can be added in series with the DRV pinFig. 8. This will prevent the DRV pin abso-lute -maximum ratings from being exceeded.Resistor R1 in Fig. 8 is selected to pass 5mA atthe minimum DC IN voltage.

Total power dissipation of the IC must notexceed the absolute maximum specificationsfor the device, Table 1. The differencebetween maximum DC IN voltage and mini-mum DC IN voltage determines power dissi-pation in the IC.

Maximum current into V+ is maximum DCIN voltage - 5V) divided by R1. Dissipation,due to the shunt regulator, is five times themaximum current into V+. Sink current intothe DRV pin also causes power dissipation.

Fast chargingThe IC enters the fast -charge state under oneof the following conditions:

Upon application of power with battery -cur-rent detection (GND, pin 13) voltage less thanBATT-, pin 12; voltage and TEMP, pin 7,higher than TLO, pin 6; and the cell voltagehigher than the WLO voltage.

Upon insertion of a battery with TEMP,7, higher than TLO, pin 6, and lower than

1.5

1.4

1.3

0.4

0

A

mA

VOLTAGE

TEMPERATUR

Jas

A1

1 2 3

1. NO POWER TO CHARGERTIME

2. CELL VOLTAGE LESS THAN 0.4V3. FAST CHARGE4. TRICKLE CHARGE5. CHARGER POWER REMOVED

4 5

Fig. 5. Charging sequence when batteries arealready inserted. Once the power -on resetsignal goes high, the IC enters the fast -chargestate.

THI

TLO

A

mA J1 2

1. NO POWER TO CHARGER2. CELL TEMPERATURE TOO LOW3. FAST CHARGE4. TRICKLE CHARGE5. CHARGER POWER REMOVED

3

TIME

4 5

Fig. 6. Temperature can be used to detect afull charge.

PIN NAME FUNCTION

1 VLIMITSets the maximum cell voltage. If VLIMIT is tied to V+, the battery terminal voltage (BATT+ - BATT-) will notexceed 1.65V x (number of cells); otherwise, it will not exceed VLIMIT x (number of cells). Do not allowVLIMIT to exceed +2.5V, unless tied to V+.

2 BATT+ Positive terminal of battery

3, 4PGMO,PGM1

PGMO and PGM1 set the number of series cells to be charged. The number of cells can be set from 1 to 16by connecting PGMO and PGM1 to any of V+, REF, or BATT-, or by leaving the pin open (see Table 2).

5 THI Trip point for the over -temperature comparator. If the voltage on TEMP rises above THI, fast charge ends.

6 TLOTrip point for the under -temperature comparator. If the MAX712/MAX713 powers on with the voltage onTEMP less than TLO, fast charge is inhibited and will not start until TEMP rises above TLO. TLO must be setbelow the minimum operating temperature of the charger.

PIN NAME FUNCTION

7 TEMP Sense input for temperature -dependent voltage from thermistors

aOpen fast -charge status output. While the MAX712/MAXLIZIaacharges the battery, FASTCHG

FASTCHG-drain

sinks current. When charge ends and trickle charge begins, FASTCHG stops sinking current.

9, 10PpGGMm23.

PGM2 and PGM3 set the maximum time allowed for fast charging. Timeouts from 33 minutes to 264minutes can be set by connecting to any of V+, REF, or BATT-, or by leaving the pin open (see Table 3).PGM3 also sets the fast -charge to trickle -charge current ratio (see Table 5).

11 CC Compensation input for constant current regulation loop

12 BATT- Negative terminal of battery

13 GNDSystem ground. The resistor placed between BATT- and GND is used to monitor the current into the bat-tery.

14 DRV Current sink for driving the external PNP current source

15 V+Shunt regulator. The voltage on V+ is regulated to +5V with respect to BATT-, and the shunt currentpowers the MAX712/MAX713.

16 REF 2.0V reference output. Sources up to lmA.

Fig. 4. Pin descriptions for a fast -charge controller.


ANALOGUE DESIGN

VLIMIT

21.5

1.4

1.3

A

2

TIME

1. BATTERY NOT INSERTED2. FAST CHARGE3. TRICKLE CHARGE4. BATTERY REMOVED

3 4

Fig. 7. Charging sequence when batteries areinserted in powered -up IC. When the batteryis inserted, the IC detects the current flowand switched to fast charge.

DC IN

01

ANIDCIA011

MAX712MAX713

Fig. 8. DRV pin cascode connections whereDC IN exceeds 20V.

D1

THI, pin 5; and the cell voltage higher thanthe UVLO voltage.

Resistor RSENSE sets fast -charge current intothe battery. In fast -charge, the voltage differ-ence between the BATT-, pin 12, and GND,pin 13, is regulated to 250mV. Sink current toDRV, pin 14, increases if the differencebetween pins 13 and 12 falls below 250mV.

Fast -charge current /FAST is 250mV dividedby RSENSE. For example, with an RSENSE of250m52, fast -charge current is 1A.Trickle chargeCircuits within the IC set trickle -charge cur-rent by increasing the current amplifier gain.

When a fast -charge (IFAST) rate C/2, C,2C, or 4C is used, a C/16 trickle -charge rate isselected automatically, Table 2. Other fast -charge rates can be used, but the trickle -chargecurrent will not be exactly C/16. For simpli-fied design, use a rate of C/2, C, 2C, or 4C,depending on recommendations of the batterymanufacturer.

Some manufacturers recommend a lowertrickle -charge rate for NiMH batteries. Figure9 shows a circuit that can reduce trickle -charge to less than C/16. When the circuit is intrickle -charge mode, some of the current isshunted around the battery because Tr2 isturned on. Select the value of R7 as follows:

R7 = (VBATT 0.4V/(/TRicKLE IBATT)

where VBATT equals battery voltage whencharged; 'TRICKLE equals the IC trickle -chargesetting and /BATT equals the desired batterytrickle -charge current.

Table 1. Maximum ratings and characteristics for fast -charge controllers.

ABSOLUTE MAXIMUM RATINGSV+ to BATT- -0.3V, +7VBATT- to GND ±1VBATT+ to BATT-

Power Not Applied +20VWith Power Applied The higher of ±20V or

±2V x (programmed cells)DRV to GND -0.3V, +20VFASTCHG to BATT- -0.3V, +12VAll Other Pins to GND -0.3V,(V+ + 0.3V)V+ Current 100mADRV Current 100mA

REF Current 10mAContinuous Power Dissipation (TA = +70.C)

Plastic DIP (derate 10.53mWrC above +70"C). 842mWNarrow SO (derate 8.70mWrC above +70*C). 696mWCERDIP (derate 10.00mWr C above +70.C) 800mW

Operating Temperature Ranges:MAX71_C_ O'C to +70-CMAX71_E -40"C to +85.0MAX71 M-JE -55.0 to +125"C

Storage temperature Range -65.0 to +150.0Lead Temperature (soldering, 10sec) +300T

Stresses beyond those listed under 'Absolute Maximum Ratings' may cause permanent damage to the device. These 819 stress ratings only, and functionaloperation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure toabsolute maximum rating conditions for extended periods may affect device reliability.

ELECTRICAL CHARACTERISTICS= 10rnA, TA = TMIN to TMAX, unless otherwise noted. Refer to Typical Operating Circuit. All measurements are with respect to

BATT-, not GND.)

PARAMETER CONDITIONS MIN TYP MAX UNITS

V+ Voltage 5mA < IV. < 20rnA 4.5 5.5 V

Iv. (Note 1) 5 mA

BATT+ Leakage V+ = OV, BATT+ = 17V 5 PA

BATT+ Resistance with Power On PGMO = PGM1 = BATT-, BATT+ = 30V 30 kfl

C1 Capacitance 0.5 µF

C2 Capacitance 5 nF

REF Voltage OmA < !REF < lrnA 1.96 2.04 V

Undervoltage Lockout Per cell 0.35 05 V

External VLIMIT Input Range 1.25 2.5 V

THI, TLO, TEMP Input Range 0 2 V

THI, TLO Offset Voltage (Note 2) OV < TEMP < 2V, TEMP voltage rising -10 10 mV

THI, TLO, TEMP, VLIMIT InputBias Current -1 1 flA

VLIMIT Accuracy1.2V < VLIMIT < 2.5V,5mA < 'DRV < 20mA.PGMO = PGM1 = V+

-30 30 mV

Internal Cell Voltage Limit VLIMIT = V+ 1.6 1.65 1.7 V

Fast -Charge VSENSE 225 250 275 mV

Trickle -Charge VSENSE

PGM3 = V+ 1.5 3.9 7.0

mVPGM3 = open 4.5 7.8 12.0

PGM3 = REF 120 15.6 20.0

PGM3 = BATT- 26.0 31.3 38.0

Voltage -Slope Sensitivity(Note 3)

MAX713 -2.5 mV/tAper cellMAX712 0

Timer Accuracy -15 15 %

Battery -Voltage to Cell -VoltageDivider Accuracy -1.5 1.5 %

DRV Sink Current VDRV = 10V 30 mA

FASTCHG Low Current VFASTCHG = 0.4V 2 mA

FASTCHG High Current VFASTCHG = 10V 10 PA

ND Input Range 1.4 1.9 V

Note 1: The MAX712/MAX713 are powered from the V+ pin. Since V+ shunt regulates to +5V, Al must be small enough to allow atleast 5mA of current into the V+ pin.

Note 2: Offset voltage of THI and TLO comparators referred to TEMP.Note 3: to is the ND sampling interval (see Table 3).

Regulation loopThe regulation loop controls the output volt-age between the BATT+ and BATT- termi-nals, and the current through the battery, viathe voltage between BATT- and GND.

Sink current from the DRV pin is reducedwhen the output voltage exceeds the numberof cells times VLIMIT or when the battery cur-rent exceeds the programmed charging cur-rent. The regulation loop provides the follow-ing functions:

When the charger is powered, the batterycan be removed without interrupting power tothe load.

If the load is connected as shown in Fig. 2,the battery current is regulated regardless ofthe load current (provided that the input powersource can supply both).

Voltage loopThe voltage loop sets the maximum outputvoltage between the BATT+ and BATT- pins.If VLIMIT is set to less than 2.5V, then the

V+OPENREFBATT- C/2

Table 2. Trickle -charge rate for fast -chargecontrollers.PGM3 Fast charge

rates4C2C

Trickle chargecurrent ('TRICKLE)'FAST/64'FAST/32'FAST/16'FAST/8

Fig. 9. Reducing trickle charge for NiMHbatteries

DI


AN yore Nei to how lbw war applies

JOHN D. LENK

SIMPLIFIEDDESIGNOF SWITCHINGPOWERSUPPLIES

no

UMW,. ',PRI.

Simplified design ofswitching power suppliesAuthor John D. Lenk,224 pages hardbackSwitching power supply basicsHeat sinks for switching power

suppliesInductors/transformers for switching

power suppliesTesting anc troubleshootingSimplified design approaches

Part of the EDN series for

design engineers, these three

books cover every aspect of

power supply circuit design

from battery charging to

inductor choice. They are

available individually or as a

set of three with a

discount of 10% on the

normal retail price.

John Lenk is an establishedwriter of international bestsellers in the electronics fieldand author of more thaneighty books on electronics.Together, John's books havesold over 2 million copies in 9languages.

SIMPLIFIEDDESIGN OFMICROPOWERAND BATTERYCIRCUITS

Simplified design ofmicropower and batterycircuitsAuthor John D. Lenk,254 pages paperbackIntroduction to

micropower/battery designBattery basicsBattery chargersSingle -cell circuitsMulticell circuits

JOHN D. LENK

SIMPLIFIEDDESIGNOF LINEARPOWERSUPPLIES

Simplified design oflinear power suppliesAuthor John D. Lenk,246 pages hardbackLinear power supply basicsHeat sinks for linear power suppliesDiscrete feedback regulator basicsIC linear regulator basicsLinear supply testing and connectionsLinear supply design examples

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ANALOGUE DESIGN

DC IN rV+

DRV

D1

BATT-

RSENSE,

GND

GNU

REF

<VLIMIT'

CELL_VOLTAGE

CURRENT -SENSE AMPLIFIER

PGM3 FAST_CHARGE Av

V+ 0 512

OPEN 0 256

REF 0 128

BATT- o 64

BATT-

1c2iIBATT-

IF THE VLIMIT PIN IS TIED TO V+ THEN THIS NODE ACTUALLY EQUALS 1 65V

Fig. 10. Current regulation loop for fastcharge controller.

IN THERMALCONTACT WITH

BATTERY

AMBIENTTEMPERATURE

NOTE. FOR ABSOLUTE TEMPERATURE CHARGE CUTOFF, T2 AND T3 MAY BE

REPLACED WITH STANDARD RESISTORS

Fig,. 11. Controlling charge cut-off with NTCthermistors.

AMBIENTTEMPERATURE

IN THERMAL AMBIENTCONTACT WITH TEMPERATURE

BATTERYNOTE: FOR ABSOLUTE TEMPERATURE CHARGE CUTOFF, T2 AND T3 MAY BEREPLACED WITH STANDARD RESISTORS

Fig. 12. Controlling charge cut-off withbattery thermistor.

maximum BATT+ voltage, referred toBATT-, is Vumrr multiplied by the numberof cells as determined by PGMO, PGM1connections. If VuTvirr is tied to V+, then themaximum BATT+ voltage, referred toBATT-, is 1.65 V multiplied by the numberof cells, PGMO, PGM1.

When the battery is removed, the IC doesnot provide a constant current. Instead, it reg-ulates BATT+ to the maximum voltage, asdetermined above.

The voltage loop is stabilised by the C3 fil-ter capacitor. A large filter capacitor isrequired only if the load is supplied by the ICin the absence of a battery. In this case, setC3, in farads, as follows:

C3 = (50 X /LOAD) / (VOUT X BWVRL)

where BWVRL equals loop bandwidth in Hz(10,000 is recommended); C3 is greater thanINF; /LOAD equals external load current inA, and Vow, equals programmed output volt-age (VuNirr times the number of cells).

Current loopIn the current -regulation loop, Fig. 10, sta-bility of the current loop is set by capacitorC2 at the CC terminal. To get the exactvalue for C2, calculate the current -regulationloop bandwidth (BWCRL) using transistorcharacteristics (0, fr, gm, etc.). For simpli-fied design, use the transistor Tr( types andcapacitor C2 values shown in Fig. 2.

The ICs dissipate power because of the cur-rent -voltage product at the DRV pin, which ispart of the current loop. Power dissipation -shown in the absolute maximum ratings, Fig.3 - must not be exceeded.

Voltage -slope cut-offThe a -to -d converter inside both the MAX712and MAX713 has 2.5mV resolution and storescell voltage at sampling intervals (tA) deter-mined by the PGM2/PGM3 connections.

At two tA intervals, the voltage differencebetween tA intervals is obtained to determinethe cell voltage versus time. Fact a -to -d con-version is averaged over five, to filter outnoise. Because the battery current is kept con-stant by the regulation loop - even when thereis a varying external load - the conversionresults are accurate.

The MAX712 terminates fast -charge when aconversion result is equal to, or less than, itspredecessor. The MAX713 terminates when aconversion is at least 2.5mV less than its pre-decessor. This is the only difference betweenthe two.

Temperature -charge cut-offCharge cut-off can be controlled with ntc ther-mistors, Fig. 11. The same -model thermistorshould be used for T1 and T2, so that bothhave the same nominal resistance. Voltage atTEMP is 1V (referred to BATT-) when thebattery is at ambient temperature.

The threshold chosen for TLO determinesthe temperature below which fast -charging isinhibited. If TLO is greater than TEMP, when

DCIN7V TO

20V

2000

POWERON

47µF

280 J2N3904

MTP12P05

1447µH 1N5818

1N5818

48.7k0 1.5k0

2N3906

33pF = 100pF

N.C.

DRV

THI

V

PGMO A4AXIAAPONT

MAX713PGM2

PGM3

REF

VLIMT

TEMPFASTCHG

CC

BATT+

BATT

TLO

GND

4700FAST CHARGE

1LLF

Fig. 13. Basic switch -mode connections.

OV

a1300mA-HrNICd CELLS

0.250

LX

5V/div

VSENSE- 270mV200mV/div

-2.0VCC

500mV/div

Fig. 14. Switching wave -forms for basiccharger circuit.

11

10

HIGH PEAK

9

1201i2 RIPPLE8

LOW PEAK7

6

0 200 400 600 BOO 1000

LOAD CURRENT (mA)

Fig. 15. Sony Radio ac adapter AC -190, 9Vdc, 800mA.

the IC starts up, fast -charge will not start untilTLO goes below TEMP. The threshold cho-sen for THI sets the point at which fast -charg-ing terminates. As soon as the voltage onTEMP rises above THI, fast -charge ends andwill not restart after TEMP falls below THI.

Cold -temperature charge inhibition may bedisabled by removing R5, T3, and the 0.022pFcapacitor and tying TLO to BATT.

To disable the entire temperature -compara-tor charge -cut-off mechanism, remove T1, T2,T3, R3, R4, R5, and the associated capacitorsthen make the following connections: TEMPto REF, THI to V+, and TLO to BATT-.

Some battery packs may come with a tem-


ANALOGUE DESIGN

perature-detecting thermistor connected to thenegative terminal of the battery pack. In thiscase, use the connections shown in Fig. 12.Thermistors T2 and T3 may be replaced withstandard resistors if absolute temperaturecharge cutoff is acceptable.

Switch -mode operationSwitch -mode operation, Fig. 13, is used for

11

10

9

8

7

6

5

1 1HIGH PEAK

120Hz

RIPPLE -

LOW PEAK

I ICI0 200 400 600 800 1000

LOAD CURRENT (mA)

Fig. 16. Sony CD player ac adapter AC -96N,9V dc, 600mA.

18

16

14

12

10

8

HIGH PEAK

LOW PEAK

120HzRIPPLE

0 200 400 600 800

LOAD CURRENT (mA)

Fig. 17. Panasonic modern ac adapterKX-A 11, 12V dc, 500mA.

5.0

4.9

48

47

4.6

4.5

44

4.3

4.2

40

38

36

34

32

30

28

26

24

AV- CUTOFF,Al

(770 30 60 90

TIME (MINUTES

Fig. 18. Three NiMH cells charged withMAX712.

5.0

4.9

48

47

4.6

4.5

44

4.3

4.2

A V- CUTOFFA t

0 30 60

TIME (MINUTES)

Fig. 19. Three NiMH cells charged withMAX713.

40

38

36

34

32

30

28

26

24

90

applications where power dissipation of thepass transistor cannot be tolerated. An exam-ple is where heat -sinking is not feasible or istoo costly). The appropriate circuit uses theerror amplifier at the CC pin as a comparator,with a 33pF capacitor adding hysteresis.

Figure 13 is configured to charge two cellsat 1A. Higher charge currents and greaternumbers of cells can be accommodated bychanging the 0.250 sensing resistor, and con-nections PGMO-3.

Switching waveforms, Fig. 14, associatedwith the circuit show that the arrangementcannot service a load while charging.

Switching frequency can be decreased byincreasing the value of the capacitor connect-ed between CC and BATT. Note that the twocapacitors connected to the CC pin must beplaced as close as possible to the pin and theleads must be as short as possible. The CCnode is a high -impedance point - capable ofproducing high voltages - so logic lines mustnot be routed near the CC pin.

Line -voltage operationConsumer -product ac -to -dc wall cubes typi-cally consist of a transformer, a full -wavebridge rectifier, and a capacitor.

Typical characteristics, Figs 15-17, showsubstantial 120Hz output -voltage ripple. Sowhen selecting an adaptor for use with the712/713, the lowest dip in the wall -cube volt-age during fast -charge should be at least IVhigher than the maximum battery voltage.

Figures 18 and 19 show the results of charg-ing three AA 1000mAh NiMH batteries fromGold Peak (part number GP1000AAH) GPBatteries at a IA rate using the 712 and 713.

The circuit from Fig. 2 is used, but withtemperature control as shown in Fig. 11.Conditions were:

DC IN uses a Sony AC -190 which is a 9V dcat 800mA ac -to -dc adaptor, Fig. 15.PGMO is V+, PGM1 is RTEF,PGM2 is REF, and PGM3 is REG./21.20052, R2=1505I, RsENsE=250maCi=lpF, C2=0.010, C3=10pF,VLIMIT=REFR3=10k0, R4=15k0,T1 and T2 are both part # 13A1002 (AlphaThermistor 00 1 800-235-5445).IfR5 and T3 are omitted then TLO=BATT-.

Absolute maximum rating for the BATT+input voltage must be limited by external cir-cuits, Fig. 20, when DC IN is not applied.

Current -sense resistor RSENSE causes a smallefficiency loss during battery use. The effi-ciency loss is significant only if RSENSE ismuch greater than the internal resistance of thebattery pack. The circuit in Fig. 21 can beused to shunt RSENSE whenever power isremoved from the charger.

Figure 22 shows a circuit used to indicatecharger status, with logic -level outputs, andFig. 23 shows a led drive circuit that indicatescharger status.

DC IN

DI DI

MAXIM BATT

MAX712MAX713

Fig. 20. Connections for high cell counts.

01

TO

BATTERYPOSITVE

TERMINAL

GND

Fig. 21. Connections to shunt -sense resistorwhen output power is removed.

V+

MAXIMMAX712MAX713

FASTCHG

10k

LOW RONLOGIC LEVELN -CHANNEL

POWER

MOSFET

OV = NO POWER

5V = POWER

VCC

DV= FASTV00. TRICKLE OR

NO POWER

Fig. 22. Connections to indicate charger status viaexternal logic circuitry.

MAXIMMAX712MAX713

Fig. 23. Connections needed to indicatecharger status via light -emitting diodes.

Part II will show how to use the MAX712/713and other ICs in practical circuits designedfor specific charging applications and cell


COMPONENTS

Buildingblocks of time

Traditionally, Radio -Code time signalreceivers have been expensive, self-contained units, but now there are low-costmodules providing access to the raw timesignal for well under f30.

Radio controlled clocks - allowing access to a time reference accurateto a second in a million years - are proving more and more popular.A considerable fall in price has led to the sale of over 6,000,000 radio

controlled clocks and radio time receiver chips in Europe - in the lasttwelve months alone.

In the near future, it is likely that radio controlled time receivers willreplace traditional clocks in many commercial, personal time keeping andcontrol applications.

Currently, radio controlled time is used for, heating system timing, accu-rate time stamping of data, encryption of data and digital signatures andsynchronising clocks to an accuracy of milliseconds. It is also used for set-ting the time on fax machines, video recorders, wrist watches, etc.

What is time?Time is no longer calculated by observing the stars but 'synthesised' in alaboratory. In Britain this is the responsibility of the National PhysicsLaboratory.

Every minute, the National Physical Laboratory, NPL, transmits a timetelegram as a binary coded decimal signal. This contains the time, the dateand the calendar day. NPL is part of an international network, each makinga contribution to co-ordinated universal time. This means that world-wide,all clocks agree to the nanosecond .

Earth loses around 5ms a day. To ensure that solar and atomic timesremain the same, laboratory time is reset approximately once a year.

MSF is the call sign of the NPL time code transmitter. Anyone can makeuse of the signal transmitted. Equipment require is a facility to receive andcondition the time telegrams, and a receiver with a suitable tuned antenna.A receiver module measuring just 7mm by 24mm is shown in the photo-graph at the end of this article.

MSF's time telegramEvery minute, the MSF transmitter at Rugby transmits a data stream con-taining time information. The first second of every minute contains 'fastcode' information relating to the minute in which it is transmitted. Timingis governed by Co-ordinated Universal Time.

The remaining 59 seconds contain 'slow code' information as UK timerelating to the minute following that in which it was transmitted.

Fig. 1. Example ofhow dateinformation isencoded in the MSFtransmission. Thisrepresents March1996.

80 40 20 10 8 4

Table. 1. Time telegram of MSF transmitter - binary code forseconds 17 to 30 and data for March 1996.

Seconds0 Fast Code Not used in modules1 DUT1 Code Not used in modules2-16 -

17 year (tens) 80 year 00-99, bcd18 year (tens) 40

19 year (tens) 20

20 year (tens) 10

21 year (units) 822 year (units) 423 year (units) 2

24 year (units) 1

25 month (tens) 10

26 month 8

27 month 4

28 month29 month 1

30 day of month (tens) 2031 day of month (tens) 1032 day of month 8

33 day of month 4

34 day of month 2

35 day of month 1

36 day of Week 4

37 day of Week 2

38 day of Week 1

39 hour (tens) 20

40 hour (tens) 10

41 hour (units) 8

42 hour (units) 4

43 hour (units) 2

44 hour (units) 1

45 minute (tens) 40 minute 00-59, bcd46 minute (tens) 20

47 minute (tens) 10

48 minute (units) 8

49 minute (units) 4

50 minute (units) 2

51 minute (units) 1

52 always set to "0" 0

53-58 always set to "1" 1

59 always set to "0" 0

month 01-12, bcd

day of month, bcd

day of week 1-7, bcd

hour 00-23, bcd

2 10 8 4 2

Seconds 17 18 19 20Year

21 22 23 24 26 27 28Month

29 30


COMPONENTS

Q1

Fig. 2. Key buildingblocks of the

Radio -Code receivemodule set. These

can be used to buildanything from a basic

received producingthe raw data streamup to a stand-aloneRadio Code clock.

LP5 Ant 1 0

Antennae Receiver Interface

6 -digit 7 -segmentAntennaBandwidth 700Hz

EM1 MCM RadioLED display

EM2MCM RS232 Serial out, Clock, Serial in

SwitchedEM3

output

Serial out, validated DCF orActive Antenna MCM Coder MSF protocol, Clock, Serial out,

Bandwidth 700Hz I. Serial in 4 x LED Reception control

Switched outputSelective AntennaBandwidth 15Hz Clock kit Serial out, Clock, Serial in

10 digit LCD displayo-

Switched output

Carrier frequency of the time telegram is 60kHz. The ampli-tude is switched off at the beginning of each second, for 100msor 200ms; these periods are the so-called second markers. Theshort ones, at 100ms, correspond to a zero bit, i.e. binary 0, andthe long ones, 200ms, to one bit, binary 1.

At the switch over to the next minute bits 52 to 59 are set per-manently to 100000012. This sequence is unique and identifiesthe following minute marker, second 00. Table 1 shows the for-mat of the MSF time telegram.

The Radio -Code receiver modules discussed in this articleonly decode the slow code, using the data starting at second 17and extending to second 59. Numbers are represented in thebinary-coded decimal form, i.e. decimal 9d becomes binary1001b.

For transmitting the complete time and date, it is sufficient tohave 35 bits. The hour decimals for example only require twobits. They can only have the value 016, 116 or 216 = 002, 012 or102. For the year, this has been confined to two digits, so 96 rep-resents 1996. Figure 1 shows the seconds 17 to 30 with the dataMarch 1996.

Decoding the time signalThere are many circuits for decoding the UK's MSF time signal.The modules outlined in Fig. 2 have the advantages of smallsize, low cost and high sensitivity. They also have a highly tunedantenna. The receiver modules contain all the support electron-ics, tuned crystal, etc, required to receive the MSF time signal.

LP6 Ant 2oC4

47n II

C577.5kHz 1p 330k

Fig. 3. Whenconnected to an

antenna this moduleoutputs demodulated

time code - in thisexample from

Frankfurt's DCFtransmissions.

17

C7

.1.C6

47n

El REFC

E2 AP2

API CK

Al ICI 100pAK2I 24 A

A2

CD

E3PON

SRCR

KS n

:1C0µSA

GND

LP40+3v

LP30 DCF

I-P2o PON

mroGnd

22n 12n22

cli

All that is needed to reconstitute the slow code, exactly as broad-cast by Rugby, is an antenna.

As an alternative to the receiver module, it is possible to buythe chip at the heart of the module. This allows the user to selecta quartz filter for receiving time signals from the UK's MSFtransmitter, Germany's DCF signal, USA's WWVB,Switzerland's HBG and Japan's JG2As. Antennas tuned forthese signals are also available.

Receiving MSFReceiver modules contain a very sensitive straight throughreceiver IC with an open -collector n -p -n output. A block dia-gram of the receiver module IC is shown in Fig. 3.

The very low bandwidth of about 10Hz is achieved by using,a 60kHz crystal filter. This guarantees good suppression of dis-turbances on other frequencies. The high impedance input rep-resents a very small load for the antenna which maintains itquality.

Internally, the radio frequency is rectified and used for bothgain regulation and to represent the envelope of the radio fre-quency. Rectified radio -frequency voltage is compared to athreshold level and the comparator result output.

Antenna designAt 500km from the radio station, field strength of the MSF sig-nal is about lmV/m. At this distance the antenna gives an outputvoltage of about 50µV, but the receiver needs only 111V forgood signal demodulation .

The connection between receiver IC and antenna should be asshort as possible with the bar axis of the ferrite antenna orient-ed at right angles to the direction to the radio station. Antennaoutput voltage is directly related to the cosine of this angle. Thismeans there is a wide range of angle in which good reception ispossible, but only a narrow range with no reception when theaxis points directly to the radio station.

As mentioned, the antenna is best mounted close to the receiv-er. Where this is impractical an active antenna is used. Theactive antenna contains a receiver module and a ferrite antennain a plastic package.

The antenna should be as short as possible. If the length of theantenna is over 20cm, the cable capacitance increases the anten-na resonant circuit capacitance and lowers the resonant fre-quency.

Microcontroller modulesA radio receiver module is available for producing a batterypowered radio clock unit or an alarm -clock radio. It is designedto drive an liquid -crystal or led display via static shift registers


COMPONENTS

LP6

LP5 EM2 MSF MCM -RS232 (MSF)Part No. FBM02010

LP4 LP3 LP2 LP1 X1 X2

Part No. FBM04000

X3 X4 X5 X6 X7

Antenna MSFPart No. FTM02010

1kVVVV-1,

PC

Fig. 7. MCMRadio

forms the heartof a stand-alone

Radio -Codecontrolled clock

system withalarm andswitching

capability.

Serial input 47k

Serial output

ClBuzzer output 100n2048Hz/3Vp-p

RL = lk_I=LB7

Alarm/Timer/Buzzer

Alarm/Timer/Radio

Out

On o-

Si

S5cKo

BC8 7

+3V

500k

11

S2 0--S6-0- 0-0S30-0- 0-0

TP.1

X

X2

X3

X4

X5

X6

X7

X8

X9

X10

X11

Y1

Y2

Y3

Y4

Y5

Y6

Y7

Y8

Y9

Y10

Y11

X8

oUB 3V

For example:Relay driver circuit

C2i +IC3100n

R1k

Fig. 6. PC -interfacingRadio -Code clockincorporating anactive antenna forincreased sensitivityand enhanced MSFreception.

R2

3k3

C4 i=1107

MCM-Radio

1-> /VDR1-> /CLOCK To LED displayI > /DATA

without multiplexing.The micro controller within the module is four bit device and it

decodes the demodulated time telegram from the receiver modules. Thecontroller also translates the time signal for different formats.

Serial i/o via RS232A second module is available to facilitate accessing of the time signalon a computer. The MCM RS232 is designed for applications in whicha host computer receives the exact time information via a serial inter-face.

The advantage of this module compared to direct host decoding ofreceiver output is the presence of exact time information all the time.Once synchronised, the controller predicts the incoming time infor-mation so that it can send out the translated RS232 data stream syn-chronously with the incoming rf signal.

There is also a switching output. Switch on and off times can be setby the host computer. If the switching output is connected to a mainsswitch the host computer can turn itself on and off by setting the appro-priate switch on and switch off times.

An application showing the MCM RS232 serial interface and the EM2MSF receiver modules is shown in Fig. 6.

An application circuit for the radio -controlled clock kit with activeantenna is shown in Fig. 7

R

3k3

Si '+'S2S3 AlarmS4 TimerS5 Snooze56 Time

(e2 Tr2BC818

VDD

MSF

PON

GND

Receiver Module

oGND

Supply voltageclock

o UB+3V

Antenna

S4 0 Radio on - Hc:) 1520mA

VS20VTriBC818

o Music on -H1.5.20mAN./20V

Options: Yll connected to GND - 12h AnzelgeX1 connected to X6 - MSF (England)

Typical MSF receiver module with a footprint of only 7 by 24mm.


Exclusive 25% discount for EW readers

Receive radio -code time signalsonyour PC ...................Modules for Radio CodeThe EM1, connected to the MSF passive antenna, receives the60kHz Rugby signal and outputs the slow code comprising

seconds 17 to 59. Operating from a3V supply, the EM1 has an antennainput, supply pins, a keying input andan open -collector MSF output.Quiescent current in standby is lessthan 1pA.MCM RS232, combined with an EM1receiver and antenna, feeds decodedtime information to a computer viaRS232 via its internal microcontroller.MCM Radio, designed for stand-aloneapplications, forms the heart of aRadio -Code clock with LCD or LEDread-out. This module includes alarmfacilities.

Plugging a radio -code receiver into your PC's COM port andrunning the dos and windows software supplied gives you accessto the atomic -clock referenced 60kHz time signal transmitted fromRugby. This signal is accurate to a second in a million years andcorrected automatically for summer/winter time.

Based on a highly -tuned and reliable receiver module withsystem automatically updates the PC's clock at

switch on and at any other desired time. Under Windows, anicon is available signalling to the operator that the receiver isreceiving the Rugby signal, and indicating the current time anddate.

Time data received by the PC is via standard RS232 and welldocumented, allowing you to use atomic -clock referenced timingand date stamping in your own applications. Sending the ASCIIletter o for example returns a 15 -character string representinghours, minutes, seconds, day of week, day of month, month, yearand summer -time and receiver status.

Normally,the receiver module together with dos and windowssoftware costs £69.50, or £99.50 for a version with in-builtliquid -crystal display for time and date display. Until 15 April1996, Galleon is offering these two products to EW readers atspecial 25% discount prices of £52.13 and £74.63 respectively.

All prices quoted are inclusive of VAT, but excluding £2postage.

This module receives radio -code data and sends it to the PC via an RS232link. From the COM port, RS232 time information can easily beincorporated into user applications. Software supplied as standardsynchronises the PC clock and - under windows - displays time/datetogether with confirmation of the received signal.

The desk -top version of the radio -code PC clock features two alarms andan integral display showing hours/mins secs or hours/mins day togetherwith day+month, signal strength indications.

Access to atomic time accuracyvia your PCApplications include: research and development synchronising encryption -key changes broadcast transmission sync timing video monitoring in security systems controlling public and distributed clocks distributed timing for remote communications access control production monitoring linking remote networks data security

Ordering detailsProduct Normal price EW discount priceEM1 £16.99 £12.74MCM RS232 £19.99 £14.99MCM Radio £19.99 £14.99Pass antenna £4.99 £3.74Act antenna £34.99 £26.24Rec. w disp £99.50 £74.63Rec. w RS232 £69.50 £52.13

Please send your order to Galleon Systems Ltd, together with payment.Alternatively fax credit card number, type and expiry date with order on 0121 6084477 or telephone Galleon on 0121 359 0981. Iff possible, include a daytimetelephone number with your order. Address orders and al/ correspondencerelating to this order to Galleon Systems Ltd, Aston Science Park, Love LaneBirmingham B7 4BJ.

*Overseas readers can also obtain this discount but details vary according to country. Pleasering, write or fax Galleon Systems.


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Just In - Microvitec 20" VGA (800 x 600 res.) colour monitors.Good SH condition - from £299 - CALL for Info

PHILIPS HCS35 (same style as CM8833) attractively styled 14"colour monitor with both RGB and standard composite 15.625Khz video Inputs via SCART socket and separate phono jacks.Integral audio power amp and speaker for all audio visual uses.Will connect direct to Amiga and Atari BBC computers. Ideal for allvideo monitoring / security applications with direct connectionto most colour cameras. High quality with many features such asfront concealed flap controls, VCR correction button etc. Goodused condition - fully tested - guaranteedDimensions: W14" x H1234" x 151/2" D. Only £95 (E)

PHILIPS HCS31 Ultra compact 9" colour video monitor with stan-dard composite 15.625 Khz video input via SCART socket. Idealfor all monitoring / security applications. High quality, ex -equipmentfully tested & guaranteed (possible minor screen burns). In attrac-tive square black plastic case measuring W10" x H10" x 131/2" D.240 V AC mains powered. Only £79.00 (D)KME 10" 15M10009 high definition colour monitors with 0.28" dotpitch. Superb clarity and modern styling.. ............

Operates from any 15.625 khz sync RGB videosource, with RGB analog and composite syncsuch as Atari, Commodore Amiga, AcornArchimedes & BBC. Measures only 131/2" x 12" x11". Good used condition. Only £125 (E)

20" 22" and 26" AV SPECIALSSuperbly made UK manufacture. PIL all solid state colour monitors,complete with composite video & optional sound input. Attractiveteak style case. Perfect for Schools, Shops, Disco, Clubs, etc.InEXCELLENT little used condition with full 90 day guarantee.

20"....£135 22"....£155 26"....£185 (F)

SPECIAL INTEREST ITEMSMITS.). FA3445ETKL 14" Industrial spec SVGA monitors £2452kW to 400 kW - 400 Hz 3 phase power sources -ex stock £POABroadcast Electronics Inc FX30 FM exciter 80-108 MHz £750Stanelco STA15 15kW RF Induction heater system £POAIBM 8230 Type 1, Token ring base unit driver £950IBM 53F5501 Token Ring ICS 20 port lobe modules £750IBM MAU Token ring distribution panel 8228-23-5050N £95AIM 501 Low distortion Oscillator 9Hz to 330Khz, IEEE £550Trend DSA 274 Data Analyser with G703(2M) 64 i/o £POAHP APOLLO RX700 system units £950HP6621A Dual Programmable GPIB PSU 0-7 V 160 watts £1800HP6264 Rack mount variable 0-20V @ 20A metered PSU £675HP54121A DC to 22 GHz four channel test set £POAHP7580A Al 8 pen HPGL high speed drum plotter £1850Marconi 6310 Programmable 2 to 22 GHz sweep generator £6500EG-NG Brookdeal 95035C Precision lock in amp £650OTC Ltd 1550 SM Stabilised IR laser calibration source £2250Ling Dynamics 2kW programmable vibration test system £POAComputar 16mm CCTV auto iris lenses 'C' mount - NEW £125Keithley 590 CV capacitor / voltage analyser £POARacal ICR40 dual 40 channel voice recorder system £3750Roken 80-250 240v single phase flow solder machine £1200ICI R5030UV34 Cleanline ultrasonic cleaning system £POAMann Tally MT645 High speed line printer £2200INTEL SBC 486/133SE Multibus 486 system. 8Mb Ram £1200Zeta 3220-05 AO 4 pen HPGL fast drum plotters £1150Nikon HFX-11 (Ephiphot) exposure control unit £1450Motorola VME Bus Boards & Components List. SAE / CALL £POATrio 0-18 vdc linear, metered 30 amp bench PSU. New £550Fujitsu M3041R 600 LPM band printer £1950Fujitsu M3041D 600 LPM printer with network interface £1250Perkin Elmer 2998 Infrared spectrophotometer £POAVG Electronics 1035 TELETEXT Decoding Margin Meter £3750Andrews LARGE 3.1 m Satellite Dish + mount (For Voyager!) £950Thurlby LA 160B logic analyser £375Sekonic SD 150H 18 channel digital Hybrid chart recorder £1995Densei MUD 0185AH 1KVa UPS system with batts NEW £575System Video 1152 PAL waveform monitor £485Test Lab - 2 mtr square quietised acoustic test cabinets £300Kenwood 9601 PAL Vectorscope - NEW £650

Please call for further details on the above items

19" RACK CABINETSSuperb quality 6 foot 40U

Virtually New, Ultra SmartLess than Half Price!

Top quality 19" rack cabinets made in UK byOptima Enclosures Ltd. Units featuredesigner, smoked acrylic lockable front door,full height lockable half louvered back doorand louvered removable side panels. Fullyadjustable internal fixing struts, ready punchedfor any configuration of equipment mountingplus ready mounted integral 12 way 13 ampsocket switched mains distribution strip makethese racks some of the most versatile we

have ever sold. Racks may be stacked side by side and thereforerequire only two side panels to stand singly or in multiple bays.Overall dimensions are: 771/2" H x 321/2" D x 22" W. Order as:

OPT Rack 1 Complete with removable side panels. £335.00 (G)OPT Rack 2 Rack, Less side panels £225.00 (G)

32U - High Quality - All steel RakCabMade by Eurocraft Enclosures Ltd to the highest possible spec,rack features all steel construction with removable .

side, front and back doors. Front and back doors are'hinged for easy access and all are lockable withfive secure 5 lever barrel locks. The front dooris constructed of double walled steel with a'designer style' smoked acrylic front panel toenable status indicators to be seen through thepanel, yet remain unobtrusive. Internally the rackfeatures fully slotted reinforced vertical fixingmembers to take the heaviest of 19" rackequipment. The two movable vertical fixing struts(extras available) are pre punched for standard'cage nuts'. A mains distribution panel internal-ly mounted to the bottom rear, provides 8 x IEC 3pin Euro sockets and 1 x 13 amp 3 pin switchedutility socket. Overall ventilation is provided byfully louvered back door and double skinned top sectionwith top and side louvres. The top panel may be removed for fittingof Integral fans to the sub plate etc. Other features include: fittedcastors and floor levelers, prepunched utility panel at lower rear forcable / connector access etc. Supplied in excellent, slightly usedcondition with keys. Colour Royal blue. External dimensionsmm=1625H x 635D x 603 W. ( 64" H x 25" D x 233A" W )

Sold at LESS than a third of makers price !!

A superb buy at only E1 95.0 0 (G)Over 1000 racks - 19" 22" & 24" wide

3 to 44 U high. Available from stock !!Call with your requirements.

TOUCH SCREEN SYSTEMThe ultimate in 'Touch Screen Technology' made by the experts -MicroTouch - but sold at a price below cost !! System consists ofa flat translucent glass laminated panel measuring 29.5 x 23.5 cmconnected to an electronic controller PCB. The controller producesa standard serial RS232 or TTL output which continuously givessimple serial data containing positional X & Y co-ordinates as towhere a finger is touching the panel - as the finger moves, the datainstantly changes. The X & Y information is given at an incrediblematrix resolution of 1024 x 1024 positions over the entire screensize !! A host of available translation software enables direct con-nection to a PC for a myriad of applications including: control pan-els, pointing devices, POS systems, controllers for the disabled orcomputer un-trained etc etc. Imagine using your finger with'Windows', instead of a mouse !! (a driver is indeed available !) Theapplications for this amazing product are only limited by yourimagination!! Complete system including Controller, Power Supplyand Data supplied at an incredible price of only:Full MICROTOUCH software support pack £145.00 (B)

and manuals for IBM compatible PC's £29.95 RFE - Tasted

LOW COST RAM & CPU'SINTEL 'ABOVE' Memory Expansion Board. Full length PC -XTand PC -AT compatible card with 2 Mbytes of memory on board.Card is fully selectable for Expanded or Extended (286 processorand above) memory. Full data and driver disks supplied. RFE.Fully tested and guaranteed. Windows compatible. E59.95(A1)Half length 8 bit memory upgrade cards for PC AT XT expandsmemory either 256k or 512k in 64k steps. May also be used to fillin RAM above 640k DOS limit. Complete with data.Order as: XT RAM UG. 256k. £34.95 or 512k £39.95 (A1)

SIMM SPECIALS1 MB x 9 SIMM 9 chip 120ns Only £19.50 (A1)1 MB x 9 SIMM 3 chip 80 ns £23.50 or 70ns £24.95 (A1)1 MB x 9 SIMM 9 chip 80 ns £22.50 or 7Ons £24.00 (A1)4 MB 70 ns 72 pin SIMM -with parity- Only £95.00((Al))8 MB 70 ns 72 pin SIMM - no parity £159.00 AlINTEL 486-DX33 CPU £55.00 INTEL 486-DX66 CPU £69.00 Al

FANS & BLOWERSEPSON D0412 40x40x20 mm 12v DC £7.95 10 / £65PAPST TYPE 612 60x60x25 mm 12v DC £8.95 10 / £75MITSUBISHI MMF-D6D12DL 60x60x25 mm 12v DC £4.95 10 / £42MITSUBISHI MMF-08C12DM 80x80x25 mm 12v DC £5.25 10 / £49MITSUBISHI MMF-09812DH 92x92x25 mm 12v DC £5.9510 / £53PANCAKE 12-3.5 92x92x18 mm .12v DC £7.9510 / £69EX -EQUIP AC fans. ALL TESTED 120 x 120 x 38 mm specify 110or 240 v £6.95. 80 x 80 x 38 mm - specify 110 or 240 v £5.95IMHOF 826 1900 rack mnt 3U x 19" Blower 110/240v NEW £79.95Shipping on all fans (A). Blowers (B). 50,000 Fans Ex Stock CALL

Issue 13 of Display News now available - send large SEIE - POCKED with bargains!

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CIRCUIT IDEAS

Do you havean originalcircuit idea forpublication?We are giving£100 cash forthe month'stop design.Additionalauthors willreceivecash for eachcircuit ideapublished. Weare lookingfor ingenuityin the use ofmoderncomponents.

WIN A TTI PROGRAMMABLEBENCH MULTIMETER"High accuracy, resolution and bandwidth -performance beyond the capability of handhelds"

C1 0 I WINNER

THULE( THANDAI INSTRUMENTS

This high-performancebench multimeter could beyours in exchange for a goodidea. Featuring a dualdisplay, the 4.5 -digit 1705multimeter resolves down to10pV, 10m52 and 0.1 NA andhas a basic dc accuracy of0.04%. Frequency measuredis 10Hz to 120kHz with anaccuracy of 0.01% andresolution to 0.01Hz.Capacitor and true rmsmeasurements are alsofeatured.

Recognising the importanceof a good idea, ThurlbyThandar Instruments will begiving away one of theseexcellent instruments onceevery six months. Thisincentive is in addition to ourmonthly £100 'best circuitidea' award and £25awards for each circuitpublished.

Inductance on a capacitance meterUsing this circuit, you canmeasure inductance by means of

a capacitance meter. It offers theadvantage over a gyrator in that theinductor is earthed.

Y = jcoL/(R8 + jat.) x (V + Y)Y= jaLV / R8U = 2V - (V + Y) = V - yoLV/R8

Since Vilin=(R8R1)/j(oL, which is acapacitive impedance,

IinRl = V -U/in = jcoLV /(R8Ri )

1 / jc0C = (R8R1)/

C = L /(R8R1)

Making R8 and RI lkOpresents a 1Hinductor as 1pF, 10mH as lOnF, etc.Marco TrinciMontecatini TermeItaly

linTP10 3

TP2o-

U

IC1

R4

, 10k Cy.

R6

10k 1%

TL084

zin= Vimc = L /(R1R6)

10

IC1

R3

10k 1%

R8

8 v+y 1k 1%

TL084

R7

10k 1%

12

R2

10k 1%

c.r =L/r =time

R5

10k 1%

oTP3

Inductance

Cold TP4lead

IC1

13TL084

Without calculation, this circuit measuresinductance in terms of capacitance, while allowingthe inductor to be earthed.

TP5

TP60

TP7

-V


SMALL SELECTION ONLY LISTED - EXPORT TRADE AND QUANTITY DISCOUNTS - RING US FOR YOUR REQUIREMENTS WHICH MAY BE IN STOCKHP New Colour Spectrum AnalysersHP1417, 8552B IF + 85538 RF -1KHz-110Mc/s -1700.HP1417+ 8552B IF + 85548 RF - 100KHz-1250Mc/s -1900.HP1417, 85528 IF + 8558A RF -20Hz-300KHz- 1700.Special Offer just in from MOD Oty 40 HP8555A RF Units 10Mc/s - 18GHzS.HP1417 85528 IF 8555A 10Mc/s-18GHzS -11200.HP ANZ Units Available separately- New Colours -TestedHP1417 Mainframe -1350.HP85526 IF -1300.HP85538 RF 1KHz to 110Mc/s- 1200.HP8554B RF 100KHz to 1250Mc/s- £500.HP8555A RF IOWA to 18GHz5 -1800.HP8556A RF 20Hz to 300KHzS -1250.HP8443A Tracking Generator Counter 100KHz-110Mc/s- 1300.HP8445B Tracking Preselector DC to 18GHz - £350.HP3580A 5Hz - 50KHz ANZ -1750 -£1000.HP3582A .02Hz to 25.6KHz - £2k.HP8568A 100Hz-1500Mcfs ANZ- 16k.HP8569B 10Mc./s-22GHz ANZ- £6k.HP Mixers are available for the above ANZ's to 40GHzTEK 492 - 50KHz- 18GHz Opt 1+2 -14k-14.2k.TEK 492 - 50KHz - 18GHz Opt 1+2+3 - 14.5k.TEK 492P -50KHz - 21 GHz Opt 1+2+3 - 15k.TEK 494AP 1KC/S -21GHz -17k.TEK 496P 1KHz-1.8GHz- E4k.TEK 514N 0-100KHz - £400.TEK 715 + L1 - 20Hz-5Mc/s -1700.TEK 7L5 + L3 - Opt 25 Tracking Gen -1900.TEK 7L12 - 100KHz-1800Mc/s- £1000.TEK 7L18- 1.5-60GHzs- 11500.TEK 491 10Mc/s-12.4GHzs-40GHts - £750. 12.4Ghzs-40Ghzs with Mixers.Tektronix Mixers are available for above ANZ to 60GHzsSystron Donner 763 Spectrum ANZ + 4745B Preselector .01-18GHz + Two Mixers 18-40GHz in

Transit Case -13k.HP8673D Signal Generator .05-26.5GHz - 120k.Systron Donner 16188 Microwave AM FM Synthesizer 50Mc/s 2-18GHzs

R&S SWP Sweep Generator Synthesizer AM FM 4-2500Mc/s- £3.5k.ADRET 3310A FX Synthesizer 300Hz-60Mc/s- £600.HP8640A Signal Generators - 1024Mds - AM FM -1800.HP3717A 70Mc/s Modulator - Demodulator - 1500.HP8651A RF Oscillator 22KC/S - 22Mc/s.HP5316B Universal Counter A+ B.HP6002A Power Unit 0-5V 0-10A 200W.HP6825A Bipolar Power Supply Amplifier.HP461A-465A-467A Amplifiers.HP81519A Optical Receiver DC-400Mc/s.HP Plotters 7470A -7475A.HP3770A Amplitude Delay Distortion ANZ.HP37708 Telephone Line Analyser.HP8182A Data Analyser.HP59401A Bus System Analyser.HP6260B Power Unit 0-10V 0-100 Amps.HP3782A Error Detector.HP3781A Pattern Generator.HP3730A + 3737A Down Convertor Oscillator 3.5-6.5GHz.HP Microwave Amps 491-492-493-494-495-1GHz-12.4GHz- 1250.HP1056 Quartz Oscillator - 1400.HP5087A Distribution Amplifier.HP6034A System Power Supply 0-60V 0 -10A -200W- 1500.HP6131C Digital Voltage Source+ -100V 1,5 Amp.HP4275A Multi Frequency L.C.R. Meter.HP3779A Primary Multiplex Analyser.HP3779C Primary Multiplex Analyser.HP8150A Optical Signal Source.HP163OG Logic Analyser.HP5316A Universal Counter A+B.HP5335A Universal Counter A+B+C.HP59501B Isolated Power Supply Programmer.HP8901A Modulation Meter AM - FM - also 8901B.HP5370A Universal Time Interval Counter.Marconi TF2370 -30Hz-110Mc/s 750HM Output (2 BNC Sockets + Resistor for 500HM MOD with

Marconi MOD Sheet supplied - £650.Marconi TF2370 30Hz-110Mc/s 50 ohm Output -1750.Marconi TF2370 as above but late type - £850.Marconi TF2370 as above but late type Brown Case -11000.Marconi TF2374 Zero Loss Probe - £200.Marconi TF2440 Microwave Counter - 20GHz -£1500.Marconi TF2442 Microwave Counter - 26.5GHz -12k..Marconi TF2305 Modulation Meter- 12.3k.Racal/Dana 2101 Microwave Counter - 10Hz-20GHz- 12k.Racal/Dana 1250-1261 Universal Switch Controller + 200Mc/s PI Cards.Racal/Dana 9303 True RMS Levelmeter+Head - £450. IFFE -1500.TEKA6902A also A69028 Isolator -£300-1400.TEK 1240 Logic Analyser -1400.TEK FG5010 Programmable Function Generator 20Mc./s-£600.TEK2465A 350Mc/s Oscilloscope - £2.5k + probes -1150 each.TEK CT -5 High Current Transformer Probe - 1250.TEK J16 Digital Photometer + J6523-2 Luminance Probe -1300.TEK J16 Digital Photometer + J6503 Luminance Probe - 1250.ROTEK 320 Calibrator + 350 High Current Adaptor AC -DC - £500.FLUKE 5102B AC -DC Calibrator - E4k.FLUKE 1120A IEEE -488 Translator -1250.Tinsley Standard Cell Battery 56446-£500.Tinsley Transportable Voltage Reference - £500.FLUKE Y5020 Current Shunt -£150.HP745A+ 746A AC Calibrator -£600.HP8080A MF + 8091A 1GHz Rate Generator + 8092A Delay Generator + Two 8093A 1GHz Amps

+ 15400A - £800.HP54200A Digitizing Oscilloscope.HP117296 Carrier Noise Test Set .01-18GHz - LEF - 12000.HP3311A Function Generator -C300.Marconi TF2008 - AM -FM signal generator - also sweeper - 10Kc/s - 510Mc/s - from £250 -

tested to £400 as new with manual - probe kit in wooden carrying box.HP Frequency comb generator type 8406 - £400.HP Vector Voltmeter type 8405A - 1400 new colour.HP Sweep Oscillators type 8690 A & 8 + plug -ins from 10Mc/s to 18GHz also 18-40GHz. P.O.R..HP Network Analyzer type 8407A + 8412A + 8501A - 100Kcis -110Mc/s - £500 - 11000.HP Amplifier type 8447A - 1-400Mcis £200 - HP8447A Dual - 1300.HP Frequency Counter type 5340A - 18GHz 11000 - rear output 1800.HP 8410 -A -B -C Network Analyzer 110Mc/s to 12GHz or 18GHz - plus most other units and

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

Racal/Dana 9301A - 9302 RF Millivoltmeter - 1.5-2GHz- 1250-1400.Racal/Dana Modulation Meter type 9009- 8Mc/s- 1.5GHz- 1250.Marconi RCL Bridge type TF2700 -£150.Marconi/Saunders Signal Sources type - 60588 - 6070A - 6055A - 6059A - 6057A - 6056 -

1250-1350. 400Mc/s to 18GHz.Marconi TF1245 Circuit Magnification meter + 1246 & 1247 Oscillators -1100-1300.Marconi microwave 6600A sweep osc., mainframe with 6650 PI - 18-26.5GHz or 6651 PI - 26.5-

40GHz - E1000 or PI only 1600. MF only £250.Marconi distortion meter type TF2331- 1150. TF2331A - 1200.

Tektronix Plug -Ins 7A13 -7A14 - 7A18 - 7A24 - 7A26 -7A11 -7M11 -7511 - 7D10 - 7512 - S1- S2 - S6 - S52 - PG506 - SC504 - SG502 - SG503 - SG504 - DC503 -00508 - DD501 -WR501 - DM501A- FG501A-7G501- PG502 - DC505A- FG504 - 7680 + 85-7892A

Gould J3B test oscillator + manual -1150.Tektronix Mainframes -7603 - 7623A -7613-7704A - 7844 -7904- TM501 - 7M503 - TM506 -

7904A -7834- 7623- 7633.Marconi 6155A Signal Source -1 to 2GHz - LED readout - £400.Barr & Stroud Variable filter EF3 0.1Hz - 100kcls + high pass + low pass- 1150.Marconi TF2163S attenuator - 1GHz. 1200.Farnell power unit H60/50 - £400 tested. H60/25 -1250.Racal/Dana 9300 RMS voltmeter - 1250.HP 8750A storage normalizer -1400 with lead + S.A or N,A Interface.Marconi TF2330 - or TF2330A wave analysers- 1100-1150.Tektronix - 7514 -7711-7s11 -7512 - S1 - S2 - 539 - 547 -551 - S52 - S53 -7M11.Marconi mod meters type TF2304 - 1250.HP 5065A rubidrum vapour FX standard -11.5k.Systron Donner counter type 60548 - 20Mc/s - 24GHz - LED readout -Ilk.Racal/Dana 9083 signal source -two tone -1250.Systron Donner -signal generator 1702 - synthesized to 1GHz - AM/FM - 1600.Tektronix TM515 mainframe + TM5006 mainframe -1450 -1850.Farnall electronic load type R131030-35-1350.Racal/Dana counters - 9904 - 9905 - 9906 - 9915 - 9916 - 9917 - 9921 - 50Mc/s - 3GHz - £100-

£450 - all fitted with FX standards.HP4815A RF vector impedance meter c/w probe - 1500-1600.Marconi TF2092 noise receiver. A, 8 or C plus filters - 1100-1350.Marconi TF2091 noise generator. A, B or C plus filters - 1100-1350.Marconi 2017 S/G 10Khz - 1024MHz.HP1807R, HP1827 mainframes 1300-1500.Philips panoramic receiver type PM7900 -1 to 20GHz - £400.Marconi 6700A sweep oscillator + 18GHz Pi's available.HP8505A network ANZ + 8503A S parameter test set + 8501A normalizer- 14k.HP8505 network ANZ 8505 + 8501A + 8503A.Racal/Dana VLF frequency standard equipment. Tracer receiver type 900A + difference 'Mt.?,

type 527E + rubidium standard type 9475 - 12750.HP signal generators type 626 -628- frequency lOGHz -21GHz.HP 432A - 435A or 13,- 436A - power meters + powerheads - Mc/s - 40GHz -1200-11000.Bradley oscilloscope calibrator type 192 -1600.HP8614A signal generator 800Mc/s - 2.4GHz, new colour 1400.HP8616A signal gen 1.8GHz -4.5GHz, new colour £400.HP 3325A syn function gen 20Mc/s -11500.HP 3336A or B syn level generator -1500-£600.HP 3586B or C selective level meter - £750-11000.HP 3575A gain phase meter 1Hz - 13Mc/s -£400.HP 8683D S/G microwave 2.3 -13GHz - opt 001 - 003 -14.5k.HP 8660 A -B -C syn S/G. AM + FM + 10Kc/s to 110Mc/s PI - 1Mcfs to 1300Mc/s - 1Mc./s lo

2600M c/s - 1500-12000.HP 86408 S/G AM -FM 512Mc/s or 1024Mc/s. Opt 001 or 002 or 003 - 1800-11250.HP 86222BX Sweep PI - 01 - 2.4GHz + ATT -11750.HP 8629A Sweep PI -2- 18GHz -£1000.HP 86290B Sweep PI -2 -18GHz -11250.HP 86 Series PL's in stock - splitband from lOMc/s - 18.6GHz- 1250-11 k.HP 8620C Mainframe -1250. IEEE -£500.HP 8615A Programmable signal source - 1MHz- 50Mc/s - opt 002 - Elk.HP 8601A Sweep generator .1- 110Mc/s -1300.HP 3488A HP- IB switch control unit - 1500 + control modules various -1175 each.HP 8160A 5OMc/s programmable pulse generator - £1000.HP 853A MF ANZ -11.5k.HP 8349A Microwave Amp 2- 20GHz Solid state -11500HP 3585A Analyser 20Hz - 40Mc/s -14k.HP 85698 Analyser .01 - 22GHz -15k.HP 3580A Analyser 5Hz - 50kHz -Elk.HP 19808 Oscilloscope measurement system -1600.HP 3455A Digital voltmeter -1500.HP 3437A System voltmeter - £300.HP 3581C Selective voltmeter - £250.HP 5370A Universal time interval counter -£450.HP 5335A Universal counter - 200Mds - 1500.HP 5328A Universal counter - 500Mcis -1250.HP 6034A System power supply- 0 -60V-0 -10 amps -1500.HP 5150A Thermal printer -1250.HP 1645A Data error analyser -1150.HP 4437A Attenuator -1150.HP 3717A 70Mc/s modulator -1400.HP 3710A - 3715A - 3716A - 37028 - 3703B - 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 - 1400.HP 3763A Error detector - 1500.HP 3764A Digital transmission analyser - 1600.HP 3770A Amp delay distortion analyser - 1400.HP 3780A Pattern generator detector - 1400.HP 3781A Pattern generator -1400.HP 37818 Pattern generator (bell) -1300.HP 3782A Error detector -1400.HP 37828 Error detector (bell) - £300.HP 3785A Jitter generator + receiver - 1750-11 k.HP 8006A Word generator -1100-1150.HP 8016A Word generator - £250.HP 8170A Logic pattern generator- £500.HP 59401A Bus system analyser - £350.HP 59500A Multiprogrammer HP -113-000.Philips PM5390 RF syn -0.1 - 1GHz - AM + FM -11000.S.A. Spectral Dynamics SD345 spectroscope 111 - LF ANZ -11500.Tektronix R7912 Transient waveform digitizer - programmable -1400.Tektronix TR503 + TM503 tracking generator 0.1 - 1.8GHz - It k - or TR502.Tektronix 576 Curve tracer + adaptors -1900.Tektronix 577 Curve tracer + adaptors - £900.Tektronix 1502/1503 TDR cable test set - 11000.Tektronix AM503 Current probe + 7M501 m/frame - £1000.Tektronix SC501 - SC502 - SC503 - SC504 oscilloscopes -175-1350.Tektronix 465 -465B -475 - 2213A 2215 2225 2235 2245 2246 1250-11000.Kikusui 100Mc/s Oscilloscope COS6100M -£350.Nicolet 3091 LF oscilloscope -£400.Racal 1991 - 1992 -1988 -1300Mds counters- 1500-1900.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 - 1400-1750 Tested.EIP 545 microwavel8GHz counter -11200.Fluke 510A AC ref standard - 400Hz - £200.Fluke 355A DC voltage standard - 1300.Wiltron 610D Sweep Generator + 6124C PI -4 - 8GHz - 1400.Wiltron 610D Sweep Generator + 610840 PI - 1Mc/s- 1500Mth - 1500.Time Electronics 9814 Voltage calibrator -1750.Time Electronics 9811 Programmable resistance -1600.Time Electronics 2004 D.C. voltage standard - 11000.HP 8699B Sweep PI YIG oscillator .01 - 4GHz - £300. 8690B MF -£250. Both 1500.Schlumberger 1250 Frequency response ANZ -11500.Dummy Loads & power att up to 2.5 kilowatts FX up to 18GHz - microwave parts new and et

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-Weir-Thurl by -Racal etc. Ask for list

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

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

Johns Radio, Whitehall Works, 84 Whitehall Road East, Birkenshaw, Bradford BD11 2ER. Tel. No: (01214i 684001. Fax: 651160


March 1996 ELECTRONICS WORLD+WIRELESS WORLD 2'35

CIRCUIT IDEAS SPECTRUM ANALYSER ADAPTOR WINNER

Remote multichannel resistance measurement'This low -power circuit measures the valueI of remote resistive sensors using any type

of connection such as wire, infrared orultrasonics; I use a vhf radio link.

With a UMC UM3758-108AMencoder/decoder, it is possible to transmit8 -bit data combined with 10 address bits.Depending upon the logical level on the modeinput, the circuit acts as a decoder or encoder.In this application, the address bits are hard-wired high and the measuring resolution islimited to 6 -bit, for reasons explained later.

In encoder mode, the Tx/Rx pin transmitsthe address/data information as long as poweris supplied. A built-in RC oscillator, needingonly R9 and C9, provides clocking; matchingof the encoder/decoder's oscillatorfrequencies is not too critical; 5% resistorswill suffice.

Serial data is supplied to the Rx input indecoder mode, where it is examined bit by bitas received. Only if two successiveaddress/data combinations match is datatransferred to the output data pins D1_8, whichlatch the data until the next valid data is beingreceived. The Tx/Rx out pin switches low ifdata matches, returning high after twosuccessive unmatched address words.

System timing is controlled by /CI, a74HC4060. The positive -going edge of theQ5 output of /CI triggers an enable signal, theduration of which is adjustable by P1 about

3.6 V

VC.0

220k

PI100K

14

ICSSHC4S38RC 0

C3

VCCO

P2RO 100K

:;; 1,5

I i"e

every 60s, depending upon RI, R2, C1. At thestart of this enable time, the counter in IC4 isreset to zero by the positive -going edge of theoscillator enable signal via C3, R4. Diode D8gates the /C4 clock signal, pulling down theclock input to disable counting. During theenable time, a sensor -dependent count isreached on the outputs Q4_9.

Be careful to avoid overflow, by selectingthe right combination between the enabletime and the IC4 oscillator frequency, whichdepends on the sensor used.

At the end of the oscillator enable time, thefalling edge of IC5b Q output triggers /C5a toswitch on the power supply for both theUM3758 and the transmitter. To be sure that aminimum of three address/data codes aretransmitted, the transmitter on time,adjustable by P2, is 250-300ms. Raising theUM3758 oscillator frequency makes itpossible to use an even shorter transmittertime, but bear in mind that the receiver mustbe capable of detecting this signal. A low -loss, dual P -channel mosfet, a SiliconixSI9933DY with Rgs<0.20, switches thetransmitter/encoder supply.

To prevent any current flow through thedata input of /C2 when it is powered down,the counter outputs of IC4 are connected viadiodes Di_6. Because of the internalarchitecture of the UM3758, an open inputwill be seen as logical 1, so there is no need

Os

164 48

MS

SENSOR 180k

2505.

4/47

467

'21

ICSAHC4S38RC 0 TX ON

250:68

to use pull-up resistors.Logic levels of data bits D7 and D8 are user

selectable to allow the use of four transmitterson the same frequency without changingdecoder address lines in the receiver. A smalldifference in transmitting interval willprevent most of the interference when morethan one transmitter is used.

Powered by a 3.6V lithium cell, thetransmitter logic draws less than 100pA,transmitting current depending upon the typeof transmitter used, although overall powerconsumption is still low because of the shorttransmitting time. A telemetry system basedon this design has been in use by our institutesince early 1994 to study activity and feedingbehaviour of the red deer. As the resistiveelement we use an electrolytic tilt sensor. Ibuilt the circuit using surface -mountedcomponents but, except for the SI9933DY,they are also available in through -hole form.Willem van der VeerInstitute for Forestry and Nature ResearchWageningenThe Netherlands.

ReferencesUM3758 series data sheet, UMC Europe,Amsterdam, The Netherlands. Telephone: 0031-20-6970766.Little Foot series manual, Siliconix Ltd, Newbury,Berks RG14 5UX. Tel. 01344-485757.

IC3ASI9933DY

000C

I " I "'

IC3BSI9933DY

IC4

10nANTENNA

11 PI 04DI

Al006 2

A2A3

0708

A4 DSCAS

10

08010412

:01

D - 46A7AB TX/RX 2

711D4 A9

610

12

PS

DS D1 RxD2D3D4DS MODE

iiit:i''

21GAO

ROT PO74HC4060

D6

D607DS

FS),6 x 1144148

IC2TRANSMITTER

UM3758-10848ENCODER

C2luF

6 .74 TX -NUMBER(0..3)

RECEIVER

R2 ICI11 PI 04

05064748

010012 4_

F6 21 CODE MATCH

820kRST PO --2- 01-D6

-47luF

74604060SENSOR -VALUE

07-08 :

Using a vhf radio link, or any other type of TRANSMITTER

connection, this six -channel circuitNUMBER

measures the resistance of remote sensors.

JP1 4P20

1 I

AlA2A34A

ASA6A7ASA9A10

DI

D3D4DSD6D7D8

IC6UM3758-10SAMDECODER I O

V

ANTENNA

F F5KRECEIVER


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CRYSTALS32K768 1MHZ 1M8432 2M000 2M1432 2M304 2M4576 3M0003M2768 3M400 3M579545 3M58564 3M600 3M6864 3M932164M000 4M190 4M194304 4M2056 4M433614 4M608 4M9152 5M0005M0688 6M000 6M041952 6M200 6M400 7M37280 8M000 8M064008M448 8M863256 8M8670 9M3750 9M8304 10M240 10M24510M368 10M70000 11M000 11M052 11M98135 12M000 12M513M000 13M270 13M875000 14M000 14M318 14M7450 14M745615M0000 16M000 17M625018M432 18M432 20M000 21M30021M400M15A 24M000 25M000 26M995 BN 27M045 RD 27M095 OR27M145 BL 27M145 YW 27M195 GN 28M4696 30M4696 31M469631M4696 34M368 36M75625 36M76875 36M78125 36M7937536M80625 36M81875 36M83125 36M84375 38M900 48M00051M05833 54M1916 55M500 57M7416 57M7583 69M545 69M55096M000 111 M800 114M8 120M000 El ea

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Acre


CIRCUIT IDEAS

They don'tcome muchsimpler thanthis one. Threeelectricalcomponentstest a coax.cable for shorts r LED1and continuity,provided youhaveremembered toisolate thesockets.

R1

390RIB

9V

LED

Co -axial lead under test

Short and continuitytest for coaxial cable

With three components, you cantest a coaxial cable for inner

and outer continuity and shortcircuits between them.

Led 1 lights for inner continuityand led 2 when the outer is in onepiece. If there is a short, neither ledlights, since they are both across the

cable, short-circuit current beinglimited by R1. To resolve the ambi-guity of both leds being out forshorts and open circuits in inner andouter, disconnect the cable and touchthe outers to the socket shells.S RobertsBude, Cornwall

Measuring conductivityTo measure the contact resistance of

physiological electrodes, currentdensity must be kept below thethreshold of feeling and be lowenough to avoid polarising theelectrodes.

+9vo

GNDo

Conductivity meteruses a current pump tosupply constant 1pA tothe contact resistanceto be measured.Resulting voltage isdigitally displayed.

SB103

R1

47k

C1,A122n 4:0P1

5iOP2

Tor, = 30s

R2

10k

3I1N1

1eINH

OSC

In the instrument shown here, thereference current comes from theHowland current pump based on theINAI05, which takes its 60Hz inputfrom the display backplane drive, PR2setting the output current at I pi A.

7 6

CKE BPP

STAGES1 - 8

RST SET

R3

10k

V+

2

MC 4536

STAGES9-24

9 10

MONO

00

MN

Voltage across the electrodes (Rx) isrectified by the AD736 and displayed.Measuring range is 0.1k52 to199.9kQ.A G BirkettLondon SE22

VB+

I

13

5

1R5

39M4-1AA.A.,-PR1

ZEROV- 1M

C6111On

IRX

C5100n

10u

R4

1 Bk

20Vin

3 CF

IC6 AD736V+ V+

SECT

BIAS R S

C7+ =C6maslOtt10µ

V+DPM500S

4-0F 116 118 119 122 129

J.c2710n

Tr1

ZVP2106

IC1

78L05

.- INmi.C3T 220n

OUTCOMM

V+

= C4T10p.

60Hz

21 137 14 20 5

CAvo5

COM

+C10 =10µ

30

36

35

2

15

7

XB3 E3 AB XG3 B.P.BGAP TEST

POL Fc

INLO HzRFH1 -- -

/ / // // /V"'"""RFLOI/ // // // / ACOM- - - -

RF+RF-

XDPDP1DP2 DP3

Ohm

V- -5 KMm

38

4

3

7

34 33 27 25 24 23 26 128

v-

13 12 3


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ECC33 7.50 E280 150 UCH81 2.50 6C6 510 12E3E6 250

ECC35 7.50 EMI 3.50 UCL82 2.00 6C864 100 128874 GE 7.50

ECC81 100 GY501 3.00 UCL83 3.00 6CD6GA 5.00 1213974 GE 1.00

ECC82 3.00 GZ32 Mull 8.50 UF89 4.00 6CL6 175 12E1 15.00

ECC83 3.50 0133 6.00 UL41 1200 6C07 7.50 12867/12017 6.50

ECC85 3.50 GZ34 GE 7.50 0184 3.50 6CH6 000 30E11/2 1.50

ECC88 Mull 6.00 G137 6.00 UY41 1.00 6CW4 8.00 30619 2.50

ECC9I 2.00 1001 1000 UY85 2.25 606 5.00 3008(PR) 110.00

ECF80 1.50 4766 10.00 06105/30 2.50 6005 GE 17.50 572B 10.00

ECH35 3.50 6188 1500 VRI50/30 2.50 62065 12.50 805 5000

ECH42 150 N78 9.00 2759 25.00 6E48 150 807 5.75

ECH81 3.00 042 2.70 08030 25.00 6E85 1.85 8114 18 50

ECI.80 1.50 0132 2.70 2021 3.50 6F6 3.50 8124 6500

ECL82 3.00 CC3 2.51 3828 15.00 6E07 E7.50 813 27.50

ECL83 3.00 003 2.50 4CO2508 STC 55.00 6046 4.00 8334 85.00

ECL86 Mull 3.50 PCF80 2.60 5R4GY 6.00 6H6 100 866A 25.00

ECLL800 2500 PCF82 1.51 5114G 525 6H56 4.95 8724 20.00

EF314 3.50 PCF86 2.50 5845 4.00 615 3.00 9314 25.00

EF39 2.75 PCF801 2.50 5Y3GT 2.50 616 3.00 20504 GE 1230

EF40 5.00 PCF802 2.50 523 4.00 617 4.00 5751 6.00

EF41 3.50 PCL82 2.00 52401 2.50 61564 GE 19.00 5763 10.00

EF42 4.50 PCL83 3.00 6486 4.00 616C 20.00 58114 500EF80 1.50 PCL81 2.00 6485 1.50 61S6C GE 2000 5842 1200

EF85 1.50 PCL85 2.50 6415 I.00 66661 100 6080 1.50

E616 1000 PCL86 2.50 64816 2.00 661 1.00 614613 GE 15.00

EF91 210 PCL805 2.50 64885 500 668 410 65504 GE 20.00

EF92 2.00 PD500 8.01 64086 4.50 616G 10.00 68838 GE 16.110

EF183 2.00 PL36 2.50 6405 3.25 6L6GCSYL 12.50 7025 GE 100

EFI84 210 PL81 1.15 6485 25 00 67600 Sierens 7.50 7027A GE 17.50

EL32 2.50 P182 1.50 6456 3.50 6L6GC GE 1250 7199 12.00

EL33 10.00 61.83 2.50 64070 9.50 677 3.50 7360 25.00

E1.34 Siemens 8.00 PL84 200 6476 2.00 61.06 20.00 75814 15.00

EL36 4.00 P1504 2.50 600501 500 607 1.00 7586 15.00

EL41 3.50 P1508 5.50 6406 250 6R1018/66.N0 12.00 7587 23.00

ELL80 2500 PL509/PL519 6.00 6AW8A 4.00 6067 3.00 7868 12.00

EL81 500 61802 9.00 687 4.00 6SC7 3.00

ELM 215 PY81 1.50 688 410 6007 2.50 Prices correct when

EL81 Mull 600 PY88 2.00 6846 I.50 6517 100 going to press

OPEN TO CALLERS MON-FRI 9AM-4PM, CLOSED SATURDAY.OVER 6,000 TYPES AVAILABLE FROM STOCK. OBSOLETE ITEMS

A SPECIALITY. QUOTATIONS FOR ANY TYPES NOT LISTED.TERMS: CWONISA/ACCESS. POST & PACKING: 1-3 VALVES £2.00,

4-6 VALVES £3.00. ADD 17.5% VAT TO TOTAL INC. P&P.

KENWOODTEST & MEASURING INSTRUMENTSA SUPERB RANGE OF OVER 100

QUALITY INSTRUMENTS.Available from

B.K. ELECTRONICS

FM -AM Signal Generators * Colour PatternGenerators * Video Signal Analyser * Video

Timing Analyser * Video Noise Meter* Distortion Meter * Waveform Monitors

* Vectorscopes *Audio Generators * Wow and FlutterMeters * Electronic Voltmeters

* Digital Multimeters * Function Generators* Frequency Counters * Bus Analyser

* Resistance Attenuator * Oscilloscopes * FullyProgrammable Digital Storage Oscilloscopes

* Regulated D.C. Power SuppliesA free, 50 page colour brochure, including pricelist, is available on request. Please make yourrequest on company headed notepaper, by postor by fax, to:

B.K. ELECTRONICSUnit 1 Comet Way,

SOUTHEND-ON-SEA,Essex, SS2 BTR.

Tel: 01702-527572Fax: 01702-420243


TOROIDAL TRANSFORMERSHigh Quality Low Prices -'--- --

e--.In addition to our standard range

,

we will be pleased to quote -for your special requirements.

PRICE LIST

Ouanti y Price Excluding VAT & CarriageVA Mail Order 2 -, 10+ 25+ 50+ 100+

15 14.59 10.21 7.69 5.69 5.52 5.35

30 16.04 11.23 8.45 6.25 6.06 5.89

50 17.83 12.48 9.40 9.95 6.74 6.53

60 18 02 12.61 9.49 7.02 6.82 6.61

80 17.98 12.60 9.49 7.02 6.81 6.60100 21.07 14.74 11.11 8.21 7.96 7.72120 21.54 15.08 11.35 8.39 8.15 7.89

150 25.98 18.19 13.70 10.12 9.82 9.53160 23.83 16.68 12.56 9.28 9.00 8.73225 30.10 21.07 15.87 11.73 11.39 11.04

300 34.32 24.02 18.09 13.38 12.98 12.58

400 46.19 32.32 24.35 17.99 17.47 16.94

500 50.48 35.34 26.61 19.67 19.09 18.51

625 53.09 41.36 31.14 23.02 21.24 20.57750 58.39 44.23 33.30 24.62 23.89 23.17

1000 78.80 55.16 41.54 30.70 29.80 28.89

1200 82.45 57.72 43.46 32.12 31.17 30.23

1500 105.10 73.63 55.40 40.94 39.74 38.53

2000 114.45 96.13 72.39 53.51 51.93 50.36

2500 163.04 114.13 85.94 63.51 61.64 59.79

These prices are for 240volt primary and two equal secondar-ies with 8" colour coded fly leads.Each transformer is supplied with a mounting kit (steel dishwasher pads, nut and bolt)Mail order prices include vat and postage.Please do not hesitate to telephone or write with yourparticular requirements.

Airlink Sales Co16 Knight Street, Sawbridgeworth, Herts CM21 9AT

Tel: 01279 600139 Fax: 01279 726379

80C188EB Processor Clocked at 24Mhz0 128k Battery Backed RAM (512k option)

0 128k Eprom (32k - 512k options)0 128k 5 volt Flash Eprom (512k option)0 Real Time Clock (On board Battery)

0 Watchdog Timer/Reset with Brownout detection0 2 Serial Ports -1 RS232, 1 RS232/422/4850 8 Channel 12 bit ADC (optional)

0 Direct Connection to Alphanumeric LCD Display0 48 Digital I/O lines

0 Set-up and Driver routines with Full C Source Code

FAST START - Use our Full ANSI compatible Embedded C Compiler for super fastapplication development. Supplied complete with Editor, Compiler, Assembler, Linker.Embedded. Debug and comprehensive Manual, you can compile and download and be inthe Debugger with a single keypress - or back in the editor at just the right place.Generate ROMable Code direct, no struggling with .EXE conversions or messing aroundwith reset code. Just £595.

For further information

Call now - 01379 644285 - Fax 650482Please ask for our catalogue

Devantech Ltd - 2B/2C Gilray Road - Diss - Norfolk - 1P22 3EU

March 1996 ELECTRONICS WORLD+WIRELESS WORLD

(LIULE NO. I I I ON REPLY CARD

239

CIRCUIT IDEAS

This simplecircuit enables

a PC RS232serial port to

controlmachines awithRS485 drivers,supplying the

power from thePC port.

DSR 6>

DTR 4 >-

RTS

CTS 8>

TX 3>

RX <

RS232-to-RS485 PC -powered converterI needed to control settings on

machines, which have RS485 ports,by means of a laptop PC, which has

1N4001

1N4001A

GND (

N4148

IT "

+V

4k7 1N4148

RS232. Since no power supply wasavailable, it had to come from theserial port but, since there is

Tr3BC184B

O 22plov

0

n lX5V1 2k2RS485Outputs

oB

2V4oGND

insufficient power on most serialports to supply an RS485 driver Ideveloped this circuit.

Transistor Tri inverts the signal onthe RS232 TX pin, buffering it fromthe A line. B is at around 2.4V, heldby the zener, since the RS485 isdifferential. Transistor Tr3 is a levelconverter to RS232 and Tr2 preventsdata from echoing to the RX pinwhen the PC transmits.

Power from DTR and CTS issmoothed by the 22pF capacitor andthe 1nF capacitors reduce noise,where this is necessary.

Eight controls can be daisy -chainedat 19200baud, if MAX487 low -powerRS485 drivers are used; with75ALS 176 drivers it still works at19200baud on three controls. In fact,it was intended for only one driver.K Guy WilkinsonBromsgrove, Worcester

Sense, but not sensibility for negative rails

Better sensing for anegative -rail regulatorimproves ripple, trackingand stability performance.

TVout oerror amp

-VOut 0error amp

To -Vreg<

+12V

To +Vreg < > +yew +30V max

10k

+12V

2k2 5 1k

+iT1op

10k1%

22n1R220k

1% 111

VR1

2k

y. 2 x1N914

LM3362.5

12k

1k

T100n

> ov

> Veet -30V max

small modification to the standardegative half of a dual power

supply regulator improves rippleperformance and tracking.

Normally, the sensing voltage for thenegative regulator comes from aresistive chain strung between positiveand negative rails. Here, it is returnedvia R1 to the common reference point.With R1,2 scaled suitably, an adjustmentof the potentiometer between OV and2.5V gives a Vout change from OV to30V.

With this circuit, the negative outputshowed increased stability withreference to both OV and the positiverail and, on a 2A load, ripple is less than0.5mV and a IkHz switching waveformcame out square. Tracking between thetwo rails is within 50mV. The filterformed by R1 and C1 removes anychance of ripple being injected into thereference from the negative rail.Gregory FreemanNairne, South Australia

No -compromise oscilloscope probeI n most situations, the standardI 10:1 oscilloscope probe,equalised by a few picofarads,works well but, when looking at

Probe applied here

2pF

fast waveforms, it can distort thepicture, as shown in the bottomtrace on a 2Ons pulse.

For this kind of work, a

Improved 10:1 oscilloscope probe forfast waveforms. Matched terminationreduces reflections.

500 co -ax

27OR

A - CMOS gate (74AC08) 62R 50R

Oscilloscopeinputconnector

properly matched transmissionline is the answer; anything elseproduces reflections.

Part of the circuit is a resistivepad, still dividing the input by afactor of ten, but terminating in5011 to absorb reflections; the27052 resistor swamps the gateoutput impedance. The top traceshows the result.Nick WheelerSutton, Surrey

Compensated pad, top trace, showsmuch improved performance,.overstandard oscilloscope probe. Extra8 its delay on standard probe is dueto greater length of coax.


New Nliski Cameras 8c Special Offers;New mini waterproof TV camera 40x40x15mm requires Used 8748 Microcontroller £3.30

10 to 16 volts at 120mA with composite video output SL952 UHF Limiting amplifier LC 16 surface mounting(to feed into a video or a TV with a SCART plug) a has package with data sheet £1.95a high resolution of 450 TV lines Vertical and 380 lines AM27302 £1.25 each (90p 100+)horizontal, electronic auto Iris for nearly dark (1 Lux) CD4007UB 10p 100+ (6p 1000+)to bright sunlight operation and a pinhole lens with a Sinclair light gun terminated with a jack plug and PP3 dip92 degree field of view, it focuses down to a few CM. It gives a signal when pointed at 30Hz flickering lightis fitted with a 3 wire lead (12v in grid and video with output wave form chart £3.95out) £93,57+ VAT = £109.95 or DC -DC convertor Reliability model V I2P5 12v in 5v

10+ £89.32+ VAT = £104.95 200ma out 300v input to output Isolation withHigh quality stepping motor kits (all including stepping data £4.95 each or pack of 10 £39.50

motors) 'Comstep independent control of 2 stepping Hour counter used 7 digit 240v AC 50Hz £1.45motors by PC (Via the parallel port) with 2 motors and QWERTY keyboard 58 key goad quality switchessoftware Kit £67.00 new £6.00Ready built £99.00 Airy ar A82903 -C large stepping motor 14v 7.5' step

Software support and 4 digaal inputs kit £27.00 27ohm 68mm dia body 6.3mm shaft £8.95Power interface 4A kit £36.00 or £200.00 for a box of 30Power interface 8A kit £46.00 Polyester caparitors box type 22.5mm lead pitch

eachStepper kit 4 (manual control) includes 200 step steep 0.9uf 250vdcmotor and control circuit 14p 100+ 9p.....1000+

Hand held transistor analyser it tells you which lead's the luf 250vdc 20p eachbase, the collector and emitter and if it is NPN or PNP 15p 100+ 10p 1000+of faulty £33.45, luf 50v bipolar electrolytic axial leads 15p each

spare 6v battery £1.20 7.5p 1000+LEDs 3mm or 5mm red or green ... 7p each yellow Ilp 0.22uf 250v polyester marl leads 15p each

each cable ties 1p each £5.95 per 1000, £49.50 per 7.5p 100+10,000 Polyymmlenpeklau, f3420802v8Ici (7timma MKP 10)

Rechargeable Batteries 75p eachAA (HP'7) 500mAH -£0.99 AA 500rriAH with solder 60p 100+AA 700mAH £1.75 tags £1.55 Philips 123 series solid aluminium axial leads - 33uf 10v &C 2AH with solder C(HPI I) 1.2AH £2.20 2.2uf 40v 40p each

£3.60 D(HP2) 1.2AH £2.60 25p 100tD 41'11' with solder PP3 8.4V 110tnAH .-£4.95 Philips 108 series long life 22uf 63v axial 9013 each

tags £4.95 Sub C with solder 15p 1000+1/2AA with solder £2.50 Multilayer AVX ceramicspacitors all 5mm pitch 100v

tags £1.55 1/3 ACM tags (Philips 100pf, 150pf, 220pf, 10,000pf (10n)AAA (HPI6) CTV) £1.95 10p each 5p.....100+ 3.5p.....1000+

ISOrnAH £1.75 500pf compssion trimmer 60pStandard charger charges 4 AA cells in 5 hours or 4Cs or 40 of 370varec motor start capacitor (dialectrol type contain -

Ds in 12-14 hours 4. I xPP3 (1, 2, 3 or 4 cells may be ing no pcbs) £5.95 or £49.50 for 10charged at a time) £5.95 Solid carbon resistors very low inductance ideal for RF

High power charger as above but charges the Cs and Ds in circuits- 27ohm 2W, 68ohm 2W 25p each5 hours. AAs, Cs and Ds must be charger! in 2s or 15p each 100+4s £10.95 We have a range of 0.25w, 0.5w, lw and 2w solid carbon

Nickel Metal Hydryde AA cells high capacity with no resistors, please send SAE for listmemory. If charge! at 100ma ard discharged at P.C. 400W PS1.7 (Intel part 201035-001) with standard250ma or less 1100mAH capacity (lower capacityfor motherboard and 5 disk drive connectors, fan andhigh discharge rates) £3.75 mains inledoudet connectors on back and switch on

Special offers, please check for availability. the side (top for tower case) dims 2 I2x149x149mmStick of 4 42x16mm Nirad batteries 171x16mm dia with excluding switch £26.00 each

red & black leads 4.8v £5.95 £138.00 for 65 button cell 6V 280mAh battery with wires (Nana MXI80 Digital multimeter 17 ranges 1000vde 750vac

5x250DK) £2.45 2Mohm 200mA transistor Hfe 9v and I.3v batteryShaded pole motor 240Vac 5mm x 20mm shaft 80 x 60 x test . £9.95

55mm excluding the shaft £4.95 each AMD 27256-3 Eproms £2.00 each £1.23 100+115v AC 80v DC motor 4x22mm shaft 50mm dia x 60 long Inmac delux ants -glare static control papal window size

body (excluding the shaft) it has a replaceable thermal' 228x161mm, overall size 264mmx200mm held to thefuse and brushes £4.95 each (£3.95 100+) monitor with hook & loop tape pads__ ...... £7.93 each

7 segment common anode led display 12mm £0.45 DIP switch 3PCO 12 pin (ERG SDC.3.023) .. ..... .... 60p eachLM337k TO3 case variable regulator £1.95 40p 100+

£1.44100+ Disk drive boxes for 125 disk drive with room for a powerGaAs FET low leakage current 58873 £12.95 each supply, light grey plastic, 67x268x247mm

f9.95 10+, £7.95 100+ £7.95 or £49.50 for 10BS250 P channel mosfet £0.45 Hand held ultrasonic remote control .... ........... .... ...... .f3.95BC559 transistor £3.95 per l00 CV2486 gas relay, 30x10mm dia with 3 wire terminals, willBC547A transistor 20 for £1.00 also work as a neon light 20p each741.105 hex invertor £10.00 per 100 £7.50 per 100

All products advertised are new and unused unless otherwise stated.Wide range of CMOS TEL 74HC 74F 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 2BHAccessNisa Orders (01246) 211202 Fax: 550959

callers welcome 9.30am to 5.30pm Monday to Saturday


System Components from IS09001 SourceHalf Size ISA Single Board Computers

386SX-40 to 486DX4-100 with PC/104, 2 Serial PortsIDE & FDD & Printer Port

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

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

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

System Enclosures with Passive BackplanesColour & Mono Flat Panel LCD Displays

System Integration and Support

ChanaosBS6 6PE

'al: 0117 973 0435923 7295

40SISO

CIRCLE NO. 133 ON REPLY CA RD

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 2.60 1.80 628128LP-85 8.30 7.20

27C128-15 2.40 1.80 62256LP10 3.60 2.8027C256-15 2.20 1.70 6264LP-10 2.60 1.75

27C512-15 2.20 1.70 MM58274CN 4.90 3.75

27C010-15 3.95 2.80 ULN2003A 0.43 0.30

27CO20-15 6.00 4.25 7805 0.32 0.25

27C040-15 8.60 6.45 MAX232 1.35 0.88

80C31-12 2.10 1.95 7406 0.35 0.23

8255AC-2 2.00 1.45 7407 0.35 0.23

Z80A CPU 1.80 1.00 74HC244 0.35 0.24

LM317T 0.50 0.40 74HC245 0.35 0.24

75176BP 1.35 0.85 74HC373 0.35 0.25

68w 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, England CR8 4HA

Tel: 0181-668 7522. Fax: 0181-668 4190.

EMBEDDED C

ASSEMELYSIMULATION

G compiler, first released in 1991, now features:Easy to use interrupt support with register bank switchingIEEE floating point arithmeticIEEE 695 source level debug outputIntegrated relocatable assembler

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

eg000Our first G compiler/assembler package

now supports floating point arithmetichas been widely adopted by many OEM's to support their68000 and 68307 hardware

CP1122

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

Now supports -the GRJ3268881 co -processor supportIEEE 095 source level debug output

Further information from:CROSS WARE PRODUCTSStJohn's Innovation Centre, Cowley Road, Cambridge, CB4 4WS , UKTel: +44 (0) 1223 421263, Fax: +44 (0) 1223 421006BBS: +44 (0) 1223 421207 (8-N-1), Internet: salesecrossware.com

CIRCLE NO. 1.64 ON REPLY CARD

March 1996 ELECTRONICS WORLD+WIRELESS WORLD

CIRCLE NO. 1.35 ON REPLY CARD

241

CIRCUIT IDEAS

Programmablefrequency divider

used to form avoltage -to -time

converter, inwhich output

period representsinput voltage.

High -power, isolated switchThis switching circuit is controlled

by logic -level input, handles highpower and the output is isolated fromthe control circuit.

Optical isolation is normal, but aseparate supply would have beenneeded for the mosfet drive; for thatreason, a transformer provides theisolation, since drive is now providedby the control circuit.

Output from the oscillator /C1(a) is

ICI 4093Tri, Tr2 PN3643Tr3 PN3645

gated by /C1(b) in response to theinput. Transistor Tri and the outputstage Tr2,3 drive the transformer,which is on a small ferrite toroid, itssecondary providing the mosfet drive,after rectification by the schottkydiodes, which have a low forwardvoltage. The 560Q resistor presents alow source impedance for rapidmosfet switching.

Keep the transformer primary and

+12v

+12v

Transformer core: High permeability ferrite ring, 15mm dia.Philips 4322-020-97060, IA = 5,000

Tr2

470nPolyester

15T 30T

2n7

56R

Power switch is transformer isolated and responds to logic -level input.

secondary well separated for a highbreakdown voltage; leakageinductance is unimportant, sincelosses can be offset by an increasedturns ratio.

Phil DennissDepartment of Plasma PhysicsUniversity of SydneyNSWAustralia

4 x BAT85

Programmable voltage -to -time converterReset

Divide -by -n inputDoCioBioAi°

Counter(7493) o OLKin

R C

Divide -by -n input

MSMV(74121)

Divide -by -nclock output

8 -bit

Analogue in 8 -bit

a -to -d

converter

programmablefrequency

divider

Divide -by -n output0

0

Switchcontact

Switchcontact

As a step towards a v -to -tconverter, Fig. 1 shows a

programmed frequency divider thatproduces an output frequency of f;,,divided by the binary input, alsogenerating a repetitive outputsequence depending on the binaryinput.

The circuit shows a four -bit circuit.Clock signals drive the counter,whose output at some point coincideswith the binary input, coincidencebeing detected by the gating circuit,which produces a rising pulse edge totrigger the 74121 multivibrator for awider pulse. Timing components arechosen to cover the duration of theclock period. Output, the clockfrequency divided by the binary input,consists of the Anded clock andmultivibrator output.

To form a voltage -to -timeconverter, use an 8 -bit circuit of theform in Fig. 1, as shown in Fig. 2,where the 8 -bit analogue -to -digitalconverter provides the binary input tothe frequency divider. Output is theperiod of the divided clock frequency,which corresponds to the inputvoltage of the a -to -d converter.K BalasubramanianCukurova UniversityAdanaTurkey


Just Take Two StepsYour MeasurementSTOP

COPE

Complete setHS508 for £ 597.00

You can simply plug the new TiePieSCOPE - HS508 into the parallelport of your portable or desktop PC. With the advanced software,you can use this two channel, 8 bits, 50 MHz measuring instrumentas a fast digital storage oscilloscope, including a lot more featuresthan a single oscilloscope! Moreover, the TiePieSCOPE - HS508 con-tains a multiple display voltmeter (up to 5 MHz true RMS), a spec-trum analyzer with an harmonic distortion meter and a transientrecorder for recording a variety of signals.The TiePieSCOPE - HS508 is supplied complete with user manual,software, and two probes.

Call now for a free demo diskette and our catalog!!

TiePie engineering (UK)28 Stephenson Rd, Industrial Est., ST. IVES, CAMBS PE17 4WJ

Tel.: (01480) 460028 - Fax: (01480) 460340

TiePie engineering, The NetherlandsP.O. Box 115, 8900 AC LEEUWARDENBattenserreed 2, 9023 AR JORWERD

Tel.: (31) 515 415 416 - Fax: (31) 515 418 819

COMPONENTS

Coaxial cableThere's a variety of coaxialcable and connector typesavailable. Nick Wheelerdiscusses how to choosethe right combination.

The simple, flexible, laboratory connectoruses one of a small number of cabletypes. Some 49 types are listed in the

American Radio Relay League (ARRL) hand-book. These vary widely in overall diameterand performance. This article is intended tohelp in selecting the right type of cable,together with appropriate end connectors.

General considerationsWhile a coaxial connector assembly has muchin common with a good -quality screenedaudio connector - and is often used for thispurpose - it is designed for use as a radio -fre-quency transmission line. Its characteristicimpedance, Z0, is proportional to logb/a,where b is the inner diameter of the outer con-ductor and a is the outer diameter of the innerconductor. If a coaxial connector assembly isdriven from a source whose output impedanceis Z0 and terminated in Z0, then the input sig-

vcc5V

2MHzTTL

vcc5V

Hex inverter74AC11004

300R(6)

nal will appear almost unchanged at the ter-mination.

There will be a slight reduction in amplitudedue to losses, and the signal will be delayedby the time it takes to traverse the length ofthe line. This is longer than the time taken totraverse the length of the line in free space.Thus in free space the velocity of propagationis some 30cm/ns whereas in typical lines it is20-27cm/ns.

Coaxial structuresThe centre conductor of a coaxial cable maybe solid or stranded. For anything other thanpermanent fixed installations such as televi-sion down leads, stranded types are essential.All other things being equal, a solid conductorwill be slightly less lossy than a stranded one.

Air is the ideal insulator, but this can only beachieved over short lengths. Next best is air -spaced PE (polyethylene). Suitably spaced PE

16R66

(3)

Short lead (9cm)

Cable under test

Note: 5012 terminations should be as closeas possible to oscilloscope CH1 and CH2 inputs

50R

CH1s-1 input

em CI -42input

50R

Fig. 1. Simple circuit providing a reliable 500, 1 Ons pulse source for assessing the performanceof a transmission line. Connecting a 100MHz oscilloscope provides good test results.

Table 1. Velocity factors of commoncoaxial cable insulators

Air space PE washers 0.89Air space PE voids 0.86Foam PE 0.79-0.80Solid PTFE 0.7Solid PE 0.66

washers keep the central conductor in positionIn a different form of air spacing, the insu-

lator has longitudinal voids so that in crosssection it looks like a spoked wheel. This isvery nearly as good as the washer approachand is much cheaper to make. It is commonlyused for satellite down leads, and also for tvdown leads.

Down leads used for reception usually havea Zo of 750. This can be shown to be lesslossy than otherwise physically similar 5052cable. The lower impedance cable has betterpower handling capability and is nearlyalways used for transmitting and receivingapplications. It is also easier to match 755Icable to typical antennas.

Next in order of merit is foam PE, followedby PTFE and finally the cheapest - solid PE.Velocity factors associated with these materi-als are shown in Table 1.

There are three types of outer conductor.The first is a solid metal tube, invariably ofcopper, and in large sizes over 1 cm, corrugat-ed. Clearly such cables are not designed to beflexed repeatedly.

The next - and the most common - typeuses copper braid, sheathed with PVC to min-imise corrosion and damage.

Braided sheath is not completely leak -proof.Small amounts of power can escape and beradiated, constituting a loss and possibly anEMI problem. Also, strong incident radiationmay permeate the cable, causing interference.

Cables are available which include a layer ofcopper foil wound without gaps between thebraid and the insulator. These can achieve sig-


COMPONENTS

nificantly better performance than braid -onlycables - but at considerably higher cost.

Limitations of coaxial cableCoaxial cable has an upper limit of usable fre-quency other than that imposed by insulatorlosses. This is due to higher order propagationmodes, analogous to those found in waveg-uides. These set in at wavelengths shorter than

k=rc(a+b)/(2\1K) (Ref. 2)

Where K is the dielectric constant of the insu-lator.

Applying this, approximately, to RG58cable, which is commonly used for laboratoryhook-up connectors, gives,

a= lmmb=2.92mmK=2.3 for PE

As a result, A, is 4.06mm, or about 65GHz. Itis unlikely that this phenomenon will beencountered in ordinary laboratory work. Notethat in some electronic warefare searchreceivers, this may be a frequency of interest.Applying this formula to PTFE-insulatedRG405 cable yields a slightly higher frequen-cy, and is specified to 18GHz.

There is another limitation, more likely to beencountered, but only in connection withtransmitters or other high power rf sources. Aswe are dealing with transmission lines, mis-match will produce current and voltage nodes

along the line. Under extremeconditions these can lead to voltage break-down or local overheating.

An open circuited line is just as liable tocause damage as a short-circuited one.

Connectors for coaxial cablesThree main professional series of connectorsare SMA, BNC and N -Type. Electrically,TNC is a close equivalent to BNC. The SMBand SMC series are miniature SMA types, butnote that SMB connectors are not positivelyretained. A circular spring provides a weaklyretained push -fit action, useful for laboratorywork.

Ideally, the following examples should notbe chosen for rf work.

UHF connectors: poor performance in allrespects. Phono: as the name implies, these areintended for audio but often used for video. Television down -lead types: these are not agood choice. Most rely on a solderless con-nection between the centre conductor and thetubular centre pin.

There is a comprehensive range of 'Inter -series adaptors'. These allow you to accessvirtually every type from BNC.

The full range of BNC accessories and con-nectors is only available in 500 form, but themore commonly used parts also come in 750form. These look identical, except that the5052 plug and socket is slightly larger than the

World's smallest surface -mountcoaxial connectors

..,

B C 6

.Designed for use in communications applications, these ultra -miniaturelow-cost SC connectors require only 1 1.5mm2 of board space and standno more than 3mm high when connected.

These 5052 Murata connectors accept two coaxial cable diameters of0.8 or 1.2mm and their maximum vswr is 1.2 in the DC to 3GHz range.Maximum contact resistance is 15mi2 while minimum insulation resis-tance is 500M52.

750 alternative. Note that mixing connectorsof different impedances can cause damage.

In addition to the wide range of adapters,there are Zo terminators. These can be either`stop end' or 'through' types. The latter cansave a lot of trouble when terminating at, say,an oscilloscope input. In addition 'through'attenuators are available.

Crimped cable attachments are quick andsimple. Provided a cable strain relief is usedthese terminations are also durable. Clamptypes impose only gentle forces on the outerbraid and a good life is obtainable without theneed for a strain relief. If a fault does occur,the connector can be disassembled andremade.

The most common clamp and crimp con-nectors suit 5mm cable outside diameter. Thisshould be regarded as the default size.Stripping coaxial cable is a difficult processbut special tools are available.

Crimp tools cost upwards of £70. Such toolsform the sleeve into a uniform hexagonalshape. Much cheaper tools designed for fittingspade -type connectors to power cables will notsuffice.

N -Type connectors appears on equipmentintended for use above 1GHz. The Type 1 canonly be used with URM67 or RG 213U cable.They are both reasonably flexible at 10.3mmoutside diameter.

For laboratory bench use the Type 2 freeplug can be used with 5mm URM43 or URM76. These parts are specially made to intro-duce the minimum possible 4 discontinuities.They are characterised up to 10GHz.

SMA connectors are physically small andare available in crimp or clamp form. They arealso made for assembly by soldering toRG402 and RG405 semi -rigid cable. In thisform of assembly they are rated up to 18GHz.

Much of the circuitry of professional equip-ment operating above 1GHz consists of mod-ules. These modules are often from differentmanufacturers, neatly plumbed together withsemi -rigid coaxial cable and terminated withSMA connectors. The small size of these con-nectors often justifies their use in lower -fre-quency applications.

There are several useful parts in the SMA,series intended for direct mounting on pcbs.These can be used to provide detachable linksto front -panel mounted connectors.

Testing for performanceIn my view, there is no better way of testing atransmission line than feeding it with a pulsesourced from the correct Z0 and observing theeffect across a correct termination at the otherend. A 100MHz or better oscilloscope isadvisable to avoid measurement errors.

There are many sources of suitable pulses. Iused a variant of the circuit on page 61 of EW,Jan. 96. This is the box marked PG on Fig. 1.

A logic -one pulse of less than lOns durationin response to ttl drive is needed. A problemhere is that a single logic gate cannot drive a500 line directly. The device used must beable to sink or source 100mA.

In Fig. 1, PG produces logic -one pulses ofabout lOns duration at a pulse -repetition fre-quency of 2MHz. These are applied to all six


COMPONENTS

Fig. 2. Test results for a length of PTFEinsulated miniature coaxial cable. Uppertrace, input signal of approximately 1.2V.Lower trace, showing acceptable results: aloss of 0.37dB and delay of 5ns.

inputs of a hex inverter. The outputs are allparalleled via 3000 chip resistors.

Making the assumption that the outputimpedance of a gate in the one or zero state iszero, we then have a 5052 source. A possiblepart is 74AC11004.

A 74AC004 will also suffice. If it is loadedwith 500, the transmitted signal will beinverted with a peak amplitude of lice/2. Thisis passed down a short length of 500 line to aresistive splitter comprising a star connection

of three 16.66611 resistors (3x5051 in parallel).One of the two outputs feeds an oscilloscopeinput in parallel with a 50f2 termination. Thesecond port goes to the connector assemblyunder test. The other end of the assemblyunder test feeds the other oscilloscope input,where it is properly terminated with 5052.

Figure 2 is the result of such a test, on an87cm length of FIFE insulated miniaturecoaxial cable terminated with SMA 'free'plugs. The upper trace is the input and is of apeak amplitude of I.2V. This result is close toVice/4, accounted for by the effect of the par-alleled matching resistors and the splitter.

The output has a peak amplitude of 1.1V,representing a loss of 0.37dB, or 4.3dB/10m.This falls between the 3.6dB/10m at 100MHzand 19dB/10m at 1000MHz quoted for thiscable, which seems reasonable.

There is a delay - estimated at 0.4ns -between the output of the splitter and thechannel -one input of the oscilloscope. Thismust be added to the 5ns delay scaled fromthe oscillogram.

Making the necessary corrections leads to avelocity factor of 0.53, which is too low forthe known figure of 0.7 for PTFE. However, itis near and making measurements to an accu-racy of ins with a 100MHz oscilloscope isquestionable anyhow.

In any case the cable is clearly fit for labo-ratory use. Undulations in the upper trace areobviously due to reflections. The amplitude ofthese undulations is approximately 0.1 that of

the main pulse, suggesting a standing waveratio of about 1:1.2, which is normallyinsignificant.

In summaryAlthough there is a bewildering array ofcables, plugs and sockets available, newdesigns should be based on the SMA, BNCand N -Type connectors. As for the cable, thisshould be RG174A or RG316/U, which suitSMA and appropriate BNC types.

Unless compactness is important, thenURM76 or the slightly cheaper RG58C, 5mmoutside diameter, are the cables to choose.These suit BNC clamp and crimp connectorsand also N -Type, type 2 free plugs. All otherN -Type free parts require the use of URM 67or RG213U. Most other cable sizes upwardsof 5mm outside diameter can be terminated inBNC, but none of these has any pronouncedadvantage over those already mentioned.

There are 75S2 cables specifically intendedfor television and satellite down -lead applica-tions. A limited range of BNC plugs and sock-ets are available in 75f form. Almost all 750cables are solid -core, intended for one-offinstallation.

Further readingAmerican Radio Relay Handbook. (A good sourceon this subject, held in the reference section of mostlarge libraries)Services Textbook of Radio, Vol 5 (Long out ofprint, but good on line theory).

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NEW PRODUCTS C_ASSIFIEDPlease quote "Electronics World" when seeking further information

ACTIVEDiscrete active devicesHigh -voltage igbt. The first device tobe available from Motorola's non-punchthrough, high -voltage, insulatedgate bipolar transistor family will bethe MHPM1A1200A120C5, which willcost about $1000 in small quantities.The family will contain devices ratedat up to 1200A at 1200V and isintended for motor drives, powerconversion and welding. Thepackage consists of a copperbaseplate with multiple coppersubstrates; since these devicesexhibit a positive temperaturecoefficient, they can be paralleled forhigher currents, so that a number ofmodules can be produced using onlya few, smaller, die sizes. MotorolaInc. Tel., 001 602 244-3831; fax, 001602 244-6002.

Digital signalprocessorsAudio processor. TDA1548T fromPhilips is an audio processorincorporating Bitstream filters fordigital de -emphasis, volume and tonecontrol, with Bitstream d -to -as andheadphone amplifiers, providing asingle -chip solution to all thefunctions needed for CD, MD andDCC personal stereo players. It iscompatible with I2S or Isb-justifiedserial input data and puts out a1.7Vpk-pk audio signal into 32G.Gothic Crellon Ltd. Tel., 01734788878; fax, 01734 776095.

Electronic trimmers. AKMAK9813/9844 are single -chipelectronic trimmers for voltage controlinput, replacing mechanical types oreeprom/multiple d -to -a circuitry. 9813has 12 channels (9844 four), controlbeing effected by a simplemicrocontroller. Output range isground to supply voltage and there isa power -down mode. DIPInternational Ltd. Tel., 01223 462244;fax, 01223 467316.

Linear integratedcircuitsVideo d -to -a. SAA7167YUV-to-RGBvideo digital -to -analogue converter isan addition to Philips's Desk -Top -Video chipset and converts digitalvideo to analogue rgb, mixing theoutput with an external analogue rgbchannel to merge digital videosources with standard VGA graphics,thereby doing away with the need toaccess the computer's frame storememory. Together with the SAA7131FMPEG decoder the new chip allows

the production of cheap videoplayback cards for Pcs. In addition,the chip will handle various inputformats, on -chip colour keyingbetween video and rgb inputs, I2C-bus control and direct drive to amonitor. Philips Semiconductors(Eindhoven). Tel., 00 31 40 722091;fax, 00 31 40 724825.

High -current driver. Driving high-speed signals into low -impedanceloads, Analog's AD815 driver hasdifferential input and output, enablingit to replace multi -chip designs inasynchronous and high bit -rate digitalsubscriber links and other twisted -pair cable driver functions, as well asin video distribution. Output is 400mAat 40Vpk-pk differential and thedevice will deliver up to 1Apk. AnalogDevices Ltd. Tel., 01932 266000; fax,01932 247401.

Memory chipsFast srams. EDI's snappily namedEDI8F32128LPBAC is a low -power,55-100ns, 128 by 32 sram in aJEDEC 68 -pin pack. It is pin -compatible with the EDI17F32128flash unit, but has a battery backupand an industrial -temperatureversion. EDI (UK). Tel., 01276472637; fax, 01276 473748.

Microprocessors andcontrollersLow-cost, 64 bits. IDT's OrionR4640 embedded microprocessor,available in 80MHz, 100MHz and133MHz versions, is designed for 64 -bit performance 'at a 32 -bit price',having a 64 -bit core and 32 -bitinterface. Its features include a two-way associative, 8Kb instructioncache, an 8Kb data cache, powersaving, a static core and waitinstructions for stand-by. Speed ismeasured at 175dhrystone.Associated chips are the 84761memory controller and R4762 PCIbridge. Integrated DeviceTechnology. Tel., 01372 363734; fax,01372 378851.

6x86 100MHz processor. The Cyrix100MHz 6x86 superscalar,superpipelined processor is availablefor immediate delivery. It wasformerly known as the MI processor,is compatible with the x86 instructionset and shows a benchmarkperformance figure of 678 on theNorton System Information v8.0, saidto be considerably in excess of thatfor the 133MHz Pentium. Flashpoint,the supplier, also offers amotherboard from DTK with up to128Mb of ram, three PCI slots andfive ISA slots. Flashpoint Technology.Tel., 01753 538715; fax, 01753538733.

PASSIVEPassive componentsS -m electrolytics. Sanyo's SMSeries OS -CON surface -mountedelectrolytic capacitors are meant forautomatic insertion and reflowsoldering. They use an organicelectrolyte, which affords a lifeexpectancy of 220 years (!), afrequency range approaching that offilm types, self regeneration afterexcessive loads, low esr and stableleakage current. Values are 1-150pFat 6.3-20V, the largest can size being8.8/8.8/13mm. Inelco Ltd. Tel., 01734810799; fax, 01734 810844.

Uhf chip capacitors. Syfer high -0surface -mounted chip capacitorscover the 0.47pF-1nF range, a 10pFcomponent in the 0805 size taking up2mm by 1.2mm of board space,although rated at 100V and having a±5% tolerance. Esr at 1GHz is 0.2G;Q at this frequency is 50 and rises to200 at 100MHz. Flint Distribution.Tel., 01530 510333; fax, 01530510275.

Accurate Al -foil capacitors. Resin -dipped aluminium -foil capacitors fromSang Jing are claimed to be the idealreplacement for tantalums, nowexperiencing a shortage, since theyhave tight specifications, have goodtemperature characteristics and arereliable. Leakage current is 0.01CVor0.5pA, whichever is larger; workingvoltages are 6.3-50V; and values 0.1 -

Optical devicesBlinking leds. Elcos offerssurface -mounted leds thatblink and four -pad multicolourtypes - the CR range, all onceramic substrates. Blinkingversions contain a blink iswhose frequency is trimmableby resistance or capacitance.All types have a wide viewingangle and a flat -top packagefor use in light -pipeapplication. There are also thered green blue types which,when correctly driven, willdisplay any colour, includingwhite. Flint Distribution. Tel.,01530 510333; fax, 01530510275.

470pF in tolerances of 10% or ±20%.Europa Components & Equipmentplc. Tel., 0181-953 2379; fax, 0181-207 6646.

Precision ceramic capacitors. NPOmultilayer ceramic capacitors offervery narrow tolerances for use inimpedance matching in hfcommunications equipment. Newproduction techniques have reducedthe cost of these devices and thisseries provides tolerances of ±0.1pFin values of less than 2.7pF, with±0.05pF available on request. Theyare suitable for wave or reflowsoldering. Philips Components. Tel.,00 31 40 722790; fax, 00 31 40724547.


NEW PRODUCTS CLASSIFIED

Please quote "Electronics World"when seeking further information

Cermet trimmer. BI Technologiesintroduces the Model 23 Series of4mm surface -mounted, single -turncermet trimmer pots in sealedpackages, which withstand infrared orconvection reflow processing andcleaning. T -cross slots are providedfor adjustment and the devices comein both J -hook and gull -wing styles.Standard range is 100-2M0 at 20%tolerance. BI Technologies Ltd. Tel.,01384 442393; fax, 01384 440252.

Audio productsCeramic speaker. Meant for use incellular telephones, Pedoka's ST-20PR piezoelectric speaker has asensitivity of 104dB±2dB at 1kHz,1Vrms at the input and 1.6k0 seriesresistance. It is 2.1mm thick and21mm in diameter and has an HPseries connector on 30mm of 32awgwire; other connectors can besupplied. Pedoka Ltd. Tel., 01462422433; fax, 01462 422233.

Notebook audio. From IBM, thePCMCIA Advanced AudioAdaptor, a PCMCIA device toadd good quality stereorecording and playback toportable computers with a TypeII expansion port. It providesoutput to headphones orspeakers, accepts joystick inputand has an electret microphonefor recording; it is compatiblewith most games that needSoundblaster support. DIPSystems. Tel., 01483 202070;fax, 01483 202023.

HardwareEmc racks. Barton Engineering has arange of emc racks for bestperformance at 1GHz of 70dB. Theyhave full-length, lockable metal doorswith detachable hinge pins and four -point locking; and drilled air waveguides for up to four fans. Theseracks consist of only ten parts. Rfiseals are beryllium copper, low -compression, clip -on contacts on thedoors and monel mesh on the sides.Finish is textured paint over nickeland the frame is nickel -plated. BartonEngineering and Export Ltd. Tel.,01227 272141; fax, 01227 771653.

Test and measurement150MHz digital oscilloscope. HitachiDenshi's newest digitisingoscilloscope, the VC -7524, has abandwidth of 150MHz and samples at100Msample/s on each of fourchannels simultaneously. Memory is2Mbyte per channel. Additions to thefacilities of its forerunner, theVC -7124, are long and split memory,compressed display, 4000 timesmagnification, storage of 2000triggered events, single -shot andslow -roll modes and glitch function toenable amplitude and time frame ofan event to be measured. In the longmemory mode, the whole 2Mbytememory is compressed and displayedto a screen capacity of 1Kbyte. Otherfeatures, too numerous to mentionhere, are incorporated. Hitachi-Denshi(UK) Ltd. Tel., 0181 202 4311; fax,0181 2022451.

A/d multimeter. Two ranges ofhandheld multimeters by AVO have adual display to give simultaneousviewing of volts/frequency,current/frequency, conductance andresistance. Two models in the M7000series are in tough cases withrubberised holsters for industrial use,one of them being of 0.2% accuracyand the other 0.3%, with a switchablechoice of 4000 or 40000 counts.M8000 models provide true rmsdc+ac and ac voltage readings andboth are accurate to within 0.08%.Capacitance and diode test areincluded on all models. AvoInternational Ltd. Tel., 01304 502101;fax, 01304 207342.

Digital handheld multimeter. Di-loG'sDL -297T is a 400 -count digitalmultimeter with a 43 -segment bargraph and a X10 zoom. It autorangesto provide V, I, R, true rms, frequency,temperature, continuity and diodetesting capability. Accuracy whenreading voltage is within ±0.3% +1digit. Facilities are offered for max/minmeasurement against storedreferences. Di-loG Ltd. Tel., 01707375550; fax, 01707 393277.

Digital delays. An improved versionof the 9650A Digital Delay Generatoris announced by EG&G. There is a

better communications link and a newpanel with an alphanumeric display; ashut -down memory retains currentsettings. Trigger is internal or externalto 2MHz and produces fourindependently variable delays fromzero to 100ms and two differenceoutputs; pulse widths are 30ns-1ms.A "scan" mode produces increasingdelays and a burst of pulses can begenerated. EG&G Instruments Ltd.Tel., 01734 773003; fax, 01734773493.

Thermal imager. ThermaCAM is asmall, portable infrared imager fortesting boards, components andassemblies. It uses a focal -planearray camera, has a 256 by 256 pixeldisplay in colour, 12 -bit digital storagein PCMCIA cards, colour viewfinderand interchangeable lenses. Video orTIFF files can be sorted and viewedinside the camera and the softwareallows Windows -based analysis. Thecamera array is maintained at aconstant temperature by amicrocooler. Inframetrics InfraredSystems Ltd. Tel., 01256 50533; fax,01256 50534.

Transducer calibration. For therapid calibration of transducers, HBMhas the DMCplus Digital MeasuringAmplifier, with which the inputquantity and output signal areprocessed to present on a PC screenthe calibration curve, using HBMsoftware. The curve is printable andsaved as archive. HBM UnitedKingdom Ltd. Tel., 0181-420 7170;fax, 0181-420 7336.

Flatbed recorders. Yokogawa'sLR120 Series of flatbed recorders areavailable with one or two pens andonly take up 320 by 323mm of benchspace. Chart width is 200mm andrecording speed is selected orprogrammed in the 1cm/h-60cm/minrange. Input is 1 mV fsd to 300V dcand versions are available for currentmeasurement, ac and temperaturemeasurement. Operation is Y/T orX/Y and an RS 232 interface allowsremote control and data logging, a

Multi -purpose tools. Three verydesirable SOG toolkits fromJensen. The Paratool is the topone, with pliers, wire -cutter, file,awl, knife blade, serrated blade,scale and a can -opener, all in onefolding tool. The other two,Toolclip and Micro Toolkit arescaled -down versions withscrewdrivers, but they all fold upvery small. So far as we areaware, they are not associatedwith the Swiss Army. JensenTools. Tel., 0800 833246 (free);fax, 01604 785573.

software package giving viewing andanalysis by PC. Martron InstrumentsLtd. Tel., 01494 459200; fax, 01494535002.

LiteratureCPC. Combined PrecisionComponents has produced a monthlyproduct supplement and a weeklyoffer list of 20 pages containingdetails of reduced prices. The 1996catalogue of 1600 pages is alsoavailable. Combined PrecisionComponents plc. Tel., 01772 654455;fax, 01772 654466.

Electrospeed. Connectors are amajor content of Electrospeed's newcolour catalogue, including those fromMolex, Cinch, Hirschmann, Thomas &Betts and Multi -Contact. Otherincreased sections are those for emcand filtering, batteries and chargers.Electrospeed. Tel., 01703 644555;fax, 01703 610282.

IDT. Company and product data fromIDT now comes in a number of ways:CD-roM; WWW; and fax. The CDuses Adobe Acrobat to display andprint pages, including data sheets; theWeb (http://www.idt.com) presentsalmost as much data and is updateddaily, more information being alsoretrieved using anonymous ftp toftp.idt.com/docs/docid.ext. Sales areon [email protected]. For



Neanderthals not on line, there is Fax-on -Demand, offering all but manuals,which are too big. Call +1-408-492-8341. Integrated Device Technology.Tel., 01372 363734; fax, 01372378851.

Bruel & Kjaer. A 9 -page brochurefrom B&K introduces an 'integratedapproach' to the measurement ofsound and vibration and describes thecompany's capability in the softwarefield, which enables the production ofdedicated programs for specificapplication. Bruel & Kjaer (UK) Ltd.Tel., 0181 954 2366; fax, 0181 9549504.

PIC handbook. A new edition ofMicrochip's Embedded ControlHandbook for the PIC 16/17 family offield -programmable, eight -bitmicrocontrollers and memory isavailable. It includes over thirty newand revised application notes andsoftware code for specificapplications. There are alsoschematic and timing diagrams andmaths routines. Arizona MicrochipTechnology Ltd. Tel., 01628 851077;fax, 01628 850259.

Snap switches. Cherry has a newpublication describing the DG range ofsnap switches, which measure 12.8by 5.8 by 6.5mm and switch up to 3A

Automatic cable cutter. Mil-Tech's Autocutter is aprogrammable, self -feedingcable, wire and extrusion cutterthat takes material up to 100mmwide, including ribbon cable,thin wire, plastic extrusions andrubber mouldings, specialsections being handled bycustom versions of themachine. Requirements are asingle-phase supply andcompressed air at 80psi. Mil -Tech. Tel. and fax, 01477571864.

at 125Vac or 2A at 30Vdc. CherryElectrical Products Ltd. Tel., 01582763100; fax, 01582 768883.

Fluke. The 250 -page 1996instrumentation catalogue from Fluke,is now available free. The company'sproducts cover a very wide range ofmeasuring instruments, latestadditions being the Multi -productcalibrator and a range of digitalstorage/analogue oscilloscopes in theCombiscope range. Fluke UK Ltd.Tel., 01923 240511; fax, 01923225067.

MaterialsCleaning solution. Electrolube has anew solution, Printasolve, to removeink from surfaces such as printerrollers, ink jets and franking machines.It is effective for solvent and oil -basedinks, is economical in use and posesno threat to the ozone layer. Availablein 400m1 aerosols, it is sprayed onto acloth or bud and applied to thesurface, following which anElectrolube Air Duster helps drying.Electrolube Ltd. Tel., 01734403014/031; fax, 01734 403084.

Production equipmentSolder -wave measurement. FromAlpha Metals comes the Solder WaveOptimiser, a portable instrument tomeasure both board/wave data andtemperature in wave soldering. Datashown includes dwell time, immersiondepth, contact length and conveyorspeed, preheat, maximum minuspreheat temperature, maximumpreheat slope and maximum slopeover the wave. It also indicates wave -to -board parallelism, all data beingdown -loaded to a PC. The unit issimply passed through the solderingoperation and collects all the data inone pass. Alpha Metals. Tel., 01816656666; fax, 0181 6654734.

Fluid dispenser. I & J Fisnarproduces a finger switch fitted, bymeans of a Velcro band, to barrels,


cartridges and soft tubes, allowingprecise fingertip fluid dispensing fromthe company's DSPE 501A pressuredispenser as an alternative to themore common foot switch. lntertronicsLtd. Tel., 01865 842842; fax, 01865842172.

Pcb coordinate measurement.Maxtascan 100 coordinate measuringmachines by Graticules are claimed toreduce the time to check hole sizeand position by over 80%, or fromthree days to half a day. Since thesystem has a cad interface, raw datafiles may be used without editing ortranslation. With a bed size of 1msquare, the machine handles twoaverage board of 450 by 250mm,measuring the average 3000dimensions in two hours to within 25paccumulative and ±5p repeatability.Associated software is Windows -based. Graticules Ltd. Tel., 01732359061; fax, 01732 770217.

UV light source. The Dymax Light -Welder 3010 -EC is a high -power,high -intensity ultraviolet light sourcefor the curing of adhesives, coatingsand encapsulants. Either manual(pedal) operation by timer and foot -pedal or automatic via interfacing todial tables, turrets etc. is possible.lntertronics Ltd. Tel., 01865 842842;fax, 01865 842172.

Power suppliesElectron beam power. A new seriesof electron beam power supplies isintroduced by AP&T, the first beingthe Carrera V, a 5kV (less than 1%ripple) type for electron beamdeposition in film coating. Theswitched -mode design includes arcdetection and recovery, whichoperates within 3ms, rapidly enoughto leave constant emission control andmelt unaffected. An arc rate monitorprotects equipment in the vacuumchamber against multiple arcs. Nowater supply is needed, since the unitis air-cooled. Advanced Products andTechnologies Ltd. Tel., 01865724863; fax, 01865 725831.

Tactile keyswitch. TACT ECOfrom Secme is a low-cost tactilekeyswitch taking up only 6mmsquare of the board andstanding 4.3mm or 5mm off it.A moulded insert prevents fluxbuildup during soldering,Operation is momentary with aSharon click for touchfeedback; ratings are 12V and50mA, with a contact resistanceof less than 100m12. EAO-Highland Electronics Ltd. Tel.,01444 236000; fax, 01444236641.

50W dc -to -dc. Features of Abbott'sNB series of 50W dc -to -dc convertersare a total size of 1.5 by 3 by 0.4inand 90% efficiency. Outputs of 2-28Vare available from inputs of 14-40Vand interfaces for paralleling, sync.,enable/disable and 'power good' areincluded, different pin arrangementsbeing optional. Abbott Electronics Ltd.Tel., 01233 623404; fax, 01233641777.

LV dc -to -dc converter. FromSemtech, the SC1630CS low -voltage,120kHz step-up converter to driveexternal power switches in higher -voltage and power application. Onlysix further components are needed toform a step-up arrangement to obtainan 80% efficiency and a few more fora step-down type to give 86%efficiency at 2A and 300pA quiescent.Output voltage can be set internally to5V or externally to an arbitrary value.Input is 7V, switch -off current 105pA,shut -down mode current 7pA,stabilisation 0.6% V," and regulation2.5% V.). Semtech Ltd. Tel., 01592773520; fax, 01592 774781.

Sla chargers. In both rack -mountedand cased versions, the SM family ofchargers for sealed lead acid batteriescan also be used as power suppliesfor other equipment, thereby beingusable for powering pcs or floating12V and 24V batteries up to 100Ah.




They are protected and can be usedin series or in parallel to provide up to250W, under 1% ripple and with auniversal input in the 95-277Vacrange. Electrospeed. Tel., 01703644555; fax, 01703 610282.

Bench supply. CPX200 from ThurlbyThandar is meant for those who need0-35V and 10A, but not necessarily atthe same time. Output power of thisdual supply is 175W per output,maximum current being adjusted in aswitched -mode regulator as voltagedecreases; 35V at 5A to 17.5V at10A. Outputs work in constant -currentor constant -voltage mode with autocrossover and mode indication. Theycan be connected in series or parallel.Thurlby Thandar Instruments Ltd.Tel., 01480 412451; fax, 01480450409.

150W, rack -mounted. Weir has aplug-in, rack -mounted unit in a 3U by14HP panel containing a three -output,100W convection -cooled (150Wforce -cooled) supply, approved to allmanner of safety and emc standardsand working over the 90-254V inputrange with no tap changes. The HSS103 is completely enclosed, has apanel -mounted IEC socket, switchand mains fuse. Weir Electronics Ltd.Tel., 01243 865991; fax, 01243868613.

Power to the Pentium. Semtech'sMP60 series of 35W switching dc -to -dc converters have a connectorconforming to Intel's voltageregulator specification for the P6processor. They supply 10Acontinuously at 2.9V and additionalfunctions can include a 'Power good'signal, output enable and upgradepresent, and programmable outputvoltage from 1.5V to 3.6V. SemtechLtd. Tel., 01592 773520; fax, 01592774781.

40W/in3 dc -to -dc. UPM convertersfrom Amplicon Liveline use asynchronous rectifier buck regulatoroptimised for 5V inputs. Power andcontrol electronics are on separateboards to obtain improved thermalperformance and isolation of thecontrol circuitry from heat sources.The devices are meant to provide2.5-3.6V, fixed or programmable,from a 5V input at 40W/cubic inchpower density and 90% peakefficiency. Amplicon Liveline Ltd.Tel., 0800 525 335 (free); fax, 01273570215.

Radio communicationsproductsLinear amplifiers. Pacific AmplifierCorporation's range of rf linearamplifiers covers the 1MHz-2GHzrange and includes power amplifiersub -systems, power modules andlow-cost lab. amplifiers. The PAC205is a remotely controlled feedforwardbase station for the Special MobileRadio band of 935-940MHz, whilethe PAC221 is a broad -band gainblock for the 746MHz-930MHzcellular and telephony bands.Intermodulation is low at -60dBc and

-30dBc respectively, for outputpowers of 80W and 30W. AngliaMicrowaves Ltd. Tel., 01277 630000;fax, 01277 631111.

Microwave amplifiers. Wessex hasa new series of PCN and PCSmicrowave power amplifiers inmodular form, in instrument cases orin rack -mounted versions. Bandscovered are 1.805-1.880GHz or1.930-1.990GHz with a gain of 29dBminimum (gain in band ±1dBpk-pk)to give 43dBm output power. Theyare unconditionally stable andprotected against open or short-circuits and can be provided withcooling fans. Harmonics are 50dBdown; spurii -70dBc. WessexElectronics Ltd. Tel., 0117 9571404;fax 0117 9573843.

Protection devicesTransient suppression. For thesurge protection of low -voltagesemiconductors, from 2.8V to 4.5V,Semtech's four -layer enhancedpunchthrough diodes are said topossess advantages over siliconavalanche types in having a leakagecurrent of 10pA and capacitance of50pF. Esd protection is to 15kV, peakpulse current is 30A and maximumclamping voltage at 1A 4.3V, 4.9Vand 6.5V. Semtech Ltd. Tel., 01592773520; fax, 01592 774781.

Snubber diodes. Fast -recovery,high -power diodes by IR are intendedas snubbers for gate turn-offthyristors and possess a soft -recovery characteristic to avoidvoltage spikes and ringing, whichcause high power dissipation andmisfiring of the switch. Devices in theSD103 N-RXX - SD453 N-RXX setare packaged as studs and there areothers in disc form and as isolatedmodules. International Rectifier. Tel.,01883 713215; fax, 01883 714234.

Switches and relaysHI relays. Matsushita's RK/RG high -frequency relays have either one ortwo changeover contacts andimposes an insertion loss of less than0.3dB at 900MHz. Powerconsumption is 200mW - less whenpulse driven - and can be made tolatch with one or two coils. Size is20.2/11.2mm, standing off 9.7mm.Matsushita Automation Controls Ltd.Tel., 01908 231555; fax, 01908231599.

5GHz reed relays. Coto Wabash(US) offers a range of small, surface -mounted reeds handling 5GHzsignals with less than 60ps rise timeswith less than 0.2dB insertion loss at1GHz. Size is 9.3 by 4.6 by 4mm.Coil is for 5Vdc, is of 1500 resistanceand 10100 insulation resistance,giving a switching speed of under0.5ms. Contact rating is 3W. CotoEurope. Tel., (Netherlands) 0031 45320838; fax, 0031 45 320838.

Secure keyboards. Bangingrepeatedly with a hammer, whileunusual as a method of testing

1

electronic equipment, was used toprove Lucas's new membrane switchpanels, claimed to be 'vandal -proof'.Exposed areas such as bezel andkey tops, are of stainless steel;below is an elastomeric pad to sealthe membrane switch againstcleaning fluids, moisture and dust.The sub -panel is of injection -moulded plastic or a laminate of pcb,aluminium and/or stainless steel.The type of hammer is unspecified.Lucas Control Systems Products.Tel., 01535 661144; fax, 01535661174.

Photovoltaic relay. PVG612 by IR isa new member of its microelectronicphotovoltaic relay family, switchingup to 60Vac/dc at 1A (2A on dc) withonly 5mA drive. It is a single -pole,normally open switch, the outputHexfet being optically isolated fromthe control circuit. InternationalRectifier. Tel., 01883 713215; fax,01883 714234.

S -s relays. Solid-state relays inCrydom's PF range handle 10Armsat 40°C ambient. They are controlledby a logic -level signal and operatefrom 280-660V mains, being opticallyisolated to 4kV, VDE certified to EN60606-1 with UL approval. Inrushcurrent can be as high as 250A at adv/dt of 500V/ps. Crydom Europe.Tel., 0181 763 0550; fax, 0181 7630499.

Transducers andsensorsAbsolute shaft sensor. ControlTransducers has a range of absolutemeasuring sensors, which areeffectively industrial rotarypotentiometers using the Mystarplastic material for long life andreliability. A three -wire connection tothe controller is needed. Design issuch that axial and radial shaft play istaken up without effect on accuracy orlife. Control Transducers. Tel., 01234217704; fax, 01234 217083.

Waverider evaluation. GECPlessey's DE6003 digital radiotransceiver is now supportedby Waverider a DE6003evaluation kit, which consistsof two transceivers, a userguide and an installation disk.It connects to a laptop ordesktop computer via theparallel port and includesdevice drivers to allow usewith Windows for Workgroups,Novell Netware or any TCP/IPnetworking software. Theresult is a 2.4GHz frequency -hopping transceiver with arange of 200 feet in a typicaloffice, offering a 625kb!s datarate. Gothic Crellon Ltd. Tel.,01734 788878; fax, 01734776095.

COMPUTERComputer board -levelproductsVGA module. DatasoundLaboratories has a mezzanine modulefor the Chameleon credit -card -sizeembedded PC The CLIO-200 usesstack -through connection to the hostprocessor and provides 1024/768/16or 800/600/256 pixel resolution forcrts and also support for lcds, elplasma panels and colour stn, tft, lcd,el or plasma flat panels. Support forspecial types of display can beprovided. Datasound LaboratoriesLtd. Tel., 01462 675530; fax, 01462482461.

Fast analogue input. From PentlandSystems, the MPX203 40Msample/sanalogue input board, giving 8 -bitresolution on a ±1V analogue input.The board is configurable in softwareand supports both scanner andcontinuous acquisition modes.



Outputs from the on -board fifo andconverter are accessible at the VMEinterface. Pentland Systems Ltd. Tel.,01506 464666; fax, 01506 463030.

ComputersRack -mount computer. AMC offersthe AMC614 computer, which isintended to be part of ISA, PCI orEISA systems in telecomms orindustrial use, taking a choice ofPC/AT compatible backplanesincluding a 14 -slot ISA, a 14 -slot EISAor combination ISA/PCI or EISA/PCItypes. Advanced Modular ComputersLtd. Tel., 01753 580660; fax, 01753580653.

Industrial workstation. AWS-822from IMS is an industrial computerwith a 14in colour crt display andsealed front -panel membranekeyboard. It has eight 16 -bit ISA slotsand comes with 286, 386,486 orPentium processor, is adequately fan -cooled and has a disk mountingassembly for floppy and 1 in high harddrives. Integrated MeasurementSystems Ltd. Tel., 01703 771143; fax,01703 704301.

Portable workstations. LogicInstrument S.A. introduces the Tetrarange of portable workstations forindustrial and scientific use. Using

processors from 486DX2-66 to theP90, the computers have five full-length slots for ISA, EISA and PCIcards, three drive bays and eithercolour or mono screens. Chassis isplated aluminium for rfi and emiprotection, in an ABS outer case.Power comes from either mains or acar battery. Logic Instrument S.A.Tel., 0033 1 39 89 96 22; fax, 0033 134 28 00 50.

Data communicationsInfrared receiver. Unitrode'sUCC5340 BiCMOS, micropower itreceiver is the first of the Air Lightseries, incorporating a limiter toprovide a wide dynamic range inwhich it complies with the InfraredData Association requirements of1cm-1m. Bandpass filtering improvess:n margins for 2.4kb/s to 114b/soperation and reduces devicerecovery time, allowing directinterfacing with IrDA-compatibledetector diodes. Output drives a 40pFload at cmos/ttl level. Unitrode (UK)Ltd. Tel., 0181 318 1431; fax, 0181318 2549.

LocalTalk tx/rx. LTC1324 fromLinear Technology is a 5Vmicropower LocalTalk transceiver,taking 1 mA in use and 1 pA when shutdown. No emi filters are needed,

since the device possesses a 400nsslew -rate mode of operation for datarates of less then 250kb/s. Receiverand driver, both differential, have achoice of active -high or active -lowenable pins to three -state the outputs.Esd protection is to ±10kV. LinearTechnology (UK) Ltd. Tel., 01276677676; fax, 01276 64851.

Development andevaluationPIC development. Microchip offersthe PICMASTER-17B universal in -circuit system, a development tool forthe PIC17C4X microcontroller family.It runs on PCs under Windows andincludes an emulator control pod, atarget -specific emulator, the PRO -MATE programmer, a PC host -interface card, emulation controlsoftware, demo hardware andsoftware and documentation. ArizonaMicrochip Technology Ltd. Tel.,01628 851077; fax, 01628 850259.

ProgrammersUniversal modules. Stag has arange of removable modules for theEclipse universal programmer to takefpga, pga, quad flat pack and shrinkdip devices. The universal pga sockethandles all fpga and pga devices upto 208 pins as standard, 256 pin

drivers accessing each pin of the pgasocket for true universality. StagProgrammers Ltd. Tel., 01707332148; fax, 01707 371503.

SoftwareStatistics for Windows. Genstat, ageneral statistics software package, isnow available for PCs runningWindows, using the familiar Windowsfacilities and providing a number ofadditions to the standard analyses. Itprovides pre -configured analyses inthe normal Windows manner and alsovia a command line and takes datafrom Excel and other spreadsheets.Nag Ltd. Tel., 01865 511245; fax,01865 310139.

OS for embedded PowerPC. TheSwedish company Enea Data is aboutto introduce a version of its OSEDelta real-time operating system forMotorola PowerPC MPC821/860processors, to include dynamicmemory management, integratederror handling and automatic process -supervision. It is a distributed systemmeant for use in embedded non-stopand fault -tolerant systems such astelecomms; applications in OSE for68xxx processors will be portable tothe PowerPC. Reflex Technology Ltd.Tel., 01494 465907; fax, 01494465418.

WE HAVE THE WIDEST CHOICE OFUSED OSCILLOSCOPES IN THE COUNTRY

RACAL 1998 Frequency Counter I.3GHz (Options GPIBS, High Stab)...... £900MARCONI 2437 Universal Counter/1i mer DC-100MHz 8 digit 1175MARCONI 2430A Frequency Counter 1011,80MHz 8 digit .i125RACAL 9916 Erequency Counter 10Hz 520MHz /175111. 3435A 3,4 digit Multimeter AC/DC/Ohms/Current. LED L100

RACAL 9906A Univprsa I Counter Timer 10Hz-200MHz ...£250SOLATRON 7150 6,4 31/2 digit OMM with IEEE. .E400SOLARTRON 7045,44 digit Muttimeter Volts/Amps/OhmsTHANDAR 1503 4P/4 digit Multi mer with Adaptor

DM£75

Fluke Handheld DMM 3I4 digit with case. 1100Fluke 8050A Bench/Portable DMH 4,/2 digit True RMS £225Fluke 80104 Bench/Portable OMM 3,4 digit True RISS . L150WAVETEK 1829 Fun Gen 0.004Hz-4MHz Sine/Su/WI/DC/Ill Pulse etc L225

DIANBAR 10501 Func Gen 0.000511,5MHz Sine/Sq/Tri/Ramp/Pulseetc E175GOULD 13B Sine/Square Oscillator 10Hz-100KHz £150

FEEDBACK F06011Sine/Sq/Tri 0.01Hz 100KHz................. ENO

H.R. SMITH ANTENNA TEST SET type 12-602 4.... . .. ... . E2000

DRACHM EP501 Audio Analyser.. t350PHILIPS PA15565 Waveform Monitor.... L300

PHILIPS PM8917 Video Line Selector....... £200

FERROGRAPH RTS2 Recorder Tee Set.. 1250

KENO Dual Variable filter VBF/3 0.1Hz 10I(Hz £200RACAL Instrumentation Recorder Type Store ADN 0350RACAL Instrumentation Recorder Type Store MS 0500

AVIA Distortion and Noise Meter F2428 EelLEADER LS0216 Signal Generator . 1450RADFORD 1.204 Low Distortion Oscillator EN*RAOFORO LDM52 Low Distodion Measurtng Se £300MARCONI TF2700 Universal Brdge. Battery Operated ..........form ..._.£150....

MARCONI TFI313 Universal LCR Bridge .1 E125-._.HAM KERR 8424 Digital Component Meter LCR............ .. VIMAWARD IB RLC Bridge L60H.P 6624A System DC Power Supply 4 Outputs_ HPIE .............................EPDASORENSEN DCR600-4.58 0-600 Volts 0-4.5Amps............. ........£1110

............................................................HI. 6268 0-40 Volts, 0-30 Amps. .. - . 4500

FARNELL H30/100 0-30 Volts; 0-100 Amps, Metered...........................0100FARRELL B30/10 30 Volts, 10 Amps Variable .................. .........£150

........................FARNELL 230-5 0-30 Volts; 0-5 Amps. 2 Meters..............-- t150

FARNELL 230-2 0-30 Volts, 0-2 Amp Metered .......................................... FAOFARNELL LT30-I 0-30 Volt 0-1 Amp. Twice E130FARNELL 1.30-1 0-30 Volts, 0-1 Amp Metered ........................................ IBSDIURLBY-DIANDAR TSP3222 Programmable 323, 24mp Twice GPIB.

11111ILBY P1.3200M0 0-30V, 0-29 Twice Digital.................................... 6225

BRANDENBURG Model 472R 4-/- 21V Metered ............................... E200

MANY OTHER POWER SUPPLIES AVAILABLE

TEKTRONIX TAS475 4 Channel 100MHz Delay/Cursors. -ELP,,....4TEKTRONIX TAS455 Dual Trace 60MHz Delay/Cursors .,...,!!TEKTRONIX 2335 Dual Trace 100MHz Delay.......c..4TEKTRONIX 485 Dual Trace 350MHz Delay Sweep tg,',,ITEKTRONIX 475 Dual Trace 200MHz Delay Sweep 'owTEKTRONIX 465 Dual Trace 100MHz Delay Sweep ..E.400

TEKTRONIX SC504 Dual Trace 80MHz in TM503 - ....,LIFA.A. 1740A Dual Trace 100MHz Delay Sweep - !T

TEKTRONIX 2225 Dual Trace 50MHz Alt TB Magnification r. 2TEKTRONIX 2215 Dual Trace 60MHz Delay Sweep .ILKTEKTRONIX 2213 Dual Trace 60MHz . - £350.PHILIPS PS13217 Dual Trace 5014Hz Delay Sweep... rv.,,KHITACHI V423 Dual Trace 40MHz Delay Sweep ...IICOULD 001100 Dual Trace 30MHz Delay Sweep L24

£2500HITACHI V223 Dual Trace 20MHz Delay Sweep --). )

BECKMAN 9020 Dual Trace 20MHz Delay Sweep. . ....... ... 12.40

KIKUSUI 55300 Dual Trace 35MHz - ...."mum 555702 Dual Trace 20MHz .......),GOULD 033011 Dual Trace 20MHz (No handle). ',I.TEKTRONIX 2230 Dual Trace 100MHz Digital Storage, Cursors P.O.A..,.

TEKTRONIX 468 Due Trace 100MHz Delay Sweep Dig Storage 1.22PHILIPS 4 Channel 35MHz Digital Storage !LIMILD 054040 Dual Trace 10MHz Digital Storage . mt.H.P. 174I4 Dual Trace 100MHz Analogue Storage .4.

THIS IS HIST A SAMPLE, MANY OTHERS AVAILABLE

EATON/AILTECH 380811 Syn Sig Gm 1-2000MHz with PM3602..............P.O.A.MARCONI 2019 Synthesized AM/FM Sig Gen 80KHz-1040MHz ............. £1 750,,,,,N.P. 8620C Sweep Oscillator Men Frame only

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AO4ET 7100D AM/FM SIg Gen IOONtt-130X: ..._.£1000MET 7100A AM/FM Sig Gen 300KHz-650MHz...

,,,qw------""-MARCOIN TF23314 EIWtortion Factor Meter 2011,201dtr 005% Uw used..........t225

MARCONI TF2163 AtMnuator DC-IGHz.ALS Video Noise Meer UPSF2 with UPSHE 40-Hz-10MHz. .11500

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WILTRON 66105 Programmable Sweep Gen I -2D: ...._........................ikiWOO Selective Level Meter SPMII with Harmonic Dieortion AnaWser

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N. 42779 LC2 Meer with Test Endure.,RAS VHF Field Strength Meter type HD 25 300MHz .......................... .. £250N.P. 8160A Programmable Pre Pulse Gen 50MHz.......................... ...... £POAPHILIPS PM5134 Sweep Fun Gen 0.001Hz-20MHz Sine/Sq/In etc .... L500PHILIPS Ph15190 Syn Foe Gen 0.001Hz-2MHz Sine/Sen E750

WI 5006 &gnature Analyser E150

H.P. 5004A Signature Analyser 1100H.P. 84958 Alien uator DC-18GHz a 70dB in 1008 Skips £350HATFIELD 2105 Attenuator 50 ohm.SCRUMMAGER

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NEW EQUIPMENTHOMES OSCILLOSCOPE HM1005 Triple Trace 100MH, Delay Timebase.... L1147HAMEL OSCILLOSCOPE HM604 Dual Trace 60MHz Delay Sweep........... L653NAMED OSCILLOSCOPE HM303 Dual Trace 30MHz Component Tester,,.,. £422HOMED OSCILLOSCOPE HM205. 3 Dual Trace 201411, Digital Storage...... £653

All other models availablo-all oscilloscopes supplied with 2 probesBRUEL & KJOER EQUIPMENT AVAILABLE

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APOLLO 10-100MHz Counter Timer Ratio/Period/Time interval etc ..........£234APOLLO 100-100MHz (As above with more functions) ...................... 5332METEOR 100 FREQUENCY COUNTER 100MHz. . .... ...EllMETEOR 500 FREQUENCY COUNTER 6DOMH: _£145METEOR 1000 FREQUENCY COUNTER 1GHz E189IUPITOR 500 FUNCTION GEN 01Hz-500kHz Sine/Sq/Tri ..........................£125ORION COLOUR BAR GENERATOR Pal/IVNideo...................................... £243

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SPECTRUM ANALYSERS.£4000

&P.180 with 85588 100KHz 150M11z............. from £1500N.P. 1411 with 8555A& 85526 10MHz 18GHz .. .£1100N.P. 141T with 85548 & 8552B 5008X0-1250MHz...... .......01200H.P. 1411 wdh 8553B & 8552A IKHz-110MHz ...... . ........£000H.P. 1411 with 85531 & 8552A IKHz.-110MHz £700MARCONI TF2370 30Hz 110MHz El 000

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CIRCLE NO. I MON REPLY CARD

March 1996 ELECTRONICS WORLD+WIRELESS WORLDCIRCLE NO. 139 ON REPLY CARD

251

LETTERSLetters to "Electronics World" Quadrant House, The Quadrant, Sutton, Surrey, SM2 5AS

Valve amplifiersmade clearerIn the editing of the second extractfrom my book 'Valve Amplifiers',the precise need for the cathodebuild -out resistor in the concertinaphase splitter was not made clear.When originally conceived in 1982,the purpose of the build -out resistorwas to equalise the outputresistances, reduce imbalance, andthereby reduce distortion.

However, when tested with squarewaves, I found that removing thebuild -out resistor caused a coggle onthe leading edge of the waveform,which could not otherwise beeradicated. Each output of the phasesplitter forms a low pass filter withany shunt capacitance, and sincethese capacitances are likely to besimilar, the output resistances shouldalso be similar to preserve high -frequency balance; hence the cogglewhen the build -out resistor wasomitted. So although the build -outresistor was originally included toimprove lkHz distortionperformance, it has been retained toimprove transient response.

Various observers havecommented that the outputimpedances are not equal, and thatwhen the stage drives a real load, itsbalance will therefore becompromised, although none ofthem have offered any analysis toshow what these impedances mightbe, or what remedial action shouldbe taken.

Looking into the cathode, we seeRk down to ground, in parallel withrk the anode path to ground;

Ra + rark

Substituting;

RRk "+rµ+lZout R

Rk + a+ ra

µ+1

Simplifying, and noting thatRa=Rk=RL;

RL(RL + ra)Zout(cathode)=

12L Cu + 2) + ra

Looking into the anode, you willsee Ra to the ht rail; which is acground, in parallel with the cathodepath to ground;

= (it +1)RL + ra

Substituting;

RL ((u +1)RL + ra )z°, =(p+1)RL +RL + ra

Simplifying;

4.,(11+1)kraZo,a(anode)=

RL(p + 2) + ra

If we inspect this equation, we seethat the terms involving p are theonly significant terms, and that if isreasonably large, then (p+1)=(p+2),

toso

thit the output impedance reduces

The cathode output impedance hasto be calculated fully, but generallygives a value of about 1kg. It isbecause the ratio of outputimpedances is so large, that it isessential to equalise them, in orderto maintain high -frequency balance.To a first approximation, a build -outresistor in the cathode equal to theload resistance would be required.

Gain to anode or cathode can becalculated;

A -RL + ra

Where

ra' = RL(µ+1)+ ra

giving;

A PRL

pRL + RL + 2ra

But very little error results from;

A= i=eµ+1

Because of this low value of gainto the anode, Miller capacitance isvery low, and the stage has widebandwidth.

It is usual to direct couple to theanode of the input stage, and let thatdetermine the de conditions of thestage, resulting in the saving of acoupling capacitor and a lowfrequency time constant. By doingso, a pair of triodes achieves about6dB greater gain than any phasesplitter solution based on thedifferential pair.

It is true that the concertina has ahigher output impedance than adifferential pair solution, but thiswas used to advantage in my design

by making this the dominant pole,which meant that further slugging(shunt capacitance) actuallyimproved high -frequency balance,as it reduced the effect of variationsin input capacitance in the outputvalves.

On a historical note, the term`build -out' resistor derives fromBBC practice in equaliser design foranalogue music lines. Individualhalf -section equalisers would oftenbe used to reduce the complexity ofthe complete equaliser, but theiroutput resistance was no longer60051, so a 'build -out' resistor wasadded to avoid disturbing the nextsection.

Regrettably, there is a typing error(my fault) in Fig. 4, where theoutput power is specified as lOWinto 411; it should be 811.

I always enjoyed Frank Ogden'seditorial when he contributed to the'Comments' column, but I found itrather sad that he resorted to abusein his letter in the February 1996issue - after failing to spot that mydesign already accounted for thevery object of his criticism.

As to who would seriouslyconsider valves for anything, Iwould ask that he visit a specialisthi -ft shop, or a show, and see howmany (British) valve amplifiers arefor sale. The demand exists, so theproduct is made.Morgan JonesSouthampton

Valve prejudice?Frank Ogden's flippant assertionthat only "a complete loonysuffering from terminal nostalgiawould seriously consider valves foranything" (Letters, February)betrays him as a devout Philistine.The absurd notion that all pastwisdom is rendered obsolescent inthe face of technological advance issimply juvenile. The 'Soviet Union'presented a shining example of thisfolly and look where that got us.

Is Mr. Ogden seriously suggestingthat musicians the world over are allsick, demented, or just plain stupid?

The idea that 'new' is inherentlybetter than 'old' is more in tune withadolescent truculence than with anyconsidered intelligence. Please,Frank, don't use science as anexcuse for your prejudices - it doesneither you, nor us, nor science, anyfavours.Simon YorkeCounty Durham

Cable communicationBen Duncan's article aboutloudspeaker cables in the February'sissue was illuminating andhighlighted very well the problemsof the design and modelling oftransmission lines.

The lumped model has itslimitations, but Ben Duncan hasapplied it well. The model he hasused describes a quarter wavesection of 6652 cable operating at10MHz, but at high audiofrequencies it is a goodapproximation of two metres of30051 cable. This is a good basis forthe analysis that followed but istricky to modify to see the effects ofdifferent cable types.

A better approach for this task is touse the distributed model, available inSpice simulators. For simplescenarios such as that consideredhere, the difference is small untilalternative cable impedances areconsidered. With a 2m, 3000 cablemodelled the high frequency roll -offis indeed still present. It is a naturalconsequence of the end -to endimpedance transformation andconsequent mismatch which takesplace when a transmission linereaches an appreciable fraction of aquarter wavelength. The greater theintrinsic mismatch, the worse the loss.

A better cable. To prevent this, andmake the whole system flat in thefrequency domain, the solution is tomake the cable the same impedanceas the loudspeaker - 80. Theimpedance of the loudspeaker isthen presented unchanged to theamplifier output at all frequenciesand there is no roll -off. The responseis flat up to the frequency at whichthe line starts to support non-TEMmodes - several GHz. Perhapscounter -intuitively, the value of theshunt capacitance increasesconsiderably to achieve this match.Interestingly the extensive speakercables which place the twoconductors far apart to reducecapacitance, are doing the worstthing possible for frequencyresponse.

Attempts have been made in thepast to produce cables of lowimpedance by weaving enamelledwire together, but they havevanished, presumably becausechafing caused short circuits. It isactually quite easy to make reliablelow impedance cables for yourself.The impedance does not have to be aparticularly accurate 852, merely


LETTERS

somewhere near.Adhesive copper tape about 18mm

wide is available from manystockists and is mainly used forelectromagnetic shielding. A goodsized reel can be had for about £10.

The copper tape is stuck on eachside of a soft plastic strip, aboutlmm thick, to form a sandwich. Thehole is then insulated with some

Feedback

Feedback

Comparator ground

tough plastic. The brown PVC tapeused for packaging is suitable. Thediagram shows a cross section of thecable. Connections to each end canbe soldered with short pieces ofthick wire. This assembly will lieflat under a carpet. In terms of thecorrosion difficulties for strandedcables by the article, this has none ofthese, and being flat the skinessentially negligible. The cable willcontribute only its resistive term tothe circuit.

Make the cable disappear. If youreally want to remove yourloudspeaker cables from theequation, the answer lies within thepower amplifier. Most designs usenegative feedback, taken from asclose to the loudspeaker terminals aspossible. This guarantees the mostuncompromised voltage sourcepossible at that point. Theloudspeaker cables then degrade thisto an extent dependant in theirlength and quality.

Power supply designers haveknown the answer to this problemfor years. Even the simplest designsusually offer remote sensingterminals to guarantee the accuracyof delivery at the load rather than thesupply terminals. They generallyhave a configuration that allows the

user the choice of high accuracywith a bi-wired remote sensing set-up, or by omitting the second pair ofwires, the standard accuracy withthe cable impedance degradingperformance.

With an audio amplifier - which isjust a fast ac power supply - this canbe achieved with couple of simplemodifications.

The feedback sensing point, whichis used to define the location of thenet voltage source, is coupled backto the comparator circuit with aresistor, usually several kilo -ohms.This sensing point can be moved bythe addition of extra resistors and bi-wiring to the loudspeaker. Theprecise value of the feedbackresistors is not critical as long as it isthe same in both channels.

The effect of a change is merelyon gain, pro rata to the change so theaddition of a few ohms - 1051 isabout right - will not changeperformance. Provided the bi-wiringis used, the new resistors can beshorted out and have no effect at all.The junction of these two resistors istaken to the far end of the speakercable with a second wire, effectivelymoving the sensing point for thenegative feedback all the way up tothe speaker.

As far as the resulting driving

Creative fictionCircuit simulators are extremely powerful tools -forinvestigating electronic scenarios. I have alwaysthought it too obvious to need saying that relyingwholly on simulation can lead you off into deep errorunless you do regular reality checks with real circuitryto ensure your model is not fallacious. I was wrong; itdoes need saying.

While I must decline to give Duncan's article'Modelling Cable' in the February 1996 issue the fulldissection it deserves, I feel it only right to reassurepeople who are appaled at the prospect of loudspeakercables made up from a Sargasso Sea of 10mVthreshold diodes. I believe the simple experimentshown below clears up the point.

A Blameless power amplifier delivers 50W into an852 load, at 0.001% thd at 1kHz. The load return pathis the cable under test A -B. This was initially 4m ofmultistrand copper - not tinned -copper - mains -cable,and the voltage drop across it was 140mV rms at1kHz. I think it is clear that if the multi -strand cablewas a cats -cradle of 10mV 'mystery diodes', thenunder these conditions some at least of them would beturning on and off and would severely degrade the

80 badresistor

Distortionanalyser

linearity. This would be particularly noticeable at thestrand ends C, D etc, which are not formally connectedto B, and according to Duncan make "occasional andrandom contact" along the length of cable. In actualfact they make intimate and continuous contact in anynormal cable.

None of this happens. It is not possible to measurethd to 0.001% on a 140mV signal due to noiselimitations, but the thd residual at points at C, D etc, isidentical to that at B, at the measurement noise floor of0.007%. Clearly this is just a noisier version of theBlameless amplifier distortion. No extra diodedistortion of any kind is detectable; this holds acrossthe 20Hz 20kHz band.

Above 2kHz the voltage drop increases due to cableinductance; by 10kHz the level is 10dB up, rising at6dB/octave. This confirms my view that in mostcircumstances the series resistance and inductance of aloudspeaker cable are the only significant parameters.If you are trying this experiment, then don't leave thecable wound on its reel; not only will this increase itsinductance, but the steel reel -centre will producespurious third -harmonic distortion.

This is good evidence that Mystery Diodes do notexist. There is also the point that a copper -oxiderectifier has a forward voltage drop of 300-600mV,and I can find no evidence in solid-state physics thatcupreous oxide could ever give a diode effect at such alow voltage as 10mV.

It remains true that an ounce of experiment candispose of several long tons of speculation.Douglas SelfLondon

Soft plastic insulatorAdhesive copper tape

Insulating tape

impedance is concerned there is nocable. The same can be done withthe ground side of the cable into thecomparator circuit. The topology ofthis section is more likely to changefrom design to design and it may bethat such a point is not accessible. Inthat case, you will have to settle forjust half a solution.

Feedback wires can be omittedwithout compromise of the originalquality, but have a care. Eitherdisconnection or reversal of themain cable with the externalfeedback in place will result thesmell of burning 1052 resistors.Donald PearceHampstead

Internet integrityThe number of Internet userscontinues to grow at a significantpace. Users have the facility to calldown virtually any page from thismassive database and also have theopportunity to create their own Webpages. How much thought has beengiven to the integrity of the datawhich can be accessed from the net?Can we really believe that all weread has not been corrupted by adetermined hacker first? With all thehigh grade of technical dataavailable, is it right that we shouldaccept its authenticity withoutquestion? The very openness of thenet should be questioned.

Interesting enough, I have recentlyread that a new encryption techniqueusing a one pad key is awaiting thegrant of its patent. It was promisedthat this would then be passed intothe public domain. If business usersare intent on passing sensitiveinformation over the net, then asecure form of encryption is anabsolute necessity.Geoff LewisCanterburyKent

More current driveI noted the letter by J.R. Allison(Bradford) in the December edition.He comments on the use of currentfeedback in audio amplifiers, or'current -drive' as I prefer to call it ina system context. I should point outthat this subject has beeninvestigated in the 1980s at EssexUniversity by Dr Paul Mills, a thenresearch student under mysupervision but now with Tannoy.


LETTERS

Aspects of this subject were alsoinvestigated by David Birt, thenwith the BBC Designs Department.Rather than discuss the merits - andproblems - of current drive, I wouldlike to draw your readers' attentionto the following publications:

`Distortion reduction in moving -coilloudspeaker systems using current -drive technology', Mills, P.G.L.,Hawksford, M.O.J., JAES, vol. 37,no. 3, pp129-148, Mar '89.

`Transconductance power amplifiersystems for current -drivenloudspeakers', Mills, P.G.L.,Hawksford, M.O.J., JAES, vol. 37,no. 10, pp809-822, Oct '89.

`Transient analysis: A design tool inloudspeaker systems engineering',80th Convention of the AES,Montreux, paper 2338 (E8), Mar`86.

`Loudspeaker power amplifiers withload -adaptive source', Birt, D.,JAES, vol.36, no.7,8, pp552-61,July/Aug '88.

I should point out that a two-way

active system was designed and builtas part of the research programme.The high -frequency channel usedpure current drive while the bass -midrange used a combination ofcurrent drive and servo technologyusing velocity sensing to controldamping. Paul Mills has also morerecently designed a sub -wooferloudspeaker for Tannoy usingcurrent -drive techniques.

At Essex since the mid 1980s, wehave also investigated digitaltechniques for crossover designwhere precision crossover and driveunit correction functions can beimplemented in the digital domain.This can result in a loudspeaker witha near -perfect impulse response,where both amplitude and phaseresponses are corrected.

Of course, the actual loudspeakermust be appropriately designed tobenefit from this technology - seeAudio Physic 'Tempo' or 'Virgo'for examples of good designpractice.

Also - and of equal significance -much of the analogue processing canbe eliminated with high-grade d -to -aconverters being interfaced directlyto the power amplifiers. The

elimination of much of the analoguecircuitry including passive crossovernetworks and pre -amplifiers,together with band splitting acrossmultiple d -to -a converters andpower amplifiers, is in my view arevelation. It represents one of themost important contributions ofdigital technology to soundreproduction.

Redundant analogue amplifierstages only downgrade audioperformance. On the other hand,products such as the Meridian 565offer digital gain control, digitaltone controls and surround -soundmodes. They also operate efficientlyin both analogue and digital worlds.As a bonus, the dual phase -lockedloop of the 565 lowers jitter fromdigital sources.

In the near future we can also lookforward to the power d -to -aconverter which could eliminate theneed for analogue power amplifiersas we currently know them.

In my view, the future of audiotechnology is about to changedramatically, and with the coming ofhigh -capacity cd with multi -channelsound*.

Finally, I hope that the

technological changes that digitalprocessing offers will put to rest therather protracted and non -convergent debates on analoguecircuitry especially poweramplifiers, that continue to appear inthese pages, much of which is soonto be of only historic interest, atleast at the leading edge of audio.The fact is all analogue circuits areflawed for numerous reasons andeach must be judged as a completeentity, circuit diagrams are only partof the story. A technology thateradicates these area of uncertaintyis far more likely to succeed whenproperly engineered.

Although I am fascinated byanalogue circuit design and I havemore than my fair share ofcontroversial views, the more I learnof it the less I want to use it. Ofcourse, treating all circuits includingdigital as an analogue process has itsmerits, but that is a different story.Professor M HawksfordCentre for Audio Research andEngineering

'Acoustic Renaissance for Audio(ARA) proposal web pages:http://www.ibmpcug.co.uki-meridian/ara/

Electromagnetic clarification?Requirements of standards vary, but in particular, EN55011 specifies avoltage maximum, a distance and an antenna. This appears to be finewhen the current measurement from the specified loop antenna, with itsfactors, is converted to a voltage. The resultant voltage can then berefereed to the standard for a pass or fail.

Fine so far. It is when one makes a measurement at 30m distant from thesource, with a loop antenna, at a frequency of less than 2MHz that I see aproblem.This measurement will be in the near field, with a current measuring

device. How, then, is to be converted to a voltage when the voltage andcurrent relationship is not established, as it is in the far field?

I consider the far field to be around 1/5 -wave length distant of the sourceand the relationship in the far field to be, in simple terms, 1V/metre to0.00265A/m or a correction factor of log 20 377, or 51.5dB.M I NicholasBournemouthDorset

Electro-magnetic confusionThe recent correspondence on electromagnetic compatibility in yourFebruary issue, barely touched on the growing electromagnetic pollutionof the environment.

There seems to be a tendency to ignore the effects of broadband 'hash'on unfashionable parts of the electromagnetic spectrum. The fact thatmost pcs blot out radio reception on nearby long and medium -wave(150kHz -1.5MHz) radio receivers is dismissed as unfortunate. But thenthe preferred band for 'serious' radio listening is fm.

The truth is that we are drowning in a sea of electromagnetic pulsesfrom electronic light ballasts, domestic appliance controls and televisionand pc displays and systems - and nobody cares.

This off -hand attitude to radio interference now extends far up thebroadcast spectrum. We are shortly to be exposed to channel 5, which willoccupy uhf channels 34- 39. According to my frequency allocation list,the band 606-614MHz in that sector was allocated for radio astronomy.The jamming of research radio reception does not end there. ElectronicsWorld readers may recall that the search for intelligent life elsewhere inthe galaxy was recently stalled by a microwave oven in the observatorykitchen. Its a moot point whether intelligent life had anything to do withthe signals.

I fear it will take some spectacular computer system crashes due torogue electromagnetic pulses to convince the slew -rate junkies, terabytenerds, surfers and vhf anoraks currently in the ascendant that limitingelectromagnetic pollution by improving the design, construction andscreening of radiating equipment is in everyone's interest.Anthony HopwoodUpton -upon -SevernWorcestershire

Early EMCElectromagnetic compatibility is widely regarded as something inventedin Brussels a few years ago, that became a legal requirement at thebeginning of this year. In fact, controls on emission have been around forsome forty years, one of the first being the requirement for 'suppression'of the ignition systems of petrol engines to minimise interference withBand I 405 -line television transmissions.

Control of immunity in volume -produced products, however, is oftenconsidered to have been introduced only a decade or so ago, as a result ofinterference from amplitude modulated citizen's band transmissions.

It is interesting therefore, to note that in the Dec 1971 issue, WWreproduced an item from The Marconigraph of sixty years previousconcerning a patent issued to Capt. H. J. Round. This is not only theearliest reference to a 'valve' in the The Marconigraph, but also perhapsthe earliest example of improvement of immunity.

For readers who do not have either of those issues to hand, the inventionconsists of a reversed -polarity diode connected in parallel with the diodedetector of a simple detector -only receiver. Both diodes are provided withvariable reverse bias and the reversed -polarity diode is biased off forsignal reception. The amount of bias, and its polarity, are not well defined.However, a 'powerful atmospheric discharge' forces both diodes toconduct. This results in a great reduction in detection efficiency, due tothe low 'back resistance', as well as heavier damping of the parallel tunedcircuit. As a result, no sound, or probably only a weak click, is heard inthe earphone.

As might be expected from the ingenious Captain, this two -prongedattack is clearly likely to be more effective than just connecting the 'crashdiode' across the tuned circuit.John WoodgateRayleighEssex


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AUDIO

Non slewincaudio power amplifier

Advancing his'non-slewing' technique,which enabled aninstrumentation amplifiercapable of ±1000V/ps,Giovanni Stochino nowapplies the principles toaudio poweramplification.

In a recent article' some high slew rate volt-age feedback amplifier architectures werepresented and discussed. A virtually non-

slewing 5012 power amplifier configurationwas finally proposed, where high speed isaccompanied with low input offset voltageand noise, as well as with low total harmonicdistortion in the audio frequency range.

In this article I show how the same basicprinciples, embodied in Fig. 9', with appro-priate adaptations, can be applied to the designof high performance audio power amplifiers.

Non-slewing amplifier performanceIn non-slewing architectures, as explained inthe previous article', all main slewing mecha-nisms are virtually eliminated. Therefore,when the input signal is within the commonmode input voltage range, the current at theoutput of both input and intermediate gainstages, is always controlled by the differentialinput voltage Vd=Vi-V2.

Figure 1 allows us to compare the perfor-mance of a non-slewing amplifier, nsa, with asimilar yet conventional and slewing archi-tecture, or csa. For clarity, only the input andintermediate stages are detailed, while the out-put stage is shown in the form of an ideal volt-age follower.

Biasing currents are the same in both nsaand csa configurations. The results of Spicesimulation for an input stimulus consisting ofa 10kHz square wave with a superposed highfrequency sinusoidal voltage of 500kHz areshown in Fig. 2.

It is apparent that the non-slewing architec-ture has no visible transient intermodulationdistortion, while the conventional configura-tion shows clear signs of the presence of inter -

modulation distortion due to slewing times Tfand Tr - both of about 7p s.

In Fig. 3, transfer curve /b, which is theintermediate stage output current, versus Vd isshown for both /B=0 and hi#0.

Three regions of operation are identified:

I - input and intermediate stage in class -Aoperation;II - input stage in class -AB, intermediatestage in class -A operation;III - input and intermediate stage inclass -AB operation.

Transconductance gm=./b/(Vi-V2) in theseregions is approximately as follows:

gn,(I)=2/(Re+2VT//A) (small signal) (1)

where VT=kTlq is the thermal voltage ofaround 25mV at ambient temperature , and,

gm(II)=2/(2Re+R)gn,(III)=1/(2Re+R)

(2)

(3)

Maximum positive and negative current /b(na)at node B is defined by the maximum inputvoltage Vmax=V +EBOV boon) that should neverbe exceeded, according to the following rela-tionship:

Ibmax=(Vmax-2Vbe(on))/(2Re+R)=(VEB0-Vbe(n,))/(2Re+R) (4)

Here, voltage VEB0 is the rated base -emitterreverse voltage of input transistors. If, forinstance, VEBor--6V, Re=5012 and R=20012,equation (4) yields 18mA. This value, addedto ig , is enough to sustain a rate of change -still linear - of ±160V/µs across a capacitance

Performance of the 'non-slewing' amplifier. Table 1. THD+noise of circuit in Fig. 4, bandwidth 80kHz.

Test conditions: ambient temperature=20°C; Vcc= V=55V regulated. Vout ( Vpp) thd+noise(%) thd+noise(%)81I load 40 load

- Gain=30dB 1kHz 20kHz 1kHz 20kHz

- Output power 20Hz-20kHz, 110W/852; 180W/42 10 0.004 0.016 0.004 0.050

- Small signal -3dB bandwidth, 800kHz (at node F before output inductor) 20 0.003 0.020 0.004 0.040

- Input offset voltage, 4mV 40 0.003 0.030 0.008 0.040

- Maximum output voltage rate of change, ±170V/ps (at node F) 60 0.003 0.040 0.009 0.050

- Overload recovery time (up to 300% input overload) 2Ons 80 0.004 0.045 0.010 0.060

- Distortion, see Table 1.thd+noise instrumentation=0.002%


AUDIO

Vb

50 v'VVV\--- 1

50

To CSA

55V22 22

IB = 6mA

50p

B

50p

1200p

Vz 1kWA-

G = 1

1100Vol

22 22

0 Is = 6mA

5V

To NSA

Fig. 1. Simplifiedcircuit diagram ofnon-slewing (nsa)and conventional(csa) amplifierconfigurations.

NSA

55V22 22

B'

1100k

IB = 6mA

700p

Vz. 1k

1100 AlvVy

22 22

G=1

IA = 2mAIs = 8mATransistors:NPN = 2N5551PNP = 2N5401

0 Is = 6mA

0Vo2

Scale: (a) = 10V/div(b) = (c) = 50V/div

(b)

AAAA.

Tf (c) Tr

14 [4r+

I

50µsI

60µsI

70µsI

80µsI

90µsI

100ps

Fig. 2. Spice simulation results demonstrate the absence of visible TIM in non-slewingarchitectures. (a) is (V a+V b)/2, (b) is output of non-slewing amplifier, Vo, and (c) is outputof conventional slewing amplifier, Vol.

of 150pF at node B, which is a realistic valuein an audio power amplifier.

It is worth noting again that this maximumrate of change is not to be confused with thenon-linear slew rate limitation due to inputand/or intermediate stage overdrive phe-nomenon in csa architectures.

The remaining problem in this type of nsaconfigurations, as well as in all other high slewrate class -AB architectures, is associated withthe large full scale non -linearity due to class -AB operation, as is apparent from Fig. 3. This

Fig. 3. Fullrange transfercurve of lbversus Vd inthe nsaarchitecture.

-VmaX

can leave a residue - although rather low -of transient intermodulation products, evenwhen overall feedback is applied to theamplifier. Additionally this limits largesignal linearity at high frequency where loopgain is reduced for reasons of loop stability.

An effective way to further limit the alreadylow transient intermodulation distortion innon-slewing audio power amplifier architec-tures, is to set the bias current of input andintermediate stages so that class -A operation isretained with actual music programs at the

CSA

max lb

(IB + IA) -

+ IA)

-(Imax)

(/,-v2) 1'

maximum expected power and frequency.Considering that the peak current needed tosustain full swing at node B is equal to27c.iVecCo, where Co includes also the base -col-lector capacitances of transistors connected tonode B, the previous reasoning leads us to set./AlmA for f=201(1 -1z, when Vcc=50V andCo=150pF. As suggested by Self2, a safety


AUDIO

100k38V

02

38V

220

(10mA)

Vi (o

IA2 (10mA)

20

181

(6mA)

1B2(6mA)

R

200 Re50 50

2R2

22 7100n 7 220w100V

Tr

Tr2

Tr

1,,

1k5 1k5

100

C3

+ 33p

RV5k

47p

1132

220p/100V2

.L 100n+.1 ,1,2R2

All diodes = 1 N444803, 04: selected for Vrev 2.120V

5k1

ICITL431

Fig. 4. Detailed circuit diagram of a viable non-slewing audio power amplifier.

55V

10p

50

50

O Va Vb

Fig. 5. Basiccircuitdiagram of a 10p

newimplementation of a highperformancehigh slewrate audiopoweramplifier.

A10mA

- 55V

T

Vahi

50p-I

100

Re +133 7 V81 Rb

(la) - 1k5---WA,-Tri

_,2132

Tr2 +IVB3

3k3

50p

HI I

22

Input stage

Val

Ibh

1bl

4

VB3

7, VB2Rb

W/s./-1 k5

(le) -i,' v B1Re -1

33

22

Tr16

Intermediate stage

)

)

Output stage

7.100n 1.,00.,..o+Vaa (55V)

Mosfets:Tr23, Tr24 = IRF640Tr25, Tra = IRF9640

100n 1000p/100V

o Vee (-55V)

VB1 = 1V

VB2 = 3.5VVB3 = 1.3V

= 9V (la = 100mA)Va = square waveVb = sine wave

ve'

22

51.tH

Diodes: 1N4448Transistors: NPN = 2N5551

PNP = 2N5401MOSFETs: N = IRF630

P = IRF9630


AUDIO

margin of about two is recommended. Thisalso takes into account the current contributionneeded to drive the output stage and to makeup for component tolerances.

In principle, this solution promises verygood thd and transient intermodulation dis-tortion performance with normal audio pro-grams. At the same time, it is capable of assur-ing the very low - if any - transientintermodulation distortion offered by non-slewing architectures, should unexpectedlyfast and/or large input transients occur, asmaintained by Duncan3.

Non-slewing, high power audioamplifier architectureFigure 4 shows the complete circuit diagramof a possible implementation of a non-slewingaudio power amplifier, designed bearing inmind the above considerations. If comparedwith the 5052 power amplifier of Fig. 91 dis-cussed in my previous article, it contains someminor changes.

Firstly, cross coupling resistance R isreduced to 20052 to improve full range linear-ity of the input stage and increase its maximumavailable output current. Current shifting com-ponent /s has been increased accordingly to8mA, while /A has been kept at 2mA.

To reduce power consumption of currentsource transistors Tr18 and Tr21, zener diodesD1 and D2 have been added. Furthermore, theoutput stage is built around a double pair ofhigh -power complementary mosfets. Theseare the IRF 640 and IRF 9640, fromInternational Rectifier.

Each power mosfet can dissipate 125W ofpower and provide more than 20A peak cur-rent. Therefore, the amplifier can safely drivevery low impedance loads, provided the out-put mosfets are adequately heat-sinked.

Transistors Tri 1_16, which serve as low out-put resistance push-pull drivers, are capable ofproviding the high peak currents needed todrive the high and non linear input capaci-tances of power mosfets. This can amount toabout 800pF worst case each. Peak output cur-rent limitation is set to about 40A by zenerdiodes D5 and D6, but a 3-4A fuse has to beinserted at the amplifier output for safe con-tinuous operation.

Due to the high gate -source voltage neededto drive mosfets into full conduction, maxi-mum output voltage swing is limited to about12V from the supply rails. This results inreduced amplifier efficiency. If needed ,betterefficiency can be obtained by operating powermosfets with separate supply rails of ±45V.

Output stage bias current is set by adjustableshunt regulator, /CI, and by trimmer RVI. Thiscomponent has to be set to its maximumbefore applying power to the amplifier andadjusting bias current of Tr23_26. A suitablevalue for total mosfet bias current was foundto be about 200mA. Unless otherwise stated,resistors are 300mW, 1% metal film types.

Measured performance of the amplifierprototype, which is in good agreement withsimulation data, is shown on the first page ofthis article.

Fig. 6. Some Spice simulationresults of the amplifierconfiguration of Fig. 5:

(a) Frequency response, Magnitudeof V o'/V (10 dB/div)(b) Frequency response, Phase of

Vo'/Vi (507div)(c) Square wave response, V1

(2V/div)(d) Square wave response, V,'(20V/div)(e) TIM test, V1 ( 5V/div)(f) TIM test, V,' (20V/div).

80

60

40

20

0

20

80

60

40

20

0

-20

(a)

100kHz 1MHz 10MHz

(c)

(d)

4ps 8µs 10µs 12µs 14µs

(e)I

11! rf !!!!!!! !!!!!!!!! " OMAN

(f)

4µs

Further developments.In the last few months I have investigatedwhether better results can be attained in termsof both maximum rate of change and thd inhigh slew rate audio power amplifiers config-urations.

Figure 5 illustrates the further evolution ofthe basic power amplifier circuit structuredepicted in Fig. 4, which I am currently work-ing on. In comparison with Fig. 4, where theintermediate stage current gain is low (1 to 2),Fig. 5's topology features an intermediatestage with high low frequency current gain,equalling Rb/Re for Rb/Re<13.

With component values shown in the figure,this gain amounts to 45. The expected advan-tages are increased low frequency open loopgain - and hence lower thd for the sameclosed loop gain - and potentially higherspeed, since the current available at the inter-mediate stage output is larger than the corre-sponding current in Fig. 4's architecture.

From Fig. 5 you will find that,

/h(Vd=0)=/d(Vd=0)=-0,

therefore bias current /B is equal to,

[Vs i-Vbe(on)]/Re=9TnA

Available peak current is defined by Vah and

61.1s 8µs 10µs 12µs 14µs

Val peak value, ie Va(pk), via the relationshipib(pk)= [Va(pk)-Vbe(on)1/Re

In the interests of reliability, this peak cur-rent has been limited to about 60mA, bymeans of the diode clamping networks at thecollector of input transistors. These limit Va(pk)to about 2.8V. With this high peak currentvalue it is now possible to sustain slew -ratesof ±400V/ps across a 150pF total capacitanceat the input node of the output stage.

I cannot provide measurement results yet,however, Spice simulations confirm the abovetheoretical predictions.

For the moment, I can report the simulationresults shown in Fig. 6, which demonstratesthe frequency response - magnitude andphase - the square -wave response and thesquare+sine wave response. They prove thestability and clean response of the amplifier -even with a severe 801/0.5pF load impedance.In addition, they show the absence of any vis-ible transient intermodulation distortion.

References1. Stochino, G, 'Ultra -fast Amplifier', EW+WW,Oct 1995, pp.835-841.2. Self, D, 'High Speed Audio Power', EW+WW,Sep 1994, pp.760-764.3. Duncan, B, 'Simulated Attack on Slew Rates',EW+WW, Apr 1995, pp.303-309.


SURVEILLANCE TELESCOPE Superb Russian zoomtelescope adjustable from 15x to 60x! complete with metal tripod(imposible to use without this on the higher settings) 66mm tense.leather carrying case E149 ref 8AR69RADIATION DETECTOR SYSTEM Designed to be wallmounted and connected into a PC, ideal for remote monitoring, w holebuilding coverage etc. Complete with detector, cable and software.£19.95 ref BAR75.WIRELESS VIDEO BUG KR Transmits video and audiosignals from a mi nature CCTV camera (included) to any standardtelevision! AJI the components including a PP3 battery will fit into acigarette packet with the lens requiring a hole about 3mm diameter.Supplied with telescopic aerial but a piece of wire about 4" long willstill give a range of up to 100 metres. A single PP3 will probably giveless than 1 hours use. £99 REF EP79. (probably not licensable!)

CCTV CAMERA MODULES 46X70X29mm, 30 grams, 12v100mA. auto electronic shutter, 3.6mm F2 lens, CCIR, 512x492pixels, video output is 1v p -p (75 ohm). Works directly into a smart orvideo input on a he or video. IR sensitive. E79.95 ref EF137.IR LAMP KIT Suitable for the above camera enables the camerato be used in total darkness! £5.99 ref EF138.REMOTE CONTROLTAN DATA TD1400 MODEM/VIEWDATA Complete system comprising 1200/75 modem, autodialler, infra red remote keyboard, (could be adapted for PC use?)psu, UHF and RGB output, phone lead. RS232 output, compositeoutput. Absolute bargain for parts alonell£9.95 ref BAR33.9 WATT CHIEFTAN TANK LASERS Double beam unitsdesigned to fit in the gun barrel of a tank, each unit has two semiconductor lasers and motor drive units for alig nem ent. 7 mile range,

full circuit diagrams, new price £50,000? us? £349. Ring for info.TWO WAY M IRROR KIT I rid udes sped al adhesive film to maketwo way mirror(s) up to 60"x20'. (glass not included) includes fullinstructions. £12 ref TW1.

NEW HIGH POWER RF TRANSMITTERSAMPLIFIERSAssembied PCB transmitters, 4 types available,12.6vdc 90 watt 1.5-30mhz 75 ohm in/out FM/AM E75 ref RF112.6vdc 40 watt 50-200mhz 50 ohm in/out FM/AM E65 ref RF228vdc 125 watt 1.5-30mhz 75 ohm in/out FM/AM E85 ref RF328vdc 100 watt 50-200mhz 50 ohm in/out FM/AM E75 ref RF4A heat sink will be required, ring for price and availability.If you intend using these as audio transmitters you will need a alsoneed a preamp. Complex module available at £40 ref RF5.COMPUTERMORKSHOP/HI-F1 RCB UNITS Completeprotection from faulty equipment for everybody! Inline unit fits instandard IEC lead (extends it by 750mm), fitted in less than 10seconds, resetAest button, 10A rating. £9 each Ref MM5.

RADIO CONTROLLED CARS FROM £7EACH!IllTHOUSANDS AVAILABLE RING/FAX FOR DETAILS!MAGNETIC CARD READERS (Swipes) £9.95 Cased withflyleads, designed to read standard credit cards! they have 3 wirescoming out of the head so they may write as well? complete withcontrol elctronics PCB. just £9.95 ref BAR31WANT TO MAKE SOME MONEY? STUCK FOR ANIDEA? We have collated 140 business manuals that give youinformation on setting up different businesses, you peruse these atyour leisure using the text editor on your PC. Also included is thecertificate enabling you to reproduce (and sell) the manuals as muchas you like! £14 ref EP74

PANORAMIC CAMERA OFFER Takes double widthphotographs using standard 35mm film. Use in horizontal or verb calmode. Complete with strap £7.99 ref BAR1COIN OPERATED TIMER KIT Complete with coinslotmechanism, adjustable time delay, relay output, put a coinslot onanything you like! TV,s, videos, fridges, drinks cupboards, HIFI.takes 50p's and Et coins. DC operated, price just E7.99 ref BAR27.ZENITH 900 X MAGNIFICATION MICROSCOPE Zoom,metal construction, built in light, shrimp farm, group viewing screen,lots of accessories. £29 ref ANAYLT.AA NICAD PACK Pack of 4 tagged AA nicads £299 ref BAR34PLASMA SCREENS 222x310mm, no data hence E4.99 refBAR67NIGHTSIGHTS Model TZS4 with infra red illuminator, views up to75 metres in full darkness in infrared mode, 150m range, 45mm lens,13 deg angle of view. focussing range 1.5m to infinity. 2 AA batteriesrequired. 950g weight. £210 ref BARBI. 1 years warrantyMEGA AIR MOVERS 375 cubic feet per min!, 240v 200 watt,2.800 rpm, reversable, Tx7" UK made, new, Aluminium, current listprice about £180 ours? £29.95 ref BAR35.LIQUID CRYSTAL DISPLAYS Bargain prices,16 character 2 line, 65x14mm £1.99 ref SM1612A16 character 2 line, 99x24mm £2.99 ref SM1623A20 character 2 line, 83x19mm £3.99 ref SM2020A16 character 4 line, 62x25mm £5.99 ref SMC1640ATAL-1 110MM NEWTONIAN REFLECTORTELESCOPERussian. Superb astronomical 'scope, everything you need for someserious star gazing! up to 169x magnification. Send or fax for furtherdetails £249 ref TAL- 1

GOT AN EXPENSIVE BIKE? You need one of our bottle alarms,they look like a standard water bottle, but open the top, insert a keyto activate a motion sensor alarm built inside. Fits all standard bottlecarriers, supplied with two keys. SALE PRICE E7.99 REF SA32.GOT AN EXPENSIVE ANYTHING? You need one of ourcased vibration alarms. keyswitch operated, fully cased just fit it toanything from videos to caravans, provides a years protection from1 PP3 battery, UK made. SALE PRICE £4.99 REF SA33.DAMAGED ANSWER PHONES These are probably beyondrepair so just E4.99 each. BT response 200 machines. REF SA30.

COMMODORE GAMES CONSOLES Just a few of these leftto dear at E5 ref SA31. Condition unknown.

COMPUTER DISC CLEAROUTwe are leftwith a let of softwarepacks that need clearing so we are selling at disc value only! 50 discsfor E4, thats just 8p each!Kour choice of discs) E4 ref EP66IBM PS2 MODEL 160Z CASE AND POWER SUPPLYComplete with fan etc and 200 watt power supply. E9.95 ref EP67DELL PC POWER SUPPLIES 145 watt, +5,-5,+12,-12,150x150x85mm complete with switch, flyleads and IEC socket.

WOINERIIAMPTON BRANCHNOM.' OPEN AT WORCESTER S

WHAMPTON TEL 01902 22039bALt Print tV.1111 rem of'001.44 DISC DRIVES Standard PC 3.5' drives but retums so theywill need attention SALE PRICE E4.99 ref E P681.2 DISC DRIVES Standard 5.25 drives but retums so they willneed attention SALE PRICE NOW ONLY 0.50 ref EP69PP3 N ICA DS Unused but some storage marks. £499 ref EP52DELL PC POWER SUPPLIES (Customer retums)Standard PCpsu's complete with fly leads, case and fan. +12v,-12v,+5v,-5v SALEPRICE E1.99 EACH worth it for the b its alone! ref DL1. TRADE PACKOF 20 E29.95 Ref DL2.GAS HOBS AN D OVENS Brand new gas appliances, perfect forsmall flats etc. Basic 3 burner hob SALE PRICE E24.99 ref EP72.Basic small built in oven SALE PRICE E79 ref EP73RED EYE SECURITY PROTECTOR 1,000 watt outdoor PIRswitch SALE PRICE E8.99 ref EP57ENERGY BANK KIT 100 TxT 6v 100mA panels, 100 diodes,connection details etc. £69.95 ref EF 112.PASTEL ACCOUNTS SOFTWARE, does everything for allsizes of businesses, i nd udes wordprocessor, report writer. w indowing ,networkable up to 10 stations. multiple cash books etc. 200 pagecomprehensive manual. 90daystree technical support (0345-326009try before you buy!) Current retail price IsE129, SALE PRICE £9.95ref SA12. SAVE £120I!!

MINI MICRO FANS 12V 1.5" sq SALE PRICE E2. Ref SA13.12V2AMP LAPTOP psu's 110x55x4Omm (includesstandard IECsocket) and 2m lead with plug. 100-240v IP. E6.99 REF SA15.COMPLETE PC 300 WATT UPS SYSTEM Top of the rangeUPS system providing protection for your computer system andvaluable software against mains power fluctuations and cuts. Newand boxed, UK made Provides up to 5 mins running time in the eventof complete power failure to allow you to run your system downcorrectly. LAST FEW TO CLEAR AT £59 SAVE £30 ref SEP149P1SOLAR PATH LIGHTS Low energy walklights powered by thesun! builtin PIR sothey work whenyou walk past. Indudes solar panel& rechargeable bat. SALE PRICE E19.95 REF EP62BIG BROTHER PSU Cased PSU, 6v 2A output, 2m o/p lead, 1.5minput lead, UK made,220v. SALE PRICE E4.99 REF EP7

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http://www.pavillon.00.uk/bull-electricalRACAL MODEM BONANZA! 1 Rawl MPS 12231200/75modern,telephone lead, mains lead, manual and comms software, thecheapest way onto the net! all this for just £13 ref DEC13.4.6mw LASER POINTER. BRAND NEW MODEL NOW INSTOCK!, supplied in fully built form (looks like a nicepen) complete with handy pocket clip (which also actsas the on/off switch.) About 60 metres range! Runs on2 AAA batteries. Produces thin red beam ideal forlevels, gun sights, experiments etc. just E39.96 refDEC49 TRADE PRICE E28 MIN 10 PIECESBULL TENS UNIT Fully built and tested TENS (TranscutaneousElectrical Nerve Stimulation) unit, complete with electrodes and fullinstructions. TENS is used for the relief of pain etc in up to 70% ofsufferers. Drug free pain relief. safe and easy to use, can be used inconjunction with analgesics etc. £49 Ref TEN/1COMPUTER RS232 TERMINALS. (LIBERTY)Excellentquality modern units,(like wyse 50,$) 2xRS232, 20 function keys, 50thro to 38,400 baud, menu driven port, screen, cursor, and keyboardsetup menus (18 menu's). £29 REF NOV4.RUSSIAN MONOCULARS Amazing 20 times magnification.coated lenses, carrying case and shoulder strap.E29.95 REF BAR73PC PAL VGA TO TV CONVERTER Converts a colour TV intoa basic VGA screen. Complete w ith built in psu, lead and sAv a re.. Idealfor laptops or a cheap upgrade.Supplied in kit form for homeassembly. SALE PRICE 625 REF SA34EMERGENCY LIGHTING UNIT Complete unit with 2 doublebulb floodlights, built in charger andtauto switch. Fully cased. 6v 8AHlead acid req'd. (secondhand) £4 ref MAG4P11.SWINGFIRE GUIDED MISSILE WIRE. 4,200 metre reel ofultra thin 4 core insulated cable, 281bs breaking strain, less than 1mmthick! Ideal alarms, intercoms. dolls house's etc. E13.99 ref EP51ELECTRIC CAR WINDOW DE-ICERS Complete with cable.plug etc SALE PRICE JUST E4.99 REF SA28AUTO SUNCHARGER 155x 300mm solar panel with diode and 3metre lead fitted with a cigar plug. 12v 2watt. E8.99 REF SA25.ECLATRON FLASH TUBE As used in police car flashing lightsetc, full spec supplied, 60-100 flashes a min. £6.99 REF SA15B.24v AC 96WATT Cased power supply. New. £9.99 REF SA40MILITARYSPEGGEIGERCOUNTERS Unused anstraightfromHer majesty's forces. SALE PRICE E44 REF SA16

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MICRODRIVE STRPPERS Small cased tape drives ideal forstripping, lots of useful goodies including a smart case, and lots ofcomponents. SALE PRICE JUST £4.99 FOR FIVE REF SA26SOLAR POWER LA BSPECIA L You get TWO Tx6" 6v 130mAsolar cells, 4 LED's, wire, buzzer, switch plus 1 relay or.motor.Superbvalue let SALE PRICE JUST E4.99 REF SA27RGB/CGA/EGA/TTL COLOUR MONITORS 12' in goodcondition. Back anodised metal case. SALE PRICE E49 REF SA168PLUG IN ACORN PSU 19v AC 14w , £299 REF MAG3P 10POWER SUPPLY fully cased with mains and o/p leads 17v DC900mA output. Bargain price E5.99 ref MAG6P9ACORN ARCH NEDES PSU +5v 4.4A. on/off sw uncased,selectable mains input, 145x 100x45mm E3.99 REF MAG7P213.8V 1.9A PSU cased with leads. Just £9.99 REF MAG10P3UNIVERSAL SPEED CONTROLLER KIT Designed by us forthe C5 motor but ok for any 12v motor up to 30A. Complete with PCBetc. A heat sink may be required. E17.00 REF: MAG17PHONE CABLE AND COMPUTER COMMUNICATIONS

PACK Kit contains 100m of 6 core cable, 100 cable clips, 2 linedrivers with RS232 interfaces and all connectors etc. Ideal low costmethod of communicating between PCs over a long distance utilizingthe serial ports. Complete kit £8.99. Ref comp 1.VIEWDATA SYSTEMS made by Phillips, complete with internal1200/75 modem, keyboard, psu etc RGB and composite outputs,menu driven, autodialler etc. SALE PRICE E12.99 REF SA18AIR RIFLES .22 As used bythe Chinese army for training puposes,so there is a lot about! E3995 Ref EF78. 500 pellets £4.50 ref EF80.PLUG IN POWER SUPPLY SALE FROM E1.60 Plugs in to13A socket with outputlead. three types available, 9vdc 15OrnAE1.50ref SA19, 9vdc 200mA £2.00 ref SA20, 6.5vdc 500mA £2 ref SA21.VIDEO SENDER UNIT. Transmits both audio and video signalsfrom either a video camera, video recorder. TV or Computer etc to anystandard IV set in a 100' range! (tune TV to a spare channel) 12v DCop. Price is £15 REF: MAG15 12v psu is £5 extra REF: MAG5P2*M INATU RE RADIO TRANSCEIVERS A pair of walkie talkieswith a range up to 2 km in open country. Units measure 22x52/(155mm.Including cases and earp'ces. 2xPP3 req'd. £30.00 pr.REF: MAG30*FM TRANSMITTER KIT housed in a standard working 13Aadapter!! the bug runs directly off the mains so lasts forever! why pay£700? or price is £15 REF: EF62 (kit) Transmits to any FM radio.

*FM BUG BUILT AND TESTED superior design to kit. Suppliedto detective agencies. 9v battery req'd. £14 REF: MAG14TALKING COINBOX STRIPPER COMPLETE WITHCOINSLOT MECHANISMS originally made to retail atE79 each.these units are designed to convert an ordinary phone into apayphone. The units have the locks missing and sometimes brokenhinges. However they can be adapted for theiroriginal use or used forsomething else?? SALE PRICE JUST £2.50 REF SA23GAT AIR PISTOL PACK Complete with pistol, darts and pellets£12.95 Ref EF82B extra pellets (500) E4.50 ref EFS°.6"X12" AMORPHOUS SOLAR PANEL 12v 155x310mm130mA. SALE PRICE E4.99 REF SA24.

FIBRE OPTIC CABLE BUMPER PACK 10 metres for £4.99ref MAG5P13 ideal for experimenters! 30 m for £12.99 ref MAG13P1

MIXED GOODIES BOX OFMIXED COMPONENTS WEIGHING 2 KILOS

YOURS FOR JUST E6.994X28 TELESCOPIC SIGHTS Suitable for all air rifles, groundlenses, good light gathering properties. £19.95 ref R/7.RATTLE BACKS Interesting things these, small piece of solidperspex like material that it you try to spin it on the desk it only spinsone way! in fact if you spin it the 'wrong' way it stops of its own accordand go's back the other way! £1.99 ref GI/J01.GYROSCOPES Rememberthese?w ell we have found a companythat still manufactures these popular scientific toys, perfect gift or foreducational use etc. £6 ref EP70HYPOTHERMIA SPACE BLANKET 215x 150cm aluminisedfoil blanket, reflects more than 90% of body heat. Also suitable for theconstruction of two way mirrors! E3.99 each ref 0/L041.LENSTATIC RANGER COMPASS Oil filled capsule, strongmetal case, large luminous points. Sight line with magnifying viewer.50mm die, 86gm. £1099 ref 0/K604.RECHARGE ORDINARY BATTERIES UP TO 10 TIMES!With the Battery Wizard! Uses the latest pulse wave charge systemto charge all popular brands of ordinary batteries AAA, AA, C, D, fouratatime! Led system showswhen batteries arecharged, automaticallyrejects unsuitable cells. complete with mains adaptor. BS approved.Price is £21.95 ref EP31.TALKING WATCH Yes, it actually tells you the time atthe press ofa button. Also features a voice alarm that wakes you up and tells youwhat the time is! Lithium cell induded. £7.99 ref EP26.

PHOTOGRAPHIC RADAR TRAPS CAN COST YOUYOUR LICENCE! The new multiband 2000 radar detector canprevent even the most responsible of driver -strum losing theirlicence!Adjustable audible alarm with 8 flashing lads gives instant warning ofradar zones. Detects X, K, and Ka bands, 3 mile range, 'over the hill''around bends' and 'reartrap facilities. micro sizejust4.25"x2.5"x.75",Can pay for itself in just one day! £79.95 ref EP3.SANYO NICAD PACKS 120mmx 14mm 4.8v 270 maH suitablefor cordless phones etc. Pack of 2 just £5 ref EP78.3" DISCS As used on older Amstrad machines, Spectrum plus3'setc £3 each ref BAR400.STEREO MICROSOPES BACK IN STOCK Russian, 200xcomplete with lenses, lights, filters etc etc very comprehensivemicroscope that would normally be around the £700 mark, our priceis just £299 (full money back guarantee) full details in catalogue. Ref95/300.

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PORTABLE X RAY MACHINE PLANS Easy to constructplans on a simple and cheap way to build a home X-ray machine!Effective device, X-ray sealed assemblies. can be used forexperimental purposes. Not a toy or for minors! £6/set. Ref F/XP1.TELEKINETIC ENHANCER PLANS Mystify and amaze yourfriends by creating motion with no known apparent means or cause.Uses no electrical or mechanical connections, no special gimmicksyetproducespoative motion and effect. Excellentforscienceprojects,magic shows, party demonstrations or serious research &development of this strange and amazing phychic phenomenon.£4/set Ref F/TKE 1.

ELECTRONIC HYPNOSIS PLANS & DATA This data showsseveral ways to put subjects under your control. I nduded is a fullvolume reference text and several construction plans that whenassembled can produce highly effective stimuli. This material mustbe used cautiously. It is for use as entertainment at parties etc only,by those experienced in its use. E15/set. Ref F/EH2.GRAVITY GENERATOR PLANS This unique plandemonstrates a simple electrical phenomena that produces an anti-gravity effect. You can actually build a small mock spaceship out ofsimple materials and without any visible means- cause it to levitate.£10/set Ref F/GRA1.

WORLDS SMALLEST TESLA COIL/LIGHTENINGDISPLAY GLOBE PLANS Produces up to 750,000 volts ofdischarge, experiment with extraordinary HV effects, Plasma in ajar, St Elmo's fire, Corona, excellent science project or conversationpiece. £5/set Ref F/BTC1/LG5.COPPER VAPOUR LASER PLANS Produces 100mw ofvisible green light. High coherency and spectral quality similar toArgon laser but easier and less costly to build yet far more effident.This part cul ardea gn was developed atthe Atomic EnergyCommisionof NEGEV in Israel. E10/set Ref F/CVL1.VOICE SCRAMBLER PLANS Minature solid state systemturns speech sound into indecipherable noise that cannot beunderstood without a second matching unit. Use on telephone toprevent third party listening and bugging. £6/set Ref FNS9.PULSED TV JOKER PLANS Little hand held device utilisespulse techniques that will completely disrupt TV picture and sound!works on FM too! DISCRETION ADVISED. £8/set Ref F/TJ5.BODYHEAT TELESCOPE PLANS Highly directional longrange device uses recent technology to detect the presence of livi ngbodies, warm and hot spots, heat leaks etc. Intended for security, lawenforcement, research and development, etc. Excellent securitydevice or very interesting science project. £8/set Ref F/BHT 1,BURNING, CUTTING CO2 LASER PLANS Projects aninvisible beam of heat capable of burning and melting materials overa considerable distance. This laser is one of the most efficient,converting 10% input power into useful output. Not only is this devicea workhorse in welding, cutting and heat processing materials but itis also a likely candidate as an effective directed energy beamweapon against missiles, aircraft, ground -to -ground, etc. Particlebeams may very well utilize a laser of this type to blast a channel inthe atmosphere for a high energy stream of neutrons or otherparticles. The device is easily applicable to burning and etchingwood, cutting, plastics, textiles etc £12/set Ref F/LC7.MYSTERY ANTI GRAVITY DEVICE PLANS Uses simpleconcept. Objects float in air and move to the touch. Defies gravity,amazing gift, conversation piece, magic trick or science project. E6/set Ref F/ANT1K.

ULTRASONIC BLASTER PLANS Laboratory source of sonicshock waves. Blow holes in metal, produce 'cold' steam, atomizeliquides. Many cleaning uses for PC boards, jewllery, coins, smallparts etc. £6/set Ref FAJLB1.ULTFtA H IG H GA IN AMP/STETHOSCOP IC M IKE/SOUNDAND VIBRATION DETECTOR PLANS Ultrasensitive deviceenables one to hear a whole new world of sounds. Listen throughwalls, windows, floors etc. Many applications shown, from lawenforcement, nature listening, medical heartbeat, to mechanicaldevices. £6/set Ref F/HGA7ANTI DOG FORCE FIELD PLANS Highly effective circuitproduces time variable pulses of accoustical energy that dogscannot tolerate £6/set Ref F/DOG2LASER BOUNCE LISTENER SYSTEM PLANS Allows youto hear sounds from a premises without gaining access. £12/set RefF/LLIST1

CRAWLING INSECT ROASTER PLANS Harmless highfrequency energy pulses destroy pests as they crawl intothe energy field! £4/set Ref F/RCR1LASER LIGHT SHOW PLANS Do it yourself plans show threemethods £6 Ref F/LLS1PHASOR BLAST WAVE PISTOL SERIES PLANSHandheld, has large transducer and battery capacity with extemalcontrols. E6/set Ref F/PSP4INFINITY TRANSMITTER PLANS Telephone line grabber/room monitor. The ultimate in home/office security and safety! simpleto use! Call your home or office phone, push a secret tone on yourtelephone to access either: A) On premises sound and voices or B)Existing conversation with break-in capability for emergencymessages £7 Ref F/TELEGFtAB.BUG DETECTOR PLANS Is that someone getting the goods onyou? Easy to construct device locates any hidden source of radioenergy! Sniffs out and finds bugs and other sources of bothersomeinterference. Detects low, high and UHF frequencies. £5/set Ref F/BD1.

ELECTROMAGNETIC GUN PLANS Projects a metal objecta considerable distance -requires adult supervision £5 ref F/EM L2.ELECTRIC MAN PLANS, SHOCK PEOPLE WITH THETOUCH OF YOUR HAND! £5/set Ref F/EMA1.PARABOLIC DISH MICROPHONE PLANS Listen to distantsounds and voices, open windows, sound sources in 'hard to get orhostile premises. Uses satellite technology to gather distant soundsand focus them to our ultra sensitive electronics. Plans also show anoptional wireless link system. E8/set ref F/PM52 FOR 1 MULTIFUNCTIONAL HIGH FREQUENCY ANDHIGH DC VOLTAGE, SOLID STATE TESLA COIL ANDVARIABLE 100,000 VDCOUTPUTGENERATORPLANSOperates on 9- 12vdc, many possible experiments. £10 Ref F/HVM7/TCL4.

WOLVERHAMPTON BRANCHNOW OPEN AT WORCESTER ST

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MINI FM TRANSMITTER KIT Very high gain preamp, suppliedcomplete with FET electret microphone. Designed to cover 88-108Mhz but easily changed to cover 63-130 Mhz. Works with a common9v (PP3) battery. 0.2W RF. £7 Ref 1(101.

ELECTRONIC SIREN KIT Impressive 5 watt power outp ut. Idealfor car/bike alarm etc 6-12v dc max current 1A, 1.2khz £6 Ref 1003.3-30V POWER SUPPLY KIT Variable, stabilized power supplyfor lab use. Short circuit protected, suitable for profesional or amateuruse 24v 3A transformer is needed to complete the kit. £14 Ref 1007.

1 WATT FM TRANSMITTER KM Supplied with piezo electricmicrophone 8-30vdc. At 25-30v you will get nearly 2 watts! £12 ref1009.

FM/AM SCANNER KIT Well not quite, you have to turn the knobyour self but you will hear things on this radio that you would not hearon an ordinary radio (even TV). Covers 50-160mhz on both AM andFM. Built in 5 watt amplifier, inc speaker £15 ref 1013.

MOSQUITO REPELLER KIT Modern way to keep midges atbay! Runs for about a month on one 1.5v battery. £7 Ref 1015.3 CHANNEL SOUND TO LIGHT KIT Wireless system, mainsoperated, separate sensitivity adjustment for each channel, 1,200 wpower handling, microphone included. £14 Ref 1014.

MOTORBIKE/CYCLE TREMBLER ALARM KIT Adjustablesensitivity, preset alarm time, auto reset. Could be connected to hornetc. £12 Ref 1011.

0-6 MINUTE TIMER KIT adjustable, will switch up to 2A mains.Perfect for alarms, photography, etc. £7 Ref 1020.

4 WATT FM TRANSMITTER KIT Small but powerful FMtransmitter, 3 RF stages, microphone and audio preamp included.E20 Ref 1028.

STROBE LIGHT KR Adjustable from 1-60 hz (a lot faster thanconventional strobes). Mains operated. £16 Ref 1037.ULTRASONIC RADAR KIT Ideal as a movement detector with arange of about 10 metres, automate your cat tap! 12v dc. E15 Ref1049.

LIQUID LEVEL DETECTOR KIT Useful fortanks, ponds, baths,rain alarm, leak detector etc. Will switch 2A mains. E5 Ref 1081.COMBINATION LOCK KIT 9 key, programmable, complete withkeypad, will switch 2A mains 9v dc operation. £10 ref 1114.PHONE BUG DETECTOR KIT This device will warn you ifsomebody is eavesdropping on your line. £6 ref 1130.ROBOT VOICE KIT Interesting circuit that distorts your voice!adjustable, answerthe p hone with a differentvoice! 12vdcE9 ref 1131

TELEPHONE BUG KIT Small bug powered by the 'phone line,starts transmitting as soon as the phone is picked up! £8 Ref 1135.FUNCTION GENERATOR KIT Produces sinusoidal, saw toothand square waves from 20-20khz, separate level controls for eachshape. Will produce all 3 together. 24vac. £16 ref 1008.

3 CHANNEL LIGHT CHASER KIT 800 watts per channel,speed and direction controlssupplied with 12 LEDS (you can tttnacsinstead to make kit mains, not supplied) 9-12vdc £17 ref 1026.12V FLOU RESC ENT LAMP DRIVER KIT Light up 4 foottubesfrom your car battery! 9v 2a transformer also required. £8 ref 1069.VOX SW ITCH KIT Sound activated switch ideal for making buggingtape recorders etc, adjustable sensitivity. £8 ref 1073.INCARSOUNDTO LIGHT IMPutsomeatmosphereinyourcarwith this mini 3 channel sound to light. Each channel has 6 led's. £10ref 1086.

7W HI Fl AMPLIFIER KIT Useful, powerful, ideal for audiosystems, intercoms etc. 12-18vdc £7 ref 1025.

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http://www.pavillon.co.uk/bull-electricalPREAMP MIXER KIT 3 input mono mixer, sep bass and treblecontrols plus individual level controls, 18vdc, input sens 100mA. £15ref 1052.

METAL DETECTOR KIT Range 15-20cm, complete with case,9vdc. £8 ref 1022.SINGLE CHANNEL SOUND TO LIGHT KITMains operated,add rythum to your party for only £8 ref 1006.SOU ND EFFECTS GE NERATOR KIT Produces sounds rangingfrom bird chips to sirens. Complete with speaker, add sound effectsto your projects for just £9 ref 1045.GUITAR PREAMP KITCompletewith tone contrds, small enoughto fit in any guitar, based on TL082 IC, 9-12vdc £8 Ref 1091.16 WATT FM TRANSMITTER (BUILT) 4 stage high power,preamp required 12-18vdc, can use ground plane, yagi or opendipole. E69 ref 1021.

TELEPHONE AMPLIFIER KIT Very sensitive amplifier whichuses a pickup coil (supplied)will let you fdlow a conversation with outholding the 'phone. £11 ref 1059.

HUMIDITY METER KIT Builds into a precision LCD humiditySOME OF OUR PRODUCTS MAY BE UNLICENSABLE Of THE UK

CAL11 SQT (FSTMIUS I) SO YEARS)

MAjl.3jopmgR.TERINIS:f.:CAS11TOOR.,CIIEQUE=WHITORBERTLIA1,13.1*P4LtISNAMMI.I.

TELL>01273 203500

meter, 9 is design, pcb, lcd display and all components included. E49

PC TIMER KR Four channel output controlled by your PC, willswitch high current mains with relays (supplied). Software suppliedso you can program the channelsto do what you want w henever youwant. Minimum system configeration is 286, VGA, 4.1,640k, serialport, hard drive with min 100k free. £24.99DIVINING RODS Expensive technology cannot challenge the foolproof art ofwater divining, pa ssed dow n from generation togeneration.Seeing is believing. Use in the home, garden, countryside or desert,it's divinely simple! £4.99 a pair ref E/3.H UGE BUBBLE MAKING KIT You'll be amazed at the the sizeof the bubbles you can acheive with this bubble making kit. Once youhave got the knack it is possible to make bubbles of up to 40 feet long.£11.99 ref E/9.FM CORDLESS M ICROPHON EThis unilisan FM broadcastingstation in minature, 3 transistor transmitter with electret condensermic+fet amp design result in maximum sensitivityand broad freque ncyresponse. 90-105m hz, 50-1500hz, 500 foot range in open country!PP3 battery required. £15.00 ref 15P42A.MAGNETIC MARBLES They have been around for a number ofyears but still give rise to curiosity and amazement. A pack of 12 isjust£3.99 ref GI/R20STETHOSCOPES A fully functioning stethoscope for all thoseintricate projects. Enables you to listen to motors, pipes, heartbeats,walls, insects etc. E6 ref MAR6P6.NICKEL PLATING KIT Proffesional electroplating kit that willtransform rusting parts into showpieces in 3 hours! Will plate ontosteel, iron, bronze, gunmetal, copper, welded,silversoldered orb razedjoints. Kit i ncludes enough to plate 1,000 sq inches. You will also need

a 12v supply, a container and 2 12v light bulbs £39.99 ref NIK39.SHOP WOBBLERSISmail assemblies designed to take D sizebatteries and 'wobble' signs about in shops! £3.99 Ref SEP4P2.OMRON ELECTRONIC INTERVAL TIMERS.

NEW LOW PRICES TO CLEAR!!!M Mature adjustable timers, 4 pole c/o output 3A 240v,HY1230S, 12vDC adjustable from 0-30 secs. £4.99HY1210M, 12vDC adjustable from 0-10 mins. £4.99HY1260M, 12vDC adjustable from 0-60 mins. £4.99HY2460M, 24vAC adjustable from 0-60 mins. £2.99HY243H, 24vAC adjustable from 0-3 hours. £2.99HY2401S, 240v adjustable from 0-1 secs. £4.99HY2405S, 240v adjustable from 0-5 secs. £4.99HY24060m, 240v adjustable from 0-60 mins. £6.99DRINKING BIRD Remember these? hook onto wine glass (sup-plied) and they drink, stand up,dri nkstand up ETC! £4 each Ref EF1SOLAR POWER LAB SPECIALVou get TWO 6*x6' 6v 130mAsolar cells, 4 LED's, wire, buzzer, switch plus 1 relay or motor. Superbvalue kit just £5.99 REF: MAG6P8BUGGING TAPE RECORDER Small voice activated recorder,uses m lac cassette complete with headphones -E28.99 ref MAR29P1

PLUG IN ACORN PSU 19v AC 14w , £299 REF MAG3P10POWER SUPPLY fully cased with mains and o/p leads 17v DC90CmA output. Bargain price £5.99 ref MAG6P99v DC POWERSUPPLYStandard plug intype 150ma 9v DCwithlead and DC power plug. price for two is £2.99 ref AUG3P4.13.8V 1.9A psu cased with leads Just £9.99 REF MAG10P3INFRA RED REMOTE CONTROLLERSOnginanymade for hispec satellite equipment but perfect for all sorts of remote controlprojects. Our dearance price is just £2 REF: MAG2MAINSCABLE Precut black 2 core 2 metre lengths ideal forrepairs, projects etc. 50 metres for E1.99 ref AUG2P7.COMPOSITE VIDEO Kr'''. Converts composite video into sepa-rate H sync, V sync, and video. 12v DC £8.00 REF: MAG8P2.UNIVERSAL PC POWER SUPPLY complete with Needs,switch, tan etc.200w at £20 REF: MAG2OP3 (265x155x125mm).GYROSCOPE About 3' high and an excellent educational toy for allages! Price with instruction booklet £6 Ref EF15.FUTURE PC POWER SUPPLIES These are 295x135x6Omm,4 drive connectors 1 mother board connector. 150watt, 12v fan, iecinlet and on/off switch. E12 Ref EF6.VENUS FLYTRAP Kr Grow your own carnivorousplantwiththissimple kit £3 ref EF34.TWEETERS 2' diameter good quality tweeter 140R (ok with theabove speaker) 2 for E2 REF: MAG2P5 or 4 for £3 REF: MAG3P46"X12" AMORPHOUS SOLAR PANEL 12v 155x310mm130mA. Bargain price just 05.99 ea REF MAG6P12.FIBRE OPTIC CABLE BUMPER PACK 10 metres for £4.99ref MAG5P13 ideal for experimenters! 30 m for £12.99 ref MAG13P1ROCK LIGHTS Unusual things these, two pieces of rock that glowwhen rubbed together! belived to cause rain!E3 a pair Ref EF29.3' by 1' AMORPHOUS SOLAR PANELS 14.5v, 700mA 10watts, aluminium frame, screw terminals, £44.95 ret MAG45.ELECTRONIC ACCUPUNCTURE KIT Buildsintoan electronicversion instead of needles! good to experiment with. £7 ref 7P30SHOCKING COIL KfT Build this little battery operated device intoall sorts of things, also gets worms out of the ground! £7 ref 7P36.FLYING PARROTS Easily assembled kit that builds a parrot thatactually flaps its wings and flies! 50 m range £6 ref EF2.HIGH POWER CATAPULTS Hinged arm brace for stability,tempered steel yoke, super strength latex power bands Departurespeed of ammunition is in excess of 200 miles per hour! Range of over200 metres! £7.99 ref R/9.BALLON MANUFACTURING KIT British made, small blobblows into a large, longlasting balloon, hours of fun! £3.99 refGI/E99R

WE BUY SURPLUS STOCK FOR CASH

FREE CATALOGUE100 PAGE CATALOGUE NOW

AVAILABLE, 45P STAMP OR FREEON REQUEST WITH ORDER.


CLASSIFIEDTEL 0181 652 3620 FAX 0181 652 8956

ARTICLES WANTED

WE WANT TO BUY!!IN VIEW OF THE EXTREMELY

RAPID CHANGE TAKING PLACEIN THE ELECTRONICS

INDUSTRY, LARGE QUANTITIESOF COMPONENTS BECOMEREDUNDANT. WE ARE CASH

PURCHASERS OF SUCHMATERIALS AND WOULD

APPRECIATE A TELEPHONECALL OR A LIST IF AVAILABLE.

WE PAY TOP PRICES ANDCOLLECT.

R. HENSON LTD.21 Lodge Lane, N.Finchley,

London N12 8JG.5 Mins, from Tally Ho Corner.

TELEPHONE0181-445-2713/0749FAX 0181-445-5702

**WANTED**Test equipment, Electronic Scrap,Valves, Transmitters/Receivers,Factory & Warehouse Clearance.

Confidentiality Assured.

TELFORD ELECTRONICSPhone: 01952 605451

Fax: 01952 677978

TOP PRICES PAIDFor all your valves, tubes. semi

conductors and IC's.

Langrex Supplies Limited1 Mayo Road, Croydon

Surrey CR0 20PTEL: 0181-684 1166FAX: 0181-684 3056

WANTEDTOP PRICES PAID

For all your Test Equipment,Receivers, Transmitters etc.Factory Clearance, Prompt

Service and Payment.

HTB ELEKTRONIKAlter Apeler Weg 5

27619 Schiffdorf, GermanyTel: 0049 4706 7044Fax: 0049 4706 7049

WANTEDTest equipment, receivers, valves,transmitters, components, cableand electronic scrap and quantity.

Prompt service and cash.M & B RADIO

86 Bishopgate StreetLeeds LS1 4BB

Tel: 0113 2435649Fax: 0113 2426881

ELECTRONICSVALVES &

SEMICONDUCTORS

Phone for a mostcourteous quotation

We are one of the largeststockists of valves etc,

in the U.K.

COLOMORELECTRONICS LTD

170 Goldhawk Road,London W12 8HJ

England.Tel: 0181 743 0899Fax: 0181 749 3934

VALVES, and CRTs AVAILABLEONE MILLION VALVES stocked for Audio, Receiving, Transmit-ting & RF Heating. Rare brands such as Mullard & GEC available.

Also MAGNETRONS, KLYSTRONS, CRTs and SOCKETS.Large stocks of Russian & Sovtek items.

Please ask for our free catalogues of valves or CRTs.

VALVES, etc. WANTEDMost types considered but especially KT88 (£48), PX4/PX2500), KT66 (05), KT77 (£15), EL34 (£10), EL37 (£9), ECC83 (E3).Valves must be UK manufacture to achieve prices mentioned.Also various valve -era equipment e.g. Garrard 301, (up to) £80.

Ask for a free copy of our wanted List.

BILLINGTON EXPORT LTD., Billingshurst, Sussex RH14 9EZ.Tel: 01403 784961 Fax: 01403 783519

VISITORS STRICTLY BY APPOINTMENT. MINIMUM ORDER E50 plus VAT

ARTICLES FOR SALE

* * FOR SALE * *Hewlett Packard HP54120T 20G1-1,

Digital Storage OscilloscopeThe unit comprises a HP54120A

mainframe and a HP54121A 4channel input

The unit is in excellent condition andis complete with comprehensive

manualOffers are invited

KFS DISTRIBUTORS LTDTel/Fax. 0121-440 2900

KL SystemsMicrocontroller based electronic controlsystems. Specialising in the applica-tion of Zilog Z8 technology. Software,hardware and consultancy. Z8 devel-opment system available for £100.

Tel: 01642 480620or see Internet for further details.http:11www.wp. comIKLsystems

SURPLUSSALE

THIS MONTH'S SALE INCLUDES: -Spectrum Analysers, Oscilloscopes,

Signal Generators, Voltmeters,Power Units, Frequency Counters,

Receivers, Transmitters, Ex PMR Equipment,Photographic & Video Equipment, Components,

& Miscellaneous items etc.

ALL EQUIPMENT IS SOLD AS SEEN.ALL PRICES EXCLUDE V.A.T.

NO MINIMUM ORDER.

RING TODAY FOR THIS MONTH'S CATALOGUE.

WANTEDSURPLUS ELECTRONIC

COMPONENTS ANDEQUIPMENT

We also welcome the opportunity to quote forcomplete factory clearance

B. BAMBER ELECTRONICS5 STATION ROAD, LITTLEPORT, CAMBS.

Phone: ELY (01353) 860185Fax: ELY (01353) 863245

CLASSIFIEDTEL 0181 652 3620 FAX 0181 652 8956

ARTICLES FOR SALE

,r0: )' At )0'

SUPPLIER OF QUALITY USEDTEST INSTRUMENTS

11.010110l Y.mym......... ...VI *N. 1.1.1 .06

' ''.... ...

_...II, t, It

III.......7.........

.........

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( IR( Li NO. 146 ON REPLY (ARO

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 542457ZEIMINIZEMZEIZZESI

INDEX TO ADVERTISERSPAGE PAGE PAGE

Airlink 239 Halcyon 183 Quickroute 178Anchor 255 Hart 211

Ralfe IBCBK Electronics 239 Ice 187Bull 260, 261 Iosis 241 Seetrax 214

CMSCPC

184200

JPGJohns Radio

241235

StagStewartSurrey

178251183

Cricklewood 178 Kestral 241Crossware 241 Keytronics 237 TDS 184Crownhill 183 Langrex 239

TelfordTelnet

195206

Dataman OBC M & B Radio 209 Those 204Devantech 239 Milford 251 Tie Pie 243Display 233

Noral 189Tsien 184

Electromail 207 No 1 Systems 246 Ultimate IFC

Eight year EW indexHard copy or diskIncludes over 600 circuit idea references

Whether as a PC data base or as hard copy,SoftCopy can supply a complete index ofElectronics World articles going back over thepast eight years.

The computerised index of Electronics Worldmagazine covers the eight years from 1987 to1995 - volumes 94 to 101 inclusive - and isavailable now. It contains almost 2000references to articles, circuit ideas andapplications - including a synopsis for each.

The EW index data base is easy to use andvery fast. It runs on any IBM or compatible PCwith 512k ram and a hard disk.

Even though the disk -based index has beenexpanded significantly from five years to eight,its price is still only £20 inclusive. Pleasespecify whether you need 51/4in, 3.5in DD or3.5in HD format. Existing users can obtain anupgrade for £15 by quoting their serial numberwith their order.

Hard copy Electronics World indexIndexes on paper for volumes 100 and 101 are availableat £2 each, excluding postage.

[K1 Circuit

Remote motor controlResistance multiplierSCR InverterSample -and -infinite holdSchmitt trigger, prog. thresholdsSelf -ID for plugs and sensorsSensor, Linear CurrentServo, High -torque positionServo, SimpleSimulator, insertion & return loss ingle-pot Polarity & Gain adjustSoft -start filament driverSpeech compressorSquare wave generator, 1:Status detection over twoStepper Motor ControllerStepper Motor ControllerStepper Motor DriverStereo expanderSwitch, Low voltage

Photo copies ofElectronics World articlesPhoto copies from back issues of

Electronics World are available at a

flat rate of £3 per article or 50p per

circuit idea, both excluding

postage.

Idvas

SIMULATOR, INSERTION & RETURN LOSSC J Hall

May 1992, p422

"Simultaneous insertion and returnloss plots".Modelling a return -loss bridge atthe relevant port allow plot ofinsertion loss, and, withoutfurther computation, return lossplot simultaneously.

Del Design: RF

Directional couplers, hybridGigahertz Systems on a ChipHF receiver performanceHF receiving oop, improvedHepa for RF power amplifier designHigh quality punch for radiocommsHybrids in RF combinersImpedance transformationMeasuring DetectorsMeasuring with TDR011=111=1MMicrowaves, Mew wave /2Noise source, self -calibratingPolyphase SSBRF Design RevolutionRF Power Measurements in milliwattsRF Transistors, Using /1

RF Transistors, Using /2RF Transistors, Using /3

RF filter for electro-explosives

MICROWAVES, NEW WAVEMike Hosking

#1 Concepts, circuits a dApril 1994, p276

#2 The Laws of MicrostripMay 1994, p418

#3 Lumped components & waJune 1994, p472

#4 Active devices for milwaves.July 1994, P571

RS Oscilator and amplifieAugust 1994, p666

F1-Hel F2 -Search F3- mo F4 Edit F5 --Other F18 -Exit

Ordering detailsThe EW index data base price of £20includes UK postage and VAT. Add anextra £1 for overseas EC orders or £5 fornon -EC overseas orders.

Postal charges on hard copy indexesand on photocopies are 50p UK, £1 forthe rest of the EC or £2 worldwide.

For enquiries about photocopies, etc,

please send an sae to SoftCopy Ltd atthe address below.

Send your order to SoftCopy Ltd., 1Vineries Close, Cheltenham GL53 ONU,tel 01242 241455, or e-mail [email protected]. Pleasemake cheques payable to SoftCopy Ltd- not EW or Reed Business Publishing.Please allow up to 28 days for delivery.

ELECTRONIC UPDATEContact Malcolm Wells on

0181-652 3620New Flight ElectronicsInternational Catalogue SetYou now have access to the world's latest:* Electronics Training Equipment* Microprocessor Training Equipment* Test and Measurement Equipment* PC Cards

via "Flight's" latest catalogue set.

We are specialists in the provision ofinnovative top quality electronicstrainers, breadboards, test andmeasurement, PC cards andmicroprocessor evaluationequipment.

Our extensive range covers everyneed, call today for your freecatalogue set.

( IR( II NO.148 ON REPLY CARD

For friendly service & fast deliveryphone Feedback

NEW Feedback T&MCatalogue

The latest edition of the Feed-back Test & Measurement cata-logue is now available. Over 60pages packed with more than800 products divided into over20 sections. The catalogue isindexed for both product andmanufacturer and is fully illus-trated. Whether you are lookingfor an individual product, a com-plete workstation, or a solutionto a particular Test & Measure-ment need the NEW Feedbackcatalogue will sove your prob-lems, send for a copy NOW!


A regular advertising feature enablingreaders to obtain more informationon companies' products or services.

NEW CATALOGUEThe new 1996 NationalInstruments InstrumentationReference and Catalogue isavailable now. Discover how todevelop integrated systems fortest and measurement andindustrial automation. Includesdetails of over 500 software andhardware products for PCs andworkstations. Includes valuabletutorials on data acquisition andinstrument control.

NATIONAL INSTRUMENTSTel: 01635 523545

1995 MASTER PRODUCTCATALOGUE NOW OUT!

Test and instrument control solutions.48 pages of full description and technicaldata on our own range of solutions to yourPC and PS2 interfacing problems; IEEE488(GPIB) * DID' Timer/Counters * RS232 *RS422/485 * A/D D/A * plus OptoIsolated versions. New Parallel/SerialRS232, Opto Dual RS232, Motion Control,Converter and Repeater for 1995!ISO 9001 Quality guarantee /UK design and manufacture /36 month no -quibble warranty /Telephone hotline support /Competitive pricing on the page /Intelligent solutions 8 friendly service /

BRAIN BOXESUnif 3f Wavertree Boulevard South

Wavertree Technology ParkLiverpool L7 9PF

Tel: 0151 220 2500 Fax: 0151 252 0446

( IRCLE NO. 151 ON REPLY CARD

TAB

'Oa

SPECTRUM ANALYSERS

HP141T1.25GHz system (85528, 8554B) £1250

HP8557A 350MHz (fitted in 182C mainframe) £1500

HP3580A 5Hz-50kHz audio frequency spectrum

analyser £750 to £1250

HP3582A audio frequency fit analyser dual -channel £2000

HP8568A high -specification 1.5GHz spectrum analyser £7500

MARCONI 2386 100Hz-26.5GHz (in 1Hz steps!) £15000

TEKTRONIX 492 21GHz portable spectrum analyser, with options 12 & 3,

and complete with waveguide mixer set (and diplexer) to cover

18-40GHz £7000

ralfe electronics exclusivelyprofessional T

36 Eastcote Lane South Harrow Middx HA2 8DB England TEL ( 44) 0181-422 3593 FAX (+44) 0181-423 4009

EST41

YRS

DISTRIBUZIONE E ASSISTENZA, ITALY: TLC RADIO, ROMA (06)871 90254

MARCONI INSTRUMENTS

20194 synthesized AM/FM signal gen

80kHz-1040MHz £2000

2305 modulation analyser 50kHz-2.3GHz £2500

2828A/2629 digital simulator/analyser £500

2382 spectrum analyser hi -spec 100Hz-400MHz £8500

2955B radio communications test sets - LATEST 'B'

MODELS £4000

2926 TV generator 8 inserter (NTSC vanant) £500

6460/6421 power meter 8 sensor 10MHz-12.4GHz £350

6500 amplitude analyser Lw 2c 6514 waveguide detectors

6960 microwave power meter with 6910 power sensor

10MHz-20GHz

OA2805A porn regenerator test set

TF2910/4 non-linear distortion (video) test set

TF2910 TV interval timer

TEST EQUIPMENTANRITSU MF76A 18GHz microwave frequencycounter

BRUEL & KJAER 1023 sine generator

BRUEL & KJAER 1027 sine random generator

BRUEL & KJAER 2619 preamplifier complete with1/2" mic

BRUEL & KJAER 2619 preamplifier complete with1/2" mic

BRUEL & KJAER 2511 vibration meter (field set with 1621filter) £1000

£1000

£1500

£600

BRUEL & KJAER 2307 level recorder

BRUEL & KJAER 2317 portable level recorder

BRUEL & KJAER 2607 measuring amplifier

£1500

£1250

£1750

£500

£500

ralfe electronics exclusivelyprofessional T&M C)

SEND FOR LATEST STOCK LIST. WE FAX LISTSAND SHIP WORLDWIDE. ALL FULLY LAB -TESTED

AND NO -QUIBBLE GUARANTEED0

urns

IS09002 ACCREDITED STOCKISTCERT 95/013 MEASUREMENT & TEST EQUIPMENT CERT.' 95/013

£2500

£900

£750

f500

£250

BRUEL & KJAER 2609 measuring amplifier £750

BRUEL & KJAER 2308 analogue X -Y pen recorder £750

BRUEL & KJAER 2639 preamplifier £325

CHASE LFR1000 interference measuring receiver9kHz-150kHz

DATRON 1061 & 1061A - various, digital multimeter & 1065 -call from £500

£1000

HEWLETT PACKARD

IT7i WV i r C --.

1111...g.: i - -::11

DATRON 1065 digital multimeter all ranges plusIEEE £500

FARNELL 2081 /100 100W RF power meterDC-500MHz (1GHz)

IDACOM PT502 protocol analyser (HewlettPackard E3910B with E3936A)

JJ INSTRUMENTS CR600 2 -channel penrecorder

KIKUSUI 8520 frequency response analyser with sweepgenerator 4600

£200

£2000

£250

£500

PHILIPS PM5167 1 mHz-10MHz function generator £275

PHILIPS PM8272 X -Y & Y -t dual -channel pen recorder £850

RACAL -DANA 1992 frequency counter 1.3 Ghz IEEEoption £700

RACAL 9008 automatic modulation meter £350

RACAL -DANA 9300 milli -voltmeter £400

RACAL -DANA 9301A true RMS RF milli -voltmeter £350

SYSTRON DONNER 1300 synthesized signal generator100Hz-1GHz GPIB £1350

TEKTRONIX AA501/SG505 distortion analyser (completewith TM503) £1250

TEKTRONIX P6303 o'scope probes NEW 250MHz X1 /X10with readout pin £50 ea

TEKTRONIX 1503 tdr metallic -cable tester withopts 03/04 £1000

TEKTRONIX 2465 option CTS oscilloscope £2000

TEKTRONIX P6201 FET PROBE £350

WANDEL & GOLTERMANN WM30 level tracer £500

WAVETEK 23 synthesized function generator 0.01Hz-12MHz £1250

WAVETEK 1067 opt 522 1-500MHz sweep generator £500

WAYNE KERR 3220 20A bias unit (for 3245 inductanceanalyser) £1250

SPECIAL OFFER THIS MONTH ONLY ON HEWLETT PACKARDDIGITAL TRANSMISSION TESTERS, PROTOCOL ANALYSERS

Examples: HP37724A SDH/PDH portable test sets -Condition as new, price £5000 (were listing at ca £20K!) - also37772A optical interfaces available for STM-1, £1500 (list over 6K).

*SPECIAL OFFER THIS MONTH ONLY*** HEWLETT PACKARD 8673M **

synthesized signal generators 2-18GHz(Similar model to 86738 but coverage as above)

Few only available at £6,000.(Will be listing at £7,500)

64000 -SERIES MDS:

64700A, MAINFRAMES WITH:6474 7B, 64771G, 64703A, 64704A, 64751A, 64172B, 64748A, 64748C,64787B, 64604A, 64783A, 64172B, 64746J, 64744A/C/E, 64780A.

SEND FOR COMPLETE LISTING AND QUOTATION

1S09002 ACCREDITED STOCKIST-MEASUREMENT & TEST EQUIPMENT

THE WORLD'SMOST

POWERFUL,PORTABLE

PROGRAMMERSCompare the Dataman 54 with any

other programmer and you'll see

why it's the world's undisputed number one.

S4 is capable of programming 8 and 16 -bit

EPROMs, EEPROMs, PEROMs, 5 and 12V FLASH,

BOOT -BLOCK FLASH, PICs, 8751 Microcontrollers and

more. 54 also emulates ROM and RAM as standard!

S4 is the only truly hand held programmer that ships

complete with all emulation leads, organiser -style

manual, AC charger, spare library ROM, both DOS and

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and ready to go! Who else offers you all this plus a three

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Customer support is second to none. The very latest

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Customers NEVER pay for upgrades or technical support.

Dataman-48

(ech

Ur

CreditCard Hotline01300 320719

w Dataman-48 programmer adds Pinsmart®

to provide true no -adaptor programming

48 -pin OIL devices. Dataman-48 connects

Orders received by 4pm will normally be despatched same day. Order today, get it tomorrow!

Access

straight to your PC's parallel port and works great with

laptops. Coming complete with an integral world

standard PSU, you can take this one -stop programming

solution anywhere!

As with S4, you get free software upgrades and technical

support for life, so now you don't need to keep paying

just to keep programming.

The current device library contains over 1500 of the most

popular logic and memory devices including GALs, PALs,

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many other Micro -Controllers. We even include a 44 -pin

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Order your Dataman programming solution today via

our credit card hotline and receive it tomorrow. For more

detailed information on these and other market leading

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copy of our new colour brochure.

The Dataman ChallengeTry the Dataman S4 or Dataman-48 withoutobligation for 30 days. /f you do not agree that theseare the most effective, most useful, most versatile

additions you can make to your programmingtoolbox, we will refund your mo,

Dataman Programmers 1,

Station Road, Maiden Newton,

Dorset DT2 OAE. UK

'telephone +44/0 1300 320719Fax +44/0 1300 321012

BBS +44/0 1300 321095 (24hr)

Modem V.34/V.FC/V.32bisHome page: http://www.dataman.corn

FTP: ftp.dataman.com. Email: [email protected]

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