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Fields andwaves on lines

Harmonics andintermod. inlong-tailed pairs

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Oscillatorsusing c-mosinvertersmommumikaWhen to useinstrumentationamplifiers

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FEBRUARY 1988 VOLUME 94 NUMBER 1624

FEATURE!'COVER

This month's cover picture is an abstractdesign illustrating the close relationship

between computer hardware and the chipson which it is based

CONVOLUTION -TIME -DOMAIN SIGNAL

PROCESSING109

Modern signal processing requires discrete -time versions of sampled data and systems

Howard J. Hutchings

POYNTING THE WAY

115Vectors and transmission lines

Joules Watt

SINGLE OP -AMPS ORINSTRUMENTATION

AMPLIFIERS?123

The simple solution is sometimes better.John Lidgey

RELATIVITY -JOKE OR SWINDLE?

126Einstein's theory contains fatal and basic

flaws. saysLouis Essen

PROGRAMMING PLDS132

Ideally, control software for programming ap.l.d. is compatible with output from a logic

assemblerV. Lakshminarayanan

INTERNATIONALPROGRAMMING LANGUAGE

136A language that is particularly good at

handling formulas can be used on almostany desk -top computer without change

INDUSTRYINSIGHT

Sesen-page r,siew oldie'' I : forinntrumentat on - what VXI is all about: a case ofevolution railer than revolution latest digital

a case of revolutiot ratherthan evolutiim in test andmeasuremen equipment top -end

will your dmrn cost more to keep than itdiscs to buy? new dsos

market integrated tendener

Industry Insight No 1 is on instrumentation, withspecial reference to oscilloscopes. frequency

and digital meters. It starts onpage 137.

measurement

INDUSTRY INSIGHT -1137

Our first in a series of special supplementscovers instrumentation

SPEECH TRANSPOSER FORRADIO HEARING AIDS

174Adding a frequency -shifter can improve

classroom hearing aidsW. J. Sokol and M. 11.1mans

MULTIPROCESSORSYSTEMS

176Linking simple microprocessors together

synchronously provides economicalhardware with high performance

G. A. M. Labib

SINEWAVE OSCILLATORSUSING C-MOS INVERTERS

187Stable performance over a wide range of

audio and sub -audio frequencies is possibleusing c-mos inverters in a twin -RC

configurationDragoljub Damljanovie

QUALITY IN A.M.BROADCAST RADIO

188Using the best of 1930s techniques in

today's a.m. receiversR. Kearsley-Brown

HARMONICS ANDINTERMODULATION IN THE

LONG TAILED PAIR190

Expressions allowing the study of the long-tailed pair when driven by large -amplitude

multisinusoidal inputsMuhammad Taher Abuelma'atti

APPLICATION SPECIFIC ICS198

In volume production of digital andanalogue designs, application -specific i.cs

reduce costs and board size

ADVANCED F.S.K.MODEM CHIP

199Higher integration significantly reducescomponent count for intelligent multi -

standard modems with auto -dialling

COMMENT 107

APPLICATIONS SUMMARY 113

CONFERENCES AND EXHIBITIONS125

CIRCUIT IDEAS 128LETTERS 134

NEXT MONTH 136

RESEARCH NOTES 172SATELLITE SYSTEMS 181

TELECOMMS TOPICS 183NEW PRODUCTS 193

BOOKS 198

TELEVISION BROADCAST 203

RADIO COMMUNICATIONS 204

UPDATE 208

ELECTRONICS & WIRELESS WORLD 105

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106 ELECTRONICS & WIRELESS WORLD

COMMENT

Words and picturesEDITOR

Philip Darrington

EDITOR - INDUSTRY INSIGHTGeoffrey Shorter, B.Sc.

01-661 8639

DEPUTY EDITORMartin Eccles01-661 8638

COMMUNICATIONS EDITORRichard Lambley

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E REEDBUSINESSPUBLISHING

It has been said - indeed, in our own columns- that there are literates andnumerates, but not many literate numerates. Engineers, runs the commoncomment, might be brilliant at explaining the operation of the newest better

mouse -trap by means of circuit diagrams and flow charts, but less than breathtakingwhen they have to describe it in words. Their lack of education in the skills of writtencommunication has failed them.

Countering this criticism, those whose facility resides in doing rather than writingclaim that, if their use of the diagram and flow chart provides a clear description of themouse -trap, then they have suceeded in communicating and have no need of apolished prose style.

Both these arguments are, of course, simplistic: the first being the result ofgeneralization and the second of reduction almost to absurdity. Engineers haveprobably been practical, green -fingered types since early youth, with only along -way -second interest in "the arts", including writing, but nevertheless are able toexpress themselves in prose of one standard or another: and it is not sufficient to relysolely on pictures when explaining one's work to the public or even to themanagement.

The fact remains that the early education of both engineers and arts people hasindeed failed them. While engineers can, as has already been mentioned, expressthemselves in prose to some extent and arts people have been known to exhibit aninterest in science and engineering, there is still a divide and the inability to use thewritten language in an effective and attractive manner exists on both sides of it. Sincethe teaching of young children started to go wrong in the 1950s, English beingconsidered unimportant and mathematics mis-taught to such an extent that vastnumbers of people in their thirties and younger are hard put to it to add fifteen per centv.a.t. to a hundred pounds, it seems that only an innate interest in a subject hasallowed success in its study, the others being too difficult to progress in against aheadwind of misguided teaching practices forced on teachers by"forward-thinking"educationalists.

These comments themselves are clearly over -simplified generalities, but contain acore of fact. There are outstanding schools and many outstanding teachers, but thebase from which they stand out is plainly very low indeed.

Articles submitted to this journal are, in the main, successful at communicatingtheir content. but some are far from easy to read and are unattractive. The commentapplies over the whole spectrum of contributors: some of those who have a valuablepoint to make send in material which is badly written, scrappy, disorganized andgenerally presented in a manner which verges on the insulting, allegedly literate artsgraduates being little, if any, better than their more practical brethen. The impressionthat must be gained from such experience is that the English language simply has notbeen properly taught.

David Brancher, writing in The Times for 26 November, 1987, expresses the opinionthat a major corporation and a good university should co-operate in developing a"communications -competence" module, to be taught in universities. He goes on tosay that "..any graduate who had taken the module, and passed well, would beinterviewed by (the corporation) on the milk round, as a matter of priority". Surely, ifthe student has arrived at the age of 18 or so without the ability to communicate inwords or pictures, one might begin to wonder what he is doing at university and howhis teachers at primary and secondary schoolswhiled away the time during Englishand science classes. The time for learning "communication" is between the ages of 5and 18 and it is an indictment of British post -War education that this is even a matterfor discussion.

Electronics & Wireless World is published monthlyUSPS6147540. By post, current issue £2.25, back issues (ifavailable) £2.50. Order and payments to 301 Electronicsanti Wireless Weald, Quadrant House, The Quadrant, Sut-ton, Surrey SM2 5AS. Cheques should he payable to ReedBusiness Publishing Ltd. Editorial & Advertisingoffices: EWW Quadrant House. The Quadrant, Sutton, Sur-rey SM2 5AS. Telephones: Editorial 01-661 3614. Adver-tising 01-661 3130 01-661 8469 Telex: 892084 REEDG (EEP. Facsimile: 01-661 3948 (Groups II & 1111 Beeline:01-661 8978 or 01-661 8986. 300 baud, 7 data hits, evenparity, one stop -bit. Send ctrl -Q. then EWW to start; NNNNto sign off. Newstrade - Quadrant Publishing Services No.01-661 3240. Subscription rates: 1 year (normal rater£23.40 UK and £28.50 outside UK. Subs.- :ptions: Quad-

rant Subscription Services, Oakfield House, PerrymountRoad, Haywards Heath, Sussex RH16 3DH. Telephone04444 591814. Please notify a change of address. USA:$116.00 airmail. Reed Business Publishing (USA). Sub-scriptions Office, 205 E. 42nd Street, NY 10117. Overseasadvertising agents: France and Belgium: Pierie Mus-sard, 1e-20 Place de la Madeleine, Paris 75008. UnitedStates of America: Jay Feinman, Reed Business Pub-lishing Ltd, 205 East 42nd Street, New York, NY 10017.Telephone 12121 867-2080 Telex 23827. USA mailingagents: Mercury Airfreight International Ltd, Inc., 10113)Engleherd Ave, Avenel N.J. 07001. 2nd class postage paidat Rahway NJ. Postmaster - send address to the above.

©Reed Business Publishing Ltd 1987. ISSN 0266-3244

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ELECTRONICS & WIRELESS WORLD

Convolution -time -domainsignal processing

Modern signal processing requires discrete -time versionsof sampled -data systems and signals.

Historically, signal processing in thetime domain has been avoided andthe equivalent operation carried out

in the complex frequency domain. But mod-ern signal processing is compelling en-gineers to revise traditional methods andconcentrate on discrete -time versions ofsampled -data systems and signals. Thisapproach is particularly rewarding becauseit unifies the signal processing operations intime and frequency domains.

Consider for example the dynamic be-haviour of a linear system described by adifferential equation in the time domain; itcan be modelled either by a Laplace trans-form in the complex frequency domain, orby a Fourier transform in the frequencydomain. Similarly, the dynamic behaviour ofa sampled -data system is described by adifference equation in the time domain andby a z transform in the z domain.

In each of these examples the time -domain behaviour may be determined by thesolution or inspection of the appropriatetime -domain model. This article describesthe operation of convolution and explainshow it provides a time -domain solution ofthe dynamic behaviour of both analogue andsampled data systems, Fig.l.

There is no distinction between the La-place transform of signals and systems. Thisbecomes clear when you examine the effectof applying a decaying exponential signal tothe first -order system. Initially the signalprocessing will be accomplished in the com-plex frequency domain, Fig.2.

ligrigi Sys ternR

x(t). eat xr74fTransfer functionTransform

xis). sci0=1 /CR

y(s).X1s) Hls)

Fig.2. The signal and system are matchedin the sense that the system impulseresponse is identical to the characteristicsof the signal.

Clearly, the system's response is obtainedby the operation of multiplication. This isequivalent to the operation of convolution inthe time domain as the following contrast-ing examples illustrate.

HOWARD J. HUTCHINGS

Time domain

hit) y(t).x(t)* hit)

s -domain and JW domain

410 )(Is)LT.

Fig.1. Time domain convolution and theequivalent signal processing operation inthe complex frequency and frequencydomains.

I-H(s) Y(s)=Xls)Hls)

IFT s.jw

Hljw) FYOU= X( jw1H ljw)

Time domain

Original signal fit)

Modified what eat fit)

Complex frequency domain

F(s) Fig.3. Frequency shifting rule.

I Replace s

by s.a

F lsal

transformfit) F Is) isi/cR)2 tet/CR

eltf Fls+o) oc(t)N.

Consider the romp- func tion f it) =t

transformt

Fig.4(a). To obtain the time -domain responseuse the frequency shifting rule. Fig.4b From equation (1)in the text it should be clear that

Consider first signal processing in thecomplex frequency domain,

1/CR 1y(s)s+1/CR s+ 1/CR

1/CRy(s)-(s+1/CR)2 (1)

To obtain the form of the time domainresponse it is expedient to use the frequency -shifting rule together with a table of Laplacetransform pairs'.

In a previous article' I demonstrated thata shift or delay of T seconds in the timedomain gives rise to a multiplication by e-sTin the complex frequency domain. A similarpattern exists for the frequency -shiftingrule. Ifs is replaced by s+a in each term of

the transform, the effect corresponds tomultiplication of the original time domainsignal by Cal, Figs 3-5.

Now consider signal -processing in thetime domain. Convolution is the name givento the ordered combination of multiplica-tion and summation. The analogue opera-tion of convolution is particularly un-pleasant and difficult to visualize. Convolu-tion of two continuous functions x(t) andh(t) is defined by the integral,

x(t)*h(t)= fx(T)hlt-TkIT-x

= fh(7)X(t-ThiT

t 1/s2

s - /Diane

Double pole atthe origin \

Pole shiftedto the left \1

11by1/CR units(

1tCR ls.1/CR12

Fig.5 The Laplace transform of the rampfunction t-'/s2 gives rise to a double poleat the origin of the s plane. The frequencyshifting rule has the effect of moving thepoles to the left by VcR units.

Where the asterisk denotes the operation ofconvolution. Dummy variable 'T symbolisesexcitation time, while the real variable tsymbolises response time. The mathematic-al scaffolding states; multiply the inputsignal x(T) by the time -reversed impulseresponse h(t-T). Finally integrate the pro-duct over all time.

Applying the convolution integral to thesignal and circuit shown in Fig.2,

y(0=x(t).h(t)

where,

x(t1=e-m h(t)=1/CRe-q"

y(t)= J x(T)h(t -T)di-oc

= fe-T".1/CRe- (L-L-r)dTCR

e-OCR re-wcaeTicsd7

= e -VCR t

CR 'Tj 0

Finally, the processed output is

Y(t)=-_et -VCR

Compare this result achieved by time -domain convolution with the equivalentoperation carried out in the complex fre-quency domain.

Reference

1. Hutchings H.J., Closing the loop (Ls and zdomain representation of delayed signals), Elec-tronics and Wireless World. January 1988. p.44.

Howard Hutchings is a senior lecturer withHumberside College of Higher Education and apart-time tutor with the Open University.

In his next article. Howard describes the digital -system equivalent of the first -order low-pass filter.

There is little that can be done to improve a blurred image by optical means but when theimage is represented in digital form, the information can be manipulated mathematical-ly. These blurred images, produced by a rotating camera, were deblurred using aconvolution filter developed by Smith Associates of Guildford. The convolution filter ispart of a high-speed image processing computer.

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Vin12 6mV

LT1004

Vref /2

Aluminium baseplate

essureport B

Signalconchtioning

ceramic

SX seriessensor

:ackaqe

housing

Silica gel-- protective

coating

Leads forelectrical

connection

Sensor for bloodpressureSemiconductor blood -pressure sensors aremore reliable than mechanical sensors sincethey have no moving parts. They have betterlong-term stability and they are more easilyinterfaced to computers and -data loggers, asthis circuit from the SenSym BP01 datasheet shows.

Within a 0 to 300mmHg pressure inputrange - the BP01 sensor's limits - the circuit

provides free -running eight -bit parallel dataproportional to pressure. Calibration of thecircuit is easy and only a 5V supply is needed.

Reference and excitation voltages, whichare independent of supply changes above 5V,are provided by the LT1014 op -amp andreference (or LM10). Reference voltage atpin 9 of the ADC0804 a -to -d converter isamplified to 1.5V so a full-scale output of allones occurs when converter input is 3V.

When input pressure is 300mmHg, asenor excitation voltage of 4.2V results in adifferential sensor output of 12.6mV. Beforeentering the converter Vin(+ ) input, thisvoltage is amplified to a level depending onthe setting of RG. Initial offset is adjusted byRI.

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Response time of the sensor is lms, itspeak -to -peak noise is 0.04mmlig and itsimpedance is 4ki1, making it suitable forportable pressure monitoring apparatus.

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Modem routinesStandard routines and demonstration pro-grams for Rockwell signal -processor -basedmodems are contained on an applicationsdisc from RCS Microsystems.

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APPLICATIONS SUMMARY60

1.J -150

-18010 100 1k 10k

FREQUENCY Hz)

Resul ant performance of both

100 1k 10k

Resistors for surfacemountingIn applications where stability is more im-portant than cost, thin-film resistors with avacuum -deposited metal film may be moreappropriate than thick -film types. 'How toselect SMD resistors for best efficiency'discusses the merits of using Beyschlagthin-film resistors against ordinary rec-tangular thick -film devices.

Long-term stability of resistance at va-rious surface temperatures is shown in thegraph on the right. Figures for rectangularchip capacitors are drawn from IEC draft401C01620,1985.

I Power -line disturbancesOf three publications covering aspects 01mains interference, 'How to correct power -line disturbances' is the latest. It deals withtypes of interference, line monitoring andmethods of reducing interference.

Typical common -mode impulse -attenu-ating capability of a high -quality isolationtransformer is shown in the top diagram.The bottom diagram illustrates how isola-tion transformer and d.c. power supply

combine to yield normal -mode impulse atte-nuation over the full frequency range. For-tunately, well designed d.c. power suppliesexhibit considerable normal -mode noise -attenuating capability.

Producer of the brochure, Dranetz, pub-lishes two other notes on mains interferencecalled, 'Understanding power line disturb-ances' and 'How to identify power linedisturbances'

cc 2cc

Lit' -3-4-5-6-7-8

125°C

-65°C

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100 000

OPERATING TIME I

Rectangular chip with thick film

125°C

Mini-MELFwith thin film

Rectangular chip with thick film

hours)200 000

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Each electrode thatenters the capacitorbody acts like a wedgeforcing the capacitorapart

Partial surfacecrack startingat or near thetermination

Side cracks starting nearor under the termination

.1101.Full circular or ellipticalsurface cracks

Side cracks

Thermal shock insurface -mountedcapacitorsSurface mounted components are directlyexposed to soldering temperatures. Thisdirect exposure causes reliability problemswhen the temperature rises too rapidly,especially with multilayer ceramic capaci-tors.

During a temperature transient, mecha-nical stress is unable to spread throughoutthe component and fractures can occur. Thisis compounded by differences in thermalexpansion coefficients and conductivities ofthe various materials within the capacitor.

Reducing thermal stress in multilayercapacitors is discussed in 'Surface mountsoldering techniques and thermal shock inmultilayer ceramic capacitors' from AVX;two other recent publications related to this Ceramic

are 'Factors responsible for thermal shockbehaviour of chip capacitors' and 'Tempera-ture profiles: the key for proper surface -mount assembly process control'.

Termination

Electrodes Ceramic Isothermal lines

A micro crack starts at or justunder the ceramictermination interface

ElectrodesCeramic

Propagated microcrack afternumerous power cycles

Termination

Solderfillet

Solderland

Poynting the way

In many of my recent discussions, facthas often shown up stranger than fic-tion. In the present case our slight

surprise rests on the fact that encoded datatransmission - and digital at that' - de-veloped before telephony. The wheel hasturned full circle and we are back to sendingmessages by similar encoded digitalmethods. In the interim, telephones con-veying direct speech dominated the scene.

The early engineers placed wires, and evenused wires with earth return to save mate-rials, alongside railway lines, on polesaround the towns and countryside and inducts underground. This is all a familiarpiece of history now. The whole telecommssystem went into very successful commer-cial operation with hardly any theory ofsignalling being properly understood. Work-ers managed just about everything withOhm's Law - even sometimes without it. Inother words, the bulk of the earliest workdeveloped empirically.

Then came Maxwell2 with his promise ofwireless telegraphs and telephones.Although an amazing revolution at the time,and eventually put to very convenient use intelecommunications, wireless propagationand the earlier wired, or line, propagationdiffered little in basic principles. Both usedelectromagnetic waves, in the one case'broadcast' to all and sundry, in the other,guided along the conductors.

What really became significant in all themethods of telecommunication turned outto be the wider and wider frequency band-width needed as the rate of signalling wentup, together with the differing effects of thepropagation media on the various frequencycomponents in the signal. People only gra-dually realised the effects of these, althoughwe note the genius of Oliver Heaviside, whofully grasped what delay and distortion pro-duced by lines would do to the telegraph andtelephone signals as the speed of sending anddistances increased. Engineers soon experi-enced these problems, especially withundersea cable systems. Professor Pupin putHeaviside's theory to use in equalizers,which gave early line communication a newlease of life.

The other effect, the connection betweenbandwidth/signalling rate and noise, even-tually gave rise to whole new disciplines,Communication and Information Theory.But the understanding of such ideas andrelationships came surprisingly late,through the thinking of Hartley, Nyquist,Shannon and others3.

Another look at transmission lines

JOULES WATT

ENERGY OF THE SIGNAL

Most people still imagine, like the earlytelegraph workers, that the electrical energy'goes in the wires' by current driven by thee.m.f. But Maxwell's theory showed thatenergy can be propagated in space with nowires at all. This problem of what conveysthe energy still causes argument. The 'cir-cuit' view bases the energy flow on thevoltage -current product VI (watts) operatingin the circuit. It makes no assumptionsabout what is the current - whether 'elec-trons' convey it, and so on. In other words,the concept is only a simplified model. Theexplanation is quite sufficient for simpleapplications - wiring a house, operatingloudspeakers across the room, getting thebrake lights working on the car. There are nophilosophical problems to worry about. En-gineers are pragmatic, "If it works, then useit" and leave the niceties of what reallyhappens to theoreticians.

We never know if such models are 'true'.In fact we suspect they probably are not, onlygood enough for the job in hand. Mind you,when the simplifying assumptions work andbecome accepted, an august body of (usual-ly) mathematical modelling and theorybuilds up, to say nothing about conservativeprofessional bodies, which to the unwarylook very authoritative indeed. Howeverbeautiful the theory, it only models thesituation in the way I mentioned - 'goodenough for the job in hand'.

In this context, other than the circuitapproach, there is another model, the 'field'view of things in which the watts flow in thespace containing the E and H vector fields ofthe signal, whether conductors figure in thepicture or not. We find the field view lookedupon as somehow more fundamental thanthe circuit concept, which is often thoughtof as a simplified field view for 'small'circuits, i.e. those whose dimensions aresmall relative to the wavelength of the E andH waves. Any size circuit is 'small' for d.c., sowave aspects do not surface at all. Yet even ind.c. circuits there are electric and magnetic(static) fields of course.

POYNTING THE WAY

Earlier I mentioned what Maxwell said' andhow Heaviside smartened up the notationand (with Willard Gibbs) gave us the modernvector field theory'. From that revisionarynibble at the ideas involved, the divergenceand curl turned out to be most significant.

The salient features of this mathematicalmodelling gave us the notation that divmeasures the scalar source strength gener-ating a vector field, while curl measures thenon -source ('closed loop') vector field thatgives rise to another one always at rightangles to the first.

In electromagnetic situations, we saw thata curl field turns up only if we change thegenerating vector field. Thus arose Max-well's equations No 1 and No2 in free space,

No I. cur1H=e0-aE e0, the permittivity,at describes the capa-

citance of free space.(farads rn-1)

No 2. curIE=-aH p.o, the permeabil-at ity, is to do with

the inductance offree space (henriesm-1)

In a medium such as the ionosphere, for ex-ample. which conducts current, there willbe a conduction term in No 1, so we have,

curIH = + e°aEat

You can see that No 2 states Faraday's Law,

in which Roll acts as a magnetic displace-

ment current.No.1 shows Maxwell's contribution, in

which he spotted that e -aE forms an elec-tric° atdisplacement current.

We notice an important point arising fromeither or both of these equations. The field Emust be at right angles to H at all places andat all times, because the curl operation is avector product that always gives an ortho-gonal result. If you remember this, thensketches and mental pictures of fields inspace, waveguides, coax. cables, around ae-rials and so on, all have the E and H fields atright angles.

In my earlier article", one theoreticalvector identity turned out to have greatimportance in giving the wave equation,namely,

curl curIA = grad divA - V2A

You will find that another one of these vectorexpansion identities turns out to have veryuseful properties35.

div (A x B) = B.curlA - A.curtB

This is a scalar equation, because div of anyvector results in a scalar and the dot, orscalar products on the right hand side, alsomeans a scalar result in each term.

Professor Poynting put this vector rela-tion to good use in the case of electromagne-tic wave radiation.

Place the vectors H (amps m-1 and E (volts) into the relation so that we have,

div (E x H) = H.curIE - E.cur1H

But from Maxwell, we know curIE and curlHin terms of the displacement currents,

div(Ex =aH-

E.(0E + al)oat

Now from your elementary school calculus,you might remember that if y = (x(0)2 thendYdt dt.

dx= 2 x- Differentiation of vectors pro-

ceeds the same way via the vector dot pro-duct, so that we can re -write the first andlast terms on the right hand side above as,

- div (E x H) = -1p.aH2

+ -1 -aE2 + aE22 ° at ° at

Remember that in vectors, E.E = E2.

As engineers, we get a little kick ofsatisfaction out of interpreting such modell-ing as this. Does the above vector equationgive us anything from an engineering pointof view? Remember the physical dimensionsof all the quantities. The conductivity of themedium in the last term, a, has dimensionssiemens (for the old hands, "mhos") permetre. E has units, volts per metre; there-fore aE2 has units,

volts2 1

ohm mWe know that V2/R gives watts dissipated ina resistor as heat with V volts across it, soaE2 means the watts dissipated by the EMwave field per cubic metre at the point inquestion.

Glance at the other terms. H has dimen-sions amps per metre, p., is the henries permetre of the space so,

1 aH22 P- at

literally means "half the amps squaredtimes henries per unit volume, per second".In other words, as LI2/2 gives the joulesstored in the field of an inductance, and

a alat k2La

indicates the rate at which this energy isstored, i.e. the watts flowing into space in-ductance. This means

1 aH22 /1° at

tells the story of the rate at which energy isbeing stored in the inductance of space perunit volume, by the growth of the magneticfield there. Similarly

2*()Tit-gives the energy rate going into and storedby, the capacitance of space, per unitvolume.

From your knowledge of energy conserva-tion, you can see that the total energy rategoing into storage and being dissipated asheat in the unit volume described by theright hand side of the above equation, must

ittlealikvia

rad1111140/

Metal cylinder

mean that its eft hand expression, that is -div(E x H) describes the flow of this amountof energy per second into the volumethrough its boundary surface.

Notice the operation 'div' has dimensions"per metre", and E producted with H (thevector product is still a multiplication ofunits) is (volts x amps)/sq. metre, so thatwith the div operation, the result is "wattsper cubic metre", just as we require.

The most interesting point here comesfrom looking at the product E x H, which is avector normal to E and H, with dimensionspower per unit area, watts/m2. We call thisvector P. Poynting's vector, which shows themagnitude and direction of the power or ofenergy current in the EM wave at any point.Now E is always at right angles to H in thesame EM wave, so that in ordinary cases therequirement for the vector product doesn'tcome into it. Only the ordinary multiplica-tion of the field magnitudes become in-volved, with the proviso that the energy flowis at the speed of light (in a vacuum) in thedirection of the EM wave propagation.

EH= energy flux density, or powerdensity (watts m-2)

Radio astronomers use a small fraction ofthis quantity in their measurements. Theycall the unit J = 10-26 W ril-2 ajan after Janski- an early pioneer.

Ground plane conductor

Groundplanes

Fig. 1. In (a) the standard fields around theparallel wire pair show the right angleproperty of F and II well. Also evident is thespreading out, and therefore the likelihoodof radiation losses and cross couplingwhen using such lines. The coaxial line (b)also has the fields crossing at right angles.But they are now confined to the interior ofthe outer sheath. The twin wire shieldedline exists. as shown in (c). Triplate stri-pline and microstrip illustrated in (d) and(e) have become quite common in m.i.cs(microwave integrated circuits). These.and the waveguide shown in (f), also sup-port fields at right angles, although in thewaveguide whatever the mode. pure trans-verse wave are not possible.

All this indicates that the energy in elec-trical circuits, as well as in free space waves,propagates at or near the speed of light in thespace around the conductors. How fast theactual charges (electrons?) move in conduc-tors is a question that isn't asked.

TRANSMISSION LINES

Most students soon arrive at consideration oflines via the standard bookwork examples;parallel -wire lines and coaxial cables shownin Fig. 1(a) and 1(b). Other transmissionlines now figure significantly in modernequipments, notably microstrip and, to alesser extent, stripline. Dielectric guides alsocrop up, together with the now venerablesingle -conductor pipe lines called wave -guides, still affectionately called r.f. "plumb -

ing". Figure 1 also illustrates some of these.You will notice usual methods used to

analyse lines involve voltages and currents.The only unusual thing in addition to ordin-ary circuit theory is dealing with a time delayto account for the finite velocity of wavepropagation. This is a kind of half -wayhouse. Circuit concepts like voltage, cur-rent, inductance, capacitance and so on, allfigure (see box) and a wave equation solutionin terms of these quantities models the line.Heaviside again gave us all this.

When waveguides turn up for considera-tion, you have to use the full field treatment.Concepts like voltage, current and so onhave little meaning for a single conductorwhich has a size significant compared to awavelength. Maxwell's equations do the jobagain. In using these, Lord Rayleigh gave thepropagation solutions for rectangular andcircular cross section waveguides in 18966.

TEM SOLUTIONS FOR TWO -CONDUCTOR LINES

We can show off our growing knowledge ofthe div and curl operations on E and H fieldsby using it to revise the theory of propaga-tion of r.f. energy along transmission lines,(and show that the results agree with themore usual 'circuit' method outlined in thebox). The field integrals you end up with,doing it this way, would apply to any kind ofTransverse Electro-Magnetic (TEM) waveguided system - if you could solve them!(These days, powerful numerical methodson computers can solve any finite integral bya vast series summing operation.)

I expect by now you have a reasonablepicture of electromagnetic fields moving astransverse vibrations in space. Guided TEMwaves only travel if we provide two separateconductors. You will find that if the conduc-tors possess randomly shaped cross sections,waves still propagate along them, but diffi-culties occur with the awkward boundaryconditions, so the messy numerical methodsI mentioned with regard to the integrationsbecome the only hope of solution. Evenshapes interesting from an engineeringpoint of view, such as those used to fashiondielectric supported microstrip lines, com-plicate the mathematics required and youwill find it necessary to use 'guesstimation'from experience, computer -aided numericaldesign, or various approximate formulae/graphs.

We often refer to the TEM waves ontransmission lines as the principal waves andyou will see in a moment that there are nofrequency cut-off limits. A principal wavewill propagate from d.c. upwards in frequen-cy. In practice, limitations at the high -frequency end are concerned with increas-ing dissipation in the dielectric and conduc-tor losses, and with energy radiating awaywhen the spacing between the conductorsbecomes comparable with the wavelength.Coaxial types of line screen against theradiation, but TE and TM wave modes(where there are longitudinal vector compo-nents of the fields) can be set up. Thesetroublesome modes have differing velocitiesof propagation and loss factors, so tend tocause havoc. In spite of this, small -size,high -quality 'semi -rigid' coaxial lines appear

Itlectricfiekj

Fig. 2. The fields, currents and coordinate system for the parallel line shown in detail.

in applications up to 18 GHz or so.The lossless line guides the EM waves

without a progressive decay in the energydensity, unlike free space waves obeying theinverse square law. The attenuation thatdoes occur arises from the conductor resist-ance and dielectric losses. We call this theJoule heating. A uniform line has an un-changing conductor cross section geometryalong the line. This indicates we should useat least one linear axis coordinate system.Nearly everyone knows the Cartesian sys-tem, so the axis scaffolding on Fig. 2 seemsmost appropriate.

The electric field lines terminate at rightangles on the conductors, (but see later for aslight modification to this statement). Themagnetic field lines completely encircle oneor other conductor; they all lie in the x, yplane, and cross all the E lines at right angleseverywhere.

How would you apply the basic EM princi-ples to show how waves propagate along theline, how the attenuation goes and what theimpedance levels are and so on? If you can

X .411

Fig. 3. The key to handling the fieldapproach to lines means constructing asmall volume in the space around the line,bounded by the E field lines, the H fieldlines and direction of propagation, z.

gH. dzto

Fig. 4. This shows a curl journey around theH field loop.

answer this question, then you could use themathematical models to go some way to-wards designing real cable and transmissionsystems. Notice that, in Fig. 3, I have takenadvantage of the orthogonal properties of Eand H to construct a small volume whoseedges lie along lines of E and H and alsoalong the z - axis.

FIRST, THE H FIELD AND THECURRENT

Imagine looking along the E lines into thesurface efgh. The circulation of H around theperimeter equals the total current flowingthrough the surface, by an application ofMaxwell's No 1. This is the same as takingthe line integral of H around the closed pathefghe, as you can see from Fig. 4. Rememberthat the circulation per unit area at a point ina vector field is the curl of the vector there.In our example, we hardly have a lineintegral to do around efghe - it is too small.All we have to do is add the components ofthe field multiplied by the lengths alongeach side all the way round, to get themagnitude of the circulation of H. This givesin symbols,

a HHdsn, + Odz - (H + -dz)ds, - Odzaz

I have deliberately shown the zero contribu-tions from the journeys along the dz's. Theresult is

aH- -dzds (amps)az

(For interest. notice that if we divided thiscirculation by the area, dzdsm, what remainsamounts to the curl of H, which is verysimple for this problem.)

The total current through the dielectrichas two components. You will notice aconduction current if the medium is leakywith conductance ad (siemens m-1). Max-well's displacement current forms the otherpart, with a density aD/at (amps m-2). UseOhm's Law on crd with the force field Esetting up a current flux densityJ, accordingto J =crd E (amps m-2). You should now seethat the total current through efgh amountsto,

a DcrdEdzdsm + -dzdsn, (amps)

The last two results for the current say thesame thing,

a aEA--Hz = E-uSm crdEdsmaz at

where I have cancelled the dz right through,so everything works "per unit length" alongthe line (z - axis ... I now. Resist cancellingthe ds, because the next move is to integratealong the H field lines completely round theclosed loop produced by them. In otherwords,

- tzf Hdsm = e--f Edsm - fadEds,at

in which I have changed the order of dif-ferentiation with respect to time and in-tegration with respect to distance (along H).

The line integral along H right round theconductor equals the current flowingthrough, see Fig. 5. That is,

Hds, = i (amps) (this is Ampere's Theo -J rem.)

(electron flow direction)

Fig. 5. A journey round the H loop gives thetotal current through the loop. by Ampere'sTheorem.

NOW THE ELECTRIC DISPLACEMENTAND VOLTAGE

Have a look now at the surface integral for Dtaken right round the conductor. The resultgives the total lines of displacement passingfrom one conductor across to the other perunit length of the line at our position along itand at the instant in time we are talkingabout. These lines end on charge, so you seewe have the charge per unit length on theconductors of the line. In other words,

fDdsm (coulombs m-1)

gives the instantaneous coulombs per metreon the conductors. a/at of this gives us thedisplacement current per unit length be-tween the conductors - and in turn, thisequals Cav/at, where C is the capacitancebetween unit length of the conductors; inother words, the Farads per metre along theline. The voltage v is that existing betweenthem. If you find difficulty seeing this,remember that q=Cv and in the situation Iam discussing here, q is the charge per unitlength on the line, which equals,

5Dd5m and v = f Edse.

Notice that the integral for v is a line integralalong a line of electric force from conductor1 to conductor 2.

fDds,. C = _ q (farads m-1)

and I have already said,

Ddsm = C (amps m')at at

INTERPRETING THECONDUCTION TERM

The conduction term in the equation for thecurrent above involves consideration of thetransverse leakage per unit length which is

is = crdEdsm (amps m-1.)

You have already seen from the precedingdiscussion that the potential between theconductors is

and from these quantities we can finallywrite,

crdEds,i = C = 2 (siemens orv Eds, mhos rn-1)

This means we now have the conductance Cbetween the conductors. By substituting allthese results, the current equation becomes,

"i "v -1-az = -C -at + Gv (amps m )

and we end up with one of the 'Telegrapher'sEquations', see box.

THE SECOND TELEGRAPHER'SEQUATION

I was tempted to suggest you derive theother equation, which involves the resist-ance and inductance per unit length.Perhaps you still might like to attempt it, butthere are one or two pitfalls that make it alittle more difficult to account for the resis-tive losses along the line. In Maxwell's fieldtheory no series resistance loss arises inspace, no matter how lossy the medium.

We can manage the interpretation by

Fig. 6. Illustrated is the similar E field curlloop. The result this time is the magneticflux rate of change through the loop. This isused to derive the second Telegrapher'sEquation.

going round efbae with E, which gives itsline integral (Fig. 6). You might notice thatthe magnetic field lines go perpendicularlythrough the small plane area of efba. RecallMaxwell's No 2 and use it like the previousderivation. You should end up with

aH aE E .1)- use = + -ads, (volts m

(after cancelling dz again). The left hand sideis the rate of change of the magnetic flux,with the minus sign of Lenz's Law in place.The first term on the right arises from thesurvival of curl H. The last term makes acontribution from any longitudinal compo-nent of the electric field. This requires someinterpretation, as Maxwell says nothing ab-out a longitudinal component. In fact, ifthere is one, we do not have a purely TEMwave.

I cannot think of a more suitable discus-sion than that from Oliver Heaviside, themaster himself.

"A line of electric force does not now startquite perpendicularly from the positivelead and end similarly on the negativelead. It has a slight inclination to theperpendicular, and therefore curves outof the reference plane to a small extent.In the dielectric itself, this peculiarity isof little importance. But the slightamount of tangentiality of the electricforce at the surface of the leads . . .

attenuate(s) and alterls) the shape of thewaves ... "

So the problem looks like arising in thefinal term of the last equation and findingthe longitudinal component of E that sets upa loss current in the conductors. We oughtto integrate first right across from conduc-tor to conductor to get the full effect, givinga brief interpretation of each term again,

Eds, = -az at

fas ,ddEZ e

(volts m'l)2

We identify fEds, as the potential between

the conductors, and a/az of this is simplyav/az (volts m' ).

The integral ip.Hds, (webers m") is the

magnetic flux per unit length linking theconductors. We know the definition of selfinductance (henries) as the magnetic flux

linking the circuit per unit current. We also

know the current i = fHdsrn. From this wehave

.12µHds,

1 -L (henries m 11

from he rate of change of flux,

td,tfOlds, = L -di (volts m II

There remains the last term. The integralonly has contributions at the surfaces of theconductors 1 and 2. Think of integratingelement by element along the E lines; eachlongitudinal side dz cancels the one before asI attempt to show in Fig. 7. Another way youcould look at this is to see that for thisintegration,

aE dE= and you can write down therise ds,following relation,

2aEiffedSe =f dEz = Ez12) Em11 (volts ml

We have nearly completed our transform-ation of above voltage equation,

- E. aiL-- + E.,(2) - E1111] (volts m )az

Fig. 7. This illustrates that if there is alongitudinal component of H field, the onlyplace where it is significant is on theconductors.

During the discussion you may have beenquestioning how there can be a longitudinalelectric field at all. Or more probably youhave already seen that because of the voltagedrop along the conductors, set up by thecurrent flowing in their resistance (per unitlength . . .1, there must be a small resultantelectric field component tangential to them,as Heaviside said. So write Rlohms m-1) forthe resistance per unit length along theconductor (for the moment, consider justone of them), then you can see from Ohm'sLaw that dv, = iRdz volts.

Vii`Therefore, iR =az

= - E, (volts rni )

This arises by dividing through by dz andmaking use of the relation between electricfield and negative potential gradient.

The conductor might have a variablecurrent density over the cross section. Itmay also have a non -uniform resistivity p(ohm ml, which is unlikely - but you couldgive a moment's thought to silver-platedcopper conductors or, very likely with mod-ern technology, a microstrip line formed by

WAVES ON LINE

A pair of conductors of any cross sectional gecmetry :hat forms a transmission line, has a

certain amount of inductance. L. capacitance. C: resistance. R: together with conductance. G

- all defined per unit length. The diagram shows an eq rivalent circuit of this situation. fromwhich we obtain the standard 'Telegrapher's Equatior s'. One further step yields the wave

equation for TEM waves on the line. Assume a simple sinusoidal wave at this point and we get

a straightforward result. even if tie wave dies away exponentially because there are losses

(the R and C) on the line.The voltage decreases by dv as we go forward a distance dx. By Kirchhoff's Law, this equals

the sum of the drop

across the inductance and iRdx across R.

dv = - + i kix. that is. Lv = - (L`li + Rilat ax at

We get similarly for the shunt path (by using Kirchhoffs Current law),

di = - + Gvkix. in other words, -(j- = (0-11 + Gv)at at

These are the 'Telegrapher's Equations'.We expect a wave on the line so. as such a wave varies 35 a function of time t and distance x.

then a glarce at the Telegrapher's Equations shows we have the appropriate variables in

place.Consider the sinusoidal wave in the form we have see., before8.

The voltage wave: v Veu"' "67 "4')In this, 0i is the angular frequency as usual, (1 is the attenuation constant for the line and 0 is

the phase change constant along :he line.This kind of assumed solution means that we can write evil. = - jwv and (*)v/igx = - + Jp)v

in the equations above. and similarly for the currant Now the two equations look like.(., + j(i)v - (j01 + R)i and (0, + j(.1)i (j0,C + G)v

If we divide the second of these into the first we get the rate v/i which has the grand title of

'Characteristic Impedance'. Z0,

V+ R) - (ohms)

(jwC + G)

By multiply ng the two equations together. vand i disappear and this is the result.4 j13) OA li)(1,0C +

This relation turns out to be quite tricky to handle. The 'multiplying out and taking the squareroot of the complex number on the right to get a and b on their own. is tedious. But if R and G

are tiny with respect to (-L and (,C (true at higi frequencies. because 0, is large ... ).then

neglect the -n. so that -0 and 0 - (ii \ LC.Now our assumed wave function is (slightly re -written).

so that the exponential decay clearly shows up in the "(," factor. and at the same time thephase varies both with time and &stance along the line (as shown by the "j" exponent factor).When we go along the line a distance x equal to the wavelength 1. the phase exponent

decreases by 27 radians. therefore.- (x + rk) - fix -27 so that - 2Tr/A

which shows us clearly the phase change property described by b. finally in this short review(0/0 = 2Trf = 27r/X = fX = c which is the velocity of the wave. and for the assumed lossless line

c \ LCIf the line conductors work in a vacuum (ornear enough. in air) then c for the wave onthe line turns out to be the velocity of light.

The usual circuit equivalent to a smallincrement of the line enables the Tele-grapher's Equations to be derived byapplying Kirchhoff's and Ohm's Laws.. .

a very thin lower layer of nichrome, followedby a layer of gold and/or copper.

The voltage drop along a filament ofconductor of length dz and cross section dA(m2) can be easily written down if youassume a resistivity p, which is constantacross the small section dA and with acurrent density of J (amps m 2) flowingalong in the z direction. Also assume thiscurrent density remains constant across dA.(If these quantities do vary as functions of,say, the radius, then working out possiblyfairly complicated integrals will give anaccurate result). The simple case gives

dzJdAp--dA = Jpdz = dv, (volts)

So from the potential gradienUE field relytion, this is,

Ez = Jp (volts m -

For our special case of uniform p and J(highly unlikely in practice) you can write

JA = j (amps) andA2 = R (ohms m 'I)

where A now represents the whole crosssection. From this,

iR = JAPA = Jp = - E,

and you see immediately E,,1) = - i1R1 andEe121 = -022. If you allow further that j1 = iand i, = - i, in other words that we have

ELECTRONICS & WIRFI FqC WORT f) 119

jatIMINIMIFZ iff - current-

- Main energy

Poyn in energy flow intoconducior$

Fig. 8. The losses in the conductors 'distort'field direction, so that there is a netmovement of energy current into the con-ductors from the field (seen by the direc-tion of the Poynting vector).

equal forward and reverse currents at thesame point z along the line, thenEz12) - Ezo) = i(R2 + R1) = iR (volts m-11where R is the total, or 'loop' resistance perunit length of the line. In the derivation, thevalues of R1 and R2 correspond to the d.c.values. This is never true in r.f. practice,because the skin effect ensures that thecurrent crowds into a thin layer near thesurface. The a.c. resistance differs oftengreatly from the d.c. value. Nevertheless ifwe place the appropriate R into the equation,a correct result turns up. So finally,

az at= - (Ifi + iR) (volts m.1)

. . . this is the second 'Telegrapher's equa-tion.

There remains just one small commentthat beady -eyed readers may already havenoticed. This concerns the total inductance.By integrating from the surface of conductorto conductor, I neglected any internal in-ductance from flux linking current insidethe conductors. The same argument aboutthe skin effect now enables us to say that asthe current is a thin surface sheet - thenthere is negligible internal inductance on r.f.lines.

CONCLUSION

In concluding this substantial discussion, ifyou have followed thus far, may I sum up bysaying that a basic grasp of the field ideas thevarious integrations and the geometry in anyparticular case, should now enable you to seea way towards a solution.

The comment that there is a currentshortage of r.f., microwave, and analogueengineers; plus the point a colleague madethat students judge the subject 'very badlytaught', or even as someone else said, 'I findit boring' - might I hope, result in thisdiscussion being particularly useful. Boringindeed!?!

References1. Tony Atherton, 'Pioneers', Samuel Morse,Electronics and Wireless World, P.481, May, 1987.2. Joules Watt, Maxwell's Electromagnetic theory. . ., Electronics and Wireless World, p.697, July.1987.3. Mischa Schwartz. "Information Transmission,Modulation and Noise", McGraw Hill.4. Joules Watt, All About Curls and Divs, Electro-nics and Wireless World, p.809, August, 1987.5. D. K. Cheng, "Field and Wave Electromagne-tics", Chap. 2, Addison Wesley (1983).6. Lord Rayleigh, On the Passage of Electric WavesThrough Tubes . . . , Phil. Mag. S.5. Vol. 43, No261, February 1987.7. Oliver Heaviside, "Electromagnetic Theory",Chap. IV, p.374 The Electrician, 1983.8. Joules Watt, "j " Electronics and WirelessWorld, p.938, September, 1987.

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Single op -amps orinstrumentation

amplifiers?The apparently magical properties of the standard three

op -amp instrumentation amplifier are explained. Astraightforward analysis shows the circuit designer thatthe instrumentation amplifier is not always better than a

simple single op -amp differential amplifier.

The ideal differential voltage amplifieris a circuit providing an output vol-tage, generally with respect to ground,

that is linearly related to the potentialdifference between two input terminals. Theconstant of proportionality is thedifferential -mode voltage gain, Ayd. In anideal amplifier, if there is no voltage differ-ence between the two input terminals butboth terminals are being fed with a commonvoltage with respect to ground, the outputshould be zero. In practice, such a common -mode input voltage will be significantlyattenuated but not totally absent at theoutput. The ratio of common -mode outputvoltage to common -mode input voltage istermed the common -mode gain, A. Inpoint of fact, the term common -mode atte-nuation would really be more appropriate,since the term gain generally implies anoutput greater than the input, which isalmost never the case. Mathematically, theoutput voltage can be written as

V.= (V2 - VI). Avd + 1/2(V2 + VI ) Avc (1)

where the differential input is (V2 - V1) andthe common -mode input is (V2 + V1)12.

The term common -mode rejection ratio,c.m.r.r., is defined as the ratio of kik. It isa useful figure of merit for comparingvarious differential amplifiers. The idealdifferential amplifier with zero A,,c wouldclearly have infinite c.m.r.r. In practicalcircuits, this figure might be in the range100 to 1,000,000, depending upon the par-ticular design and component matching.

Probably the other most important para-meter to be considered when using differen-tial amplifiers, is the input common -modevoltage range (input c.m.v.r.), defined as therange of common -mode input voltages thatthe amplifier can tolerate and still performcorrectly as a linear differential amplifier.The input c.m.v.r. is limited because of thenecessity to keep the op -amp or amps oper-ating within their linear active region, withinputs neither excessively high or low in

JOHN LIDGEY

potential nor the outputs reaching voltageor current clipping levels. The value of inputc.m.v.r. for a particular differential amplifiercircuit depends very much on the choice ofamplifier topology and is likely to range inpractice from 10 volts to 5000 volts.

Generally higher values are achieved witheither an opto link or an a.c./d.c. link ofsome description.

CONVENTIONAL DIFFERENTIALAMPLIFIER

The standard differential amplifier circuitshown in Fig.1. is designed to have Ad = N.However, as the following analysis shows,the c.m.r.r. is critically dependent uponprecisely matched resistors.

Assuming that the op -amp is ideal andusing normal op -amp analysis for circuitswith negative feedback (that is V(-) V( + )

and I (-) -= 0 = I ( + I), then the outputvoltage is given by

= ki V1 - k2 V2 (2)

whereR4 /1-2-1RA kR2

I k(R3+R4)) RI I 2 RI

Now, if the input signals are common -modeonly, that is V1 = V2, then (2) gives thecommon -mode voltage gain,

Avc = ki - k2 (3)

Similarly, if V1 = Vd/2 and V2 = -Vd/2, thatis the differential -mode voltage is Vd and thecommon -mode voltage now is zero, then (2)gives the differential -mode voltage gain,

Avd = 1/2 (kJ + k2) (4)and from the definition of c.m.r.r.

C.m.r.r. = = (k1 + k2)/(k1 - k2)(5)

from (3) and (4). Rewriting (5) by substitu-tion for ki and k2

Awl = 1/21R1R4 + R2R3 + 2R2R4)/(R1R3 +RI R4) (6a)

Avc = R1R4 - R2R3)/(121R3 + R1R4) (6b)

c.m.r.r. = 1/2(111R4 + R2R3 + 2R2R4)/(R1R4-R2R3) (6c)

Remember that in all this we haveassumed that the op -amps are ideal: how-ever, unless the matching of the resistors isperfect, the c.m.r.r. will not be that high.The match condition from (6c) that giveshighest c.m.r.r. ideally infinite, is clearly

R1R4 = R2R3 or RI/R2 = R3/R4 (7)

The best choice from the viewpoint of satis-fying 17) and simultaneously providing biascurrent compensation to minimize outputd.c. offset is to make

RI = 12; R2 = NR; R3 = R and R4 = NR (8)

Now these components will each have thevalue shown in (8) subject to variation due tonormal manufacturing and practical toler-ances and therefore it would be moreappropriate to write the values of (8) asfollows

R =11(1+81); R2=NR(1 +62);113=1211+63) and R4=NR(1 + 64) (9)

where 81 refers to the departure of the R1from its nominal value and soon. That is, theset of equations (8) are the nominal values ofthe resistors and the set of equations (9)refer to the exact values of the resistors. Ifthe components are, say, ±1% tolerancethen the range of 6 will lie within - 0.01 and+ 0.01.

Returning again to ( 6a) for thedifferential -mode voltage gain, substitutionof the nominal values of resistors from (8)gives

Avd = N (10)

this being the expected (nominal) value ofdifferential -mode voltage gain. Clearly thenominal value of c.m.r.r. from (6c) is infi-nite, but what is of greater interest is theexact value of c.m.r.r. for any particular setof resistors or, even more useful, the worst -

case c.m.r.r. for a given tolerance of compo-nent. This is relatively easily obtained bysubstituting the expression for resistorsfrom (9) into (6c), which if 818k terms areneglected as they are relatively small forhigh -tolerance components, gives thec.m.r.r.

N(1+82+64)+11+62+64)/2+11+82+821/2

(84+81)-(82+83) (11)

which further approximates to

c.m.r.r. = (N + 1)/(81 + 84 - 82-83) (12)

for high -tolerance components in which6,<<1.

So what does equation (12) actually tellus? Suppose we are dealing with a unitydifferential -mode voltage -gain amplifier andwe have used ± I% tolerance resistors, then(12) provides a figure for the worst -casec.m.r.r.

Worst -case c.m.m.r = + 50-0.04 -This means that, unless the resistors areaccurately trimmed to better than ±1% wemight obtain a circuit with unity Ayd thatonly attenuates common -mode voltages by afactor of 50; not a particularly high value ofc.m.r.r. At first sight, one might be temptedto think that trimming to better than ±1%is simple. Initially, perhaps, but will the trimbe that accurate over the temperature rangethat the circuit is to operate and will thetrimmer setting be a once only operation?Clearly the answer to both these questions isalmost certainly no.

DIFFERENTIAL INSTRUMENTATIONAMPLIFIER

The conventional differential instrumenta-tion amplifier is shown in Fig.2. Essentiallythere are two identifiable voltage gainstages: the one to the right hand side of thebroken line AA being exactly the same circuitas Fig.1, the analysis of which we havealready carried out. The circuit to the lefthand side of AA is a differential -input todifferential -output amplifier which, as theanalysis will show, has unity common -modevoltage gain, and the differential -mode vol-tage gain, determined by 126, R7 and R5, canbe very high.

Let us analyse the pre -amplifier stage tothe left of the line AA and then consider the

total performance of the amplifier. Againassuming that the op -amps are ideal, theninputs Vi and V2, will produce node voltagesof

V. = V 1 and V, = V2

and, using Kirchhoffs laws, the outputnodes X and Y of this circuit are given simplyby

V = VI + (V1 - V2) R6/R7and Vy = V2 - (VI - V2) R5/R2 (13)

There is zero differential -mode input if V1 =V2 and then V, = Vy = VI, giving a common -mode voltage gain of unity.

If we now consider the situation in whichthe inputs are differential only, that is

V1 = Vd/2 and V2 = - Via

then, from equation (13), we obtain the nodevoltages of

Vx = I V2 + R6/R7)VdV, = -(1/t2 + R5/R7) Vd

The nominal value of total differential -modevoltage gain is

Avditotall = (1 + (R5+ R6)/R7).R2/121 (16)

where, as before, R2/RI = R4/R3The most interesting feature of the instru-

mentation amplifier is the fact that thecommon -mode voltage gain of the totalcircuit remains determined solely by thecommon -mode voltage gain of the secondstage. Since/4,,l = I then c.m.r.r., is

R5(1 + 65) R6(14- 66)Avdi- (1 (17)

nr 4-ov nr -1-o71,

Generally, to preserve circuit symmetry andenable equal value components to be used,R5 is nominally set to equal R6 and may bewritten as R5 = R6 = MR7, and so equation(17) reduces to

c.m.r.r.i= (I +MI1 + 65)+MI+ (18)(1+87) (1 +87)

and, since we recognise that component

(14) tolerance must be good, we can neglect the8, terms and equation (18) approximates to

and the differential -mode voltage gain of thefirst stage is

Avd = (Vx Vy)Nd = (1 + (R5 + R6)/R7)(15)

As nodes X and Y are at low impedance, thenthe overall gain of amplifier is simply theproduct of the gain of each stage calculatedseparately, that is

Avd(total = Avd2; Avcitotall = Avcl Avc.2C.m.r.r.itotai) = c.m.r.r.1.c.m.r.r.2

Fig.1. Standard differential amplifier,which common -mode rejection is heavilydependent on resistor matching.

Fig.2. Conventional differential instru-mentation amplifier. The circuit to the rightof the dotted line is identical to that in Fig.l.

c.m.r.r.1 -7-- (1 + 2M) = Avd1(nominall) (19)

We can now obtain an expression for thetotal c.m.r.r. using equation (19) and (12).

c.m.r.r.6441= (1 + 2M1.11s1 + 1/181 + 84 -82 - 83) (20)

STANDARD DIFFERENTIAL vINSTRUMENTATION AMPLIFIER

The additional differential input-outputstage of the conventional instrumentationamplifier (Fig.2.) has improved the overalldifferential -mode gain and the c.m.r.r. com-pared with the simple standard differentialamplifier (Fig.1), both the total Avd andc.m.r.r. apparently increasing by a factor of(1 + 2M), the differential -mode voltage gainof the first stage of Fig.2. The key question tobe answered is, "when should the morecomplex, and therefore more expensive,circuit of Fig.2 be chosen in preference tothe simpler circuit of Fig.1?" The answer tothis question is not simple; however, a clearanswer can be obtained with some care.

Since the differential amplifier of Fig.l. isa sub -circuit of Fig.2, to make a comparisonbetween the two we will assume that thesame quality of components are used in bothcircuits. Also assume that the requiredclosed -loop differential gain -bandwidth pro-duct is less than that of a single op -amp, sothat the circuit of Fig.1 could satisfy thedesigner's needs in terms of differential -mode performance. Using the equationsdescribed earlier a comparative table can bedrawn up and it is shown in Fig.3. Since thecircuits are to be independently designed,resistor designations for the circuit of Fig. 1have been changed to R', R' R' R: so thatthey are not confused with the resistors usedin the circuit of Fig.2.

The same quality of components will beused in both circuits and this means that theterms lb; + 8: - -8) and (61 + 84 - -SO will lie within the same range.

Refer to the c.m.r.r. of the two circuits of

Fig.1 and Fig.2 as c.m.r.r.1 and c.m.r.r.2respectively. From Fig. 3 we may write

c.m.r.r.i = (1 + 10/(8: + -(21)

and c.m.r.r, = (1+k + 2R5/R7)/(81+ 84- 82- 63) (22)

where k is the overall differential -modevoltage gain required.Nominally the 8 terms equate so that

c.m.r.r.2 = (1+ (2R5/R7)/(1 + lc)) c.m.r.r.i(23)

Equation (23) shows that c.m.r.r.2 is indeedgreater than c.m.r.r. I. However, since thetotal differential -mode gain is k, the term(2R5/R7)/(1+ k) must be less than unity. sothat c.m.r.r.2 is not even twice that ofc.m.r.r.i.

In practical electronic engineering terms,an improvement of c.m.r.r. of less than afactor 2 does not warrant using the instru-mentation amplifier of Fig.2. with its addi-tional complexity over that of the standarddifferential amplifier of Fig.1. This conclu-sion does not mean that the circuit of Fig.2 isnever worth using, since we have yet toexamine the case where the specified closed -loop differential gain -bandwidth product re-quired is greater than that of the op -ampsthat are to be used in the circuit.

CASCADED -STAGE DIFFERENTIALAMPLIFIER

In many differential -amplifier applications avery high differential -mode voltage closed -loop gain is required perhaps 10,000 or moreover a specified bandwidth, and the totalamplifier gain -bandwidth product may wellbe too high to be obtained with a single -stagecircuit such as the standard differentialamplifier of Fig.1. If this is the case, there aretwo basic options available to the electronicsengineer. Either the circuit of Fig.2 can beused, or a simple, single -ended post ampli-fier can be added to the standard differentialamplifier, as shown in Fig. 4. On the

assumption that with either arrangementthe specified differential gain -bandwidthproduct can be achieved, the circuit of Fig.2is, without doubt, the best, as it can bedesigned to provide a much better c.m.r.r.than is possible with the circuit of Fig.4, asthe following discussion shows.

The second gain stage of Fig.4 is a single -ended input/output stage, and so the totalc.m.r.r. of this amplifier (c.m.r.r.4) is equalto the c.m.r.r. of the first stage, which isidentical to the circuit of Fig.1, hence

c.m.r.r.4 = c.m.r.r.1 = (1 +12712:/(8:+ 8:- - (24)

Rewriting equation (20), which is thec.m.r.r. of Fig.2, we have c.m.r.r.2 = (1 +2R5/R7)(1 + R2/110/(81+84- 62- 8-1) (25)Comparison can now be made betweenequations (241and (25), giving

c.m.r.r.2 (1 +2R5/R7)(1 + R2/R )(26)c.m.r.r.4 (1+RYR;)

where the 8, terms have been cancelled as itis again valid to compare the two circuitsonly if the same tolerance of components areused in both. Equation (26) cannot besimplified further, as the choice of relativevalues of resistors for each circuit is madeindependently. But a specific example willserve to illustrate that the circuit of Fig.2will produce a much higher c.m.r.r. thanthat of Fig.4.

Suppose identical op -amps, each withopen -loop gain -bandwidth products of1MHz, are used and that the applicationdemands a closed -loop differential voltagegain of 10,000 over a bandwidth of lkHz. Thetotal differential closed -loop gain -bandwidthproduct is therefore 100 MHz. To maximizesignal-to-noise ratio, both Fig.2 and Fig.4circuits should be designed with maximumgain in the first stage. The maximum possi-ble closed -loop gain for a 1kHz bandwidth is1000 and so, for the circuit of Fig.2.

R'/R: = 1000 127)

parameter standard differentialamplifier

conventional instrumentationamplifier

total /km Vic = R4/R;

total c.m.r.r.

(1 + 2R5/R7)R2/R1where R2/R1=R4/R3 and R5=R6

(1 + Ifli(N+N-A;-N) (1 +2R5/137)(1R

+64 - -fi3)

Fig.3. Characteristics of the two types of amplifier. At first sight. the improvement inc.m.r.r. is not spectacular.

Fig.4. One way of obtaining a high gain, which can only provide a c.m.r.r. equal to that ofthe first stage.

and similarly for the circuit of Fig.4

(1+ 2R5/R6) = 1000 (28)

In both cases the second stage gain needs tobe equal to 10 which in the case of the circuitof Fig.2 gives

R,/RI = 10 (29)

The comparative ratio of c.m.r.r. betweenthe two amplifiers can now be calculatedusing equation (26) from which we obtain

c.m.r.r.2 (1000) (1+101_11c.m.r.r.4- (1001)

So, the c.m.r.r. for the circuit of Fig.2, theinstrumentation amplifier, is 11 times, or21dB, greater than the best that can beachieved using the circuit of Fig.4. Thereason for such a significant advantage isbecause both gain stages in the instrumenta-tion amplifier provide high c.m.r.r. whereasthe amplifier of Fig.4 has a c.m.r.r. equal tothat of the first gain stage.

The analysis- is above shows that if a closed -loop differential amplifier is needed with again -bandwidth product which is greaterthan that of the op -amp to be used, implyingat least two gain stages are required, thenthe conventional instrumentation amplifiershown in Fig.2 will give the best totalc.m.r.r. available. But if a closed -loop dif-ferential amplifier is needed with a gain -bandwidth product which is less than that ofthe op -amps available then no significantadvantage is gained in terms of c.m.r.r. byusing the instrumentation amplifier and it isprobably perfectly acceptable to use thesimple, standard. single -op -amp differentialamplifier.

In passing. it should be noted that theinstrumentation amplifier does provide abuffered high input impedance at both non -inverting and inverting input terminals. Thesame cannot be said of the rather asymmet-rical input impedances of the standard,single -op -amp differential amplifier. Afurther point to note is that none of thecircuits described in this article are particu-larly useful in the presence of high common -mode voltages.

Dr F.J. Lidgey. B.Sc.. Ph.D.. M.LE.E.. isPrincipal Lecturer in the School of En-gineering. Oxford Polytechnic. Oxford.

RELATIVITYjoke or swindle?

Louis Essen re -states his view that Einstein's theory ofrelativity contains basic and fatal flaws

Some of your contributors find it diffi-cult to accept my contention (WWOctober, 1978) that Einstein's theory

of relativity is invalidated by its internalerrors. Butterfield for example (EWW,February, 1987) denies that there is anyduplication of units or any harm in obtain-ing results from thought -experiments.Moreover, if my contention is correct, thenew experimental work described by Aspden(EWW, August, 1987) is not required todisprove the theory, although it might con-firm that his assumptions were wrong. Thisis not to suggest that experimental resultsare not important but they should be consi-dered as steps in the development of newtheories.

Discussions about the theory tend to bevery involved and your readers may beinterested in a brief history of the subjectwhich I wrote some time ago for a friend whowanted to know what the controversy wasabout and in particular what was the signifi-cance of the clock paradox.

The theory was an attempt to explain theresult of an experiment which had beenmade to measure the velocity of the earththrough space. Scientists reasoned that,since light is an electromagnetic wavetravelling through space with a velocity

L. ESSEN

denoted by the symbol c, and the earth istravelling through space with a velocity v, itshould be possible to measure v by an opticalexperiment carried out in the laboratory.Michelson and Morley designed and used aninterferometer for this purpose. A beam oflight was split into two parts which weredirected along the two arms of the instru-ment at right angles to each other, the twobeams being reflected back to recombineand form interference fringes. The instru-ment was turned through a right angle sothat, if one of the arms was initially parallelto earth's motion, it became at right anglesto this direction. It was expected that there

There have always been...critics: Rutherford treatedit as a joke; Soddy called it aswindle; Bertrand Russell

suggested it was allcontained in the Lorentz

transformation equations;and many scientistscommented on its

contradictions

would be a movement of the fringes, fromwhich the velocity of the earth could becalculated, but no change at all wasobserved.

Fitzgerald and Lorentz pointed out thatthis result would be obtained if the arm ofthe interferometer which was moving par-allel with the earth was, in consequence ofthis movement, reduced in length by theamount (1-v2/c2)11. Such an arbitraryassumption did not constitute a satisfactoryexplanation and scientists tried to think of amore fundamental cause.

Einstein came to the conclusion that theanswer rested on the way time was measuredand the simultaneity of two events wasdefined; and on the basis of these ideas andtwo additional assumptions he developed histheory, published in 1905. It was essentiallythe electromagnetic theory of Maxwell andLorentz modified to incorporate theMichelson-Morley result. Later, in 1907, heextended the theory to include gravitationaleffects and predicted that light would bedeflected as it passed near the sun. Theprediction could be tested only by observingthe path of the light from stars during anexlipse of the sun and in 1919 Eddington ledan expedition to the island of Principe,where the eclipse was total; and when the

results had been studied, announced thatthe prediction was confirmed. The theorywas then gradually accepted, eventuallybeing regarded as a revolution in scientificthought.

But there have always been its critics:Rutherford treated it as a joke; Soddy calledit a swindle: Bertrand Russell suggested thatit was all contained in the Lorentz trans-formation equations; and many scientistscommented on its contradictions. Theseadverse opinions, together with the fact thatthe small effects predicted by the theorywere becoming of significance to the defini-tion of the unit of atomic time, prompted meto study Einstein's paper. I found that it waswritten in imprecise language. that oneassumption was in two contradictory formsand that it contained two serious errors.

...he concluded that, at theend of the journey, the time

recorded by the movingclock was less than that

recorded by the stationaryclock. The result did not

follow from the experiment,but was simply an

assumption slipped inimplicitly during the

complicated procedureThe essential feature of science is its

dependence on experiment. Results of ex-periment are expressed in terms of unitswhich must not be duplicated if contradic-tions are to be avoided and units of measure-ment are the only quantities which can bemade constant by definition. When Einsteinwrote his paper, two of the units were thoseof length and time. Velocity was measured interms of these units. Einstein defined thevelocity of light as a universal constant andthus broke a fundamental rule of science.

One of the predictions of the theory wasthat a moving clock goes more slowly thanan identical stationary clock. Taking intoaccount the basic assumption of the theorythat uniform velocity is purely relative, itfollows that each clock goes more slowlythan the other when viewed from the posi-tion of the other. This prediction is strangebut not logically impossible. Einstein thenmade his second mistake in the course of athought -experiment. He imagined that twoclocks were initially together and that one ofthem moved away in a number of straightline paths, at a uniform velocity, finallyreturning to the starting point. He con-cluded that on its return the moving clockwas slower than the stationary clock.Moreover. since only uniform motion is

...I do not think Rutherfordwould have regarded (thetheory) as a joke had he

realised how it would retardthe rational development of

science

Einstein defined thevelocity of light as a

universal constant and thusbroke one of the

fundamental rules ofscience

involved there is no way of distinguishingbetween the two and each clock goes moreslowly than the other. This result is knownas the clock paradox or, since the clocks aresometimes likened to identical twins, one ofwhom ages more slowly than the other, thetwin paradox.

Hundreds of thousands of words havebeen written about the paradox but theexplanation is simple, arising from Ein-stein's use of the expression, "as viewedfrom". Clearly if the time of one clock isviewed to be slower than the other evenwhen it has returned to the same position asthe other then it must indeed be slower. Butthe rates of distant clocks are not comparedby viewing them. Ticks from them arereceived and counted on a separate dial, aprocess now carried out continuouslythroughout the world for the synchroniza-tion of atomic time. It is the reading on thissubsidiary dial which would be less and notthat on the dial of the clock itself. If thethought -experiment is carried out correctly,the result is that the time of the movingclock as measured at the position of thestationary clock is less than that of thestationary clock. This is the same as theinitial prediction, which is as it should besince a thought -experiment cannot give aresult differing from the information putinto it.

Einstein's use of a thought -experiment,together with his ignorance of experimentaltechniques, gave a result which fooled him-self and generations of scientists. He con-vinced himself that the theory yielded theresult he wanted, because the contraction oftime is accompanied by the contraction oflength needed to explain the Michelson-Morley result.

The round trip could not have been madewithout accelerations being applied, butEinstein ignored their possible effect on therate of the clock, thus implicitly assumingthat they had no effect. Some years later, in1918, he used another thought -experimentin an attempt to answer criticisms of theparadox result. One of the clocks again madea round trip, the changes of direction beingachieved by switching gravitational fields onand off at various stages of the journey, thetime recorded by the moving clock was lessthan that recorded by the stationary clock.The result did not follow from the experi-ment, but was simply an assumption slippedin implicitly during the complicated proce-dure. The slowing down of clocks which hehad previously attributed to uniform veloc-ity, acceleration having no effect. he nowattributed to acceleration, a line of argu-ment followed in many textbooks.

Claims frequently made that the theory issupported by experimental evidence do notwithstand a close scrutiny. There are gravedoubts about Eddington's claim, both as

regards the predicted value which was in-creased by a factor of 2 from that first givenby Einstein and the way the results wereanalysed - some of the readings beingdiscarded. The same criticism applies to amore recent experiment performed, at con-siderable expense, in 1972. Four atomicclocks were flown round the world and thetimes recorded by them were compared withthe times recorded by similar clocks inWashington. The results obtained from theindividual clocks differed by as much as 300nanoseconds. This absurdly optimistic con-clusion was accepted and given wide public-ity in the scientific literature and by themedia as a confirmation of the clock para-dox. All the experiment showed was that theclocks were not sufficiently accurate todetect the small effect predicted.

Why have scientists accepted a theorywhich contains obvious errors and lacks anygenuine experimental support? It is a diffi-cult question, but a number of reasons canbe suggested. There is first the ambiguouslanguage used by Einstein and the nature ofhis errors. Units of measurements, thoughof fundamental importance, are seldom dis-cussed outside specialist circles and theerrors in clock comparisons are hidden awayin the thought experiments. Then there is

Einstein's use of a thoughtexperiment, together with

his ignorance ofexperimental techniques,gave a result which fooledhimself and generations of

scientists

the prestige of its advocates. Eddington hadthe full support of the Royal AstronomicalSociety. the Royal Society and scientificestablishments throughout the world. Tak-ing their cue from scientists, importantpeople in other walks of life referred to it asan outstanding achievement of the humanintellect. Another powerful reason for itsacceptance was suggested to me by a formerpresident of the Royal Society. He confessedthat he did not understand the theory him-self, not being an expert in the subject, buthe thought it must be right because he hadfound it so useful. This is a very importantrequirement in any theory but it does notfollow that errors in it should be ignored.

Insofar as the theory is thought to explainthe result of the Michelson-Morley experi-ment I am inclined to agree with Soddy thatit is a swindle: and I do not think Rutherfordwould have regarded it as a joke had herealised how it would retard' the rationaldevelopment of science.

Dr Louis Essen, D.Sc., F.R.S., has spent alifetime working at the NPL on the measure-ment of time and frequency. He built thefirst caesium clock in 1955 and determinedthe velocity of light by cavity resonator, inthe process showing that Michelson's valuewas 171cm/s low. n 1959, he was awarded thePopov Cold Medal of the USSR Academy ofSciences and also the OBE.

n' I.s.b

2 3 8m

19 18 17 165

19 18 17 16 15 14 13 12

6 5 4 3 2

11 10 9

15 14 13

6 5 4 16 15 14 13

39k1S1

6 5 4 3 2

1 24 13

9 12,1

CIRCUIT IDEASProgrammableamplifier with widedynamic rangeAmplifiers with programmable gain tend tobe based on analogue multipliers or, if underdigital control, may use a multiplying d -to -aconverter or op -amp with switchable feed-back. Analogue multipliers can drift and in adigitally -controlled circuit considerable out-put spikes can occur when the digital inputvalue changes.

Neither of these problems occurs with thislow -noise, low -drift and transient -free pro-grammable amplifier. It has two identicalamplifying paths, called main and standby,each using a 1232 d -to -a converter. One pathat a time feeds the output buffer dependingon the position of a DG243 single -poletwo-way switch.

Initially, output comes from the main

amplifying path. New data is latched into thefirst HC574 and transferred to the standbyamplifier, setting it to the new gain value.Next, output is switched to the standby path,the main amplifier is set to the new gain, andoutput is returned to the main path.

Neither converter is switched through tothe output while its digital input is beingchanged so switching transients do notoccur. Transients produced by the DG243make -before -break switch are negligible.

Normally d -to -a converters provide atten-uation but here, amplification is needed. Ahigh -stability potential divider with buffer-ing determines amplification. This does notdegrade temperature performance sincetemperature tracking of the converter resis-tor network is still used.

In this mode however, leakage currentthrough the converter switches introducesoutput offsets of up to several millivolts,depending on the digital input word; epromsprogrammed to suit the converter compen-

sate for this. Data values for the eproms arequite easily determined and are reasonablypredictable once the individual contributionof each converter switch is known.

Gain accuracy is eight bits but twelve -bitconverters are used because of their superiornoise and leakage -current performance. Inthis configuration, the four least -significantbits of the twelve track the four mostsignificant so gain error introduced remainsless than one bit.

Overall bandwidth is limited to the 20kHzrequired for the original application by asecond -order low-pass filter. Circuit per-formance is degraded if the source impe-dance is greater than 500 since transientsfrom one converter feed to the otherthrough the common input line. Adding aninput buffer solves this problem at theexpense of noise performance.

Tim WilmshurstDepartment of EngineeringUniversity of Cambridge

A18 -A5C22 "--A16

C21 -A17C20 -A18A13 -6_5Al2 '-DS1A14 /74

A16DTACK

25LS2521

7x 4k7S1

18IN EOUT

1 19MASEL

%-, ea=

VMEbus eprom boardAny convenient address boundary can beused for this VMEbus eprom board occupy-ing 128Kbyte of memory space. The circuitis economical, easy to build and easilyexpanded to take up to eight eprom banks.

Dip switches feeding an eight -bitAM25LS2521 comparator determine the

A5 73A16A 15.17 aOr 6

74LS244

7 I3A16 1

12 gni18 BR/17/

G2A 62B

74LS138

100--11

74L S9 5

8MHzclock

MASELBA'S

R C M1L 0 12 ROMOLO

ROMIHI ROMOHI

rElD7)

address space and acknowledge signal irraciicomes from the LS95 shift register. Onreceipt of a valid address, the local 8MHzclock oscillator starts clocking the shiftregister to provide additional wait states ateach successive output. Shift register outputQ, gives one wait state and output Q3 givesfour.Frank KellyComputing Science DepartmentUniversity of StirlingScotland

VME bus eprom board continued overleaf

rCIRCUIT IDEAS

74LS373

M A SEL

16-BA8EN a

8 74LS373 9

[A153- _BA14)

DTA CK

D7 2-10

74LS373

-3 807

015 --

74LS373

18-80817

ROMOLO ROMSIZE

22 20 2710

ROMOH1 ROMSIZE

22 20 27

ROMSIZE(27128 or 272561

27128Or

2 7256

ROM1L0 ROMSIZE

22 20 270

ROM11-1 ROM SIZE

22 20 27

Video converter forRGB to compositemonochromeVideo RGB signals compatible withextended -graphics -adaptor systems can beturned into monochrome composite videowithout the need for a separate powersupply.

Line sync. at 21kHz is a short 5V pulsewhile the 60Hz frame sync. signal is a longernegative -going 5V pulse. Using thenormally -high frame sync. line as supply,the transistor inverts the line sync. pulsewhile the 4714F capacitor and diode shift thecombined sync. signals consisting ofnegative -going pulses.

Sync. signals are summed with the RGBsignals into the 75,12 load. Variable resistorsallow adjustment of the relative RGB levels;a blue background may look good on acolour monitor but a grey background does

nothing to enhance the appearan c of amonochrome picture.Keith WoottenReadingBerkshire

Circled numbers are RIBM 9 pintrconnections 330 2k

(-5) B

___23SV 330 2k

_r_rut_OV8 sync

3908[107 IN914 < Load

The New GenerationThermal Linescan Recorders from Waverley

Waverley ThermalLinescan Recordershave been developedin the UK to overcomethe well-knowndisadvantages of existingelectrographic hardcopyprinters, which includefumes, dust and the needfor a moving stylus orchemicals.

All recorders incorporate arevolutionary full width thermal printhead, enabling high definition drypaper grey scale recording with nomoving parts other than the paper

For further details, contact:

transport. Therecorders are ruggedand reliable givingdust and fume -freeoperation. The onlyconsumable requiredis the low-cost paper.Routine maintenanceof the printingassembly has been

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with 16 grey levels and 1/12mmimage edge definition.

Waverley offer a comprehensiverange of models including:

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A Dowty Electronic Systems Division Company

3700 - illustrated leftDual channel analogue or digital input

with IEEE control and built-in charactergenerator for annotation.

A single channelanalogue or digital unitwith variable sweep,trigger, delay times andinput level.

s A single channel, multiapplication printer with ageneral purpose digital

',interface.

PROCESSOR PROJECT.?For complete turn -key instrumentation and systems, Cavendish Automation offers delivery at little morecost than stock items. This is achieved by our calling on our own comprehensive range of standard hardwareand configuring it to customers' exact requirements. In addition to hardware, we are able to write andinclude user -requested software drivers for scanning keyboards, driving displays, sensing front panelswitches, driving DACs or reading analogue.

Our existing experienceincludes medical diagnosticequipment, marineinstrumentation, control ofreal-time video as well asmany forms of industrialprocess control.

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Very low cost No advance payment Guaranteed working system Delivery normally around 6

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So, for professional implementations at super -low cost, call us on (0480) 219457.

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ENTER Id ON REPLY CARDELECTRONICS & WIRELESS WORLD 13 I

Programming p.l.dsControl software for programming and verifying

a programmable logic device is often fed by outputfrom a Boolean -logic assembler.

Programming a p.I.d. takes three pro-gramming and verifying steps, one foroutput polarity, one for the And mat-

rix, and one for the Or matrix. In myprogram these tasks are independent of eachother and the overall program integratesthese functions in the proper sequence.

Before the p.l.d. can be programmed ithas to be checked to make sure that it is inthe virgin state which is characterized bythe presence of all the NiCr links, presenceof both the true as well as complementterms of the input variables, the presence ofall 48 P terms in the Or matrix, and theactive -high polarity of all the outputs.Software should therefore be modular andeach of the above tasks performed by asubroutine. My program was written inIntel 8085 assembly language.

Coding of output -polarity data. There areeight output functions and each of them canbe programmed to be active high or activelow. Thus each function requires one bit ofdata to store its status and a byte to storeinformation about the polarity of all theoutput functions, with b0.7 in F0.7. Data b, iszero for active -low output polarity and onefor active high output polarity.

Coding of And -matrix data. There are 48And gates each with 16 input variablespresent in both the true as well as comple-ment form. Each input may be present orabsent, and, if present it may be in the trueor compelement form; one bit is required tostore this information for each input line tothe And gate.

Since there are 32 input lines to each Andgate and 48 And gates, four bytes arerequired to store the programming data foreach And gate and a total of 48 x 32 bytes, i.e.192 bytes, for the entire And matrix. Pro-gramming data for P term 0 has 115.8 in thefirst byte. l7_ in the second, 115.8 in the thirdand 17.0 in the fourth. The next byte ofprogramming data in the memory for P term1 contains 115.18 and so on.

Presence of an input variable is indicatedby a logic one, and absence by a logic zero.For example, if P Term 0 in a particularBoolean function contains L. 12, 14, 16, 17, 19,III, 114, 115, the four bytes of programmingdata for P term 0 would be,

Byte Data1 010000102 100100013 100010004 01000100

V. LAKSHMINARAYANAN

While forming the fusing pattern careshould be taken to see that the input linkscorresponding to unused P terms are notfused.

Coding of Or -matrix data. There are eightOr gates each with 48 inputs from the Andmatrix. Each And gate output may or maynot be present as an input to a particular Orgate, i.e. a particular P term may be presentor absent. The presence or absence of a Pterm is indicated by a logical one or zero asin the case of input variables. Therefore,each Or function requires 48 bits i.e., 6bytes of information for programming, anda total of 8 x 6=48 bytes are required for theentire Or matrix.

Or -matrix data for programming isstored in memory for function F1, with P7.0in the first byte, P15.8 in the second, P23.16in the third, P31.24 in the fourth, P39.39 andP47.41 in the sixth byte. The next byte inmemory will be programming data foroutput function F1, and so on.

For example, if F1, is defined as

F0= P1+ P3-1- + P9+P11+

P20 + P24 + P3I + P32+ +P47

fusing data stored in the memory would be;

Byte Data1 100010102 000010103 000100004 111111115 111111116 11111111

You will notice that P terms P31.47 are notbeing fused; it is assumed that these Pterms are not being used in the function Fo.

PROGRAMMING PROCEDURE

Programming a p.l.d. involves the followingsteps,- check the virgin state of the p.l.d.- program and verify output polarity.

SOFTWARE

The 48.page p.l.a. programmer listing in 8085assembly language is too long for us to print in themagazine. We also have the author's 15 -pagePascal listing for reading an input file for the Andand Or terms and outputting data in Intel hex form.They can be obtained by sending an A4 s.a.e. withyour address on it and a £3.75 copying charge toPLA listing, E&WW Editorial. Room L303, QuadrantHouse. The Quadrant. Sutton, Surrey. Chequesshould be payable to Reed Business Publishing.

- program and verify the And matrix.- program and verify the Or matrix.

Before programming, the necessary datashould be stored in the memory in thecorrect format and the routines performingthe above tasks should be sequentiallycalled.

To illustrate the programming technique,a specimen set of Boolean equations is givenin List 1, and the corresponding fusingpatterns in List 2. I will now look at the waythe fusing patterns are formed for outputpolarity, a P term and an output function.

From List 1 you can see that outputs Fo,F2, F4, F5, F6 are to be programmed activelow and F3 is to be programmed active high;outputs F1 and F7 are not used. Therefore,the polarity fusing pattern is,

F7 F6 F5 F4 F3 F2 F1 Fo1 0 0 0 1 0 1 0

i.e., 8A16 which, as you can see from List 2, isstored in location 100016.

Coming to P -term 1, you can see that itcontains 10, 12 and I. Therefore, the links tobe blown are all of 10.15, and all but 1,,, 12 and15 in 1045. Corresponding bytes stored inmemory are,

115-8 0000 0000 (0)17.0 0010 0101 (2516)

!15-5 0000 0000 (0)17-0 0000 0000 (0)

These bytes are stored in locations 100516to 100816. Fusing patterns for other P termsare formed in a similar way. To programoutput function Fo the fusing pattern re-quired would be in the form of six bytesdefined as follows,

P23-16

P31-24

P39-32

P47-40

0000 0110 (616)0000 0000 (0)1111 1110 (FE16)1111 1111 (FF16)1111 1111 (FF,6)1111 1111 (FF16)

These patterns are stored in locations10C116-100616. Fusing patterns for otherouput functions are formed on similar lines.

ASSEMBLER REQUIREMENTS

In preceding sections I have explained how ap.I.d. can be programmed by using thefusing patterns for the And and Or matricesand the output polarity. Essentially the c.p.u. reads the fusing patterns stored inmemory and as decided by the assembly -language algorithm either fuses the NiCrlinks or leaves them intact.

List 1. Specimen programming data for p.l.a.

Product termsPI =10.12.15

P2 =103.111P3 =10341104113)4P4 =10.14.111

P6 =102.111P7 =1041417.112

P8 =11414174.112P9 =1112414111PIO =103419014111PI I =114013)P12 =104.194113)

P13 413).114P14 =10.124(115)

PI 5 =10124113PI6 =10.13.15419)4110)

Other P -terms are not used.

Sum terms(F0)=P1 + P2

(F2)= P3+ P4 + P5

(F3 = PI + P6(F4)= P7+ P5

(F5)= P9+ P10+ P14+ P15+ P16(F6)= P11 + P12 + PI 3

Outputs F1 and F7 are not used.

Note: Terms in parentheses are active -lowoutputs/complementary variables.

List 2. Example of programming data for the p.l.d.programmer produced from Boolean equationsin List 1 by the author's assembler.

Here the fusing pattern for output polarity datafor F7.0 is stored in location 1000, for the Andmatrix in locations 1001 to 1000 and for the Ormatrix from 1001 to 10F0.1000 8A ;Polarity1001 FF FF FF FF ;PO1005 00 25 00 00 ;P1

1009 08 09 00 00 ;P2

100D 84 29 20 00 ;P3

1011 08 11 00 00 ;P41015 00 26 00 00 ;P5

1019 08 05 00 00 ;P6101D 10 81 00 20 ;P7

1021 11 82 00 20 ;P81025 08 06 00 20 ;P91029 08 09 06 00 ;P10102D 00 42 20 00 ;P111031 02 41 20 00 ;P121035 40 00 20 00 :P131039 00 45 80 00 ;P14103D 20 25 00 00 ;P151041 00 29 06 00 ;P16

To prevent fusing input links of unused P terms,terminate program after P16. Or matrix fusingpattern follows.

1001 06 00 FE FF FF FF ;FO

1007 FF FF FF FF FF FF ;F1

10CD 38 00 FE FF FF FF ;F2

10D3 42 00 FE FF FF FF ;F3

10D9 80 01 FE FF FF FF ;F4

1 ODF 00 C6 FF FF FF FF ;F5

10E5 00 38 FE FF FF FF ;F6

10EB FF FF FF FF FF FF ;F7

My Pascal assembler is described in thissection to give you ideas for writing yourown software. The assembler produces thefusing patterns for the And and Or matricesdirectly from Boolean equations. In otherwords, the assembler converts user -readableinputs into machine-readable format.

Final output of the assembler is a file inthe Intel hex form which can be directly readfrom disc into microcomputer ram for useby the c.p.u. The assembler accepts data in aparticular form. For example, the repre-sentation of a typical P term and an F term is

/P07=100.005... 109/ (1)/F2 =P00+P12+P23+... P19/ (2)

Here P stands for the product term, its indexvarying between 0 and 47 for the 48 Andterms. In (1), it is set as a combination of I's(true inputs) and C's (complemented inputs)which are specified by the accompanyingindices.

Similarly. in (2), F is a sum term desig-nated by its index which lies between 0 and 7for the eight outputs, and is set to be thecombination of the P terms on the right ofthe equal sign. Both these equations areenclosed within obliques to indicate the fieldof each And/Or term. For each p.I.d. therequired Boolean equations are written forthe And and Or matrices in the form ex-plained above, and an input file is produced.The assembler is structured to that it readsthe input file and creates an output file in theIntel hex format.

ASSEMBLER ALGORITHM

My assembler assumes that input data, thatis to say the P and the F terms, is present inan input file called DATA.IN. First, data isread from this file. The assembler recognizesthe end of P term data when it encounters anasterisk in the field of the character P (eachline in the input file is declared as a record):similarly the end of F -term data is indicatedby a hash symbol.

Each P term has a combination of I and Cterms. Since these cannot exceed 32 (10-15and C015) a four -by -eight matrix is associ-ated with each product term. Each row isequivalent to a byte. The structure of eachmatrix is.

115 Is-111C15 - C8C, Co

These matrices are initialized to null mat-rices for the P terms: the 1 and C termspresent in each P term decide which of thematrix elements become 1 (logic one in abyte is equivalent to presence of that inputvariable and hence the corresponding NiCrlink need not be blown).

Once the matrices are formed, each mat-rix row is converted into hexadecimal formby grouping the bits four at a time. Thehexadecimal code lies between 00 and FF. Anabsent P term requires none of the links tobe blown: hence it will have FF FF FF FF.

Thus all P terms have a hexadecimal codewhether they are present or absent. Thesecodes are combined to form the Intel hex filein which each line has 16 bytes ofhexadecimal -form data.

A similar procedure produces hexadecim-al code for F terms. Since there are 48 Pterms (0 to 47), each F term has a six -by -eight matrix associated with it. Proceduresfor both And and Or matrices have numeric-al test facilities built into their algorithms toarrange the terms in ascending numericalorder.

CONCLUSION

With this programmer it is possible totransform a blank p.l.d. into a device con-taining a custom algorithm, microprogram.or Boolean transfer function in a fewseconds. Such a logic i.c. has applicationsincluding character generators, look -up anddecision tables, function generators, micro-programming, sequential controllers andfrequency synthesizers.

I would like to thank Dr N.W. Nerurkarand Mr V.B. Taneja of the Centre for Adv-anced Studies in Electronics, New Delhi, fortheir encouragement during this work andfor their permission to publish this article.Furl her readingBipolar and mos memory data manual. Signetics.USA. 1980.Programmable -logic data manual. Signetics.USA. 1986.PAL/PLE programmable -logic handbook. Mono-lithic Memories USA. 1985.Programmable logic data book. Advanced MicroDevices. USA. 1986-87.

V. Lakshminaravanan obtained his B.E. inElectronics Engineering from BangaloreUniversity in 1981 and an M.E. in ElectricalCommunication Engineering from the Indi-an Institute of Science in 1983.

He is currently on the technical staffat theCentre for the Development of Telematics inBangalore, involved in the design of digitaltelephone exchanges and v.h.f./u.h.f. com-munication systems.

Moving -coil headamplifiers

In the article by Doug Self whichappeared in the December issue, anerror appeared in Fig. 6, the completecircuit diagram. A correct version of therelevant part of the diagram is shownbelow. Apologies to readers and to MrSelf and thanks to Mr D. Symons. whopointed out the error.

A.m. stereoWith reference to the item "A.m.stereo for Europe" in EWW,November, 1987, page 1167, I

would like to point out that, inmy opinion, it is much better forEurope to have a.m. higher -fidelity than a.m. poor stereo.

That is, instead of sending Land R, which are two band -limited (5kHz) audio channels, itwould be more enjoyable if theadded information extended thebandwidth of the transmittedprogramme (at the speaker).

The latter could be done byshifting down (e.g. by 5kHz) thehigher frequencies of the audioprogramme (probably from5kHz to 10 kHz) and then addingthem (now bandlimited to 5kHz)to the old programme (alsobandlimited to 5kHz) in quadra-ture as proposed in stereo sys-tems.Kerim FahmeAleppoSyria

Mechanicaltelevision

I was most impressed to read theletter by Mr A.S. Henderson inyour December issue on mecha-nical tv under Feedback. I wasthe first engineer to join theScophony Company in 1932, andprobably I am more fortunatethan Mr Henderson in that I havekept records and photographs ofmost aspects of the Scophonysystem for over fifty years.

Adam Hilger Ltd produced ourfirst high-speed scanners in bothstainless steel and glass, butwhen it became established thatthe definition of television wouldbe either 240 lines 50 frames or202.5 lines interlaced to producea 405 line picture, the polygonwas designed for 20 facets andwas in stainless steel and notglass. We manufactured 50 poly-gons on a mandrel, using a veryaccurate Zeiss optical dividinghead, and it was possible to use35 of these in the centre of themandrel - the outside polygonswere discarded. We could carryout this work when Ted Wilsonjoined us and I am obliged to MrHenderson for reminding me ofhis name. I retain all the costsheets, which were carefully pre-pared, and note that the high

FEEDBACKspeed motor and stainless steelpolygon as a complete unit had atotal material and labour cost of£8.12.6, the polygon represent-ing the magnificent sum of£3.10.0.

I am at a loss to find the reasonfor the 49 facet polygon; we werethinking in 1939 of front projec-tion rather than the rear projec-tion of our standard cinema sys-tems, and the 49 facet wouldreduce the angle between eachfacet and so give us a longerprojection distance than the 20facet polygon. I have known ofmulti -facet polygon tests forfront projection, and for a 405line picture the lower -speedhigh-speed scanner would meanan increase in the distance be-tween the ultrasonic light celland the scanner from 13 tosomething like 35 cm. in order toobtain the immobilising of thewaves in the liquid column.Another reason for the 49 facetpolygon was to accommodate theintended 441 line 60 frame stan-dard in the United States toreduce the high-speed scannerspeed which, on the British stan-dard, was running at 30,375r.p.m.

Incidentally, the total cost in-cluding labour of the complete24in Scophony Home Receiverwas just under £52, excludingcabinet, the reason being thatTed Wilson was getting £3 aweek and I, as a Design Engineer,got £450 a year! Converting£.s.d. into present day metricpounds by multiplying every-thing by 2.4 and 50 years ofinflation, multiply by at least 20and you will get a cost of nearly£2.500!Joshua SiegerPooleDorset

Couplingcoefficient

We thank Mr Clifford for hisinterest (Letters, December1987) in the article "Does yourcoupling coefficient matter?, byTom Ivall, June 1987 issue, andare ourselves interested that hehas written on allied topics (anyreprints left. Mr Clifford ?).

May we reply to three of thepoints he raises:1. If the receiving part of thecircuit shown in Fig.2 were in-deed a "test circuit", then of

course it would be better to doaway with the transformer andmeasure 12 as the voltage drop-ped across a small (0.5 ohm)resistor, as Mr Clifford suggests.But what the figure portrays isnot a test circuit; it is a practicalcircuit for an implantable receiv-er whose output must match theresistance of the tissue to bestimulated - of the order of half akilohm, rather than half an ohm,with a typical electrode setup.Hence the need for a step-up r.f.transformer, which does indeeddegrade the range -independencyof the link, but not by much.2. Tongue doubtless in cheek, MrClifford suggests that if one ex-pects the frequency to fall as oneapproximates oscillator and re-ceiver, it will in fact surely rise,and vice -versa; and that this isundesirable. On the contrary, itwould not matter which way thefrequency went, but in practice,with the various series oscilla-tors the MRC Unit has published,the frequency always falls andnever hops to the higher, theore-tically possible, value.3.Using an operational amplifierto drive Vmos transistors hasthrown up no noticeable prob-lems with reliability. In any case,it is the implanted receiverwhich must be ultra reliable; theexternal -to -the -body series oscil-lator need only be reliable.P.E.K. DonaldsonMRC Neurological ProsthesisUnitLondon SE5T.E. IvallStainesMiddlesex

In an article in the June. 1987Electronic & Wireless World, en-titled "Does your coupling coeffi-cient matter?" Tom Ivall reportswork funded by the Medical Re-search Council. He purports toreport a "little-known, possiblyhitherto unknown. fundamentalproperty of inductively coupledoscillating circuits".

I am sure that by now you willhave received many other lettersin addition to this one from'old-timers', protesting that farfrom being the "unknown" prop-erty claimed, the results are wellknown (even to a now non -practising ex -electronics personas I am). I referred to one of mytext -books last used in 1951when I took my physics degree."Principles of Electricity" by

Page & Adams (first edition June1931, second edition 1949) by D.Van Nostrand Company, Inc,New York. Pages 509-517 dealexplicitly with coupled circuitsin forced oscillation and containanalogous results.

I trust that Mr P. E. K. Donald-son will make an acknowledge-ment of at least this prior work infuture publications.D.C. ChadneyChinnorOxfordshire

Catt's anomalyThere is no rigid rod in my story(January, 1987). Indeed, I chosethe two examples, a cable and abody of water, in order to steerclear of such dubious idealiza-tions. Any number of other ex-amples could have been used,such as ordinary sound in air.The point of them all would bethe same - that the speed of theelements of the medium can befar below (and is certainly quite aseparate issues from) the speedwith which displacementsagate. Indeed, I mention in thecase of the water, but the pointholds also for the cable, that thedisplacement propagates at thespeed of sound. There is a closemathematical parallel betweenthe mass (or density) of an acous-tic medium and the inductance(or inductance per unit length)of a transmission line, as there isbetween elasticity and capaci-tance. There is simply no prob-lem about a pulse of chargetravelling at the speed of lightwhile the electrons themselvesmove at speeds that are orders ofmagnitude slower, and Catt'sself -named anomaly is no morethan an elementary misunder-standing.

At the time of writing myletter it did seem funny, and atleast has the merit of being on alevel of pottiness comparable toMr Catt's declamations.Alex WildingRedditch

The Conquestof thought

Ivor Catt (December. 1987)seems to think I have been goingon about Bohr's CorrespondencePrinciple in articles on electro-magnetism and vectors recently.

If I put my physicist's cap on, theprinciple is familiar and could bediscussed, but I did not haveanything like it in mind whilewriting the tutorial articles.

Regarding the little bit that Irelated to Kuhn's statement -and Kuhn says quite a number ofcontradictory things - I wouldonly add the following extracts:

"Second, the new paradigmmust promise to preserve a re-latively large part of the concreteproblem -solving ability that hasaccrued to science through itspredecessors."

and:- '

"paradigms...usually preservea great deal of the most concreteparts of past achievement andthey always permit additionalconcrete problem -solutions be-sides".

These, by the way, are on page169 of his book "The Structure ofScientific Revolutions", in caseIvor Catt gets time to read thebook.

On the correspondence fromC. F. Coleman in the Novemberissue, I wonder what point hewas making? One flavour in hisletter seemed to be the delusionarising yet again that 'progress'is everything, and frenetic atthat. "0", "A" and BTEC levelpeople should study tensors,number pairs, up-to-the-minutebits and pieces that the 'mathspushers' say is in fashion. Manyof us do not go along with thefiction that progress is occurringin this naive way at all. Whatabout the chlorinated com-pounds and the ozone layer - andthe nuclear fiascos?

Much closer to home, howwould Mr Coleman offer the bud-ding electronic engineer ex-pressions for the reactance of aninductor, jcul. for example, orFourier transforms. More to thepoint even than that, all theexams I have seen from en-gineering institutions containquestions about j and the conciseway phasors show phase andfrequency and soon.

On the other topic, vectors,I'm afraid it is the same story.Yes, division by a vector is notdefined, and that's O.K. as thereis no physical or engineeringneed for it anyway. Would MrColeman throw away all algebrasthat didn't commute? Out wouldgo matrix algebra too, I suppose.Tensors might very well turn upwith anisotropic media, like per-meability and ferrite material, or

FEEDBACKbirefringent dielectrics. If MrColeman's students study Gener-al Relativity, then sure, tensorswill turn up. But I'll wager they'llnot turn up until all the studentshave a good knowledge of vectoranalysis for electromagnetismstudies, and so on.

No, I repeat, Mr Colemanmust be reading some remoteesoteric stuff to think he canargue about obsolescence in theway he did. In any case I disagreeentirely that everything studied20 years ago has gone - we stilluse Newton's laws and those ofthermodynamics for nearly allengineering design task anymotor engineer), and for rocketdesign and launching - to saynothing about those Maxwell'sequations I discussed in thearticle...Joules WattStapleKent

Moving -coilpreamplifier

I read with great interest Doug.Sells article on m. -c. stages inEWW for December 1987. I'mglad to see at last a proper,practical approach to circuit de-sign. The article was well writ-ten, fluent and not bogged downwith largely irrelevant mathema-tics. Figure 2 clearly demons-trated the fact, little knownamongst most engineers, thatBi-fet and Met op -amps are ex-tremely noisy. Any engineer willtell you, after reading any datasheet on modern op -amps thatthey are all very low -noise, veryhigh-performance devices. Thatfet op -amps are low noise devicesis sheer nonsense. Any engineerworth his salt who can wire up acircuit and measure it will findthat, for impedances below50kHz, bipolar junction transis-tors are quieter than fets. A fetonly comes into its own in twoareas; for high impedances or forr.f. from 50MHz to 500MHz.Above this frequency, b.j.ts againexhibit superior noise specs. Fetop -amps are far noisier than even741s in audio applications, asshown by Mr Self, their main usebeing for high input impedancesand low bias -current usage in,for example, sample -and -holdcircuits. Outside this limitedarea they are best put to use forbuilding motorways.

However, I must point outthat Mr Self fell down on thedefinition of which noise he isactually measuring. He mea-sured unweighted noise andwithout RIAA correction. This isgrossly in error for a practicalm. -c. stage.

The reason is that a high -gain(hFE typical 1200) BC650 willexhibit exceptionally low flickernoise (low frequency), but un-weighted measurements showhigh wideband noise in excess ofthat of virtually, any other type.Since an RIAA stage has roughly30dB differential gain betweenlow frequencies and mid audio -band frequencies, a transistormust be measured under theseconditions to give a true indica-tion of whether it is audibly quietor not. Secondly a CCIR filterfitted with a true peak detectormust be used to simulate theear's response. Unweightedmeasurements are meaninglesseven for comparisons. A selectedlow rb ZTX655 will give a verygood performance in Mr Sellssetup due to its low -gain. lowwhite -noise level. However,when fed through a RIAA circuitit is dominated by flicker noise,which makes the system almostuseless, with a continuousgrowling sound.

One last point on noise; thekey to the whole performance isrunning the input transistor atthe optimum collector currentfor a given source impedance, asMr Self mentions. He then uses astandard 3R3 resistor as a sourceload. I have found many timesthat optimum for minimumnoise cannot be set on a pureresistor. Presumably one intendsto actually use the circuit with aparticular cartridge, thereforeshould be optimized for thatcartridge. I have found that if acartridge (carefully screened) isactually substituted for the 3R3resistor, the audible and measur-able noise is significantly worse,typically by 8-10dB. The reasonis that the cartridge is inductiveexhibiting a rising impedancewith frequency. Since noise withmost low -noise transistors issubjectively worse at mid -audiofrequencies, the input stage's Icmust be lowered to give a bettermatch. Empirically, this opti-mum operating current with anactual cartridge connected hasbeen found to be around 1/3 thatobtained with a shorted input,and gives a real, practical noise

voltage within 2dB of that of a3R3. It is also interesting to notethat a lower input -stage noise inmedical electronics is normallyobtained by operating the inputdevice at optimum collector cur-rent and with a fixed VcE of lessthan 3V. Mr Sells is a little highat 5V and with an op -amp outputstage linearity is not a problem.

Whilst I agree entirely with MrSells view of a single input stageand the avoidance of differentialinputs due to 3dB worse noise, Icannot agree with the idea ofusing an electrolytic at the input.Whilst I myself cannot measureany degradation in t.h.d. down to1p.p.m., it has been demon-strated many times that there isan audible difference between ashort circuit and a high -qualitypolypropylene capacitor. The useof a 220p input capacitor israther excessive; whilst I

appreciate the value has to belarge in order to present a lowimpedance at the base terminalat low frequencies, low -frequency noise is of impulsenature, with most of its energy athigher frequencies, and little atthe fundamental pulse -repetition frequency. Subjective-ly, a 22p is satisfactory with noaudible change even at 4117. Tostabilize the individual transis-tors' collector currents, as emit-ter degeneration would degradethe noise, the first stage's d.c.loop being local, individual col-lector resistors, say 220ohms,and individual base -collectorfeedback resistors would servethis purpose without noise de-gradation as the signal level atthis point is greater than at thebase -emitter input. This wouldthen allow three separate inputcoupling capacitors, say 10p pol-propylene filmcaps, connectingto each isolated base.Les SageBingleyYorks

ELECTRONICS

AND WIRELESS WORLD

1988 COMPETITION

For news of our 1988 competition, do not fail tosee this issue. The prizes are truly spectacular and

there is no hardware design involved - simplywriting. All will be revealed in the March issue, on

sale Thursday, 18 February, 1988.

V -series microprocessors and 'C'. Two articles from NEC describe theV -series of high-speed c-mos micros, which are pin -compatible with

8086 and 8088 types. The V25 incorporates features which allowefficient handling of internal peripherals, residing in separate I/Oaddress areas, directly from the C language -a process which is

normally difficult in high-level languages.

The goniometer. Gregor Grant contributes a piece on the goniometerand its decades of application in direction -finding equipment for air

navigation, from the Bellini-Tosi antenna to the standard VOR beacons.

High -definition television. Geoff Lewis reviews the proceedings of theThird International Colloquium on h.d.tv held on Ottawa recently. The

NHK Muse/MAC controversy continues.

Shockley, Bardeen and Brattain are the subject of this month'sPioneers piece, by W. Atherton. It is forty years since the world firstheard of their invention, the point -contact transistor, which took

several years to find any serious application.

Einstein's relativistic ether. Einstein has the reputation of having killedoff the ether. Dr Ludvik Kostro, of the University of Gdansk, points outthat this is not the case: Einstein denied the fixed ether, but proposed a

new conception of the ether which is non -stationary.

Confessions of a frustrated inventor. Heinz Lipschutz, who inventedinertial navigation in 1939 but was unable to interest anyone in the

system, recounts his experiences over many years of trying to exploit hiswork. "Unless an inventor has... financial muscle... he is better off

growing roses on the centre lane of the Ml".

InternationalprogramminglanguageA computer language that can be used onalmost any desk -top or home computerwithout change is the aim of 1 -APL, aninternational version of APL (A program-ming language) which conforms to ISO andproposed British standards. The language isfree to users.

APL was originally devised as a method ofnotating mathematical expressions in a lan-guage that could be understood by a compu-ter. Its first practical use in 1956 was apaper -and -pencil exercise to design themicroprogramming of the IBM 360 compu-ter. Since then the original 400Kbytes ofcode have been reduced to the 25Kbytes of1 -APL which will fit into two 16K roms on,

for example a BBC micro, withenough space left for a

character font and a printerdriver. The main advantage

of APL is that it is particularlygood at maths. Formulae can be

entered almost as written. Consequentlyprogramming time is reduced to a tenth ofthat of other programming languages. Typi-cally, statistics students can be shown howformulae are entered without needing toknow that they are using a specific program-ming language at all. This method is used atthe Statistics department at University Col-lege, Swansea, by Prof. Hawkes. Similarly,Prof. Spence of Imperial College, Londonhas written a book on circuit theory with theequations in APL notation. A disadvantage isthat on smaller computers APL is slow;benchmarks to complete a given task com-pare poorly even with Basic. However this isoffset by the complexity of mathematicspossible, such as matrix transformations.

I -APL is free to all who wish to use it. Theonly cost is the disc or eprom copying fee andfor the manuals and textbooks. Tutorial,encyclopaedic and installation manuals arein preparation and will cost less than aphotocopy of the same texts. Versions of1 -APL are in preparation for IBM -PCs, BBC,Sinclair Spectrum, Commodore CM, Apple11, Atari ST and many other computers.Details from Anthony Camacho, Chairman1 -APL Project, 2 Blenheim Road, St Albans,Herts ALI 4NR.

Enhancing IBM PCs, XTsand clonesIn this article presented in the Novemberissue, the reference to jumper E was incom-plete; it is in fact jumper E2. The photographon p1094 is of IBM's new PS2 computer,which would not benefit a great deal fromthe modifications described in the article.

FEBRUARY 1988

DUSTRYNS GHT

Seven -page review of the VMEhns extensions forinstrumentation - what VXI is all about: a case ofevolution rather than revolution latest digitaloscilloscone architecture : a case of revolution ratherthan evolution market trend, in test andmeasurement equipment top -end and dsohoing will your dmm cost more to keep than itdoes to buy? new flat -screen dsos PC-bi..1instfunieritatiol market integrated tendency

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INDUSTRY INSIGHT

INSTRUMENTATION

FIRST VXI PRODUCTS EMERGE0 nly five months after the

announcement of the VME-bus extensions for instru-mentation, VXI for short, the

first products to be designed around it arerevealed. Companies active in the high-speed instrumentation business - the 30 orso registered potential users highlightedelsewhere in this Insight - have been keep-ing their instrument cards close to theirchests, some aiming to release details atJanuary's ATE Show West in Anaheim, Cali-fornia. But what we have been able toestablish as we go to press in mid Decemberis included in this report. First product details came from one of thesmallest companies in the business, UnitedTest Equipment of Anaheim. The VXI Modu-lar Test & Monitor System is based on anA -size card using the P1 connector andmeasures 25 by 30 by 15cm without thecomputer. It is software -driven from an IBM

139First VXI productsemerge k ho's doing whatplus an alternative view ofVXI from Steve Lekas of

Keithley Instruments, Cleveland. Report byGeoffrey Shorter

140VXIbus and its impact oninstrumentation LouKlahn of Colorado DataSystems explains why the

VXIbus is an evolutionary necessity in theworld of test systems

The VXIbus - anemerging industrystandard Larry DesJardineof HP's Loveland r & d

centre analyses the VMEbus extensions forinstrumentation

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PC or compatible and the monitor screenshows i.c. pinpouts, logic signals with labels(just visible in the photograph on page 167),and connector details when cable testing. Another product on show in Anaheim isColorado Data Systems VXI PrototypingSystem,. which they claim is the first VXIproduct. According to Lou Klahn of CDS it isthe first of many: "We plan to announce anew product at the rate of one a monththroughout 1988" he told Insight.

The prototyping system, type 73A, con-sists of a 488 mainframe, a 488-to-VXIinterface board that also provides the re-quired VME and VXI interface clock andcontrol signals and other slot -0 functionstwo wire wrap cards with power filtering(one with VXI interface), an extender card,and an adapter to allow the 60 or so modulesof CDS's 53A series of 'instruments -on -a -card' to be used. Detailed user and servicemanuals with circuits are included "One of

INSIDE153

PC -based test equipmentis growth area Marketresearch analyst Mike Newreports on bus and control

issues in this fast growing market

154IEEE488 control usingan IBM-compatible PCFor multi -instrument set-ups the PC used as the

display and control element has to be paidfor only once. And it can be put to other uses

Oscilloscope architectureThere's little point intrying to improveperformance in one area if

the underlying architecture leads to areduction in capability elsewhere, saysRobert Stubbings of Tektronix

Survey Prices andessential specs of highaccuracy digitalmultimeters and 100M/1z

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Integrated tendencyHP's latest CAT systemcombines measurement,control and computation

in one box, with high speed card -to -cardcommunication

the most exciting possibilities of having anumber of instruments in a common,closely -coupled environment is tighter timecoordination leading to a higher level ofsystem performance than has ever beenpossible" enthuses Lou Klahn. "The 73A-PRT allows users to explore the ramifica-tions of this capability in their own marketplace". Tektronix had been working on a VME-based architecture for Card Modular Instru-ments prior to the development of theVXIbus standard. Other instrument com-panies and a.t.e. end -users had independent-ly determined a need for a card instrumenta-tion architecture and, significantly, VMEbushad been indentified by them all as thefoundation bus.

The VXI spec reflects the early Tektronixwork, as well as that of the four othercompanies who participated in the VXIbusdiscussions. Many of the higher perform -

Continues on page 167

162Seen these before?Flat -screen d.s.o. fromPhilips/Createc's hand-held d.s.o. and

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171Increasing role ofdistribution in t&m Asdistributors become morespecialized they offer

greater service to the customer and a moreefficient selling effort to the manufacturer.By Graham Sibley of Electronic Brokers.

Cover story Time -varying signals areanalysed in this cross between a spectrumanalyser and oscilloscope - turn to page 171for the details.

01988 Reed Business Publishing. Industry Insight isedited by Geoffrey Shorter and designed by Alan Kerr.Potential contributors for April's Insight oncommunications should make immediate contact on01-661 8639. send an abstract by fax on 01-6613948, ormail articles to Industry Insight. Electronics & WirelessWorld, Quadrant House. The Quadrant. Sutton. SurreySM2 SAS. Potential advertisers contact Martin Perry on01.6613130 or James Sherrington on 01-6618640.

ELECTRONICS & WIRELESS WORLD February 1988 139

INDUSTRY INSIGHT

INSTRUMENTATION

VXIBUS AND ITS IMPACTON INSTRUMENTATION

The recent announcement byfive major instrument manu-facturers of a new bus stan-dard for instrumentation,

dubbed the VXlbus for VMEbus extensionsfor instrumentation, raises two importantquestions: why is the VXIbus necessary, andsecondly, what is it and why is it importantin the instrument world?

The fact that five instrument manufactur-ers who are traditional competitors haveagreed to a new bus standard is a goodindicator of the importance of this step.These companies, CDS, Hewlett-Packard,Racal -Dana Instruments, Tektronix, andWavetek, have wholeheartedly endorsed theVXlbus, and believe that it will enhance thedevelopment of automatic test systems byallowing the user to more easily utilizemodular instrumentation. By virtue of itbecoming a standard, it will provide a greatvariety of available 'Instruments on Cards'.

In order to understand why VXIbus,although technologically an innovative con-cept, is an evolutionary rather than a revolu-tionary step, it is first necessary to under-stand the historical motivation that led to itsdevelopment. Two fundamental and basical-ly independent forces have combined tobring VXlbus to where it is today. The firstfactor, primarily driven by military require-ments, is an increasing need for morecapable test systems that are smaller andlighter. The second factor, driven by all usersof a.t.e., is a growing requirement for testsystems that have the higher levels of sys-tems performance that can be achieved byintegrating multiple instruments in a com-mon instrument environment.

Since the VXlbus will be a standard, it willallow users to select from a wide range ofinstruments, interface cards and computersfrom different manufacturers, with full con-fidence that these modules will operatetogether when used in a single test system.Test system designers that use the VXIbuswill be able to tailor their test to their actualneeds, since they will be able to design theequipment for the test rather than the otherway around.

A short historyAlthough test systems using modular tech-nology have been around for a number ofyears, they have all suffered from the prob-lems caused by a lack of standardization. Auser could typically not get all or enough of

Lou Klahn of Colorado

Data Systems explains

why the VXlbus is an

evolutionary necessity in

the world of test systems

the instrumentation that might be neededfor a given requirement in a common for-mat. (In fact, a system that uses a relativelylarge mainframe into which only a few of theneeded complement of functions can beplaced, can actually make a test systemlarger rather than smaller.) In addition,since some of these systems used either anunmodified computer backplane or an ex-tension of the IEEE -488 bus itself, theproblem of properly distributing instru-mentation signals within a mainframe stillremained, although these approaches didsolve many of the command and controlproblems.

In 1985, the US Air Force asked the MATEUser's Group (MUG) to make specific recom-mendations regarding standardization ofinstrument -on -a -card (IAC) technology. Itwas their intent to take these recommenda-tions and turn them into a standard thatcould be added to the Air Force's ModularAutomatic Test Equipment (MATE) Guides.This task was completed and the recom-mendations submitted to the Air Force earlyin 1986 - a set of recommendations thatwere based on extensions of, and minormodifications to, VME. The Air Force thenundertook an extensive evaluation of thoserecommendations. The major stumblingblock to Air Force adoption of an IACstandard was a lack of consensus on the partof industry, especially the manufacturers, asto the exact technical content of the stan-dard. The actual need for a standard hadalready been endorsed by both industry andusers.

In a parallel effort, each of the five com-panies was in some stage of developing aninternal IAC standard. Colorado Data Sys-tems was in the process of updating the IACsystem they had been delivering since themid -70's. In 1985, Tektronix had announceda concept, an open architecture, and initial

products for a product line they dubbed CBIfor computer based instrumentation. In1987, Wavetek announced their Model 680,which included a product from Racal -Dana.Hewlett-Packard was in the process of defin-ing upgrades and replacements for some oftheir modular equipment. The commondenominator for all of these efforts was VME.

Private conversations between the fiveconsortium companies started during 1986.By early 1987, it had become apparent that,for the good of the industry, it was necessaryfor these companies to temporarily set asidetheir differences and see if they could agreeupon a working standard. A series of meet-ings started in April of this year that culmin-ated with the announcement, in July, of theVXlbus. (An interesting sidelight - theVXlbus not only meets all of the recom-mendations of the MUG IAC Subcommittee,but its backplane is also functionally verysimilar to the backplane defined by thatgroup). The consortium also intends tosubmit the VXIbus to the IEEE with the fullendorsement of each of the five companiesinvolved, and a strong recommendation thatit be adopted and published.

What is VXIbus?Before beginning to describe what VXIbus isand how it works, one basic question needsto be answered: why was it necessary toextend VME rather than use it intact? Thefundamental reason is that VME is a compu-ter bus, and while it solves the problems ofcommand and control, it is not ideally suitedto the world of instrumentation. For exam-ple, it tends to be somewhat noisy, a realproblem in the world of low-level analogueand r.f./m icrowave instrumentation. Inaddition, it contains no provisions for hand-ling some of the signals necessary to instru-ments, such as triggers and analogue sig-nals.

Moreover, to create an environmentalconducive to the higher level of systemperformance that instrumentation userswant, the consortium found it necessary todefine additional clocks and signal paths.Another problem with the VMEbus was thatit did not supply the kind of power needed byinstruments, so additional power andgrounds had to be included.

The VXlbus standard builds on the ex-isting standard for VME (IEEE -1014): it inno way violates VME and in fact containsspecific provisions that help ensure that

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INDUSTRY INSIGHT

standard VME cards will operate properlywithin VXIbus systems. Where VME specifiestwo card sizes, VXIbus specifies four diffe-rent card sizes (designated in the standard asA, B, C, or D), drawn from the Eurocardstandard. Depending on the card sizeselected, these cards may use one, two orthree 96 -pin DIN connectors. The size -Acard utilizes a single DIN connector (P1).Size B, which corresponds to the standardVME card, and size C cards also use P1, andoptionally, P2 connectors. Size D cards usePI and. optionally P2 and P3 connectors.

Like VME, each additional connectoroffers increased power and performance, butunlike VME there are no user -defined pins.All connectors are fully defined. The VXIbusPI connector conforms exactly to the VMEdefinition for the PI connector, which isused for command and control. Likewise,row B of the P2 connector is exactly perVME. VXlbus uses rows A and C of the P2connector, and all of the P3 connector, todefine additional power and ground, twolocal buses, two additional clocks, triggerand sync signals, and a sumbus, all of whichare explained in more detail later in thisarticle.

Because the potential application areas forthe VXIbus include all of the areas whereautomatic or semi -automatic testing isbeing used today, the architecture had to beextremely flexible. It also had to makeprovisions for the future growth of instru-ments on cards. As a result of these needs,special care was taken to ensure that theVXlbus could accommodate almost any sys-tem hierarchy or topology. It deliberatelydoes not specify the use of any particulartype of microprocessor, operating system orinterface to the host computer. Similarly,the content of the individual instrumentcommands is left solely to the manufacturer,although IEEE488.2 is suggested as a guide-line.

What the specification describesIf these areas are left up to the manufacturer,what then does the new spec. address? Whatthe proposed standard describes, in detail,are the technical requirements (hardwareand software) necessary for a variety of cardsfrom different manufacturers to be used on acommon computer/instrumentation back -plane.

As a start, the VXIbus defines the hierar-chy of device types with an automatic con-figuration protocol defined for all types. A setof configuration registers, which are accessi-ble from the P1 connector, are specified foreach device type. Through these registers,the system can identify each device and itstype, together with model number andmanufacturer, plus additional memory re-quirements, if any.

The simplest of these devices types, called"register -based devices", are normally"dumb" devices in that they will normally

not contain local intelligence. A second classof devices, "memory devices", may includesuch things as rams and roms. A third class,"message -based devices", is required to havecommunication registers that are accessibleto other modules within the system, and areintended for use where higher levels ofcommunication are desired. The latter classwill typically be a smart device that containsparsers that an interpret ASCII commands.They can also be designed to controlregister -based devices.

Communication between VXIbus devicesis based on a hierarchical device relationshipinvolving Commanders and Servants. With-in a system containing multiple comman-ders, each commander can control its subsetof instrument modules ("servants"). AVXIbus system can contain as many as 256different devices if multiple chassis are used.

The most common VXIbus configuration,especially over the next few years, willprobably be a system with an IEEE -488 toVXIbus interface card controlling the instru-mentation within the cardcage. In thismode, the VXlbus can be made transparentto 488 users, although higher level users (socalled "power" users) will have direct accessto the bus if they need it. Another possibleconfiguration is a stand-alone system withits own c.p.u., memory cards, and optionallyits own mass storage. This would allow it tooperate independently of, or in conjunctionwith, an external system controller.

Fundamental communication within aVXlbus system is based on a byte -serialprotocol. This allows users to choose, forexample, between the IEEE -488.2 forcommercially -oriented systems, or CIIL forMATE -oriented test systems, as well as util-ize other test languages now or in the future.It also means that VXIbus instrument mod-ules can be configured in a wide variety ofways as required by the application, limitedonly by the user's imagination, and by thesuite of instrument functions available at thetime the test system is built.

One of the most exciting possibilities ofhaving a number of instruments in a com-mon, closely -coupled environment is tightertime coordination, leading to a higher levelof system performance than has ever beforebeen possible. The VXIbus trigger lines havebeen defined with just this possibility inmind. Traditional rack -and -stack instru-ments connected via cables cannot hope tomatch the control over signal characteristicsand propagation delay that is possible in awell-defined and controlled backplane en-vironment. Signals that have been added onthe VXlbus specifically for this purposeinclude a 10MHz and a 100MHz e.c.l. clock,e.c.l. and t.t.l. trigger lines, and a "localbus". To give some idea of the performancelevels possible, t.t.l. triggering is possible atrates in excess of 10MHz, while e.c.l. triggerrates exceed 50MHz. Data transfer rates wellin excess of 100MHz can be generated.

The local bus, defined for both P2 and P3,is a daisy -chained structure between cardsthat allows manufacturers or users to definetheir own unique protocols and uses. Forexample, the local bus can be used totransfer analogue signals, t.t.l. data, and/ore.c.l. data between adjacent cards of a instru-ment set. IAC modules that use the local busmust follow a hierarchical classificationscheme based on a given module's intendeduse of the local bus. This scheme includes amechanical keying mechanism designed toinsure that an IAC module that falls into agiven class regarding its utilization of thelocal bus is not accidentally connected to anincompatible class, which could result indamage to either or both of the IAC modules.Classifications currently defined the VX1businclude t.t.l., e.c.l., low-level analoguemedium -level analogue and high-level ana-logue. A given IAC module may occupy morethan one classification.

One of the stickier problems faced by thearchitects of the VXlbus was that of powerand cooling requirements. The standardsolved the problem by requiring manufac-turers to always specify the power andcooling requirements for each card using astandard, easily reproduced, method. Simi-larly, manufacturers of cages must alsospecify the power and cooling capacity fortheir cage. This means that users can easilydetermine whether or not a given card or setof cards can be used with a given card cage. Aside benefit of this approach is that manufac-turers can choose to build either IAC mod-ules, or cages, or both, while still allowingusers full freedom of selection.

Similar to VME's impact on the computerindustry, adoption of the VXIbus standardrepresents a major step forward in theinstrumentation industry. Some industryobservers have stated that its potential long-term impact may even rival that of IEEE -488. Not only will it widen the areas wheremodular instrumentation is being used, butit will also, due to its ability to offer a higherlevel of systems performance, open newapplication areas. It is important to empha-size that the VXIbus architecture is an openarchitecture available to all manufacturersand users. In the short time since its originalannouncement, more than 25 different com-panies have expressed an intent to produceproducts designed in accordance with theVXIbus standard.

Designers desiring a copy of the VXIbusspecification are free to contact the author atthe address below.

Louis J. Klahn is vice-president of sales atColorado Data Systems nc, 3301 W. Hamp-den Avenue, Unit C, Englewood, Colorado80110, one of the five originating companiesof the VXIbus.

INDUSTRY INSIGHT

INSTRUMENTATION

THE VXIBUSAn emerging industry standard

VXlbus, a backplane bus speci-fication, will enhance theconstruction of automatictest systems by providing

greater flexibility in mixing and matchingmodular instrumentation. The name itselfcomes from VMEbus Extensions for Instru-mentation, as the VXIbus builds on top of theVMEbus standard.

The VXIbus will allow users to select awide range of instruments, interface cards,and computers from different manufactur-ers and to have these modules coexist withinthe same cardcage. Like the IEEE -488 bus,VXIbus users will be able to tailor theirautomatic test system to the applicationwith a broad range of products offered bymany manufacturers, while gaining thebenefits of integrated instrumentation.

As shown below, there are four standardcard sizes and up to three connectors. Thesize A card only uses the standard DIN P1connector, which remains as defined byVME. This connector accesses the VME datatransfer bus, and is capable of up to 20Mbyte/second data transfer rate between modules.Size B and C cards use P1, and optionally,the P2 connector. Size D cards use P1 andcan also use P2 and P3. Each additionalconnector offers increased power and per-formance. The VXIbus is designed so thatsmaller card sizes can fit into the largermainframes.

Since the application range for VXIbusproducts is extremely broad,the architecture was designedto be very flexible. For exam-ple, the VXIbus spec. does notdefine a specific system con-troller or topology nor does itspecify the type of micro-processor, operating systemor interface to the hostcomputer. Likewise, instru-ment commands are left to thechoice of the manufacturer.What is defined by the VXlbusspecification are the technicalinterface requirements andprotocols so a variety of cardscan be used on a commonbackplane while ensuringcompatibility between differ-ent manufacturers.

The VXIbus has an automa-tic configuration protocolthat is required of all de-vices. A given device must

Larry DesJardin, of

Hewlett Packard's

Loveland r&d centre,

analyses the VMEbus

extensions for

instrumentation.have a set of configuration registers whichare totally accessible from the P1 connector.This allows the system to identify the mod-ule, its device type, model and manufactur-er, and memory space requirements.

The simplest of these devices are calledregister -based devices. Memory devices suchas rams and roms have also been defined.Typically, register -based devices are dumbservices, and only a few simple logic chipsare needed to fully implement their VXlbusprotocols. If a higher level of communica-tion is desired, a class called message -baseddevices is defined to have standard com-munication registers accessible to othermodules within the system. These typicallyare smart devices that interpret ASCII com-mands and may also be designed to control anumber of register -based devices.

A device that controls other devices iscalled a commander, and its subordinate

modules are called servants. When a multi-ple commander system is assembled, eachcommander can control its subset of instru-ment modules. In other words, the bus canbe shared by more than one c.p.u., using thearbitration features of the VMEbus. A fullyconfigured VXlbus system can have as manyas 256 devices in a multiple chassis con-figuration.

By having the language of the message -

based cards the same as for IEEE -488 con-trol, VXIbus cardcages may be easily inte-grated into standard rack -and -stack 488systems. Several possible configurations forVXIbus systems are shown on page 147.

One of the most popular configurationswill be a system with an 488-VXIbus cardcontrolling all the register -based instru-mentation within the cardcage. The internalVXIbus will be transparent to '488' users.

Among other possible configurations is a488-VXIbus card which interfaces with theother message -based cards in the system. Inturn, each of these cards may have its ownsubordinate register -based instrumentcards. By having each message -based instru-ment accessible through a unique IEEE -488address or secondary address, the deviceslogically appear as separate instruments tothe programmer. It is also possible for acomplete system to stand alone with its ownc.p.u. and memory cards, allowing it tooperate off-line from a host controller.

The close proximity of instruments in acage, combined with tight timecoordination using the triggerlines, will lead to new levels ofperformance. The short andwell -matched propagation de-lays, only possible on a wellcontrolled backplane structure,substantially improve both per-formance and ease of con-figuration over the traditionalrack -and -stack instrumentsconnected via cables. Noise onthe backplane, which cancause timing jitter, is reducedby surrounding the triggerlines with a.c. grounds, andsandwiching them betweenground layers on the back -plane.

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INDUSTRY INSIGHT

had believed to be impossible in a bus -

based environment. Performance rangingfrom six -digit voltage accuracies tomeasurements of signals in excess of 1

GHz are expected to be available on theVXlbus within the next year.

The VXlbus retains compatibility with theVMEbus solution of defining the centre rowof the P2 connector to complete the 32 -bitarchitecture. This doubles the system band-width to 40 Mbytes. The VMEbus standardfurther allows the 64 pins of the outer rowsof P2 to be defined by the system. On theselines, the VXlbus adds a 10MHz e.c.I. clock,logic and analogue power supplies, e.c.l. andt.t.l. trigger lines and a daisy chain structureknown as the local bus with 24 pins (12 linesin, 12 lines out); t.t.l. triggering is possibleat rates exceeding 10MHz, e.c.l. trigger ratesmay exceed 50MHz.

The P3 connector is aimed at high per-formance instrumentation and includes a100MHz clock and 48 additional pins for thedaisy chain local bus (24 lines in, 24 linesout). It also defines a star trigger system toallow precisely matched triggering betweenmodules regardless of module position with-in the cardcage.

Some cardcages may also 'segment' theVXlbus backplane. That is, they may con-form to the P2/P3 VXI subsystem definitionfor some slots, and define these pins dif-ferently for others. They may even keepthese pins undefined, to be connected by theuser. This is useful for integrating somepresent VME cards that have implementedalternative bus structures on P2 (such as theVSB subsystem bus), or are using these pinsfor internal i/o. Of course, P1 will alwaysremain as defined by VME and VXI.

To maximize compatibility betweenmanufacturers, standard trigger protocolshave been defined. Trigger protocols includea synchronous mode where a source moduledrives a single line. The semi -synchronous

Shieldedsingle -widthinstrument (1 slot)

Unshieldedslot 0resource card

Shield double -widthinstrument(2 slot)

Unshieldedsingle -widthinstrument

Emi shieldbetween slots

Shown here is a VXIbus mainframe used forinternal product development at HewlettPackard Co. Also shown is a prototypeinstrument module and a carrier assemblythat allows standard B size VME modules tobe integrated into C size mainframes.

mode allows acceptor modules to handshakeon the same line. Asynchronous triggeringusing a pair of lines further expands trigger-ing capability, and will commonly be used tointerface to standard rack -and -stack instru-ments.

For applications requiring very high datatransfer rates - approaching 1 Gbyte/s usingemitter -coupled logic - the local bus struc-ture defined on P2 and P3 is available. It isdaisy chained between adjacent cards. allow-ing manufacturers to define their own uni-

VXI bus manufacturer list with ID codes

ID Codes Company 4082 Grumman4095 Hewlett-Packard Company 4081 John Fluke Manufacturing Co., Inc.4094 Wavetek. Inc. 4080 Bruel & Kjaer4093 Tektronix. Inc. 4079 Sciteq Electronics. Inc.4092 Colorado Data Systems, Inc. 4078 Westinghouse4091 Racal -Dana Instruments. Inc. 4077 Emerson Electric Company4090 Electro Scientific Industries, Inc. 4076 Radix Micro Systems4089 North Atlantic Industries 4075 NH Research4088 Systron Donner Instrument Division 4074 Autek Systems Corporation4087 Elgar Corporation 4073 ICS Electronics4086 National Instruments 4072 ILC Data Device Corporation4085 Analogic Corporation 4071 California Avionics Labs. Inc4084 Schlumberger 4070 Universal Test Equipment4083 LeCroy 3839 General Purpose Breadboards

General Purpose Breadboards refer to custom breadboard modules a user may build to add to commercially availablemodules. By having a unique code for breadboard modules, these wit never be identified as belonging to a particularmanufacturer, which could cause a system module to mistake a breadboard module as a commercially available VXIinstrument. The breadboard modules we offer, as well as our competitors, will have this code. 3839 happens to be a simplecode to implement

Power supplycooling

3 connectorback plane

D -size chassis

Carrier with C -sizeVXlbus card

To become a VXlbus manufacturer, a uniquemanufacturer identification code is re-quired by the VXlbus autoconfiguration pro-tocol. There is no fee, and no further obliga-tions. An application form is in the beginningof the VXlbus System Specification Rev. 1.1.Alternately. a company may apply by send-ing its official company name. VXI point ofcontact title, address, and phone number tothe author or any of the other VXlbus consor-tium representatives. The author's mailingaddress is Larry DesJardin, P.O. Box 301A,Loveland, C0.80539, USA. Identificationcodes are usually granted within a month.

que protocols and uses. The local bus canalso be used to transfer analogue signals andt.t.l. data between neighbouring cards of aninstrument set. A keying mechanism on thefaceplate ensures that one signal class on alocal bus is not accidentally connected to anincompatible class, which helps avoid poten-tial damage.

First, there has to be a critical mass ofmodules on the market to choose from. Theoriginal set of five manufacturers has ex-panded to over 27 (see list), and productannouncements are expected throughout1988. Next, the user must check that therequirements of the modules match that ofthe mainframe. The VXlbus specificationrequires the power and cooling require-ments for each module to be specified by themanufacturer. Since the power and coolingcapacity of the cardcages must also bespecified, users can intelligently match therequirements of their cards to be equal orless than the capacity of the cardcage.

The A and B -size modules, with theirsmaller, stiffer form factor, will be mostsuitable for portable and ruggedized applica-

INDUSTRY INSIGHT

tions, as well as where compatibility with present VME cages isimportant. C -size modules will find many of their applicationsreducing the size of present rack -and -stack test systems, whiledelivering a more integrated solution. Much of present day instru-mentation can be implemented in this form factor. D -size systemswill address applications requiring high bandwidth and tight timecoordination that is difficult, if not impossible, to achieve usingdiscrete instruments.

The acceptance in the industry looks extremely promising. TheIEEE has formed a committee (IEEE P1155) to pursue adoption of theVXlbus specification, and Working Group 3 of the IEC is also trackingthis effort. Defence contractors, needing to downsize test equipmentfor quick deployment, are welcoming the new standard, and theUnited States Air Force is considering adopting the VXlbus as itsstandard "instrument on a card" architecture. Many commercialusers, driven by needs of higher throughput, functional density,flexibility, and easily customized solutions, are also consideringadopting the VXlbus as their future test platform.

A VXIbus standard will open new application areas for modularinstrumentation by simplifying the configuration of an automatictest system. It will allow users to select from a variety of manufactur-ers and to mix and match their products within the same cardcage.The VXIbus architecture is open to all manufacturers, not just theoriginal five. Already over 20 additional companies have beenassigned identification codes to allow them to design to this emergingstandard.

Larry DesJardin is R&D section manager and VXIbus consortiumrepresentative at Hewlett-Packard Co, Loveland, Colorado.

AN INVITATION TO MAKE

-vim .ogion"rwlliatPri.& ..

. - Tt ,iwkiroo

A FEW POSSIBLE VXIBUS CONFIGURATIONS

Host controllerIEEE 488 to VXlbus card with c.ommander capabilityRegister -based Instrument -#1Register -based Instrument -#2Register -based Instrument -#3RAM card

Host controllerIEEE 488 to VXlbus cardMessage -based Instument-#1 with commander capabilityMessage -based Instrument -#2 with commander capabilityRegister -based Instrument -#3 (subordinate to Instrument-# 1)Register -based Instrument -#4 (subordinate to Instrument -#2)RAM card

IEEE -488 bus

Host controller on a card with commander capabilityMessage -based instrument -#1Message -based Instrument -#2Register -based Instrument -#3RAM card

AILED COMPARISONS

ENTER 36 ON REPLY CARD,

ELECTRONICS & WIRELESS WORLD February 1988

The Gould 1425 Digitising Storage Oscilloscopeallows detailed comparison of active with storedwaveforms. up to a frequency of 20MHz. Fivereference waveforms can be held in the non -voltagememoryEasily controlled cursors with an alpha -numericdisplay, enable automatic measurement of time.voltage and frequency, to be made quickly andaccurately Any on -screen data with its relevant rangesettings, can be quickly transferred to an externalcomputer, via the RS423/232 Interface and recalledfor reference purposes. Software 'starter packs' areava lable for popular personal computers.Waveforms can also be copied directly to ananalogue or digital plotter -the latter with multi-colour plots, grid and full scaling information.For application -specific waveform processing, such asaveraging (up to 256 events) filtering (over 130 stages)or mathematical manipulation and scaling, an optionalkeypad is available.The 1425 is just one in a family of three instruments...PRICES START AT LESS THAN £1000!

To allow you to make the right price and performancecomparison, please contact: Gould Electronics Ltd.,Instrument Systems, Roebuck Road, Hainault, Ilford,Essex IG6 3UE. Tel: 01-500 1000. Telex. 263785.

Electronics

INDUSTRY INSIGHT

INSTRUMENTATION

WILL YOUR DMM COSTMORE TO KEEP

THAN IT DOES TO BUY?he wide span of price tagsattached to the many digitalmultimeters currently on themarket presents a difficult

selection problem to users anxious to securethe best value for money. In the absence of aWhich? Guide to Multimeters there are noclear, independent recommendations onbest buys, and the user is left to sift throughreams of specifications which, at the end ofthe day. may give scant consideration to theunderlying issues involved. Current think-ing is that determination of the true life -

cycle cost of ownership must take intoaccount a large number of obvious or hiddenfactors which are often less a matter ofspecification than of the traditions and phi-losophy of the manufacturer.

Only one cost is obvious, that is cost ofacquisition. It may come as a surprise tomany to discover that widespread opinion inthe T&M industry puts this cost at typically30% of total lifecycle cost, or cost of own-ership for the full lifetime of the instrument.Here is a summary of the costs that must beconsidered and their relative importance:

Initial purchaseIntegration into systemPeriodic re -calibrationSupport documentationLifetime maintenanceUpgrade/expansion

30%30%15%10%10%5%

It isn't enough to read

specifications and price

tags and leave the rest to

chance. A little probing

could pay off handsomely

over an instruments

lifetime.

It follows that the manufacturer who canminimize the hidden costs and ensure thathis selling price is still competitive is givingthe user a much fairer basis for his choice. Afurther, and fundamental requirement isthat the manufacturer support the instru-ment during its entire lifetime - a pointwhich should not be taken for granted.

British manufacturer Schlumberger(formerly Solartron) has a unique traditionin design and manufacture of these instru-ments, and the newly -launched 7150plusmultimeter embodies the knowledge andexperience gained over two decades of tech-nological innovation. Minimization of thehidden costs is achieved through measures

which include testing to military standardsfor optimum reliability, careful design forease of use, and comprehensive measure-ment capability.

Down with cost of ownership!The figures given show that it can cost moreto install and operate the instrument than tobuy it, so ease of use becomes a key factor inselecting a cost-effective instrument. Timeto train operators and calibration personnel,to develop software, and to document testprocedures and results, frequently have a bigimpact on total cost of ownership. A goodmanual is a benefit, but even better is aninstrument which is so easy to operate thatthe manual is redundant. A simple frontpanel layout and a clear easy -to -read displaygiving total user information avoids costlyerrors and reduces operator training time.Autoranging is an essential practical steptowards ease of operation. Features such asthese, together with digital calibration andbuilt-in IEEE interface, all help to minimizeoperating costs.

Second only to operating costs comecalibration costs, and here the concept ofcalibration for life can have a profoundinfluence on the choice of an instrument.Gone are the days when calibration intervalsmust be strictly adhered to because of theunpredictability of performance thereafter.

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Careful choice of components and gooddesign techniques, together with thoroughmanufacturing quality control and testing ofthe finished product, can eliminate therandom variations of calibration and ensurethat drift is attributable to the inherentstability of the critical precision componentsonly.

For example, long-term drift to the bestquality wirewound resistors is less thanlOppm, but by using them as matched pairsin the ratio mode actual drift can be reducedto one tenth that of individual components.Tests conducted over ten years on precisionresistors reveal that drift is proportional tothe square root of time, allowing drift to bepredicted for long periods.

The reference voltage is usually derivedfrom temperature -compensated zenerdiodes, with long-term stability one of themost important parameters. Optimum sta-bility for d.v.m. applications is achieved bypre -conditioning or burn -in at high curr-rents to produce accelerated ageing, fol-lowed by a stabilization period. Long-termdrift can be reduced to less than lOppm persquare -root year by this method, andtemperature compensation factors stored innon-volatile memory can be used in associa-tion with temperature -sensing circuitry toproduce an overall change of calibration ofwell below five parts per million.

Excellent though the drift figure ofcommercially -available input amplifiersmay be, amplifiers built with discrete com-ponents using drift correction techniquescan be better, producing less than onemicrovolt per year drift.

The accurate prediction of long-term driftand performance of precision measurementinstruments enables the user to select thecalibration interval that best suits his ap-plication, to the extent of making calibrationa thing of the past in some applications. Thetechnique eliminates downtime for calibra-tion and the need to provide backup instru-mentation, particularly useful in a.t.e. ap-

INDUSTRY INSIGHT

plications or in remote locations. A higherinitial purchase price with minimal re -calibration costs may thus provide thelowest cost of ownership.

When calibration is necessary, digitalcalibration with non-volatile storage ofcalibration constants eliminates the need forpreset potentiometers with their inherentreliability problems. Another point worth amention, storage of calibration constants issafer in floating gate semiconductor mem-ory than in battery -backed memory, giventhe unreliability of batteries.

Maintenance costs, estimated to be atleast 10% of cost of ownership, can begleaned by the prospective buyer frommean -time -between -failures and mean-time -to -repair ratings, which will be freelyavailable from the manufacturer who isproud of them! Decades of experience indesigning for military markets givesSchlumberger the edge in manufacturingfor built-in reliability, using techniquessuch as design type testing to DefenseStandard 56-31, purchasing high -qualitycomponents from reputable manufacturers,and performing 100% hot soak testing. Ahigh degree of mechanization allows forcontinuous soak testing for 168 to 1000hours, using computers to weed out earlyfailures to provide more thorough testingthan manual methods at much lower cost.

A combination of component stress datain the circuit and historical test failure datais converted to m.t.b.f. ratings according toMIL specifications. The figure of 30,000hours m.t.b.f. which Schlumberger quotesfor its 7150plus means that there is a 63%probability that the unit may fail during thattime; Schlumberger's verification proce-dures suggest that its instruments are atleast three times better than this prediction,due in part to detection of early failuresduring hot soak test. When breakdowns dooccur, self -diagnosis integrated in softwarelocates the fault to board or part -of -boardlevel for speedier repair. Analysis of failures

during test or in service is carried out toensure a long-term improvement in quality.

Finally, although only 5% of overall costof ownership is allocated to expansion itshould be regarded as 5% too much, sincecareful consideration of requirements withan eye to future needs would ensure thatmeasurement capability is adequate. If indoubt, it would seem sound policy to go formore capability than currently required toavoid subsequent need to update or purchasea second instrument. It is important that thebenefits of some of the newer technologiesare fully understood before a choice is made.

In summary, it isn't enough to read thespecifications and price tags and leave therest to chance. A little extra probing couldwell pay off handsomely over the instru-ment's lifetime; an instrument which has ashort payback time, say one or two years, andthen lasts seven to ten years can be consi-dered the correct choice.Umar Qureshi, is marketing manager fordigital multimeters with Schlumberger-Solartron, Victoria Road, Farnborough,Hants CU14 7PW. Tel: 0252544433.

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INDUSTRY INSIGHT

INSTRUMENTATION

TEST AND MEASUREMENTMARKET TRENDS

study of the market for testand measurement instru-mentation since 1984 indi-cates that it enjoys extremely

steady but very unspectacular growth.Growth figures for the overall market

need to be examined against the backgroundof falling prices - especially in the oscillo-scope area. Limited growth in financialterms does not necessarily indicate a fallingoff in discrete instrument sales, which areobviously rising at a higher rate than themonetary totals might suggest.

In the breakdown of oscilloscope sales.more than 50% of the oscillscopes of100MHz or below come from Japan. Abovethis (regency, Japanese manufacturers havea share of around 15% - but it is a growingshare and a trend which UK manufacturersneed to monitor very closely.

Whilst t & m equipment continues toadvance in terms of the provision of facilites,better presentation of controls and otherergonomic aspects, and either progressivelysmaller footprints or more features packedinto the same footprint area, the two factorsthat are really generating real growth andinterest in t & m are in the area of businterfaces and mini/micro computers.

The electronic industry's needfor greater throughput, moredata and greater versatility in t &m can only be effectively met bysome form of systems approach.The power of today's micro andminicomputers can be employedin this area with enormous effectbut such aids can only workeffectively if they are linked tot &m instruments, printers, controlsystems etc in what is effectivelya network system. The need isbeing met with the growing useof interface buses as integralparts of both instrumentationand computer products.

It is no longer necessary formost users to purchase highlyexpensive t & m systems - theycan now create their own usingreadily available products andtailoring to meet both their tech-nical requirements and budgetlimitations.Bussed instrumentsThe Hewlett Packard Interfacebus (HP -1B) development of theearly seventies was design -

Unspectacular money -

value growth may hide

increasing unit volume

sales in some areas.

Tony Leach finds

the bus interfacing

business thriving.

ed as a means of externally connecting upto 14 independent devices, such as volt-meters, disc drives and oscilloscopes, onto asingle computer port. This was a highlysignificant breakthrough as the previousrequirement had been to provide a separateport for each instrument. In 1975, theconcept was adopted by the Institute ofElectrical and Electronic Engineers who,

with slight revisions, published it as theIEEE488-1978 Standard with manufactur-ers (other than Hewlett-Packard) referringto it as the General Purpose Interface Bus. Aswith all such standards, similar conceptswere already - or were to become - available.The most important of these was the IEC625International Standard which used a diffe-rent connector system to the IEEE versionbut was eventually brought into line interms of compatability.

In a typical bus arrangement up to 14instruments will be linked to a controllerwith the maximum cable length beinglimited to 20 metres in total. It is not,therefore, possible to use a GPIB over parti-cularly long distances but this is rarely arequirement in the vast majority of automa-tic test equipment applications.

The advantages to the user include com-plete flexibility in that any instrument com-forming to the standard can form part of asystem. This means that a variety of instru-ments from a variety of manufacturers canbe assessed to ensure that the technical andeconomic requirements can both be met. Inaddition, of course, a system can be up-graded at any time - often by the substitu-tion of a single instrument.

Typically, a controller such asthe Hewlett-Packard Vectra canbe programmed to set the rangesof any measuring instrumentsconnected to the bus and adjustthe output levels of operation.The test can be run through inthe correct sequence and, furth-er, since the controller is a com-puter, the information gatheredcan be processed in terms ofaveraging, fast Fourier trans-formation, and soon.

With improvements in tech-nology and competitivenessbeing the main factors causingthe price of the business compu-ter to fall, both mini and microcomputer manufacturers are an-xious to seek out all possibleavenues to increase their sales. Abenefit arising from these hasbeen the growing co-operation ofthese manufacturers with in-strumentation companies spe-cialising in computer interfacingto generate better and easier -to -use control systems.

In addition, the mini/micro

INDUSTRY INSIGHT

computer approach to solving industrialproblems satisfies yet another need - thistime in the laboratory and scientific environ-ment. Here, by linking individual engineer-ing and manufacturing functions into aunified automated system, elements of con-trol systems can be physically or functionallyseparated yet also be part of a hierarchy ofintegrated computers.

It is the advent of bus interfacing that hasplaced instrumentation distributors in aunique position to provide advice to custom-ers on building their own t & m system.Unlike a dedicated manufacturer, they areable to propose a wide selection of alterna-tives based on sound technical knowledge.They are not committed to plugging any oneparticular range of instruments or any oneform of technology - they should be simplyinterested in giving the customer what heneeds at the price he can afford.

Value for moneyThe number of instruments coming onto themarket featuring GPIB and a host of featuresat a reasonable price is increasing at a quitedramatic rate. Three very recent introduc-tions provide a guide to what is available.

Hitachi's VC6165 is a digital storageoscilloscope with a 'sampling rate of 100Msamples per second, a 100MHz equivalentsampling bandwidth, a 100MHz real-timebandwidth, and a memory capacity of 4Kwords per channel. Other features includean ability to save stored data in 2 x 4Kmemories using battery back-up, and en-velope mode to capture the glitch andextract the envelope, averaging and rollmodes, x -y display, pre- and post -triggerfunctions, magnified display, and a plotterinterface - all for under £7000.

In the area of function generators, theGlobal Series 8200 20MHz programmableinstruments are available in three versions:the 8210 20MHz with burst, the 8230 withburst, phase lock and frequency counter,and the 8232 synthesized unit with burst andwith phase lock and frequency count asstandard. These provide universal sources oftest stimulus waveforms - sinewave, triang-le, ramp, squarewave, pulse (± or t.t.l.), -thus replacing many instruments in labora-tory or production environments. The threeunits are available in the range £1895 to£2495.

And Marconi's latest synthesized signalgenerator, the 2022C, really does offer out-standing value for money due to noveltechniques employed in its manufacture.Easy to use, the instrument offers compre-hensive amplitude, frequency and phasemodulation, a frequency range of 10kHz to1GHz, 100 non-volatile memories, 10Hzfrequency resolution to 100MHz, and 0.1dBlevel resolution. Additional features includea high r.f. output of +13dBm, auxiliary f.m.input on the rear panel, and a memory clear

Counters/Timers

Oscilloscopes

(Total JK T&M Market estimated at f200M for 1988)

1984 1985 1986 1987 (1988 est.)

Spectrum Analysers 7% Micrcwave T&M 5%

DMMs 8%

LinearPowerSupplies8%

SwitchingPowerSupplies11%

Others 16%

ATE 17%

LogicAnalyses3%

Spectrum Analysers 8% Microwave T&M 7%

DMA's 7%

LinearPowerSupplies5%

Signal SwitchingGenerators Power11% Supplies

Oscilloscopes14%

Others 8%

ATE 20%

LogicAnalysers3%

SignalGenerator13%

Oscilloscopes17%

The market sector figures provided in this article have been collected from a variety ofindustrial and other resources. These figures have been assessed in relation to STC's ownmarket appraisals to provide the most realistic estimates possible.

facility. The basic cost of the 2022C is justover £3000.

OptionsHaving expounded the merits of the GPIB, itshould not, however, be assumed that otheroptions are not available. Keithley, for exam-ple, have produced a new software package(Asystant+ ) for use with IBM-compatiblecomputers that not only runs a range offunctions specifically for scientists (calcula-tion, graphics, curve fitting, tile i/o, statis-tics, waveform processing, polynomials,waveform generation, differential equations.file -based processing), but also makes possi-ble interactive data acquisition that is menu -driven and very easy to perform.

In general, other menu -driven systemsrequired the filling out of extensive promptlists to define i/o parameters. The software,however, simply requires that just one ofeight modes is selected - such as strip -chart

recorder or x -y recorder - that simulatecommon laboratory data collection instru-ments. The x -y recorder mode, for example,will display two channels of data in an x -yformat. Such capability allows the user toconcentrate on the meaningful parameters(acquisition speed, triggers and data storageoptions) and thus make data collection easywithout the need to concentrate on unneces-sary detail.

Tony Leach is marketing manager for STCInstrument Services of Harlow, Essex.

Totalconfidence

is what you'll derive fromSchlumberger's new 7150plus 61/z digitDMM

. because its components are specially chosenfor performance and reliability and it is tested to

military standards. because you'll readily master its

comprehensive range of facilities. because it will meet all your measurement needs

with outstanding accuracy and sensitivity. and because, to underline our own total

confidence, it comes with a two-year warranty.

Technologies

Instruments

Schlumberger-Solartronvictoria Road, Farnborough, Hampshire GU14 7PW, England.

Telephone: Farnborough (0252) 544433Fax: Farnborough (0252) 543854. Telex: 858245 Solfar G

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WHEN IT COMES TO INSTRUMENTATION.IT'S THE DETAILS THAT COUNT!

Whether you are involved with signal condition, . .r general measurementrepeatability. quantification and possibly compen,,,ition will be your goals

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INDUSTRY INSIGHT

INSTRUMENTATION

PC -BASED TESTEQUIPMENT

he personal computer testequipment market has beengoing through significantchanges during the late

1980s, centering about bus and controlstandards and technologies. Initially, mostof the participants in this market had pro-ducts that were based around the IBMPersonal Computer or an Apple computer,or a clone of the PC. Now, however, eventhough there are still a lot of these products,manufacturers are no longer limiting thecomputer part of their systems to either ofthese buses. The market is beginning to bedefined as a microprocessor -based computertest system that is dedicated solely to testapplications. This puts the PC -based instru-ment in competition to what used to beminicomputer or mainframe systems. Butthere is a difference, which is why these are"personal" computer -based test systems.

In older computer -based test systems,testing was only one of the many functionscarried out by the computer. The cost of themainframe and minicomputers made itnecessary to incorporate as many functionsas possible into the system. With today'spersonal computer prices so low, test en-gineers are able to construct systems forthemselves where every function of thecomputer, even word processing andgraphics, is designed to enhance testing.

Today's personal computer instrument isbasically a cardcage hooked up to a

microprocessor -based compu-ter. The cardcage can have aVME bus and be connected tothe PC via an IEEE488 inter-face. If the cardcage has thebus of an IBM PersonalComputer or an Apple compu-ter, then the PC -based instru-ment looks more or less likethe computer on top of anoffice desk. This is the waymany of these instrumentslook. But an equal or greaternumber have either externalcardcages tied to them or evenstandalone instruments withIEEE488 connections.

The component in thesesystems that is of most impor-tance to test equipment manu-facturers interested in the

Market research analyst

Mike New reports on bus

and control issues in this

fast-growing market.

PC -based test equipment market are theactual boards or 'instruments on a card' thatgo into the cardcages. These boards allowdata acquisition, signal analysis, recording,metering, frequency counting. and more.These boards are the substitutes for thestand-alone instruments.

Manufacturers of traditional stand-alonetest equipment are acutely aware of thepossible impact of the PC -based instrumenton their sales and they are developing anumber of strategies to counteract this. Tomake rack -and -stack systems easier to confi-gure and develop programs for, newIEEE488 standards have been proposed andothers are in the negotiating stage. Partici-pants on the 488 committee, which iscomposed of companies such as Keithley,Fluke, Tektronix and Hewlett-Packard, hopeto have significant changes made to thegeneral purpose interface bus by 1989.

Source: MIRC. For further information onreport A278 PC -Based Test Equipment,contact Bob Pearce (415) 961 9000.

Spect. Logic Freq. Oscillator Recorder DDMAnalyser Analyser Counter

DataAcq

Tota ,,,,

1983 11.8 10.4 0.7 7.0 4.7 0.6 25.8 60.9 ;1964 15.4 14.0 0.9 9.1 5.9 0.8 37.7 83.6

1985 197 17.5 1.1 11.4 7.5 09 51.8 110.0

1986 25.8 23.0 1.4 14.7 9.4 12 112.6 188.1

1987 346 31.2 1.8 19.1 12.2 1.6 122.5 223.1

1988 46.7 43.7 2.3 26.0 15.9 2.2 136.1 273.0

1989 61.2 59.5 29 34.1 19.7 3.0 139.3 319.6

1990 79.5 79.1 3.5 43.3 23.6 39 149.6 382.6

1991 99.4 99.7 4.1 52.4 28.1 5.0 168.3 457.0

1992 116.8 120.5 4.7 61.3 33.2 6.1 196.2 538.9

At the same time they are certainly notputting all their eggs in one basket. Severalinstrument manufacturers have bandedtogether and developed a modification of theVME bus which will make it easier to developtest systems. This new bus, described else-where in this Insight, has an openarchitecture which simplifies assemblingmodules from different manufacturers into asingle chassis. What types of boards will beintroduced? Undoubtedly, board develop-ment for the VXI will follow the trends in therest of the PC -based market. There, in termsof board sales, the largest segment hasalways been data acquisition. Part of thereason for this is that end users with existinganalysis equipment -scopes, logic analysers,spectrum analysers - can through an 488controller take advantage of the personalcomputer's data storage ability and continueto use their stand-alone boxes for theanalysis.

The most popular analytical boards arealso the most popular analytical instru-ments: oscilloscopes, logic analysers, andspectrum analysers.

Since personal computers lend them-selves readily to data acquisition it is notsurprising that another popular instrumentthat is being replaced by these instrumentsis the graphics recorder. Especially in indus-tries like the medical field, computers withassociated peripherals for data acquisitionare becoming well accepted.

The estimated total 1987world market for PC -based testequipment is $223.1 million.With a projected compoundannual growth rate for 1986-1993 of 19.0%, this market isexpected to amount to $635 mil-lion by 1993. The largest andslowest growing segment of thePC -based test equipment marketis data acquisition, representing55% of the 1987 total. As shown,most product areas in the PC -based test and measurementmarket are projected to grow inthe 25-30% annual range for1986-1993.Mike New is senior analyst withMarket Intelligence ResearchCompany 2525 Charleston Road,Mountain View, California.

INDUSTRY INSIGHT

INSTRUMENTATION

IEEE 488 CONTROLUSING AN

IBM -COMPATIBLE PCHE usefulness of the decade -old 1EEE488 bus is that itenables a computer to controlmany types of test and

measuring instruments from multimetersto pressure calibrators. In computer controlof instrumentation the collection of resultsis faster and more accurate, repetitive tasksneed only be programmed once, calculationson data can be more readily carried outreporting of results can be completed auto-matically and there are convenient massstorage devices available.

Up until recent times the use of IEEE 488instruments left few options. Generally theprospective purchaser bought basic instru-ments and wrote his own applications soft-ware or purchased expensive applicationsoftware - usually running on dedicatedIEEE 488 controllers. And the implementa-tion of IEEE 488 controllers could be veryexpensive. But in the age of the £500 PC* itis possible to implement an IEEE 488 con-troller for as little as £600.

*By which is meant IBM-compatible MS-DOS personal computer

Desk File Help Setup

International

standardization of GPIB

software should ensure a

healthy future for bus -

based instrumentation

Also, by using a PC as a controller it ispossible to do many more things on the samemachine. It is possible for instance to have aPC data logger which can say, control amultimeter or number of multimeters and ascanner (i.e. an analogue relay multiplexer)to enable the collection of widely divergentdata such as voltages, currents or the outputof various transducers. All data can becollected and conditioned and presented in auseful form for the end user.

Manufacturers of test and measurementequipment appreciate these advantages andcan now supply a package which includes a

SIEMENS PC- Instrunents - Transient Recorder 8bit Alliz I FC 07

l 1111111111

-13 wIPP Pl*S

Divider

multimeter, scanner and software packagewhich will run on a PC to allow the imple-mentation of a low-cost datalogger. Thereasoning behind this type of package isclear. there are as many users committed tothe use of IEEE 488 instruments as there areusers committed to IBM compatible PCs. Ifthe two are put together there are manyadvantages: IBM compatible PCs such as theSiemens Sicomp PC 16-20 offer more advan-tages than simply the portability of a singlesoftware package. They can, for example,run scientific spread sheets, wordprocessorsfor reporting, and c.a.d. software for design.

High -resolution, multi -colour displayscan be used as can pointing devices such asgraphics tablets and mouse systems. Mousesystems can be used interactively with thescreen and select particular fields.

The example in Fig.1 shows a screenrepresenting the control and display of atransient recorder. The graphic display usedthe IBM Enhanced Graphics Adapter screenwhich has a 640 x 350 panel display with upto 16 colours. This enables the clear, conciserepresentation of data and controls. The topline of the screen shows one of the immedi-ate advantages of this type of system, thenames indicated are titles of menus whichcan be pulled down in conjunction with amouse pointing device. This is one of themain features of the Graphics EnvironmentManager system as supplied by the DigitalResearch Company.

The first title shown for a pull -down isDesk which is a general GEM utility, itenables the user to have a real-time alarmclock, a print spooler and to save screenimages. The second is File which is used inconjunction with the transient recorder,allows the user to save files which may haveinformation on the way the instrument is setup. It also allows transients to be saved inGEM format. Once in this format the col-lected transient can be sent to a graphicaloutput device such as the screen, plotter,printer or even an RS232 camera.

The next title shown is Help which can becalled upon at any time and has specificinformation on the device being used.

The title Set Up allows the user to returnto the instrument default set-up or display

INDUSTRY INSIGHT

the transient information in a differentformat.

The blue section of screen shows therepresentation of the collected result. In thisexample the captured transient data consistsof a square wave and a sine wave. The signalhas been captured by sampling at a 5msperiod, which is shown in the windowmarked 'Clock'. This sampling period can bechanged by using the mouse to point to theclock window and clicking the mouse but-ton, a pop-up menu in the centre of the mainscreen gives a selection of sampling periodsfrom 0.5ps to 1 second.

The titles in white boxes show the otherfeatures available for the transient recordersuch as voltage range, trigger level, signaloffset coupling etc. One of the most powerfulfeatures of this instrument shows the advan-tage of the PC -based IEEE 488 controller,this is the zoom feature. It enables a windowto be opened over the signal, which is 16K ofcollected samples and any single or group ofsamples can be viewed. The zoom featureuses the high -resolution graphical displayand mouse pointing device to the bestadvantage.

The main idea behind PC instruments isthe fact that control and display elements areseparated from the instrument and given toa more flexible device in the form of the PC.

If other instruments are installed into asystem the same PC is used as the display andcontrol element of the instrument by havinga front panel which is a piece of software.

This has a major advantage in that thedisplay and control element of the instru-ments has to be paid for only once.

The basic philosophy of modular instru-ments using a common PC has been takenfurther with the Siemens range of PC instru-ments. The range includes many otherinstruments such as a multimeter, voltage -current source, counter -timer, functiongenerator, scanner, a range of transientrecorders, digital input-output and a localarea network tester. A common bus connec-tion eliminates multiple IEEE cable connec-

tions and enables sets of instruments to bestacked neatly. A number of additional in-struments are being developed as well asmore software tools.

Future advances in user-friendly softwarefor PC IEEE 488 controllers plus interna-tional standardization of the software stan-dard of the IEEE 488 bus should ensure ahealthy future for bus -based instrumenta-tion systems.

Frank Healey is manager ofSiemens electro-nic test and measurement instruments.

`MEASURECOMP' PCINSTRUMENT SYSTEM

For full data pack fill in card

Company

111111111111111111 11111

* PC interface card drives up to 12instrument modules in stand alonecase.

* Measurecomp Software gives highlevel, menu driven, multitasking realtime ATE capability to PCs.

* Universal IEEE 488 Software driverallows inclusion of other instrumentsin a system.

* 8 different types of instrumentmodule currently available.

* The shortest software route to beworking Automatic Test System yetdevised.

Position

Address

EWW/2/138

PPM Instrumentation Ltd, Freepost, Guildford, Surrey, GU1 4BR ENTER 730N REP1.1 UMW

INDUSTRY INSIGHT

INSTRUMENTATION

OSCILLOSCOPE ARCHITECTUREA case of revolution rather than

evolution

The first microprocessor -baseddigitizing oscilloscope re-volutionised the test andmeasurement industry. For

the first time, users could analyse signals inways which had not previously been possi-ble. Because waveforms are stored in mem-ory, they could be saved for future reference,output to hardcopy devices such as printersand plotters, transferred to computer forstatistical analysis, averaged over time toremove noise, or plotted on the screen as anenvelope, enabling the user to see change ordrift. Digitizing also enabled users to ex-amine signals with low repitition rates.

With the passage of time, however, capa-bilities such as these became commonplace.In addition, the performance demandsplaced on digitizing oscilloscopes increasedto the point where a single microprocessorsimply could not cope, and the industry wasin need of another revolution.

When the Tektronix 11400 series of digi-tizing oscilloscopes was launched lastspring, most of its advanced features were

Sample'

Timebas,

Acquisit.memo',

There is relatively little

point in trying to improve

performance in one

particular area if the

underlying architecture

leads to a reduction in

capability elsewhere.

readily visible. Examples of these are themachines touch screen operation, pop-upmenus and uncluttered control panel. Also.unlike conventional digitizing oscilloscopes.the 11400 series products feature real-timeoperating speed, which makes them feel andbehave like analogue scopes. Underpinningall of the visible improvements, however. issomething far less tangible.

Controller

C.r.t. driver

C.r.t.

GPIB/RS232'Cent

The oscilloscopes incorporate a radicallynew architecture. which owes more to com-puters than to traditional oscilloscope tech-nology. At the heart of the 11400 main-frames are three Intel microprocessors, giv-ing the scopes the combined power of threepersonal computers. In addition to these, allthe plug -ins incorporate dedicated micro-processors. The advantages that this bringsover more traditional architectures. interms of speed, flexibility and performance,are enormous. Before looking at these indetail, however, it's important to understandthe Tektronix product development philoso-phy which has allowed them to be realised.

A little historyIn 1946, when Jack Murdoch and HowardVollum founded Tektronix, it was with theexpressed intention of designing and manu-facturing the world's finest oscilloscopes.There is no question that they achieved theirgoal, and that which became the 500 seriesdominated the oscilloscope market through-out the 1950s and '60s.

By the late '60s. however, it was apparentthat the architecture on which the 500 serieswas based had been stretched to the limit.and that a new technology was needed. Theresult was the enormously successful Tek-tronix 7000 series, which again set newstandards of quality and accuracy, and in itsturn came to dominate the market. Therange was continually developed throughoutthe '70s. and still sells well today.

Despite the success of the 7000 series,however, by the mid -1980s it too hadreached the limit of its realistic develop-ment. and another new architecture had tobe sought. The pressure to do so was in-creased by the 1983 launch of the HewlettPackard 54000 series of digitizing scopeswhich, throughout its lifespan to date, hassold well into a wide range of applications.

Digitizing oscilloscope or computerizedmeasurement device?By its nature. a digitizing scope is as much acomputer as it is an oscilloscope. In the sameway that a computer takes characters from akeyboard, processes them and displays themon a screen: a digitizing scope takes asampled waveform and digitizes, processesand displays it. Similarly, just as a compu-ter's overall performance depends on the

136ELECTRONICS & WIRELESS WORLD February 1988

INDUSTRY INSIGHT

power of its central processorand the extent to which thatpower is harnessed, so a digi-tizing oscilloscope will only beas good as the hardware onwhich it is based.

When the HP 54000 serieswas launched, the Motorola68000 microprocessor was inits ascendancy. Not only did itform the basis of the HP 54100design and all the models thathave followed it. but it alsospawned, among other things,a host of multi-user micro-computers running under theUnix operating system.

One of the drawbacks of68000 -based micros has beenthat as the number of usersincreases, so do the responsetimes, and the overall perfor-mance of the system deteriora-tes dramatically. The essenceof the problem is this. Withone 68000 handling the tasksof central processing, pollingof terminals, screen display,print spooling and all other i/ofunctions, there simply isn'tenough raw horsepower for itto be able to cope. The HP54000 series has had similarproblems.

In the HP 54000 series, the 68000 micro-processor handles digitizing, processing andscreen display functions. The overall per-formance of the system is therefore limitedby the 68000's power. And as the 54000'ssingle -processor architecture has continuedto be exploited - up to and including therecently -launched 54112 and 54120 - so thedemands placed on the 68000 have in-creased. Some of the drawbacks that this hasresulted in. such as the long screen updatetimes, are widely recognised. Others werenot so obvious until an alternative approachwas made available. This is precisely whathas happened with the launch of the Tektro-nix 11400 series.

Three chips are better than oneThe 11400 series is based on three 16 -bitIntel microrpocessors. Specifically, themachines incorporate an 80186 which isused purely for digitizing; an 80286, used tohandle the executive functions of the scope;and another 80186 which handles screendisplay. Clearly, the provision of three pro-cessors rather than one has a dramaticimpact on the overall speed of the machines.Indeed, the raw processing power of the11400 is about three times that of the 54000series. What is equally important, however isthe flexibility that the three processors offer,without comprising overall performance.

With a single microprocessor, perform-ance is something of a juggling act. Withvariables such as bandwidth (both repetitiveand single -shot), sample rate, record lengthand screen update to be considered, it is

clear that with an oscilloscope performing at

its limits, as one measure of performance isincreased, another will suffer. To achievelonger record lengths. for example, the timebetween screen updates will almost certainlyhave to increase. If longer record lengths areneeded, then the rate at which they need tobe sampled should increase. Higher samplerates can then lead to less bits, and thereforelower vertical resolution. With only a singlemicroprocessor in control. compromises areforced between the various capabilities of thescope.

Distributed processing, as used by the11400 series, avoids these clashes of need.For example, the fact that the processor incharge of digitizing is having to work harderto sample a longer record length will betransparent to the executive processor.Similarly, although the executive processoris working harder to process the longerrecord length, this will not affect the waythat the resultant waveform trace is display-ed. And because each processor is handling aspecific task, none will be stretched to itsoperating limits.

The result is an oscilloscope design whichguarantees high performance however it isbeing used. The following are just a fewexamples of what this means for 11400 seriesusers.

Maximum bandwidth. The advance of com-munication technology is something of achicken and egg situation. As transmissionrates increase, so faster oscilloscopes arerequired that can analyse the signals beingproduced. Conversely, without adequate

oscilloscopes, it is impossibleto ensure transmission quality.As the technology currentlystands, data transmissionequipment capable of com-munication at 560Mbit/secondis now in use, while large scalecommunication in the 1-2Gbitrange is still in the future. Asfar as bandwidth is concerned,therefore, the fact that the11401 and 11402 can handlebandwidths of 500MHz and1GHz respectively, means thatthey are both well placed todeal with many of the needs ofcurrent technology.

Single -shot sampling. Twoexamples of events where asingle -shot capability is im-portant are in isolating non -repetitive 'glitches' in a micro-processor's clock signal, whichwould impair its performance,or in analysing its power -upsequence.

Single -shot samples can onlybe taken at 20MHz on the 11400series. Indeed, the 11400 is notintended as a transient single -shot machine, and if this is aprime requirement of a parti-cular installation, then there

are a variety of other products, both ana-logue with higher bandwidth, and digitalwith higher sample rates, that are bettersuited to the task.

However, complete single -shot waveformrecords from up to three channels can beacquired at slow and moderate timebasesettings, and a unique 'trigger -to -trigger'mode can measure time intervals as short as2Ons between trigger events on a single -shotbasis. Even if incomplete records are pro-duced. interpolation routines are availablewhich enable them to be completed. As aresult, the 11400 series can, in practice, beused for single -shot sampling.

Sample rate. The 11400 series samples at20MHz, which is more than adequate todigitize repetitive signals containing fre-quencies up to 1GHz. This is combined withan interesting sampling method which iscentral to the overall performance of themachines.

The Tektronix scopes use the randomequivalent -time sampling method. With thistechnique, the time between the triggerpoint and the sampling strobe is measuredfor each triggered acquisition cycle. Thetrigger -to -strobe time is then used to sortdata into its proper position in the finalwaveform record.

By combining random equivalent -timecfigitizing with a dedicated custom proces-sor, d.m.a. channels for waveform data, andother special display hardware, the 11400series scopes are able to acquire and displaywaveforms with the update rate of analogue

INDUSTRY INSIGHT

scopes (between 30 and 40 waveforms persecond). This gives them a major perform-ance advantage over the HP products, whichcan generally display only two waveformsper second (and a maximum of 15 on the54111). Indeed, the slowness of 54100 seriesscreen updates has been one of the majorcriticisms that has been levelled against theentire family.

Record length. From the record lengthonwards, the key specifications of the 11400series products point to the clear improve-ments in flexibility that they offer to theirusers. By offering variable record lengths -between 512 and 10K points - the 11400series enables users to tailor their samplingto the complexity of the waveform beinganalysed.

Variable record lengths are combinedwith a unique windowing facility whichenables users to 'window -in' on a particularpart of the waveform being displayed. Anexample of where this would be useful is for aradar signal which could be analysed using a512 -point main record in order to maintainspeed, with two 10K -point window recordsbeing used to re -sample specific parts of theoverall trace. In this case, in-depth examina-tion of the echo pulses in the 10K windowscould clearly reveal target identificationinformation which would be invisible in the512 -point main record.

The key here is that the part of thewaveform displayed by the window is resam-pled as 10K points, rather than using moreconventional delayed sweep technology. As aresult, the resolution capability of the 11400series is massively enhanced, way beyondanything else available on the market today.

Channels. Many advanced oscilloscope ap-plications now require the ability to look atfour or more channels. With the 11400series any eight of 12 input channels whichcan be digitized and displayed at the sametime. Example applications of this would beto configure the oscilloscope with up totwelve 300MHz channels for sophisticateddata acquisition and timing analysis. Alter-natively, three 150MHz differential channelscould be used for power supply measure-ments; six 600MHz channels for a.c. para-metric analysis on high-speed logic devices;

bits levels verticalresolution

6 64 1.5625%7 128 0.7813%8 256 0.3906%9 512 0.1953%

10 1024 0.0977%

11 2048 0.0488%12 4096 0.0244%13 8192 0.0122%14 16384 0.0061%

Optical oscilloscope: Waveform analysis of the fibre -optic communication bands of850, 1300and 1500nm is possible on the 11400 oscilloscopes with new probes from Tektronix. Theopto-electronic converters - believed to be the first in direct probes - enable the scopes to actas calibrated optical waveform analysers. "Having redefined the digitizing scope market withthe introduction of the 11000 series" Robert Stubbings says "we're now expanding on itscapabilities with some of the most innovative add-ons ever produced. And at around £2000our 6701 and 6702 converters have a significant price -performance edge over their(non -probe) competitors". One extends from 450 to 1050nm with 700MHz bandwidth whilethe other covers from 1000 to 1700nm with 500MHz bandwidth.

or three 1CHz channels for high bandwidthanalogue and digital testing. The 11400series will support as many active andpassive probes as there are channels.

In these ways, the 11400 series scopes areeminently suitable for application areaswhich the two channels offered by the HP54100 series simply will not support.

Vertical resolution. The 11400 series offers10 -bit vertical resolution (14 -bit with aver-aging), and has established new standards inoscilloscope resolution. The table leftemphasizes what this leap in technologymeans.

The high resolution offered by the 11400series is only part of the story. A newanalogue amplifier design enables theaccuracy of the scopes to be improved by afactor of between two and ten over theprevious industry standard set by the Tektro-nix 7000 series. This enables accuracies of1% on average, and in certain cases 0.25%,to be achieved. There is absolutely no pointin building the best digitizer in the world if itisn't supported by the best analogue front-end.

Finally, the 11400 series can store over100 waveforms concurrently. This obviouslyadds dramatically to its usability, since manywaveform measurements need to be com-pared with standard or reference signals.The fast processing power of the 11400 seriesactually supports real-time analysis of multi-ple 10K record length waveforms, thusgiving Tek a major competitive advantage inthis area.

Specifications alone though are only partof the story. What is ultimately of primeimportance, as with all products, are itsusers. For some time now, published pro-duct specifications have, not surprisingly,highlighted those areas in which a product isparticularly strong, leaving the potentialuser to surmise what the downside of aparticular performance characteristic islikely to be. The architecture of the Tektro-nix 11400 series removes this necessitycompletely.

Robert Stubbings is product manager forlaboratory oscilloscopes and systems at Tek-tronix UK Ltd, Globe Park, Marlow, Bucks.

100MHz digitizing oscilloscopes on the UK marketMaker & Model Equiv time Sample rate Channel/ Memory Smallest Auto - Mass Price Comments/interface

supplier bw(MHz) per ch (Ms/s) traces length/ch glitch(ns) setup kg

Gould 4072 100 (k) 400 2/8 IK 5 V 11.4 7750 (XY,RS,GPIB

4074 100 400 4/8 1K 5 11.4 dual timebase

Hewlett 5185T 110 250 2 16K 4 4.8 31,200 Discdrive. GPIB on all HP scopes

Packard 16500A 100 400 2-8/2-8 4K 2.5 V 18-21 9-6-18.6K RS237. Card options

54112D 100 400 4/4 16K 2.5ss, 40p rep 25 17,800 Colour. Logic trigger. 6 bit

54201A 300(50ss) 200 2/4 1K 5 V 5907 27 bit logic trigger. 6 bit

54111D 500(250ss) 1G 2/4 8K lss 10 rep V 27 18,600 Colour. Logic trigger. 6/8 bit

54110D 1G 40m 2/4 1K 10 rep V 2S 15,100 Colour. Logic trigger

54100 1G(4ss) 40m 2/4 1K 10 rep V 19 10,000 113k6 with logic trigger. 7 bit

54120T 20G 10K 4/4 1K 0.25p V 24 25,200 Vertical error 0.4%. TDR. 12 bit

Iwatsu 8130A 12.4G 70K 2/2 1K V 19-8 GPIB&RS 10bit. 3.5GHz option

(Datron)

Kikusui 7101 100 50 4/8 1K V via 10 4695 dmm, freq. counter

(Telonic) 7201 200 50 4/8 1K V bus 10 5895 memories

LeCroy 9400 125 100 2/4 32K 14 7495 XY.7 x 5in screen. Setup store

Nicolet 4180 100 200 4/32 4K 25 14,300 FFT, disc option 12 bit

Panasonic 5741A 35(100R) 100 2/4 10K V 17 7 x 7in screen, mem. expn

Philips 3320 200 250 2/8 4K 3 V ;8 7995 GPIB, RS options. 12 bit adc

(Pye Unicam) 3308 100 40 2 8K 6.5 N/A 8 x 4in I.c.d XY,RS, G PIB option

Schlumberger 5602 100(4R) 40 2/4 1K V 13.64MHz realtime.

4750GPIB or RS232. XY

Tektronix 2230 100 20 2/5,52 4,1K 100n 8.3 2995 100MHz real time 52-vi form store

2430A 150 100 2/6 1K 2 V 10.9 6249 Automodes, memory

2432 300 100 1K 2 V 10.9 7995 GPIB

7854 400 500k 4-40 128-1K 13,895 10bit. 14GHz option GPIB

11401 500 20 12/100 512.10K 20 10,000+ with 11A52. 10bit. Cent. RS

7912HB 700 100G 1/2 512 25 29,682 9 bit. GPIB. Digitizer

11402 1G 20 12/100 512.10K 20 12,000+ 10bit. Cent. RS. GPIB

7250 6G IT 1/15 512 60 90,318 5yr memory split screen

Vertical resolution based on 8 bits unless shown otherwise. R: real time, ss: single shot.

High accuracy multimeters on the UK marketMaker &supplier

Digits Model Sensitivityd.v.(nV)

Basic errord.v.(ppm/yr)

Speed Basic Interfacerdg/s price (GPIB)

Datron 81/2 1281 10 -±-(5rdg+0.2fs) 150 3550 inc

71/2 1081 10 -±-(8rdg + 1 fs) 2 2950 250

1071 10 ± (20rdg+ 2fs) 2 2450 250

61/2 1061A 100 ± (30rdg + 4fs) 200 1750 200

1065A 100 -±(60rdg+4fs) 200 1895 Inc

Fluke 71/2/61/2 8506 100 10 500 4995 572

8505 100 10 500 2995 572

6'/2 8502 1µV 20 500 4755 572

8520 10.V 90 500 3115 inc

Hewlett- 7'/2 3457A 10 27 1350 2095 inc

Packard 61/2 3456A 100 25 330 2700 inc

Keithley 61/2 196 100 30 1000 1195 inc

Prima (ppm) 81/2 6048 10 7 30 4500 inc

Rohde &

Schwarz51/2 UDS5 11AV 30 80 1590 inc

Solartron- 81/2 7081 10 11/V7r 100 4495 inc

Schlumberger 71/2 7071 10 20/V7rr 100 3495 inc

71/2/61/2 7061 100 25 1500 2595 inc

7062 100 25 1500 2395 inc

61/2 7060 1µV 80 250 1355 inc

Microprocessor Otherfeatures features

Options Comments

1-5,7,10,11,13 frequency. Self cal

1-5,7,10.11,13 temperature1.5,7,1011,131-5,7,10.11,131,4,10,11,13

a.v.,11, I, analogue o/pa.v.,I1, ratio, analogue Rack mounting

a.v.,11, I, ratio, analogue kits available

a.v.,11, I, ratio, analogue

1.5,10,11,13 highest rms accuracy

1.5,10,11,13 fast systems meter1-4,10,11,13 fast systems meter

1-i3 extended maths

ohms, currentohms, currentohms, currentextended s/w

RS232 /471RS232 /471RS232 /471

1-13 1000rdg store1-13

relay mux,CIIL,3yr w.

35Orcla store, o.c. 3yr warranty floffset comp(o.c.)

1,2,4-7,9,10,13 Translator softw.ire, o.c.

1-13 20 way scanner

300MII range

1,2,3,5,6,7,10,11 2/4 wire res. shunts. probes

1 131.131.13

140,12,133,5,13

true ohms, temptrue ohms, dig (tertrue ohms, temo, ratiotrue ohms, temo, ratioratio

16 ch scanner RS232 included

scanner, 9000rdg store power fail recovery

scanner, 8000rdg store power fail recovery

a.c.rms, I, scanner

Microprocessor features: 1 auto calibration, 2 compute (offset, scale, % dev), 3 ratios, 4 max, mm, hold, limits, 5 averaging, 6 results store, 7 dB, 8 linearizing, 9 statistics (variance, T. ms.),

10 self test, 11 error display, 12 timer, 13 null facility.

Arbitrary waveform generatorsMaker Model Channels Sum Vertical D.S.O. Clock Looping Operating Waveform Price

mode 'res' (bits) readout rate (MHz) Linking memory memory (nv)

LeCroy 9100 2 V 8 V 200 V 64K 350K 7500

DataPrecision

2020-100 1 12 100 V 128K

Hewlett 8770A 1 12 V 50 V 128K 19,508

Packard 8175A option 002 2 10 50 Link 255 files 1K 10,812

Wavetek 680/01 1-8 V 12 20 Link 4 files 28K

Our mm205-2 must be an award winner...

MasterclassOSCILLOSCOPES

For those who compareWith the phenomenal success of the HM205, with its Component Testerfeature, pioneered by Homeg, we now take pleasure in introducing theHM205-2. This improved version contains oll the previous features, buthas increased capabilities in the following areas:

Increased sampling rate of SMHzgiving a digital tImehose range of20ps cm to Ss cm, with automaticrefresh every sweep

Dot joining facility as a frontpanel push button, combines thewaveform samples to forma solidcontinuous trace

Memory of 1024x8 bits per channelprovides high resolution capture ofcomplex signds, for as long asrequired

because at £527 it deservesthe prize of the year!

20 MHz analogue bandwidth forfull general purpose applicationsproviding any signol shape, largeor s-ol'

A digital timebose of 5s2ps perdivision makes it possible to see asolid picture of a signal from kilohertzright down to 05 Hertz.

Maximum sensitivity of 2mV perdivision means even the smallestsignals con now be seen, triggeredand stored for careful examination

HAMEG74-78 Collingdon Street, Luton, Bedfordshire, LU1 1RX Telephone (0582)413174 Telex 825484

Oasis Instruments

OASIS VIRTUAL INSTRUMENT SYSTEM

For faston 0603 747887. Technical queriesanswered and requests for furtherinformation on this number.

NEW VERSION - NEW INTERFACES - HIGH SPEED OPTIONThe OASIS Virtual Instrument System (VIS) emulates conventional OSCILLOSCOPE,CHART RECORDER, PROCESS MONITOR, MULTI -CHANNEL DVM, X/Y PLOTTERand DATA LOGGER in one easy to use package.

HARDWAREVIS includes a precision 16 channel A -D converter, with programmable rangesand read rates of 50k Ft/s at 8 bit, 25k at 12 b't (100k and 60k with high speedoption). This simply installed unit has proven long term stability and reliability.

SOFTWAREThe menu -driven acquisition, analysis and display programs combineon -screen set up of measurement parameters, SPREADSHEET datamanipulation and a _range of display formats. with ZOOM and ON -SCREEN

.7.. MEASUREMENTS

. a . .

Total data mobility from measured information to memory, disk, screen andHARDCOPY output, including screen dumps.The OASIS VIS carries full documentation to allow the beginner orprofessional programmer to create new interface applications or personalisedinstrument emulations.

PRICEThe price of the complete system is less than any one of the instruments it replaces.Prices exclude VAT, P&P (£8). High speed option £160.

The Virtual Instrument System is supplied complete - no further components arerequired - just plug in to your laboratory computer.Digital to Analogue and industrial interface options - POA

PC-XT/AT - £499, Nimbus - £499, BBC/Master - £399, New Archimedes Version - £599

1f .il 1 A

de ivery, phone your order

The Street. Old Costessey, Norwich N R8 5DF Tel 0603 747887 Design ConsultancyENTER 17 ON REPLY CARP

161) ELECTRONICS & WIRELESS WORLD

INDUSTRY INSIGHT

INSTRUMENTATION

INTEGRATED TENDENCYhe tendency to integratecomputers with test andmeasurement instrumentshas taken various paths.

Plug-in cards for personal computers werean obvious starting point, but it soon be-came clear that this was not an optimumsolution, not only for the noisy environmentbut also from the inherent limitations ofpower, number of slots, and even card size.Using PCs for GPIB controllers suffers fromthe complex programming required com-pared to dedicated controllers, as well asgenerally lower performance. Increasing in-telligence within instruments can still havelimitations in computational facilities - ingeneral it's not programmable and a built-inprocessor will run a custom operating sys-tem and not standard software. And at thetime when Hewlett Packard decided theyneeded to integrate a bus controller intotheir multi -instrument cardcage (6942), theVME-based VXlbus hadn't emerged.

It became clear to H -P's system designersthat the additional cost of a computer boardwould justify its inclusion in a newinstrument -computer. So with the object ofachieving a more integrated solution, cou-pled with an overall cost reduction throughshared housing, display and power supply,H -P developed a new cardcage instrumentthat would not compromise computationalfacilities. It is a highly integrated stand-alone test system controller that is based onstandard 32 -bit HP hardware and software. Ithas an operating system optimized for in-strument control, but will run other prog-rams as well, and H -P say interface boards'will give it "compatibility" with future VXIsolutions.

Called a 'multiprogrammer', whichstrange name dates from the 6940 multiple -use power supply programmer of the early

HP's latest CAT system

combining measurement,

control and computation

in one box also features

high-speed card -to -card

communication.

seventies, the 6954A has eight slots, expand-able in 16 -socket frames to 120, a 300 seriescomputer. 1Mbyte of ram and a 20Mbytedisc, whilst running Basic 5.0 and maintain-ing compatibility with the previous seriessoftware. The computer, actually a 310series with 68010 c.p.u., replaces the 68000series 300, which in turn supersedes theseries 200 introduced six years ago.

In 'local mode' a keyboard and monitorwill allow it to function as a developmentstation, and in 'remote mode' a terminal orhost computer can control the 6954A overRS232 or the interface bus. File exchangewith a remote host is facilitated by an HPIBfile transfer utility, Remcon (remote consoledriver), and Kermit. A 'run -only' mode withautostart program on disc can dedicate the6954 to a specific task and eliminate oper-ator intervention if required.

The cards, of which there are over 30originally developed for the 6942, are de-signed to communicate directly with one

data lines, hand-shaking control, triggering and status sig-nals. This permits the triple synchronization- stimulus to d.u.t., d.u.t. to response, andstimulus to response - for tests requiringcomplex timing. New cards are added to therange: 69774 3.5MHz universal counter,69734 timebase and 69544 high-speed datacapture and remote monitor for componentevaluation, with an FFT card on the way(transforms are much faster in hardwareform than software, typically 10ms ratherthan 200ms). The 6954 controls up to 14other GPIB instruments, and does not ofcourse require a separate interface bus con-troller. Price is £8000, keyboard and moni-tor for local control £460, and extensioncardcage £2,938. with cards typically cost-ing around £230. Contact H -P's enquiryoffice 0734 696622.

Controller

Response: digital 'scope

Simple stimulus response test using standard instrumentation (left) has limited adaptability and an excess of features. In the 6954A setup(right) the relationship between cards is not fixed and is determined by the test designer. Features can be adapted by 'rewiring' the blocks.

and as the selection of i/o cards is determined by the test designer unnecessary functions can be omitted.

INDUSTRY INSIGHT

Handheld digitaoscilloscopeA combined digital storage oscilloscope,multimeter and frequency counter/timerweighs only 700g in a new 'Signal Compu-ter', model SCO2, made by Createc of Berlin.And the world's smallest d.s.o. also containsa signal processor and store for 46 wave-forms. The miniaturization makes use ofcustom v.l.s.i. circuits in 2m cmos, fourmicroprocessors, three layers of surface -mount boards, and a 128 x 128 element I.c.display. The two -channel instrument is animproved version of the SCOT, first marketed18 months ago (though not in the UK) whosetwo -channel inputs were multiplexed andwhich had nine waveform data stores.

The 7 -bit oscilloscope with 10mV/div de-flection factor samples at 20Ms/s with anoverall bandwidth of 5MHz. Single -shotoperation has a resolution of ls/div or 5Ons,while periodic signals can be displayed at5Ons/div giving a resolution of 2.5ns/pixel.Trigger and other measurement parameterscan be set up automatically or enteredmanually through a numeric keypad, andfour cursors provide for accurate measure-ment. Measurement results are displayed intwo scrolled data fields at top and bottom ofthe display.

In the multimeter mode the instrumentdisplays true r.m.s., d.v. component, andpeak voltages and is unusual in also showingmaximum error figures. Using a zener refer-ence and what is claimed to be a noveltechnique of feeding captured signals backthrough the a -d converter, the error figuresare presented free from temperature orrange dependence. Bandwidth extends use-fully to 5MHz with an error of around 1%,

continues on page 164

INSTRUMENTATION

Multimeter takes in scanner forr&d production testingSet for release early this year is Keithley'stwo -in -one multimeter/scanner. Givenmodel number 199, its mainframe is a fullyprogrammable 51/2 -digit multimeter with sixfunctions while an eight -channel scannercan be incorporated for switching applica-tions.

Measuring signals from multiple sources- transducers for example - is a requirementnot only in r&d but also in productiontesting, incoming component acceptance,and quality control. Life test evaluation of asample of eight cells or batteries is a typicalsituation in which the 199 would be anappropriate solution.

"Being microprocessor controlled themeter already has the 'intelligence' neces-

sary to control a switching module" BobGreen of Keithley's parent plant in Cleve-land, Ohio told Insight "and the eight -channel option can therefore be added to thebasic instrument very cheaply".

In addition to the scanner option, theinstrument will function as a data loggerwith a 500 memory store under computer orfront -panel control. Other features include athermal offset in the relay contacts of <10,running average filter to reduce noiseeffects, a controller message display, andKeithley's Translator software to allowemulation for existing software. Basic sensi-tivity is 1p.V, with a 12 month error of70ppm. Further details from Keithley In-struments in Reading, 0734 861287.

100MHz flat- screen digitaloscilloscope from PhilipsPhilips t&m have developed a 100MHz digit-al sampling oscilloscope with an unusuallylarge display area - 96 by 192mm. Thelarge -area flat screen with freedom fromparallax errors allows more accuratemeasurement tham c.r.t. displays and alsomakes the new design more easily portable.Model 3308 with display lid after the style oflap -top computers weighs 6.5kg and is de-signed for shoulder -strap carrying.

It is a 40 megasample per second machinewith eight kilobyte memory length. A204Kbyte random access memory will storeup to 100 signal waveforms or 100 instru-ment settings.

Pye Unicam, Philips t&m marketing armin the UK, said its release in the UK is set forJanuary - just before publication of thisissue in fact - but they didn't want us toinclude it in our 100MHz oscilloscope listing!

"It's a pretty small battery -powered PROM programmer- so what?"

Tools which are convenient get used a lot - that justifiestheir existence. There is no way we couldexplain all the usefulness of S3 here.Instead, if you're interested we'regoing to let you see it, use itand evaluate it in your ownworkshop. We went to a lotof trouble to design S3 justthe way it is - no otherPROMMER is all CMOS andall SMT. So we must be con-vinced that S3 would be a for-midable addition to yourarmoury. Now all we have to dois to convince you.

"Such a little thing can't bepowerful, like a big bench -programmer - er - can it?"Yes, it can. It is more powerful. S3 leavesother prommers streets behind. S3 hascontinuous memory, which means that youcan pick it up and carry -on where you left offlast week. S3 has a huge library EPROMS andEEPROMS. S3 can blow a hundred or morePROMS without recharging. S3 also works re-motely, via RS232. There's a DB25 socket on theback. All commands are available from your computer(through a modem, even). Also S3 helps you developand debug microsystems by memory -emulation.

"What's this memory -emulation, then?"It's a technique for Microprocessor Prototype Develop-ment, more powerful than ROM emulation, especiallyuseful for single -chip "piggyback" micros. You plug thelead with the 24/28 pin headerin place of the ROM/RAM.You clip the Flying -Write -Lead to the microprocessorand you're in business. Thecode is entered using eitherthe keyboard or the serialinterface. Computer -assembledfiles are downloaded in standard format - ASCII, BINARY,INTELHEX, MOTOROLA, TEKHEX.Your microprocessor can WRITE to S3 as well as READ. Youcan edit your variables and stack as well as your program, ifyou keep them all in S3.S3 can look like any PROM up to 64K bytes, 25 or 27 series.Access is 100ns - that's really fast. Memory -emulation ischeap, it's universal and the prototype works "like the realthing".

S3 loads its working programs out of aPROM in its socket, like a computer

loads from disk. Software expansion isunlimited. Upgrades will come in a

PROM. Programs can be exchangedbetween users. How's that for

upgradability?

"Can I change the way it works?"You surely can. We keep no secrets. System Variables can he"fiddled." New programming algorithms can be written fromthe keyboard. Voltages are set in software by DACs. If youwant to get in deeper, a Developers' Manual is in preparationwhich will give source -code, BIOS calls, circuit -diagrams, etc.We expect a lively trade in third -party software e.g. dis-assemblers, break -point -setters and single -steppers for variousmicros. We will support a User Group.

"I'm bound to let the battery go flat."Ouite so. But in practice it doesn't matter. S3 switches

Er ()tf after a half-hour of non-use anyway, or when the, battery gets low. You don't lose your data. Then a

slow -charge overnight or boost -charge for threelk hours will restore full capacity. You can keep usingA, it when charging. So there really is no problem.

"I already have a programmer."Pity it doesn't have S3 features, eh? Buthere's a trick worth knowing. If you plug

S3's EMULead into the master socket of aganger then you get an S3 with gang

capacity. Isn't production separatefrom development anyway?

"It looks nice. Will I bedisappointed?"

Dataman tools are designed tobe used by Engineers. Notjust sold to Management.

Have you ever been misledby some mouthwateringad for a new product?Great artwork and ex-citing promises which

feed your fancy? Onimpulse you buy and

when the thing arrivesyou feel let down. The pic-

ture looked better. The claimsare hardly justified; not exactly

misrepresentation, justpoor implementation.But you've bought it.And you're stuck with it.It stays in the cupboard,most of the time. So howabout this: buy S3 anduse it for up to a month.If you're not still thrilledthen you can have yourmoney back.

Softy3 is here!"Refund in the first month!that?"We trust S3 to fire your enthusiasm.as a free hire -service. We bet youwould you manage without it?

How can you offer

We trust you not to use uswon't send it back. How

"These things cost a fortune and take months toarrive."We wouldn't get you all excited and then let you down. It Costs£495 plus VAT. That includes P & P, Charger, EMULead,Write Lead and a HELP program in ROM. S3 is in stock. Buyit today. Use it tomorrow. (That's a fair promise. But pleasereserve product by phone or telex to make it come true).

DATAribillLombard House,Cornwall Rd.DORCHESTERDorset DT1 1RX.Phone 0305 68066 Telex 418442If you purchase while this ad is current, you have 28 days toexamine the goods and return them for refund. Carriage will becharged at cost. The right to charge the cost of refurbishmentof damaged goods is reserved.

Writ° ENGINEERING

At PS,

AftVISA

INDUSTRY INSIGHT

but no figures are given for direct voltagereadings.

Settings for the frequency converter arefully autoranging, and readings from 1Hz to7MHz are made with a best error of 0.04% ath.f.

During data acquisition incoming wave-forms are tracked by the 'signal computer' toadjust timebase trigger, trace and cursorpositions, and which also allocates memoryspace. Post signal processing on previouslystored data allows analysis relative to areference or across channels. Prices in Ger-many are DM2500 SC01, DM3750 SCO2.CVG, Limburger Strasse 42, 1000 Berlin 65.Tel. Berlin 4535083.

Crompton to sellSignal ComputerNegotiations for a new t&m division ofCrompton Instruments to take on UK dis-tribution of Createc's instrument were at anadvanced stage as Insight went to press.Headed up by Steve Figures the new divisionwill market handheld instruments - chieflythe d.s.o. - from its Witham base in Essex."There are still one or two problems to sortout" said Figures. "One is that Tektronixmay also be selling it, though their modelshould be a simplified version. Price hasbeen fixed at £995 including mains adapter,with a Vidor battery pack still at the planningstage."

If the deal goes through Crompton t&mdivision will be exclusive importer, and as asign of their confidence in the product areprepared to take on a field sales force of six.Crompton Instruments are at FreebournesRoad, Witham, Essex CM8 3AH, tel 0484862894.

0 Market research has revealed to MarconiInstruments that the demand for spectrumanalysers with a frequency range upto4.2GHz accounts for 35% of the existingmarket. Major users of spectrum analysersin this sector are civil and military v.h.f. andu.h.f. cellular and mobile radios to 1GHz,u.h.f. fixed links to 2.3GHz, tv and radiobroadcast, 1.5 and 1.6GHz Inmarsat satellitelinks, high bit -rate p.c.m. and data links, andavionics systems and radios. MI thereforeaddressed the need to improve on criticalspecifications - resolution, accuracy andfrequency range - in the model 2383 achiev-ing a minimum resolution bandwidth of 3Hzand an unprecedented level accuracy of ±1dB upto 1.5GHz. Marconi say that theextensive temperature cycling, environmen-tal and performance testing carried out onthe 2383 have been supported by an invest-ment of over £1 million in test equipmentfor this one product. The 2383 is also one ofthe first instruments to benefit from thecompany's thin-film facility.

INSTRUMENTATION

New use for old scopesThurlby's new adapter DSA524 will convertany single -channel oscilloscope into a highperformance dual -channel storage instru-ment - but at a fraction of the cost of a d.s.o.Sampling rate for single -event signals is

2 x107 per second, and repetitive signals of upto 35MHz can be captured with an equivalent -time sample rate of 2x 109 per second. Inter-polation is either linear or sine, the sine givingnear perfect reconstruction at four samplesper cycle, with its 'cubic spline' algorithm.This gives the adapter a single -event band-width of 5MHz, substantially higher, sayThurlby, than most other 20M sample/s in-.struments.

DSA524 also features many of the facilitiesfound on d.s.os - summation averaging for upto 256 recordings, cursor measurement, auto -ranging, program memory for 50 front panelsettings, full programmability through RS232(optionally GP1B), and memory for 16 wave-forms. The adapter annotates the scope displaywith up to 30 characters of text to aid inoperating the instrument. UK price is £585.from Thurlby on 0480 63570.

0 Increasingly complicated nature of mul-tiprocessor systems makes analysis by con-ventional logic analysers extremely difficult,if not impossible, according to Dolch LogicInstruments. Their latest model M128 in-corporates a twin -slot capability that allowstwo cards to be linked together and analysedata on two independently clocked andsynchronized processors.

A typical system might be based on an8086 c.p.u. with a Z80 i/o controller orgraphics processor, or even a pair of 68000processors. all operating at different clockspeeds and with different synchronizationmaking accurate time -correlations impossi-ble. By providing three 64 -channel cardslots, two of which may be linked, the M128allows accurate tracking of dual processorswith proper time correlation. The two chan-nels may also be combined for use on a singleprocessor with up to 128 channels. Stimuliare provided by word generator moduleswith up to 48 channels and 20MHz clockrates. The M128's channels can be confi-figured for static and timing analysis up to200MHz. Dolch Logic Instruments are on0635 48630.

0 Acquire is a new modular waveform ac-quisition and processing package from Data -lab for use with HP200 and 300 Seriescomputers. It provides an integrated systemsolution for Datalab Multitrap 1200 and2000 Series multichannel waveform recor-ders and includes facilities for the acquisi-tion, display and processing of analoguedata, graphics plot generation and creationof permanent files. In addition to a compre-hensive selection of time and frequency

domain processing functions including FFT,Acquire enables users to easily create theirown dedicated measurement routinesthrough its sequence generation functionand user hook capability. It requires aminimum of 1Mbyte r.a.m. and Basic 3.0 orlater, a waveform digitizer and graphicsplotter. Contact Data Laboratories on 01-640 5321.

O Nicolet are back in the real-time spec-trum analyser market as the newlyappointed sole UK distributors for the Rock-land Scientific FFT spectrum analysers.First product is a battery powered, portableFFT analyser, believed unique with largeI.c.d. as seen on lap -top computers. Featuresof model 5840A include direct digital plot-ting via HPGL, RS -232 interface for postprocessing, optional non-volatile memoryfor up to 78 spectra, input for direct couplingto i.c.-piezo accelerometers, powermeasurement, and go/no-go comparator.Price below £5,000. Enquiries to Nicolet on0926 494111.

0 Since Hewlett Packard introduced thefirst automatic network analyser 8542 19years ago, and its 8510 successor four yearsago, the US military build-up has created anew generation of phase -sensitive activecomponents, systems, and antennas. Thesenewer systems demand more agile, fast -acting test equipment, Wiltron Companysay, who have stretched the upper frequencylimit of their new vector network analyser to40GHz using a new sampler design and newcoaxial 'K' connector. Details from WiltronUK on 0344 777778.

Tb e ATM 451 databridge from Prism Electronics

AccurateEasy to useLCR component measurement

PRISM4 Measurement of R. L, C, D & Q.A Auto -ranging and autofunction

for maximum ease of use.A Push button selection of 100Hz,

1kHz or 10kHz measurementfrequency.A Accuracy 0.1%4, Full 5 digit display.A Optional 4 terminal accessory

test leads including sirface mountfixtures.

Optional IEEE-488/RSZ.z2interface.A Optional applications software

for the IBM PC.

The 451 databridge has beenspecifically designec for maximumease of use combine] with :Ughaccuracy. Simply switch or andplug in a component, the AIM 451will identify the corrponem type,and display the value.

For full details contact is now.

ELECTRONICS

Prism Electronics Ltd,Burrel Road, Industrial Estate,St. Ives, Huntingdon,Cambridgeshire PE17 4NFENGLAND.'Iblephone (0480) 62225Fax (0480) 494047lblex 32303 PRISM G

LOGICANALYSERS

TA3000 from £4795 + VAT TA2000Up to 1 2 channels.100MHz Timing; 20MHz State.Multilevel conditional triggering.State/Timing cross -triggering and correlation.Easy tc use soft -key control.Optional disassemblers for 68000, 8086/8088, Z80, 8085. 6502, 6809.

£2950 + VAT32 data channels; 100MHz maximum sampling rate.5rs glitch capture; glitch triggering.4 level trigger sequencer with event count and delay.Non -Volatile memory for data and set-ups.Easy to use soft -key control.Optional disassemblers for 68000. 8086/8088, Z80, 8085, 6502, 6809.

thandarELECTRONICS LIMITED

Thandar Electronics Limited,London Road. St Ives. Huntingdon.Cambridgeshire PE17 4HJ. EnglandTelephone (0480) 64646 Telex 32250 Test

THE LOGICAL CHOICEENTER 56 ON REPLY CARD

COUNTERS & OSCILLATORS LEVELL OSCILLOSCOPES

COUNTERS MET100/600/1000/15008 digit 0.5" LED 5Hz up to 100600 1000,1500MHz.Resolves 0.1Hz Sensitivity 5mV up to 10MHz Low passfilter Mains/rechargeable battery powered

LEVELL RC OSCILLATORS TG152D/DM3Hz-300kHz. 5 ranges, acc 2% + 0.1Hz up to 100kHz,3% at 3100kHz. Sine or square <2000/ to 2.5Vrms. Distn.<0.2% 50Hz-50kHz TG152DM has an output meter.

LEVELL RC OSCILLATORS TG2000/DMP1Hz-1MHz 12 ranges, acc 1 5% + 0.01Hz to 100kHz, 2%

at 1MHz. Sine or square outputs <20013V-7Vmis.Distortion <0.05% 50Hz-15kHz. Sync output >1V.TG2000PAP has output meter and fine frequency control.

LEVELL FUNCTION GENERATORS TG302/30.02Hz-2MHz in 7 ranges Sine, square, tnangle, pulse andramp 20mV to 2OVpp from 500. DC offset 0,±10V TTLoutput TG303 also has a CMOS output and 6 digit 10MHzcounter with INPEXT switch.

TEST METERS

LEVELL AC MICROVOLTMETER TM3 B16 ranges 15oVfs 500Vts, accuracy 1%* 1%fs + 11aV

20dB 6dB scale 3dB 1Hz 3MHz 150mWs output

for INSTRUMENTS

LEVELL BROADBAND VOLTMETERS TM6B16 LF ranges as TM3 B 8 HF ranges lmVfs 3Vfs.accuracy 4% 1%fs at 30MHz -3dB 300kHz 400MHz

HC DIGITAL MULTIMETERS HC5040/5040Tdigit 12 7mm LCD. Up to lkVdc. 750Vac.

10A, 20MS2 Resolution 10001. 100nA, 10m1-215040T: 100mf21 Buzzer dcV 0.25% Battery life2000hrs 5040T: has a TR testHC DIGITAL MULTIMETER HC45104 . digit 11(11M LCD Up to 1 kVdc 750Vac, 10A. 20M0Resoln. 1012V, 100nA, 10mS2 Buzzer dcV 0.05%

LEVELL DIGITAL CAPACITANCE METER 77050 10F 2000oF acc 0 5°o 3' digit 12 7mm LCD

LEVELL INSULATION TESTER TM14Log scale covers 6 decades 10MS2 I OTS2 at 250V. 500".750V, I kV: 1M ITS? at 25V 100V: 100k 100012 at2 5V 10V 10k 10G0 at IV Current 100pA 100v.A

CROTECH SINGLE TRACE 20MHz 3031/362mV 10V div 40ns-0 2s div Cal 0 2V Component test3031: CRT 1 5kV 5x7cm 3036: CRT 1 8kV 8x10cmHAMEG DUAL TRACE 20MHz l@l2rnV) HM203-62mV 20V cm Ch2t Chl X Y Cal 0 2V 2V 1kHz sq20ns 0 2s,cm Auto normal or TV trig Component testHAMEG DIGITAL STORAGE 20MHz HM205-22mV 20V cm. Chl tCh2 Single shot and X -Y modes2Ons0 2s cm Auto, normal or TV trig Component test.Cal 0 2V 2V lkHz.5MHz sampling Two 1K memoriesDot Joining feature Y out CRT 2kV 8x10cm

HITACHI DUAL 20MHz V212/222/223lmV 12V cm 20MHz at 5mV Chl tCh2 X Y Ch1output 100ns-0 5s cm Auto, normal or TV triggerCal 0 5V 1kHz square Z input CRT 2kV 8x10cmV222: Plus DC offset and alternate magnify functionV223: As V222 plus sweep delay los 100ms

LEVELL DECADE BOXES

C8410/610 4 6 decs. 10pF steps, acc 1% -±2pF.R401/410 4 decs 10 or 1062 steps, acc 1%, 2.5WR601/610 6 decs. 10 or 100 steps, acc 1%, 2.5WR601S 6 decades. 10 steps, acc 0.3%. 2.5WR701 7 decades 10 steps, acc 1%. 2.5W

LEVELL ELECTRONICS LTD. Moxon Street, Barnet, Herts., ENS SSD, EnglandTelephone: 01-440 8686 8 01-449 5028

TRANSFORM YOUR CONVENTIONAL SCOPESWITH THE SCOPADAPTOR INTO A

2.CH. 20KHz FFT ANALYSER

+DIGITAL STORAGE SCOPE4 MODES OF OPERATION02 CH. FFTA.00-50Hz Span to 0-20kHz Span.OFull ANTI -ALIAS filtering.0200 line resolution.040 dB dynamic range.OSelectable LOG/LIN Amplitude.0Hanning/Rectangular weighting.OFast update speed.OUp to 128 averages + peak.00verload indicators.

02 CH. D.S.O.050kHz sampling rate (max.)00.5% vertical resolution.OTimebase from 5 sec/div to 1 msec/div.0Comprehensive trigger facilities.OSingle shot.01% or 25% pre -trigger0512 point horizontal resolution.ODisplay 'freeze' control.

OSPLIT MODEOSimultaneous display of frequency and time

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INDUSTRY INSIGHT

First %Al products emerge, from page 139

ance aspects of VXlbus, sucii as the datatransfer rate of nearly 1Gbyte per second andprecision timing, are a direct outgrowth ofTek's prior activities.

Tektronix is establishing a VXI productline to take advantage of the significantperformance improvements made possibleby the VXlbus spec and will be offering aD -size mainframe which provides the datacoupling, tight timing, and power to supportboth current and future instrumentationtechnologies. The Tek mainframe providesnecessary VXlbus slot 0 system resources,slots for 12 instruments, and power and willsupport a line of high performance stimulusand acquisition instruments.

Coupled with Tek's wide variety of pro-grammable instruments, software, switch-ing and d.u.t.-interface components, theTektronix VXlbus products will offer a.t.e.system integrators and end -users a widechoice of configurations and functionality tosupport test and measurement needs. AsGPIB-based a.t.e. suppliers for a number ofcompanies, Tek feels it knows that marketplace quite well. "The VXI product range willcomplement existing products and will alsoadd capabilities by exploiting the perform-ance capabilities of the new VXI busarchitecture", said Robert Stubbings of Tek'sUK Instrument Marketing Group, "And itwill be exploiting our prior knowledge andexperience in card modular design. We thinkwe have spotted some opportunities thatothers haven't" he told Insight.

Racal -Dana are adapting their 1993 uni-versal counter for the VXlbus. This counter,not shown in their current catalogue, is acard -based instrument developed specifical-ly for the Wavetek 680 multifunction instru-ment system. Though VME based, this pro-duct was announced last April prior to VXIagreement, and is not VXI compatible.

Among the group comprised by HP,Wavetek, CDS, Tektronix, Racal -Dana, andmore, Sciteq of San Diego, California standsout for two reasons. "First", says presidentHenry Eisenson "we are by far the smallest ofthe players -a young firm with a staff of 30.Second, we control the frequency synthesiz-er technologies most needed by the VXI field.We plan to produce the only synthesizedsignal sources for the VXI industry. Manyapplications exploit the phase manipulationcapabilities of our designs, because thistechnique provides a degree of accuracy notpossible with other approaches, whetheremployed as a clock generator, r.f. source,phase shifter, general purpose signal gener-ator, or modulator. "We currently produceseveral frequency synthesizers in VME/Eurocard format which we're converting toVXI." They include these four:

Band- Step Phase Switching Phasewidth size(Hz) control speed noise 1kHz

03MHz 0.0010-15MHz 0.10-35MHz <50-110MHz <1

0.36°0.09°

0.5 Rs -136dBc/Hz0.3 Rs -130dBc/Hz0.07 Rs -110dBc/Hz0.15 Rs -110dBc/Hz

United Test Equipment's VXI Modular Test & Monitor System was developed within fivemonths of the announcement of the VXIbus specification last July.

"We have applied for patent coverage on thecircuitry that makes such performancepossible, and have further embedded ourdesigns in custom integrated circuits. Wefeel confident enough to place ourselvessquarely atop the VXI juggernaut." Another VXlbus user is Universal TestEquipment which began three years ago inAnaheim, California. The initial product wasa universal grid bare board circuit boardtester which remains today as the onlytable -top grid tester. It operates using anIBM or compatible PC, XT or AT computerand includes simple fixturing. high speed,and component failure redundant circuitrythat they claim no other manufacturer hasincorporated.

What initially involved much custom

AN ALTERNATIVE VIEW 0 VXI

The VC specification is primarily targeted towardmarkets where density is a major requirementKeithiey. however, focuses on *he worldwide semiconductor research and industrial test markets. Atthis point Keithley feels that the best value for thecustomer still lies in traditional IEEE -488 GPIBboxes and systems. A VXI system will cost morethan a comparable rack-anc -stack impleme na-tion. VXI instruments are nct targeted for non-prog -arnmable operation. There are not likely to beany push buttons or displays on the front pane s ofthese instruments. And. of course, stand-aloneoperation and portability are r of attributes of VKI.

Ks ithley will be assuming 3 greater role in VXIstan lardization due to their experience in design-ing '/ME based systems and their desire to havefutu-e products conform to in industry -acceptedstandard.

The proposed standard is a sound begin ling.However. it will be a few years before all of thesystem integration and software issues stabilize.With VXI products only just emerging. the expectedcompatibility of different manufacturers' productsis still in question. Until the standard has evoked toa steady state, IEEE -488 systems will clearly havethe advantage. The initial GPIB implementationsvar ed greatly between instr intent manufacturers.A few years passed before the user could 3asilycombine several manufacturers' products. Weexpect VXI to follow a similar path.Steve Lekas. Keithley Instrumelts.Cleveland, Ohio.

hardware and software engineering has be-come a complete corrosion monitoring sys-tem operated remotely by computer on aserial cable because of the adverse radioac-tive environment. The system was originallydesigned around the VME cardcage due to itsconvenient size and availability, and at thattime (mid 1987) used a backplane buscustomized for the monitor system. Theemergence of the VXlbus for instrumenta-tion however prompted the company tore -design the corrosion monitoring systemto comply with the newly proposed stan-dards.

"The development of many electronicproducts created a requirement for signaland bus monitoring, interface monitoring,logic state analysis, and system testing"president Tom Reimer told us. "Investmentin fixturing and expensive test equipment forthe research and development process is notusually practical until the product is manu-factured in quantity to support the cost ofthe test equipment, so with this in mind, andto fulfil future needs, we have designedpractical solutions utilizing the new VXlbusproposed standards."

Their VXI Modular Test & Monitor Systemreferred to earlier, is pictured above. Fortruly portable operation, this system may beoperated from a laptop computer. It issoftware driven by an IBM or compatible PC,XT or AT computer. The software graphicallypresents information on the users' computerwith most types of monitors although bestresults are obtained with an EGA monitor.ICs are shown complete with pin -out in-formation. For logic monitoring, signalsmay be labelled on the screen showingaddress, data, and control lines on a bus. Forcable testing, the cable connectors areshown so that in a production environmentquick repair can be made.

National Instruments of Austin, Texas,will supply VXlbus cards that will interfacethe VXIbus to the IEEE -488 bus, as well as

INDUSTRY INSIGHT

software support for external controllers,such as the IBM PC and Apple Macintoshcomputer families, to use the IEEE -488 busfor controlling and monitoring the VXIbus.These products will be supplied to VXIbusintegrators, o.e.ms and end users. Sincemost VXI bus instruments will not haveconventional instrument front panels, soft-ware such as LabView and LabWindows canbe useful because they provide user -

configurable, graphic front panels on thecomputer screen.

They also provide the instrument drivercode for communication between the per-sonal computer and the VXIbus instrument.Linking the VXIbus instrument to personalcomputers provides an ideal way of im-plementing test and measurement systems.LabWindows is an integrated, interactiveapplication software system that runs onIBM PC and PS/2 computers which featuresthe function panel user interface and theinstrument control library. LabView is agraphical system that runs on the MacintoshPlus/SE/II. With a VXI system interfaced to aMacintosh and LabView, a sophisticated sys-tem consisting of several VXI boards fromdifferent manufacturers can be made to lookand "feel" like an off -the -shelf instrument.LabView provides the knobs, switches,

Looking identical to their 53A series ofcard -based instruments, this 73A series pro-totyping system is Colorado Data Systemsfirst VXI product. (CDS is represented in theUK by lnstrumatic UK Ltd of Marlow, tel.06284 76741.)

meters, etc., on the Macintosh screen thatallow the user to monitor and control systemwith the mouse.

National Instruments are represented inthe UK by Amplicon of Richmond Road,Brighton. As one of the five originators of the jointspecification, HP is completely committedto modular instrumentation and is activelyworking on projects that will implementVXI. "Our products will be integrated offer-ings to span the very wide range of instru-ment system needs" is all that Bill Porter of

the Loveland instrument division would say."We are also taking care to ensure full HP-IBcompatibility in our VXI products. Custom-ers will want to mix and match VXI bus andHP-IB instruments in the same test systemto solve their whole test problem." ICS Electronics (San Jose, California)believes that the proposed VXIbus standardwill become one of the major standards formilitary a.t.e. systems in the next four years,with eventual migration into commerciala.t.e. systems after that. "We are currentlyexamining several potential VXI products,some of which will be based on our existingIEEE 488 bus products" says Robert Prosin,vice president of marketing. "One productwe are considering as a joint venture effort isa series of switching modules for audio-to-r.f. signals."

Tailpiece. VXI is not yet standardized bythe IEEE, despite frequent references to a"standard" in the press, but the five -

company consortium of CDS, HP, RacalDana, Tektronix and Wavetek are encourag-ing product development so that evaluationof the first products can be taken intoaccount before the specification is put finallyto the IEEE. The IEEE P1155 subcommitteemet this January to discuss details of thesoftware interfacing elements of the spec.

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INDUSTRY INSIGHT

INSTRUMENTATION

Cover story - frequency and time -interval analyser

Anew type of instrument foranalysing time -varying sig-nals that is a cross between aspectrum analyser and a digi-

tizing oscilloscope has been developed byHewlett Packard. Called a frequency and atime -interval analyser, it provides statisticalanalysis and a time profile of frequency,phase, time -interval and jitter on dynamictransients, repetitive and non -repetitive sig-nals up to 500MHz. The analyser is ahle toreveal phase, frequency or time -intervalinformation on complex signals used incommunications systems, both analogueand digital, in such applications as pulse -to -pulse jitter in p.c.m. systems, timing anddata jitter in electromechanical designs,radar frequency profiling and phase codeddemodulation, frequency -agile radio sys-tems random event and error totalizing,zero dead -time variance measurements, andanalysis of v.c.o. operation.

The patented time sampling technique, or'continuous measurement technology', usesreciprocal counting at rates up to 10 timesper second to continuously track frequency.Because the register counters are not resetbetween measurements, thus eliminatingdead time, count rate can be increased to

10MHz, and by sampling fast enough thetime variation of frequency or time -intervalscan be reconstructed.

The analyser measures carrier signals upto 500MHz for sampling intervals as short as100ns, each sample having a 150ps resolu-tion. A high-speed 1000 -measurementmemory stores the sampled input -signaltiming information from the registers, andsignal processing firmware then reduces thestored data according to the measurementmode selected. The fast measurement rateprovides frequency or phase modulationanalysis - if frequency is sampled oftenenough the plot of samples versus timeshows the modulating waveform.

The new instrument's capabilities in mod-ulation analysis, jitter analysis and frequen-cy profiling should have application in a widerange of activities in electronics and com-munications. In f.s.k., the switching carrieris easily profiled, as is the distribution andmean value of each carrier frequency, andanalysis of frequency overshoots now be-comes possible. Data -to -clock jitter (h.f.errors greater than about 10Hz) in com-munications networks can be characterizedwith the histogram facility, which will dis-play mean and standard deviation of timing

variance. Timing jitter in magnetic or optic-al discs or magnetic tape can be analysedwith the instrument's statistical andgraphical analyses. (Though fuzzy oscillo-scope traces can indicate jitter, the 5371Aprovides statistical analysis with a histogramof frequency or time -interval measurementsto show whether the effects are random ofsystematic.)

The single -shot capability means thatsettling time of frequency hops and random -channel usage on the agile carriers of spreadspectrum communications can be investi-gated, obviously including display of thehopping algorithm. In radar systems, chirplinearity is measured on a cycle -by -cyclebasis in a single pass, and pulse risetime,width and repetition frequency are allmeasurable to within 150ps r.m.s. resolu-tion. Step resolution in v.c.os. as well asovershoot, ringing and settling time are alleasily found from the time -variation plot,and steady-state performance can be mea-sured from the histogram feature. Furtherdetails in April's Insight.

The 5371A frequency and time -intervalanalyser costs £16,730 and is available fromJanuary. Hewlett Packard's enquiry office ison 0734 696622.

Increasing role of distribution in tamor many years, manufactur-ers of electronic componentshave appointed authorizeddistributors to stockhold

their products and offer fast delivery to thecustomer. Test and measurement equip-ment manufacturers have always had adifferent approach to selling. The technicalnature of the products necessitated the useof a highly skilled sales force, demonstratingeach product to the customer. While thisensured that individual customers receivedgood technical presentations, it did not givethe manufacturer as wide a coverage asperhaps he would have liked.

It was in the mid -1970's that companiesfirst began selling test equipment purelyfrom a catalogue, and several high streetelectrical outlets started to stock multi -meters and the like. The reason for thisdevelopment was that the products involvedhad matured to such an extent that themajority of users knew enough about themto make a quick decision on what to buy.This meant that all they were interested inwas the delivery. The first advantage of thedistributor becomes apparent, since theyhold the product in quantities, and are thusable to deliver ex -stock.

Since that time, much low-cost instru-mentation is available almost exclusivelythrough distributors, with the manufacturerhaving very little contact with the end -user.

Several companies, such as Hameg, Thandarand Fluke have built their UK businessesalmost entirely by having a set of stockistsaround the country. In these low-cost areas,a large distribution network gives the manu-facturer far wider market coverage than theycould achieve with only their own salesforce. Probably 40% of oscilloscope sales, upto 100MHz, go through distribution,although the figure is nearer 80% up to20MHz.

The majority of these distributors arethemselves very small, either being highstreet outlets or 'one-man bands' workingout of the upstairs bedroom. Such peopleoperate on very low overheads and often givethe customer discounts, leading to pricewars in the low-cost sector.

The other end of the distribution spec-trum is the larger company supplying abroad range of equipment, with exclusiveagreements on certain high technology,high value equipment. These companieshave grown in the 1980's and operate withlarge catalogues and a technical sales team.It is a sign that the market is becomingbetter educated and aware of products thatsuch operations can exist, since the majorityof sales are made to people approaching thedistributor for a certain product, knowingexactly what it does and only requiring fastdelivery. Thus, distributors offer the cus-tomer the advantage of delivery from stock.

Major manufacturers have also becomeaware of the advantages of having theirproducts available through other outlets.Until a few years ago, it was almost unthink-able that companies such as Marconi Instru-ments or Philips would have their productsavailable other than through themselves.But, as the overheads of a technical salesforce became higher, they looked to certainoutlets to offer a limited range and act as anadditional salesman. A major move by Mar-coni was to appoint Electronic Brokers astheir distributor, so that customers could bevirtually guaranteed delivery of a £19,000spectrum analyser from stock.

This 'top -end' of the distribution market isdeveloping further, and companies areattacking niche markets with more special-ized product ranges. As the rate of technolo-gical improvement gets faster, so productsare maturing in the market earlier, andbecome available through distributors soon-er. Customers have now become more tech-nically aware and buying patterns are chang-ing: the role of the distributor is likely tobecome even greater in coming years. Asthey become more specialized they will offereven greater service to the customer and amore efficient selling effort for the manufac-turer.

Graham Sibley is marketing manager forElectronic Brokers.

RESEARCH NOTES

Using bubblesto spot faulty

memoriesComplex memory chips (or in-deed other devices) can now havetheir faults pinpointed to anaccuracy of 10-6m using a tech-nique developed by StandardElektrik Lorenz in Stuttgart. Itneeds nothing more than millingor etching equipment, a micro-scope and a power supply.

The technique depends on thefact that many failures lead toshort-circuits, latch -ups and thepresence of spurious conductiv-ity. This in turn causes the faultyarea to overheat. Until now theonly way to pinpoint such local-ized overheating has been toemploy infra -red thermographyor liquid -crystal thermography,techniques which are either ex-pensive or imprecise.

What Standard ElektrikLorenz have done is to exploitthe fact that liquids, when heat-ed, form tiny bubbles at pointswhere heat is applied. Just watcha saucepan of water coming tothe boil: it's possible to seethousands of bubbles forming atthe points where most heat isbeing transmitted. To apply thisprinciple to dud chips, the en-capsulation is first removed,either by acid etching or carefulmilling according to whether itis plastic or ceramic. The ex-posed chip is then sprayed with athin layer of some low boilingpoint liquid such as acetone orpropanol. The precise chemicalis immaterial as long as it has awell-defined boiling point and isnon -conducting and non-poisonous.

Under a microscope, power isapplied to the suspect chip,which is scrutinized for bubbles.Under carefully controlled light-ing conditions, a bubble willappear as a black circular spotapproximately 10-5m in dia-meter. Such a spot is relativelyeasy to detect against the back-ground of the chip's structure. Inthe middle of the black spothowever, there is a bright dotwhich pinpoints the fault to anorder of magnitude greateraccuracy. This spot is in realityan artefact that marks the pre-cise centre of the bubble. It is thepoint at which the bubble's sur-

face is parallel to the chip subs-trate and at which incident lightis not diffracted away.

Standard Elektrik Lorenz saythat bubble thermography is asaccurate as any other currentlyavailable technique for analysingchip defects, but is infinitelycheaper. No special equipment isrequired and it takes less than anhour to carry out a comprehen-sive bubble search of the chip.

Newpiezoelectric

polymersPiezoelectric polymer materials,although by no means new, weresomething of a rarity until the1970s. Then it was realised thatthe relatively large piezoelectric(and pyroelectric) properties ofpolyvinylidine fluoride (PVF2)could be used commercially inthe manufacture of mechanicaltransducers and radiation detec-tors. In the former case thematerial acquires an electricpolarization as mechanical stressis applied, this polarization hav-ing a relatively linear rela-tionship to the stress. The poly-mer can thus be used to providean analogue signal in response toa whole range of mechanicalinputs.

Of the various polymers avail-able today, the semi -crystallineforms such as PVF2 are by far themost common. These materialsare also known as electrets be-cause of their readiness to ac-quire a permanent polarizationwhen crystallized in the presenceof an electric field. Because thepolarity can be reversed by thesubsequent application of anelectric field, such materials arealso said to be ferroelectric. Per-manently polarized piezoelectricpolymers find widespread use indomestic electret microphoneswhere their movement relativeto a fixed plate is translated into achanging voltage.

The search for alternative andbetter piezoelectric polymers iscurrently based on the startingpoint of a molecular bond with ahigh dipole moment. Thecarbon -fluorine bond is particu-larly good in this respect, whichexplains its universality. A poly-mer sub -unit (monomer) com-prising these bonds must then

02 0-3

add together with other sub-units to produce a chain capableof molecular rotation in re-sponse to an external field.

Within these constraints re-searchers have been looking atpolyvinyl fluoride (PVF) andpolytrifluoroethylene (PVF:;).Neither is ideal. PVF crystallizesonly with difficulty and PVF3 is abulky molecule that does notrotate easily. Other related sub-stances such as nylon have alsobeen investigated.

In a recent edition of the GECJournal of Research, vol.5 no.3,experiments are reported inwhich a whole range of difficultmaterials and fabrication proces-ses are analysed. Four VF2NF3co -polymers of varying composi-tions were assessed for stabilityand for their use in a particulartransducer application - hyd-rophones. (A co -polymer is onein which different monomer sub-units alternate along the lengthof the molecule.) The paper con-cludes that these recently dis-covered co -polymers open upnew areas of application and ex-hibit superior properties to manyestablished ceramic piezoelec-tric materials. Much researchalso remains to be done on eva-luating the piezoelectric prop-erties of polymers in other che-mical classes -a field that clearlyholds much commercialpromise.

Cadmiummercurytelluride

transistorsTransistor action continues to bedemonstrated in an increasingnumber of exotic and unlikelymaterials. This is the result part-ly of a search for improved prop -

COLLECTOR- EMITTER VOLTAGE

alms but more often than notthrough constraints of integra-tion. It is no use having a circuitelement that shows enhancedproperties if its method of fab-rication makes it incompatiblewith other essential circuit ele-ments. Frequently, however, theincompatibility arises the otherway round. Solid state lasers, forexample, are difficult to inte-grate with their control circuit-ry; so too are transducer ele-ments based on materials otherthan silicon or gallium. Difficul-ties with resistors are discussedelsewhere in this column.

In some cases an extremesolution may be to create newcomponents that are compatiblewith their intended environ-ment, even if this seems a bit likere -inventing the wheel. An in-teresting example of this phi-losophy, described in ElectronicsLetters vol.23 no.24, is the de-velopment of a transistor basedon cadmium mercury telluride(c.m.t.). This material is ex-tremely valuable as an infra -reddetector, for which it has obviousmilitary applications in areassuch as heat -seeking missiles.But to integrate a c.m.t. detectorwith an amplifying device im-plies a c.m.t. amplifying device.

Last year transistor action wasdemonstrated for the first timein c.m.t., but only at low temper-atures. As the temperature wasincreased there were leakageproblems due to high baseminority carrier generation.That situation has now improvedas a result of research by theRoyal Signals and Radar Estab-lishment and Mullard Ltd atSouthampton. At a temperatureonly a little below ambient(263K) they now have a devicecapable of maintaining transis-tor action with a current gain(hfe) of 15 or more. Interestinglyenough, this gain remains un-

04(Nice)

Unusual character-istics of the cad-mium mercurytelluride transistorby Mullard andRSRE.

RESEARCH NOTESchanged as the base is driven intoreverse bias (see curves. A re-verse base -emitter bias of>40p.A is necessary to turn offthe collector current because ofthe thermal generation ofminority carriers within the baseregion. These act as a sort ofcurrent offset.

The researchers believe that,given more development. espe-cially geometry optimization,the c.m.t. transistor has thepotential to become a practicalhigh -gain device suitable for in-tegration into specialist infra -redand other transducers.

How to stopsparks flying

When engineers talk about de-vices being blown up by static,the expression does not usuallyrefer to anything more cataclys-mic than a dead piece of c-mos.However, given the increase inthe use of flammable fluids forcleaning and degreasing, a moreserious hazard could be lurkingaround.

A symposium on electrostatichazards held at a meeting of theAmerican Institute of ChemicalEngineers considered amongstother things what can happenwhen a flammable liquid is car-ried in a partially -filled plasticbottle. One speaker described anincident in which a lab techni-cian began to pour methanolinto a metal can from a plasticbottle that had been carried in aplastic bag. Movement betweenthe bag and the bottle had cre-ated a static charge which had inturn induced an opposite chargeon the methanol. As the metha-nol flowed into the metal can aspark occured igniting the li-quid.

Methanol is particularlydangerous in this respect be-cause it is electrically conductiveand highly volatile. The AICEwarns, however, that any liquidcan become charged up either bybeing transferred from one con-tainer to another or indirectlythrough the walls of a non-conducting container. Even pas-sing through a filter of criticalpore size can effect a significanttransfer of charge.

Care is necessary not only withvolatile liquids that are obviouslyflammable, but even when trans-

ferring chemical powders in andout of metal bins or drums.Because of the friction betweenindividual particles, powders aremore likely to acquire a chargethan liquids. In finely -dividedform they can also be just asexplosive. Serious damage hasresulted in the past from spon-taneous ignition of such unlikelysubstances as custard powder.

Experiments conducted byUnion Carbide using granularpolyethylene have shown thatwhen such material is poundinto a silo there is nearly alwayswidespread discharge as the pow-der settles down. This occursbecause of charge concentrationand results in thousands of mic-roscopic sparks. The finer thepowder, the worse the effect.What can also happen, often withcatastrophic results, is one bigspark instead of harmless micro -sparks. Why this happens is notprecisely known, though it doesdepend on the type of materialand the size of the particles.

Until more is understood ab-out the precise mechanisms ofstatic build-up, the most obviousadvice must be: think before youpour.

Stable resistorsfor gallium i.cs

One of the many problems in thefabrication of gallium arsenidemicrowave integrated circuits isthe design of the humble resis-tor. Jon -implanted or mesa -etched GaAs resistors mightseem the easiest in terms of themanufacturing technology, butsuffer from non-linear behaviourat high electric fields. They alsohave an unacceptably high posi-tive temperature coefficient.Currently used alternatives in-clude nichrome, tantalum nit-ride and cermet, but none ofthese is entirely free from prob-lems of stability of manufacture.

A team working for BritishTelecom's research laboratoriesat Martlesham Heath (Electro-nics Letters vol.23 no.23) reportspromising results from tungstensilicide, a material usually em-ployed in mesfet technology.Tungsten silicide resistors havebeen fabricated on a GaAs subs-trate using r.f. sputtering. A ratioof 1.6 parts of tungsten to onepart of silicon was chosen to give

a resistance of 50-3000./squareand from this material resistorswere etched using a sulphur hex-afluoride plasma. Values of up to9ka were obtained, with highreproducibility and goodtemperature stability. As for longterm stability, a newly -constructed resistor decreased invalue by 1.25% after 1000 hoursat 125°C. A pre -aged one that hadbeen encapsulated by a layer ofsilicon nitride changed in valueby less than 0.1% under the sameconditions.

The BT team claims that itstungsten silicide resistors arecompletely compatible withGaAs i.c. fabrication technologyand superior to alternative formsof resistor.

Medical effectsof power lines

Two recent studies have added tothe tantalisingly inconclusiveevidence on this emotive subject.Each of them in different wayshas unearthed what seems likecompelling anecdotal evidencethat low frequency electric andmagnetic fields do indeed have aharmful effect. The problemfaced by all studies of this sort isthat of establishing a true causalconnection from what. at best,are barely significant statistics.Another difficulty in this particu-lar case is reconciling theepidemiological evidence withlaboratory work showing thatfields much higher than thoseassociated with power lines havelittle or no effect on biologicaltissue.

So what is one to make ofevidence from a British medicalpractice that migraine suffererstend to be clustered near powerlines? Obviously there could besome direct effect of the lines onthe blood vessels in the patients'brains. But why then does itaffect only a tiny minority of thepeople living near power lines?Could it be that the mere sight ofnasty great pylons is enough toinduce migraine in those whoare susceptible to stress? Severalother possibilities suggest them-selves, including pure chanceassociation. As with similarepidemiological problems suchas the speculative link between

radioactive discharges andleukaemia, most of us incline toan opinion based more on emo-tion than on scientific evidence.

For that reason another studyin the USA costing $5 millionwas undertaken to try and estab-lish the true facts. Financed bythe US government, the NewYork electricity companies andvarious charities, it reviewed allthe existing evidence and alsofunded a number of major newstudies. The New York PowerLines Project, now published as a153 -page report, makes interest-ing reading, covering not onlythe 765kV overhead lines thatwere the prime objects of thestudy, but also electric andmagnetic fields in the home andwork place. Diseases looked atinclude cancer, mental illness,strokes, infertility and problemsassociated with fetal and childdevelopment. Studies on isolatedbiological cells were likewise in-cluded.

To summarize such a study ina few words is difficult. Most ofthe individual research projectsreported no effects of concern.No effects were found on repro-duction. growth or development.Several attempts to demonstrategenetic or chromosome damagethat might lead to inherited de-fects or cancer also failed com-pletely. Brain studies showed noeffects of power lines except ahint of a small but consistenteffect on body rhythms thatmight interfere with sleep pat-terns. Experiments on ratsshowed changes in their re-sponse to pain and in their abilityto learn.

One effect of power lines thatthe authors of the New Yorkstudy do believe warrants furtherinvestigation is a possible linkbetween leukaemia and elevated60Hz or 50Hz magnetic fields.Although they admit that moreresearch is necessary before acausal link is properly estab-lished, they claim that only twoof four studies showed any con-nection at all and that the two inquestion are from the samegeographical region. Perhaps ithas something to do with thebirds that sit (sic) on the lines?

Research Notes is written byJohn Wilson.

Speech transposer for radiohearing aids

For some types of deafness, adding a frequency shifter to aclassroom hearing aid brings a marked performance

improvement.

Many people with sensory -neural deaf-ness receive some benefit from con-ventional amplifying aids. But they

may find it difficult or impossible to hearcertain high -frequency speech and othersounds. Such patients usually have residualhearing in the low frequencies but little ornone in the high frequencies, producingwhat is known as a 'ski -slope' hearing loss.Since vowel information is concentrated inthe lower speech frequencies and consonantinformation in the higher speech frequen-cies, hearing loss of this kind tends to impairselectively the perception of consonants - inparticular, fricative and stop consonantswhich have major energy components in thehigher speech frequencies (e.g. from 4kHzto 8kHz). In addition, the perception ofmany environmental sounds, including im-portant ones such as water running, gashissing and the ringing of door bells andtelephones may be greatly impaired. Pa-tients in this group often complain that theiraids amplify but do not clarify speech.

Over recent years, therefore, variousattempts have been made to modify theresponse of conventional hearing aids so asto improve intelligibility for patients withsloping losses. Evaluation studies have beencarried out with various configurations oflow-pass and high-pass filtering, with ex-tended low frequency and extended highfrequency response, with selective ampli-fication (typically of the higher frequencies)and with various forms of amplitude com-pression.

Although a number of studies have sug-gested modifications that may be ofbenefit", in general the effects of suchmanipulations have been found to be com-plex and the findings inconclusive3.4.5.Moreover, none of these techniques can beexpected to restore missing high frequencyinformation in cases where its loss is verysevere or profound - for instance, where theaverage loss at 4kHz, 6kHz and 8kHz exceeds80dBb. Furthermore, in cases where nomeasurable hearing in the higher frequen-cies exists, such techniques become in-adequate in principle. For these patients,therefore, frequency transposition (i.e. con-verting the non -detectable high frequencysignals to some detectable low frequencyform) may be an appropriate alternative.

There have been many attempts over thelast 20 years to produce devices whichaccomplish such conversions' but few ofthese have proved to be superior to conven-tional amplifiers. In some ways this is hardly

B.J. SOKOL AND MAX VELMANSsurprising as the vast majority of thesedevices produce versions of speech whichsound grossly distorted both to those withnormal hearing and to the hearing impaired.Furthermore, the recoded high frequencyinformation provided in the low frequenciesmay in fact be treated by the ear/brainsystem as noise and may also interfere withlow frequency information already availablein the residual hearing range8.9".

During the last decade, however, a fre-quency recoding device (Fred) has beendeveloped whose output is highly speechlikein character' s . The Fred system subtracts aconstant 4kHz from signals in the 4-8kHzregion, thereby mapping them on to the0-4kHz range. This transposed informationis then combined with conventionally ampli-fied speech in a second, non -transposingchannel. One realization of the Fred systemin the form of a radio hearing aid is outlinedbelow. Before turning to this, however, it isworth noting the effects of the recodingoperation on both speech and environmen-tal sounds.

EFFECTS OF FRED

In speech, very little energy related to vowelsounds occurs in the region above 4kHz.Vowels, therefore, remain largely unaffectedby the transposition process. But fricativesand stop consonants do have significantenergy components in this region, and Fredtransposes these in such a way that theyblend with consonant cues that already existin the low frequency range (transmitted by aconventional amplifying channel).

Recoded speech sounds much like normalspeech. To a normal hearing person, howev-er, transposed speech cues are redundantand phonemes affected by such cues areunnecessarily emphasized. For those withhigh -frequency hearing loss, the subjectiveeffects vary. Where the loss is severe, re -coded cues may improve the identifiability ofconnected speech. If the high frequency lossis profound, this improvement may be con-siderable, because the recoded cues may fillwhat would otherwise seem to be gaps in thespeech stream. On the other hand, a patientwith a relatively flat hearing loss may receivelittle or no advantage from transposition,since high -frequency cues can, in general,be made audible for such patients by the useof a conventional amplification technique.

Transposition also affects a range of en-vironmental sounds, i.e. sounds with signifi-cant energy in the region above 4kHz. These

include natural sounds such as rain, bird -song, wind in the trees, etc., sounds aroundthe house, baby cries, doorbells, telephonesand so forth. These not only provide in-creased contact with the environment butmay also be important for safety or forcommunication. By and large, transposed.environmental signals sound very similar tothe originals (to a normal hearing person)although their lowered frequency may, insome cases, give them the appearance ofcoming from a larger object - keys janglingmay, for example, sound more like cowbellsand water running into a glass may appear to -be running into a bath. With a little practice,such sounds are easily identified.

In principle, transposition may improvethe discrimination, identification and arti-culation of various phonemes and it maytherefore help in the speech training ofsensory -neural deaf children. For example,transposed information may improve theirability to discriminate between soundswhich are otherwise commonly confused,e.g. z/v, t/k. To test such claims, however, itis necessary to compare the effects of con-ventional amplification on learning to dis-criminate such sounds with the effects ofadding transposition to conventional ampli-fication. Furthermore, the children involvedin the present study were already equippedwith radio hearing aids for classroom use. Itwas necessary, therefore, to construct anadapter for these aids so that they could beused either as a conventional amplifier or asa frequency transposing device.

DEVISING A TRANSPOSING ADAPTER

The engineering difficulties in making atransposing adapter for radio hearing aidsresulted from physical and economic con-straints. The children were already requiredto carry radio receivers and so there was arestriction on size and weight. Sixty unitshad to be produced in little time and within alimited budget.

At the two schools designated for thetrials, the partially -hearing units were pro-vided with different types of very expensiveradio hearing aids. It was uneconomic toreplace or even retrofit these units, and so anearly decision was made to find a means toadd to the existing apparatus without mod-ifying it.

It would have been easier and cheaper toapply transposition to the transmitted sig-nals rather than the received signals becauseteaching is often a one -to -many coin -

munication and so fewer transposers wouldhave been needed. Transposition beforetransmission is advantageous because itreduces bandwidth and enables the narrow -band f.m. channel to carry a wider effectivespeech range. Furthermore, the placing ofprototype equipment in the care of adultteachers rather than children might haveincreased reliability.

This desirable solution ran into problems.however. Inputs to the children's hearingaids could come from a local microphone aswell as from the radio channel, and this'environmental' signal could not of coursebe transposed at the teacher's transmitter.In addition, the design of the experimentrequired students to have identical appar-atus, yet half of them at any time had to be acontrol group without transposition. Ifteachers were to transmit transposed sig-nals, the need for a control group wouldrequire them also to transmit non -transposed signals simultaneously onanother channel. That would have meant theunacceptable use of different -coloured re-ceiving crystals which would have identifiedthe control and test groups, and it would alsohave required more frequency channels thanwere available.

Thus it was necessary to overcome theproblems of providing identical transposersfor each student and to fit these withinvisible on/off control.

The transposer connection had to be atthe output terminal of the radio receiverhearing aids to achieve transposition bymeans of a non-invasive jack -socket connec-tion. This arrangement also allowed trans-position of both radio and environmentalsignals. However then the transposers had tomatch or duplicate the output impedanceand levels of the radio receiving hearing aids.

Both types of radio receivers were de-signed to drive multi -turn inductive loops,to be worn like necklaces, that could coupletheir outputs magnetically to normal post -aural hearing aids. These loops require 2Vpeak drive and have impedances of about 100ohms.

From the block diagram (Fig.1), it is clearthat the transposer output must be added tothe non -transposed audio output. This non -transposed output was already provided atsufficient power level by the radio receiverhearing aid, so an ideal solution in energyterms would be to place the transposedpower in series with the receiver output andprovide extra output only for transposedsignals. To achieve this the transposer out-put stage would need four active elements ina full bridge configuration (Fig.2). With thisarrangement, even when the main channelhad large signal currents flowing, only basedrive currents would be needed to drive thetransposer output to zero, if there was notransposed signal.

In the event a compromise circuit (Fig.3)was used instead. This was due to constraintson space within the transposer units and tothe greater importance of quiescent cur-rents than running currents because of thevariable level and intermittent nature ofspeech.

The energy budget was saved by the verylow quiescent current of the audio output

Fig.1. Transposer -type hearing aid.Sound components above 4kHz aresuperimposed on the 0-4kHz compo-nents. This treatment improves intelligi-bility by adding emphasis to speechconsonants and other sounds.

Radiohearing

Fig.2. Modifying a radio hearing aidusing a full bridge transposer outputstage.

Feedbec,,

Fig.3. Final version of the combine-. Theop -amp alone supplies the load currentfor outputs of less than 700mV.

stage. This is a crude current -dumpingcircuit: an op -amp delivers small outputsitself, but for higher outputs it supplies driveand difference signals to control and correctthe transistors. The output transistors re-main cut off for signals whose peaks do notturn on their base -emitter junctions. Evenwith larger signals the transistors have adead zone between the drive levels of ±0.7V.This dead zone of course allows this outputstage to operate with no more quiescentcurrent than the op -amp alone, but on theother hand guarantees crossover distortion.The problem in this case was effectivelyeliminated because the entire output stagewas used as part of a low pass filter.

Low power op -amps, a high quality mono-lithic multiplier, nine poles of filtering(some to compensate deficiencies of theradio channel), and the special output stagecompleted the design of the adapters.

RESULTS OF THE STUDY

At the time of writing the results of the studyare still being analysed. But the initialfinding is that Fred transposition may in-deed improve children's ability to discrimin-ate amongst and to produce transposedsounds. Whether it does so, however, de-pends, at least in part, on the nature of thechild's hearing loss and, in particular, that athigh frequencies. Children with a severe orprofound loss in the high frequencies (anaverage loss of 71dB or more averaged over4, 6 and 8kHz) are likely to benefit fromtransposition. But children with mild ormoderate losses at these frequencies copejust as well (or better) with conventionalamplification.

It is clear, furthermore, that requiringchildren to wear a module additional to theirbody -worn receivers causes considerablepractical difficulties. This was particularlytrue of the school where a binaural systemwas used and therefore two additional mod-ules were required. For everyday use itwould be necessary to incorporate the Fredcircuitry within the receiver of the radiohearing aid.

References1. Lippman, R. (1980) Review of research on the

selection of frequency -gain characteristics forhearing aids. American Otol. Rhino!. Laryngol.(Supplement), 89, pp 79-83.

2. Skinner, M.W. (1980) Speech intelligibility innoise -induced hearing loss: Effects of highfrequency compression. J. Acoust. Soc. Amer..67,111. pp 306-317.

3. Bess, F.H. and Bratt, G.W. (1979) Spectralalterations of hearing aids and their effects onspeech intelligibility. In Larsen, Egolf. Kirlinand Stile (eds.) Auditory and Hearing Prosthe-tics Research. Grune and Stratton, N.Y., pp287-311.

4. Braida. L.D., Durlach, N.I., Lippman, R.P.,Hicks, B.L., Rabinowitz, W.M. and Reed. C.M.(1980) Hearing Aids -A review of past researchon linear amplification, amplitude compress-ion, and frequency lowering. ASHA Mono-graphs. No.19, pp 1-115.

5. Villchur, E. (1978) A critical survey of researchon amplitude compression. In Ludvigsen, C.and Barfod, J. (eds.) Sensorineural hearingimpairment and hearing aids. Scand.Audiol.Suppl., 6, pp 305-314.

6. Velmans, M. and Marcuson, M. (1980) Aspeechlike frequency transposing hearing aidfor the sensory -neural deaf. Report No.1 to theDepartment of Health and Social Security.,Contract No. WE 1049/84. pp 1-227.

7. Risberg, A. (1969) A critical review of work onspeech analysing hearing aids. IEEE Transac-tions on Audio and Electroacoustics vol. AU -17no.4, pp 290-297.

8. Velmans. M. (1973a) Speech imitation in simu-lated deafness using visual cues and 'recoded'auditory information. Language and Speech.16, pp 224-236.

9. Velmans, M. (1974) The design of speechrecoding devices for the deaf. Brit. J. Audio!., 8,pp 1-15.

10. Velmans. M. (1975) Effects of frequency "re -coding" on the articulation of perceptivelydeaf children. Language and Speech. 18. pp180-194.

11. Velmans, M. (1973b) Aids for deaf persons.British Patent Office, No. 1340105.

Multiprocessor systemsIn this illustration of a multiprocessor system, two 8080processors running synchronously produce economical

hardware with high performance.

Some microprocessors are not fast orpowerful enough to keep up withdemanding real-time applications. An

alternative to choosing a faster and muchmore expensive device is to use many cheapmicroprocessors working in parallel. Havingeach processor executing a different taskcompensates for the slow processing speed:

In a synchronous multiprocessor system,each processor takes control of the commonbus whenever it requires it, independently ofthe other processors. Synchronous bus con-trol is achieved by dividing the bus -controlcycle into equal time slots, each of which ispermanently assigned to one processor.

Last month's article outlined various waysof connecting microprocessors in a multi-processor system. This article is a specificexample of how two economical eight -bitprocessors can work together efficiently overa common synchronous bus.

A block diagram of this system was shownlast month. Output of the 18.432MHz cen-tral clock generator 4:0 synchronizes the

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Fig.1. Processor control signals modifiedto allow two processors to operatetogether. In this synchronous system, 4,1and (1.2 clocks of each microprocessor areshifted in relation to each other so that theprocessors access the bus alternately.

clocks of both processors with the multiplex-ing operation of their buses over the com-mon bus. It feeds the circuit producingphase -shifted clocks 011,2) and 401,2),and control signal SELECT.

Figure 1 is the system timing diagramshowing that each machine state takes 16 CKpulses i.e. 868ns. Within each machinestate, 4)1 is generated during the first twocentral -clock pulses, resulting in a pulsewidth of 108ns, and 4)2 is generated from thefourth CK pulse until the eighth, resulting ina pulse width of 271ns. Remaining central -clock pulses in each machine state are usedto produce 4)1 and 4)2 clocks for the otherprocessor in the same manner.

Signal SELECT determines which processoris to gain the control of the common bus.When it is low, the first processor controlsthe bus, and when it is high, the secondprocessor controls the bus. Each processoris allowed to control the bus during the firsttwo CK pulses ahead of its machine state, andduring the first six cm pulses of its machinestate. This timing allows each processor tocontrol the common bus for about 108nsahead of the rising edge of its 4)1 clock pulse,and for about 325ns following that edge.

Like single -processor systems, eachmicroprocessor in this multiprocessor sys-tem has an associated circuit for producing

Fig.2(a). Chip -select decoders for the com-mon memory, opposite page top. (b) data -bus multiplexers, opposite page bottom.and (c) clock drivers.

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memory and i/o control signals. The multi-processor system controller combines thesecontrol signals to produce common bus -control signals. Overlapping of combinedsignals can cause disturbed system opera-tion. To prevent this, signals from eachsystem controller are activated only during

Status byte availableon common data bus

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the time slot of the bus -control cycle of theappropriate processor.

Each processor's system controller de-codes the status byte together with data -businput signal DBIN and data -write signal NRfrom each c.p.u. Controlling the periodduring which DeiN and NN signals are active

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affects the duration of activation of theoutput signals from both system controllers.This is achieved in this design by control -signal alignment modules which act uponottiN and 1sK signals of each processor, andproduct 1)81N* and me modified signals.These signals are activated only during thebus time slot of their associated processor.

Central clock CK is a crystal oscillatorrunning at 18.432MHz whose output feedsphase -shift generator IC1.5. Four -bit binarycounter ICI produces the 16 states of eachbus -control cycle from clock CK. Output ofIC, is fed to open -collector decoders IC2.3 toproduce the clocks of both processors,Fig.2(c). During the first eight states of thebus -control cycle, IC2 is activated to producethe first processor's 4)1 clock during the firsttwo states by wiring together 2Y,, and 2Y,outputs of IC,, and the 4)2 clock of the sameprocessor between the fourth and eighthstates by wiring 2Y3 and I Y,,.:, of

Decoder IC3 is activated during the nexteight states of the bus -control cycle byfeeding the inverted most -significant bit(Q II of IC, to its I G and 2G inputs. Duringthese eight states, the clocks of the second

processor are generated in a similar way tothose of the first. Pull-up resistors areconnected to the wired outputs of IC,.;,resulting in t.t.l. compatible signals. Out-puts of IC2.3 feed open -collector invertersICA.5 which produce processor clocks4)1(1,2) and 4)2(1,2) at mos levels, and4)1(1.2) at t.t.l. levels.

Signal SELECT, which is responsible forswitching both processors on to the com-mon bus, is produced during the seventhstate of the bus -control cycle until thefourteenth. This is achieved by decoding thethree most -significant bits of counter IC,using Nand gates IC7a,h, And gate andinverter IC,;,.

The SET input of D -type bistable deviceis low at the seventh state, while the

CLEM input is high causing sEi.Ecr to be sethigh. At the fourteenth state, the SET input ishigh while the CLEAR input is low, causing theSELECT signal to be set to low. When sm.F.cr islow, the first processor controls the bus andwhen it is high, the second processor con-trols the bus.

Signal -alignment modules of both proces-sors are composed of D -type bistable devices

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And gates IC8b., and inverters IC5e.f.These modules modify oitiN and signalsof both processors to fit in each time slot ofthe associated processor. Signal intiN isnormally produced by the processor duringthe 4)2 clock pulse and lasts until the next 4)2pulse. For the first processor inliNill is fed toD input of and the bistable device is

clocked by 4)2(1) at t.t.l. level causing signalImmo to be latched at the falling edge of the4)2(1) pulse.

Output Q of IC,,,, is Anded with theinverted SELECT signal at !CFA output. generat-ing the aligned miNiu", Fig.2113). At thenegative edge of the following 4)2(1) pulse.intiNo I will be low causing bistable to bereset, and thus insislol* goes low.

The same method is applied to DisiN121 ofthe second processor but in this case ELECT IS

applied as a clock to IC Note that in spite

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of the availability of si--.Lr at the Q output of117,2,,. the inverter IC5, is used to invert the

r signal prior to Anding it to the latched',BIN( I. signal. This is because the suEcr signalis used for latching oiriNd and there must bea delay before it is reapplied to align thelatched state of mum h. Inverter IC 5; providesthis time lag. The same applies to bothprocessors.

Signal is normally generated from theprocessor during rtils clock pulse, and lastsuntil the next pulse. For the first processor

is inverted by IC5. and then fed toD -type bistable IC,,, as clock input. At thenegal ive edge of y RII 1, a binary one is latchedat the Q output of this bistable device.Whenever the second processor is controll-ing the common bus, output of IC71, goes lowfor the duration of the seventh state of thebus -control cycle, causing IC,,, to becleared. Thus aligned signal wro 'I* is acti-vated only during the time slot of the firstprocessorwheneveruRl II is active.

The same applies to i2i of the secondprocessor but in this case, the output of IC7is used to clear bistable IC, lb whenever thefirst processor is controlling the bus.

System controllers for the first and secondsections are composed of 17. For thefirst processor. ICI:, is a four -bit latch whichsaves part of the status byte generated by thefirst processor when it is connected to thecommon bus. At the first machine state ofeach machine cycle of the first processor.SYNCl1 goes high and feeds And gate 1C%,together with 6( 1)t.t.I.: output of this gatelatches the status byte of the first processor.

Only bits 11).t6.7 of the status byte are usedto produce the necessary control signalsINTAI I I. Di I I. NIDIRf I r. MOM( and wriThe first three signals are produced byAnding the latched least -significant bits ofthe status byte with the aligned BIN i I1*

signal. The last two signals are produced byadding the second and fourth latched statusbits with the aligned 11* signal. Thesystem controller of the second processor issimilar to that of the first.

In the multiprocessor system controller.control signals of both processors arealigned with their associated c.p.u. timeslots so Oring the corresponding controlsigna's of both system controllers results incommon bus -control signals R 1""f and

MF.IW. Open -collector Nand gates of IC15 17perform these Or functions.

Data bus multiplexing is done byThe multiplexer is bidirectional in that itswitches the data buses of both processors inthe outward direction to the common buswhenever the time slot of the correspondingc.p.u. is due. Multiplexers IC performthis function whenever 5T* is active. andthe switching process is controlled by SELECTwhich feeds the select inputs of both i.cs.

Also in the inward direction, the multi-plexer switches the common bus to eitherprocessor data bus depending on the currenttime slot. Drivers IC.,, .1 perform this func-tion according to 21* states.

Components IC .1.7 form the address -busmultiplexer. It is a unidirectional multiplex-er which switches the address buses of bothprocessors at the corresponding time slotsunder control of the I signal. Fig.3.

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[SATELLITE SYSTEMSUplink stationfor UK's d.b.s.

Programmes and spacecraft con-trol signals will be transmitted toBritain's direct broadcastingsatellite from an earth station atChilworth, Hampshire, aboutfour miles north of South-ampton. The IBA is responsiblefor designing, building and oper-ating this uplink station. Con-struction work is now goingahead on the site, which lies nearthe M27 motorway, and the in-stallation is expected to be com-pleted in October 1988.

Brian Salkeld, the IBA's Headof Satellite Engineering, gave anoutline of the uplink arrange-ments at a recent IEE lecture onthe forthcoming d.b.s. service.Sited in fairly open country, thestation is being landscaped sothat it will not be an environ-mental eyesore. Like all IBAtransmitters it will operate un-attended, though office accom-modation is being provided.

Four parabolic antennas willbe installed. A pair of these, witheight -metre reflectors, will beused for transmitting program-me signals to the satellite in the17.3 - 18.1GHz uplink band, oneacting as the main antenna andthe other as a redundant spare.Step -tracking will automaticallykeep the antenna beam pointedat the satellite in its 31°Wgeosynchronous slot.

The third antenna will be fortracking, telemetry and com-mand (t.t.c.) and will operate inthe 14 - 14.5GHz band. Finally,the fourth antenna will be usedfor testing and t.t.c. of BSB'ssecond spacecraft held in an in-clined storage orbit as a spared.b. satellite. Having this fourthantenna available means that thespare satellite can be tested at thesame time as the main one isoperating.

As already reported, the trans-mission standard to be used isencrypted D-MAC/packets (seeSeptember 1987 issue, p.928).Incoming baseband video signalswill be in component form togive compatibility with the CCIRworld digital coding standard forstudio equipment and to allowflexibility for future develop-ments. Each baseband signal inthe three programme channels(4, 8 and 12 in the WARC-77plan) passes through a D -MACencoder and subsequently theD -MAC multiplex frequency -

modulates the appropriate car-rier. Details of the carrier fre-quencies and digital audio sys-tem were given in the September1987 issue. Finally, each mod-ulated carrier passes through ahigh -power r.f. amplifier andinto a combiner, which sends allthree signals via waveguides tothe two 8m uplink antennas.

The specified uplink e.i.r.p. is84dBW. On being questionedwhether he didn't consider an8m antenna something of anoverkill for the task required, MrSalkeld replied that this size wasrequired in order to give thenecessary power flux densityover the whole of the geostation-ary slot area, allowing for thepermitted satellite movementwithin it. An additional safetymeasure to ensure reliability ofservice will be a transportableuplink terminal available to thestation.

During 1988 the IBA hopes tobe able to provide some D -MACtest transmissions, both from aterrestrial source in the Londonarea and from a satellite.

Further details of the satelliteitself were given in this lecture.The Hughes HS376 was chosenby BSB mainly because of thismanufacturer's ability to deliver,in orbit, in the required time oftwo years (by August 1989).Other spacecraft considered atthe time included designs byBritish Aerospace. Eurosatellite(manufacturer of Germany's TV -Sat 1 and France's TDP-1) andRCA Astro-Electronics.

The HS376 is required to pro-vide three operational transpon-ders but will carry six separatechains of equipment throughwhich any of the three channelscan be switched, thus giving a6 -for -3 level of redundancy. Asshown by earlier experience, themost critical part of the high -power d.b.s. transponder is thetravelling -wave tube amplifier.Each 110W r.f. amplifier will infact be formed by two 55W t.w.tsrunning in parallel from a com-mon power supply.

These tubes are made byHughes themselves and werechosen by BSB because of theircurrent reliability record both inspace and in simulated spaceconditions on the ground. Some40 are operating in space at themoment: 32 of these have beenrunning for 11/2 years; and 198have been ordered for varioussatellites including the new In-telsat VI, Anik E (Canada) and

Eutelsat 11 spacecraft.After launch on a Delta rocket

from Cape Kennedy, USA, inAugust 1989 the first HS376satellite is expected to be readyfor broadcasting by Christmas ofthe same year. Mr Salkeld saidthat the e.i.r.p. should be about61 - 62dBW in the London areaand about 59dBW at theperiphery of the UK coverage.With the resulting power fluxdensity, small receiving dishes of30 - 40cm diameter should beadequate to obtain good signalstrength.

Bert Horlock, an engineeringconsultant to BSB, was ques-tioned about methods to be usedfor collecting subscription pay-ments for use of the d.b.s. ser-vice. (Initially it will be financedin a 7:1 ratio of subscriptions toadvertising.) He said that thepay -per -view method would beextremely difficult to put intopractice and that technical solu-tions were very much dependenton business decisions which hadto be made first. Discussions onwhether local authority planningpermission would be required forinstalling the small receivingdishes were speculative and in-conclusive.

Digital soundfor Hong Kong

BBC External Services recentlyopened a new sound broadcastrelay station at Hong Kong. Likeother relay stations in the worldnetwork, it now receives a digitalprogramme feed via satellite.This gives much better soundquality than the old method ofre -broadcasting short-wavemulti -hop transmissions fromthe UK and is cheaper than air -freighting tapes of non -topicalprogramme material.

From London the programmefeed signals are sent to BTI'searth station at Madley andthence to Hong Kong via anIntelsat V comsat at 63°E abovethe Indian Ocean. Analoguespeech and music waveforms aresampled at a rate of 14.2kHz,then encoded into 11 -bit num-bers and companded down to9 -bit numbers. The resultingI28kbiUs stream digits mod-ulates a 70MHz carrier byquaternary phase shift keyingand this signal is upconverted tothe 6GHz satellite uplink fre-quency. The downlink to the

Hong Kong earth terminal is at4GHz. In a 36MHz comsat trans-ponder, which will carry 800telephony channels, one BBChigh bit -rate programme feedtakes up the bandwidth normallyrequired for two 64kbit/s s.c.p.c.telephony channels.

Overall, the low -noise satellitecircuit to Hong Kong has anaudio bandwidth of 50Hz to6.4kHz. Distortion is 1.2% atkHz zero level.

Kicked upstairsWhen geostationary satellites be-come defunct or obsolete theirowners remove them elsewhere,if possible, to make more posi-tions available in the preciousorbit. This has now happened tothe last of the Intelsat IVspacecraft. Comsat F-1 of thatgeneration has been taken out ofservice by the international co-operative and propelled from itsslot at 50°W to a higher altitude,some 280km above the geosta-tionary orbit. It had been inoperation for 12 years.

Such a process depends, ofcourse, on there being enoughfuel left for the reaction -propulsion thrusters. It's a tri-bute to the manufacturer andoperator that sufficient fuel re-mained in the comsat after sucha long period of service.

OU video forschools

Communications and remotesensing satellites are among thetopics included in a video cass-ette lecture produced by theOpen University for use inschools. Called "Space at Work",its purpose is to give childrensome idea of what it would be liketo work in this sector of industry.Other subjects dealt with areequipment testing at the Euro-pean Space Technology Centre,Netherlands. and the space ex-hibition gallery at the LondonScience Museum.

Supplied with support notesand priced £28.75. the videocassette is available from the OUat the following address: ASCO,PO Box 76, Milton Keynes, Buck-inghamshire MK7 6AN.

Satellite Systems is written byTom lvall.

LANGREX SUPPLIES LTDClimax House, Fallsbrook Rd., Streatham, London SW16 6ED

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-TELECOMMS TOPICSGEC Plessey

TelecomsThe combined GEC Plessey tele-communications company isplanned to begin operations ear-ly this year. Study groups arealready finalizing the market andproduct strategy. While GEC Pri-vate Systems Group (PSG), adivision of GEC Telecommunica-tions, has just announced majoradditions to its iSLX integratedservices p.a.b.x. product range, itdoes not appear that these willform part of this internationalstrategy - especially as Plessey'sISDX is already achieving exportsuccess.

PSG has extended the switchrange downwards to provide 80to 600 extensions whilst still, itclaims, matching the perform-ance of the larger systems. "Wenow have switches to suit anyuser" says Mike Bateson, thedivision's marketing manager.Larger switches in the familyhave been significantly upgradedso that the biggest in the range

now support over 5000 ex-tensions and 35 000 busy -hourcall attempts.

The iSLX is based on SL -1technology licensed by GECfrom Northern Telecom. Accord-ing to Brian Meade, PSG's man-aging director, the Group doesnot have "specific rights toEurope" but exports mainly on aspecific project basis. He pointedout that around is requiredfor territorial software as well asan infrastructure being neededto support operations. As theseare all up -front costs there is amajor disincentive to export.

While agreement would haveto be reached with NT prior toexporting the iSLX. there is nosuch constraint with respect toPlessey's ISDX which uses in-house technology. Possibly 10%of its sales go to export.

First pocketabletelephone

Libera Developments Ltd.formed to develop productsbased on the recently publishedUK CT2 standard for second -generation cordless telephones,has announced its Zonephonepersonal portable telephonetogether with associated basestations for both private and pub-

lic access. Ferranti will manufac-ture the Zonephone equipmentunder a UK exclusive licence. Inaddition, agreements coveringthe same equipment have beensigned with two French com-panies, Secre and Alcatel Thom-son Radiophone.

In the home or office,Zonephones will operate (in con-junction with a book -sizedsingle -line base station) as adirect replacement for the con-ventional handset, with a rangeof around 200 metres.

On the move, the same hand-set can access multi -channelbase terminals situated at air-ports. railway stations and otherlocations used by the public.

These base stations, which areto be linked into the p.s.t.n.,create a radio microcell called aPhonezone in which anyone witha Zonephone will be able to makean outgoing telephone call. Thecall charge, expected to be set atabout the same unit cost as for apublic payphone, is billed to thesubscriber's Zonephone accountso that the user is spared theneed for coins and queuing.

Global e-mailThe first around -the -world, con-tinuously available electronicmail demonstration, linking theworld's leading computer com-panies in the USA. Australia andEurope was held at the Compecshow in London. It offered X.400messaging and file transfer, ac-cess and management.

EurOSlnet, the EuropeanOpen Systems Interconnection(OSI) association. has forgedlinks with similar organisationsin the USA (OSINET) and Austra-lia (OSICOM) and has carried outinter -operability testing overseveral months to ensure that

participants adhere to the samestandards - and not differinginterpretations of the standardsas is frequently encountered atpresent. It is intended that thiswill be a permanent demonstra-tion, continuing 24 hours a day,as a resource to be accessedanywhere in the world to showwhat is practical in the real worldof multi -vendor communica-honsusing(iSlprodtkls.

C&W gettinginto Japan

The Japanese Minister of Postsand Telecommunications,Masaaki Nakayama, has said thatlicences to operate an interna-tional telecommunications busi-ness will be issued to the consor-tium in which Cable and Wire-less is a major partner. Its mem-bers have been campaigning forthis for the past two years. Whenformal approval, expected beforethe end of the year, is granted.C&W will be able to participate inthe potentially lucrativeJapanese market.

BICC optocable factory

BICC Cables has opened a £15Mplant which it claims is the firstfactory in Europe purpose-builtfor the production of fibre opticcables. At the opening ceremony.Sir William Barlow, chairman ofthe BICC Group, said that thecompany's manufacturingcapacity in fibre optic cables wascurrently half a millionkilometres per year but that itcould be expanded greatly whenneeded.

Mercury tocarry Vodafone

trafficMercury Communications andRacal-Vodafone have signed anagreement for the former to de-liver both national and interna-tional calls from customers ofthe latter's cellular radio net-work. By using Mercury's net-work, Vodafone will benefit fromhaving. for the first time, achoice of carrier to deliver calls.This also means that an increas-ing number of calls by Vodafone

customers will be carried fromend to end on digital networks.

European travelnetworks

Multi -carrier travel reservationsystems Amadeus and Galileo aresetting up their operations cen-tres in Germany and UK respec-tively.

The former, founded by AirFrance. Iberia, Lufthansa andScandinavian Airlines System todevelop, market and operate anindependent and neutralEuropean -based, global traveldistribution system will have itsoperating centre in Munich,West Germany while Galileo,consisting of Aer Lingus, Alitalia,British Airways, British Caledo-nian. KLM, Swissair. TAP AirPortugal and Covia. the UnitedAirlines subsidiary, is to estab-lish its world headquarters inSwindon.IViltshire.

Terminologicalinexactitudes

"TMA Preferred Terms for Tele-phone Systems Facilities" is thetitle of a booklet prepared by theindependent consultancy Inter-connect Communications. En-dorsed by the Telecommunica-tions Managers' Association.members of which are the majorUK users, and sponsored by anumber of suppliers, the bookletis primarily addressed to tele-phone or telecommunicationmanagers and other purchasersof business systems.

Significant confusion existsbecause there is no commonlyaccepted terminology to describethe facilities which may beoffered by modern p.a.b.xs. In-deed, different suppliers may usethe same term for incompatiblefeatures. The booklet will enableusers and those within the indus-try to compare and contrast theTMA-preferred terms with thefeatures on actual products.

The booklet may be obtainedfree of charge from: Intercon-nect Communications (Consul-tants) Ltd, Merlin House, LowerChurch Street, Chepstow,Gwent. NP6 5H.1, tel. 02912-70425.

Telecom Topics is compiled byAdrian Morant.

Pioneers14. Alan Dower Blumlein (1903-1942):

the Edison of electronics

During his working life he accumu-lated 128 patents, roughly one everyseven weeks. M. G. Scroggie has

called him the greatest circuit designer andoriginator ever. Sir Bernard Lovell saw himas one of the best electronics engineersBritain has produced. To a few electronicsenthusiasts Blumlein is a legend, to mostand to the general public he is unknown.

Hardly any of his inventions (some ofwhich were team work) bear his name. Theycovered telephony, measurements, audio,television, time -division multiplex andradar. Many of them, alone, would havegranted him renown.

Alan Dower Blumlein was born on 29June, 1903 at Hampstead in London, the sonof Semmy Joseph Blumlein, a French min-ing engineer, and Jessie Dower, the daugh-ter of a Scottish missionary. His parents metin South Africa but had settled in Londonwhere Blumlein spent most of his childhood.

British subject.At five Alan Blumlein began prep school

which, years later, he still liked to visit. Itwas on one of these visits that he met hisfuture wife Doreen. They were married in1933 and had two sons, Simon and David.

At primary school he was allowed con-siderable freedom in his choice of studiesand it has been said that at the age of twelvehe "could not read, but knew a lot aboutquadratics"I .

Subsequent schooling improved his read-ing but perhaps there was a legacy. In 1924one of his few published papers was returnedwith the request that the authors "go care-fully through it, to rectify errors and im-prove the English".

A year earlier he had graduated with afirst-class honours degree in heavy electricalengineering from the City and Guilds Col-lege, part of the Imperial College, London.He remained at the College as a demonstra-tor working with Professor Edward Mallettwho was running a telephone engineeringcourse. Together they devised a method ofhigh -frequency resistance measurement. Itwas the publication of this work that led theIEE to demand that they "improve theEnglish". They must have done so, for thefinal version was awarded a premium. Blum-lein was just 21 years old.

TELEPHONE ENGINEERING

In September 1924 Blumlein's industrialcareer began when he joined InternationalWestern Electric (now part of STC). Tele-phone networks were growing nationally

W.A. ATHERTON

and internationally and his first task was tolook at interference caused by electric powerlines. His boss. John Collard, "at first foundhim somewhat raw and "a difficult person totake to meetings". He could also be veryrude, having little patience with anyone lessbrilliant than himself and being intolerant tothose who would not work all hours as hedid. Time mellowed him, however, andaccording to Collard, "he acquired a certainamount of tact"' I.

Thorn -EMI Central Research Laboratories

Philip Vanderlyn remembers the sameman at EMI, but twenty years on, quitedifferently. "He would keep in daily touchwith all the work in the laboratories, and hewould talk with the most junior of us asequals without ever making us conscious ofour lack of status, which was good for ouregos and even better for our technicaleducation. In this task of training his staff hehad unbounded patience."2

Two years after joining InternationalWestern Electric Blumlein was asked tosolve the problem of crosstalk in telephoneloading coils. His success brought him abonus of £250, which was /25 more than hisstarting salary. The work also led to his firstpatent (with J.P. Johns) and to the first of hismany inventions: the tightly -coupled induc-tive ratio -arm a.c. bridge (above). One of theits uses was for measuring small capaci-tances in the presence of much biggercapacitances to earth, but Blumlein was

Tightly -coupled inductive ratio -arm bridgecircuit, 1928: Blumlein's first invention.The coils were bifilar-wound.

forever finding other applications. Duringthe war he used it as an aircraft altimeter.

AUDIO RECORDING

Blumlein was soon looking for wider hori-zons and so he moved to the ColumbiaGramophone Company in March 1929.According to Benzimra I Blumlein told IsaacShoenberg, the general manager, that hemight not still want him when he heard thesalary he was asking. Shoenberg's reply wasto offer him even more!

By that time the knowledge and skillsslowly acquired by telephone engineers hadbeen applied to make a new audio discrecording method which made mechanicalsystems obsolete. Any record company thatstuck with the old techniques would soon beobsolete too. The patents for the newmethod were held by the Bell System (West-ern Electric) in America to which a royaltywas paid for every record pressed. Blumleinwas given the task of inventing an alternativeelectrical method which would not violatethe American patents.

To do this he adopted the moving -coilprinciple which the Americans had not used.He and his colleagues are known to havebeen working on the design in October 1929and a prototype was tested the followingFebruary2. Electrical damping replacedmechanical damping to control the reso-nance of the cutting head and, with electric-al filters, a wide frequency range wasachieved with excellent linearity. A completesystem was designed and built in-house,from new moving -coil microphonesthrough the intermediate electronic circuit-ry to the final moving -coil recording head.

The first recordings were made in 1930and they set a new standard for fidelity.Blumlein received a £200 bonus. But his

thoughts had by now ranged beyond others'horizons to consider how a spatial impress-ion of the artists' performance could beachieved using only two loudspeakers. Hetook out an incredible patent in 1931 withseventy claims relating to 'binaural' record-ing - in other words. stereophony. He was 25years ahead of his time. When stereo recordsbecame a commercial reality in the 1950sEMI received nothing from this patent. Evenafter an extension, the patent had expired.

Blumlein's system was intended primarilyfor cinema use, but it also included recordsand was essentially that used for stereorecords from the mid -1950s. The only wide-spread use that Blumlein lived to see was oneof the few applications not covered by thepatent. In World War Two a couple ofthousand stereo sound locators were madefor assisting in aircraft detection. Withprevious systems nearby gunfire coulddeafen the operators. Blumlein electronic-ally limited the sound and used a cathode-ray tube (instead of earphones) for indicat-ing the results.

TELEVISION

In 1931 Columbia merged with The Gra-mophone Company (HMV) to form Electric-al and Musical Industries Ltd. now Thorn -EMI. It was this new company that developedthe 405 -line electronic television systemwhich became the standard British formatand which remained in use until 1985. Theformat for the picture signal became a worldstandard, altered only to include colour andstereo sound. Blumlein was the principalarchitect of the waveform and some peoplecall it the Blumlein signal.

The development of television at EMI wasa team effort and involved names which havebecome legendary in British television: IsaacShoenberg. J.D. McGee, E.L.C. White andothers with of course Blumlein. Blumleinwas a major contributor to the circuit designand he had a hand in other areas includingthe Emitron camera tube, transmissioncables and aerials. Among the circuits heinvented or developed were a novel sawtoothgenerator for scanning, negative feedbackcircuits and the cathode -follower. He alsoinvented and named the long-tailed paircircuit which was devised to reduce interfer-ence at the receiving end of a new video cablelaid to Alexandra Palace.

When the second world war began engineersin Britain already had considerable experi-ence of radar development. all of it con-ducted in secret. EMI had barely touchedradar work but the television team had theexpertise for dealing with pulse techniques.So it was that the team which developedtelevision turned to radar. Blumlein, Whiteand others were soon at work on a 200MHzairborne -interception radar. This was fol-lowed by a model which searched for andlocked on to an echo, thus allowing a fighterpilot to operate without a radar operator.The radar work involved a range of activitiesincluding frequency -shift keying, klystronsand magnetrons. anti -jamming circuits andsoon.

Some circuits invented by Blumlein: from left to right the long-tailed pair, Millerintegrator and cathode follower.

Above: Blumlein's stereo disc cutter, 1933 (Thorn -EMI): decades ahead of its time.

Moving -coil recording head, 1930/31 (Thorn EMI Central Research Laboratories).

ELECTRONICS & WIRELESS WORLD I

H2S radar display: success for the RAF, untimely death for Blumlein.

It was during this radar work that Blum-lein designed a ramp waveform or timebasegenerator more linear than any previouslyachieved. To do it he made use of a usuallyunwelcome effect in a triode valve circuitfirst noticed by John M. Miller and subse-quently called the Miller effect. Blumleincalled the circuit the Miller integrator, aname which stuck and kept his own nameout of the electronics text books.

The next major work was a plan -positionradar which gave a picture of the groundbelow the aircraft, so permitting very accu-rate navigation. It was code -named H2S andwas developed jointly by EMI and THE (laterthe Royal Radar Establishment).

With two EMI colleagues and a goodproportion of the THE team, Blumlein wastesting the equipment on board a Halifaxbomber on 7 June, 1942 when an enginecaught fire. The plane crashed, killing all onboard. Despite this catastophe H2S wascompleted and produced for Pathfinder andCoastal Command aircraft.

BLUMLEIN'S REPUTATION

Blumlein's name is not as well known as itshould be. Most of his publications are in theform of patents, rarely easy reading, and hiscircuit inventions do not bear his name. Buthis work is all round us in stereo recordings,bridge measurements, television signals,

plan -position radar, and the many circuitswe use without realising they are his, solelyor jointly with others: the closely -coupledinductor ratio arm bridge, the cathode (andsubsequently emitter) follower, the long-tailed pair, the transversal filter, the Miller/Blumlein integrator and others.

M.G. Scroggie has summed up his charac-ter: "a grasp of essential principles, fore-sight, versatility, originality, soundness ofengineering and insistence on 'designabil-ity' ". Others have remarked on his honesty,integrity and humour, and his conviction ofthe importance of understanding fun-damentals. "He would repeatedly - I remem-ber it as clearly as if it were yesterday - begoing back to Thevenin's theorem", J.D.McGee has recalleds.

This fondness for Thevenin is remem-bered by several who worked with him. "Oneof his favourite devices was to bring adiscussion to its close by quoting Thevenin'stheorem, and he would often be half waydown the corridor, puffing his pipe andshouting 'Thevenin' over his shoulder beforewe were able to gather our wits together,"says Vanderlyn2.

Once he forgot this ritual. The team dulypresented him with a "Thevenin Medal"made from the lid of a cocoa tin. As far as Iknow it was the only medal ever presented tohim by engineers.

Previous articles in this series byDr Tony Atherton dealt with thefollowing:

1. Stephen Gray, who discoveredelectrical conduction.

2. H.C. Oersted, who found the linkbetween electricity andmagnetism.

3. A.M. Ampere, father of elec-trodynamics.

4. Charles Wheatstone, inventor ofthe first practical telegraph.

5. Samuel Morse, pioneer of long-distance telegraphy.

6. Lord Kelvin, who persuaded thetransatlantic cable to work.

7. A.G. Bell, who conceived theidea of 'speech -shaped current'.

8. Oliver Heaviside, who rewrotethe theory of telecommunica-tions.

9. Guglielmo Marconi, whobridged the Atlantic by radio.

10. V.K. Zworykin, whose charge -storage principle has beenused by every tv camera tube.

11. Edwin Armstrong, inventor ofthe superhet and of workablef.m. radio.

12. Jack S. Kilby, inventor of theintegrated circuit and the elec-tronic calculator.

13. Heinrich Hertz and the discov-ery of radio waves.

His achievements would be a fittingmemorial if better known. Despite oneattempt, no full-length biography of himexists. The profession he served so wellshould put that right. Perhaps through theInstitution of Electrical Engineers, whosemeetings he graced, this omission could becorrected.

References1. B.J. Benzimra, "A.D. Blumlein - an electronicsgenius", lEE Electronics & Power June 1967,218-224.2. P.B. Vanderlyn, "In search of Blumlein: theinventor incognito," Journal of the Audio En-gineering Society vol.26, no.9, September 1978,660-670.3. M.G. Scroggie, "The genius of A.D. Blumlein",Wireless World September 1960, 2-7.4. B. Fox gives a list of publications on Blumleinin "Where stereo began", HiFi for Pleasure,January 1984, 29-37.5. Seminar Report, "The world of Alan Blumlein",BKSTS Journal July1968, 206-218.The author acknowledges the help given byThorn -EMI Central Research Laboratories duringthe preparation of this article.

Next: Shockley, Bardeen and Brattain -inventors of the transistor.

Tony Atherton works for the IBA and isauthor of a book "From Compass to Compu-ter, a history of electrical and electronicengineering."

Sinewave oscillator usingc-mos inverters

This twin -RC oscillator gives stable performance over a widerange of audio and sub -audio frequencies

Oscillators with two RC circuits areemployed mainly when a sinewavesignal having widely variable fre-

quency is needed. The most simple oscillatorof this kind contains only one operationalamplifier. More complex circuits with two ormore amplifiers and other components cangive a more stable output level and lowerdistortion 1-3.

This article describes a simple and in-expensive circuit using inverters instead ofamplifiers (Fig.1). It easily covers the wholerange of audio frequencies from 20Hz to20kHz and can produce far lower sinewavesas well. Frequency is determined almostentirely by the RC constants and it can bevery stable if stable resistors and capacitorsare used. The influence of the inverters isnegligible thanks to their high input resist-ance.

CIRCUIT DESCRIPTION

In the analysis which follows, resistors R,'and R," are treated together as Ra. Anequivalent diagram of the circuit is shown inFig.2. With the link closed, the inverters areassumed to have infinite gain; without it, thegains more realistically assumed to be finiteand equal.

Referring to Fig.1, we can express allvalues in Laplace transform as follows:

= I(S) (1)i(v1(0) = V1(S) (2)1(v1(0) = V2(S) (3)i(v3(0) = V3(S) (4)£(v4(t)) = V4(S) (5)

Z1(S)-R'CIS

"CIS1Z2(S)=R2+u (7)

A= --RRk,

DRAGOLJUB DAMLJANOVIC

For Fig.2, V4(S) = AV2(S) and thusZ2(S)I(S) = AV2(S)

-ZI(S)1(S) = V2(S)From this we getRiR2C1C2S2+(ARICI+RICI+R2C21S+1=0 (9)

To have an imaginary S it is necessary thatthe second factor is zero, i.e.

ARICI+RICI+R2C2 = 0From this we get the necessary amplificationA,

+R2C2A-R IC2

The frequency is

27rVRICIR2C2

Expression (10) shows that the RC compo-nents should not be varied independentlybecause this would require an adjustment ofA. Thus, it is necessary to fulfil conditionsR, = R2 = R and CI = C2 = C. Gain isindependent of the values of the resistorsand capacitors and has a fixed value of -20.The frequency is 1/2-nRC and the period27rRC.

Let us analyse now the more real case ofFig.2 with the link broken. According toFig.1 and expressions 1 to 5, we may write

V2(S) = aVi(S)V4(S) = aV3(S)

V2(S)-V3(S) V3(S)-K4(S)

Fig.1. In place of op -amps with their inputsbiased at half the supply voltage, thecircuit uses c-mos inverters.

V4 IS)

Vi IS) Link

V2 iS1

Fig.2. Equivalent circuit of the sine -waveoszillator of Fig.1. With the link closed, thecircuit assumes inverters having infinitegain: practical devices have a finite gain(link open).

From this we have

aV2(S)RbV4 (S) -

Ra+Rb-aR,(11)

To test the result let a tend to infinity. Thisyields V4(S)/V2(S)= -Rb/R,=A, as at thesimplified analysis of equation 8.

To find the necessary amplification A, letus rearrange equation 11,

a2V1(S)

V4(S1= , _1 a

Continued on page 191

Quality in a.m.broadcast radioA method of providing variable selectivity while maintaining a

level i.f. frequency response, in an attempt to regain the qualityof a.m. reception that was common in the pre -War years.

The author of the article in the October,1986 issue of EWW entitled "Puttingthe quality back into a.m. radio", 1.L.

Linsley Hood, is to be congratulated onproducing such an interesting design. Thereis, however, some room for improvement ifthe standard he set is to be met.

It is profitable to examine the reasons forthe high standard of performance achievedby the better 1937-1939 broadcast receivers,re -discover their underlying circuit princi-ples and to utilize the best of those principlesin today's receivers.

The majority of commercial receivers andof those designed by Wireless World staff inthe immediate pre -War period included anr.f. stage and two tuned circuits at signalfrequency. The provision of an r.f. stage wasconsidered essential to reduce cross -modulation and to eliminate superhetero-dyne whistles. To meet today's conditions,this scheme seems to be just as essential andto eliminate i.f. breakthrough an i.f. rejectorshould also be included in the aerial circuit.

I.F. BANDWIDTH

Good quality broadcast receivers of this eraincorporated variable selectivity to ensure alevel i.f. frequency response up to theselected bandwidth. Linsley Hood claims amodest overall i.f. response which is -6dBat ±6kHz, but this bandwidth seems to beunattainable with the specified transfor-mers.

Wireless World Radio Data Chart No 19(5th edition) is one of the easiest methods ofdetermining bandpass curves. The i.f.ts de-scribed by Linsley Hood have a working Q of100 and are critically coupled. The chartshows that the i.f. response of three suchtransformers will not be -6dB, but -33dBat ±6kHz.

Greater accuracy is obtained by using thefollowing formula, which gives the frequen-cy response, in dB of one i.f.t.

Qkloss =20logio

-(Qy)2+1Qk1212+41Qy12

Y=2 A f

f= centre frequencyA f= semi -bandwidth

k = coupling factorQk= 1 for critical coupling

R. KEARSLEY-BROWN

Q=100, kG1 =1% ka =1 k(lr.2 kaz 3

FREQUENCY (kHz)

Substituting gives a loss of 10.8 dB, relativeto that at fo, at ±6kHz. For three i.f.ts, theresponse will be -32.5 dB at ±6kHz, whichagrees well with the chart.

To this must be added the response of ther.f. tuned circuit. If this is a normal ferriterod, the Q will be about 200 and the overallr.f. plus 1.1. response at ± 6kHz is as shownin the table.

signal frequency r.f. plus i.f. response at 6kHz

1500kHz550kHz200kHz

-38db45.5dB-54dB

The reduction 'n high -frequency responseis clearly unacceptable.

P.K. Turner' showed that one couldobtain a r.f. or i.f. response flat to within±0.01dB over the required bandwidth: anovercoupled bandpass circuit adjusted to 1.1times the required bandwidth was used.producing the usual double hump. Turnershowed that by adding a single tuned circuitof half the bandpass circuit Q the dip waseliminated and an almost perfectly levelresponse obtained. The two circuits were, ofcourse, separated by a stage of amplification.Wheeler and Kelly Johnson' showed that thelevel response given by Turner was main-tained even when the bandpass couplingcoefficient was altered to vary the band-width.

To apply Turner's principles to LinsleyHood's design, the first and third i.f.tsshould be overcoupled using tertiary coils tocouple the secondary to the primary. Tap-

Fig.1. Semi -bandwidths of variableselectivity, two -stage i.f. amplifier. IFT 1and 2 have Q = 80 and switched Qk valuesas shown. IFT 2 has a Q of 49 with Qk = 0.5.Dotted curve is for three i.f.ts having Q =100 and Qk = 1.

pings on the tertiary coils should be providedand switched in to give, say, three degrees ofvariable selectivity; in -circuit coupling fac-tors could usefully be Qk= 1, 2 and 3. Theuse of tertiary coils for mutual -inductancecoupling has the merit of switching at lowr.f. voltages with negligible displacement ofthe centre frequency and the facility ofsimple alignment. Capacitor coupling toobtain variable selectivity usually results inthe centre frequency being displaced byseveral kilohertz.

To remove the dip in the response causedby IFTs one and three. one could add twoseparate 465kHz single -tuned circuits of halfthe Q. Alternatively, the second i.f.t could beused to provide suitable correction withalmost as good results. Calculation showsthat an overall i.f. amplifier response, levelto within 0.15db up to 7.5kHz can beobtained with i.f.ts having the characteris-tics shown in the table.

i.f.t. Q overall bandwidth at±0.15dB -3dB

coupling factor

- ±2.75kHz Qk= 1 variableI and 3 80 ±4.7kHz ±6kHz

± 7.5kHz ±9kHzQk =2 couplingQk=3 coupling

2 49 - - Qk = 0.5 fixed

OFF -TUNE FREQUENCY IN KILOCYCLES PER SECOND

40 30 20 10 9 8 7 6 5 4 3 1 0908 07 06 05 04

20 30 40 50 60 70 80 90 100

CIRCUIT Q

200 400 500

..........

offlomigWvIIIL .&111EW2111111.A11111111A

AMFAVA111112

IVAMILINMill.--1001 16911N11111111

-.4411111

-Illii"41:1517r1111111WIMPWAIIRi&\5

6SINGLE TUNED CIRCUIT ---..,.....,,,,,a,psdaptrAmonr

8 IWOmilk

---1 16710 s.-I, ,11 Clk.0.5

mom * 4 1 1

_ -16 _Sal

41.11W 18

immolleAMI19 db:2020 ma L 2121

2323W F

2424 7 2525 F--1 ' 2626

27 UNIVERSAL SELECTIVITY CHART 27

3030,71,1111 I171,1111' 1,1.1. 11, rpwrinTworyiurminir rl ni Ili I r .., I PI HI 1 r1,1 I r 'I I

4 3 2 1 0'9 0'8 0'7 06 0'5 0.4 03 0'2Mc/s

WORKING FREQUENCY IN MEGACYCLES PER SECOND

Chart No 19 from the collection of Wireless World Radio Data Charts. published many years ago and now, unfortunately. no longer available.

The increase in Q of 1FT2 from 40 to 49 isneeded because its tuned circuits are notisolated.

Figure 1 shows three bandwidths whichare obtainable by switching the couplingfactors of IFTS 1 and 3; the dotted curveshows the response of Linsley Hood's circuitfor comparison.

Wider bandwidths may be obtained bydividing the Qs of all i.f.ts by the same factor.For example, a Q of 60 for IFTs 1 and 3 and 37for IFT2 will provide a practically levelresponse up to ±10kHz, with Qk =3. Thecoupling factors, measured in terms ofcritical coupling, should remain the same. IfQ is reduced, then k must be increased sothat Qk remains equal to the chosen valuesof 1,2 and 3.

R.F. BANDWIDTH

To widen the r.f. circuit pass band when awide i.f. bandwidth is selected, series resis-tors can be switched into the inductive armsof the r.f. signal tuned circuits: a seriesresistor reduces the Q of a variable tunedcircuit mainly at the low -frequency end ofthe band, so widening the bandwidth whereit is most needed - about 10 ohms issufficient. The r.f. bandwidth should bewider than the i.f. by about ± 3kHz to allowfor oscillator tracking errors.

I .F.STABILITY

An i.f. amplifier should be designed with astability factor of at least 4 to allow for a

worst -case component tolerance building -up: a factor of less than 4 causes the i.f.response to become misshapen and difficultto align. Unfortunately, the L.H. design doesnot seem to meet this requirement.

Two i.f. stages with bandpass couplings ofsimilar Q will be "just stable" when

(gm.B8d)/G1,2<1.5 mho (2)

where gm = maximum fet transconductance(mho)

Bad= maximum gate -to -drain suscept-ance (mho)GD=working dynamic conductance of thetuned circuit (mho)

To provide the required stability factor of 4,

(gm.Bgd)/G02 <0.375 (3)

For a 3N201, the maximum g. is 0.02mho.Gate -to -drain internal capacitance is 0.03pFand to this must be added external straycapacitance, say 0.02pF, which gives a totalCad of 0.05pF. Hence

Bgd=wCgd=146/109mho

Given that the i.f.ts have a working Q of 180,fo=0.465MHz and the tuning capacitors are0.001 µF. then

G1)=6- = 29.22/10"mhoQ

01 90 ScMc1s

Wireless WorldCOPYRIGHT

gmBgd = 3.423GD2

Because (gm.Bgd/Gd2) exceeds 1.5, the LEamplifier will be unstable. Even when fetswith the average gm of 0.014mho are substi-tuted, the amplifier will remain unstable.Many fets are better than average, so thedesign must be based on 0.02mho. It will benecessary to increase Go by a factor of(3.423/0.375)9.5 or about 3 to provide aminimum stability of 4. In other words, thedynamic resistance of the i.f.ts should bereduced to 11 300 ohms.

References1. P.K. Turner, The Design of Broadcast Receiv-ers. BBC World Radio. April 7,1933.2. H.A. Wheeler. J Kelly Johnson. High -FidelityReceivers with Expanding Selectors, Proc. I.R.E.,June 1935.

Harmonics andintermodulation in the

long-tailed pairUsing a simple empirical equation to describe the current -

voltage characteristic, closed -form expressions are obtained forthe harmonic and intermodulation performance of the long-

tailed pair.

MUHAMMAD TAHER ABUELMA'ATTI

The long-tailed pair, shown in Fig.1 is

the basic building block of many ana-logue electronic circuits; for example.

the input stage of operational amplifiers, fullfour -quadrant multiplers and high -

frequency, voltage -controlled amplifiers.Recently, Lidgey 12 obtained the expressionof equation (1) to represent the current -voltage characteristic of the long-tailed pair.

V I I I 1 I Rt= loge (4)/0 - (i10)) + ( (4) it (1)

where Ven=VI-V2 and VT= thermal voltage.Equation (1) in its present form cannot be

used to quantify the nonlinearity in thelong-tailed pair, since this requires an ex-pression for the output current as a functionof the input voltage. By rewriting (1) as

Vn=ain+loge114-!"1 (2)1- in,

where V,,=Ve,,NT is the normalized inputvoltage, in= i/IL is the normalized outputcurrent, IL=I0/2 and a = ILRNT. Expanding(2) as a power series, Irvine obtained, byusing power series inversion, the expressionof (3) to represent the output current as afunction of the input voltage.

In=2--aVn (2 -7o7V"3(3)

Equation (3) is valid only for a limited rangeof input voltage, where Vn4a +2, and there-fore cannot be used for predicting theharmonic and intermodulation performanceof the long-tailed pair under large values ofinput voltage.

It is the purpose of this paper to present analternative expression for the output currentin terms of the input voltage. The expressioncan be used to predict the harmonics andintermodulation performance of long-tailedpair under large signal conditions.

PROPOSED FORMULA

The development of this formula proceededalong empirical lines by comparing thetruncated Fourier -series model of (4) withthe normalized input-output characteristicof (2) for each a.

sin(Iff V -9n n=1,,5 B

,-5Vn.-5.9 (4)

The parameters B and yn were obtained byusing the twelve -point method, which re-sulted in a family of parameters Yn whichdepend on a. The parameters, ye, were thenfitted to simple, closed -form analytical ex-pressions, giving

y1= -0.05036a+ 1.208 (5)y3= 0.0777a +1.27332 (6)

y5= -0.0283a+0.0651 (7)and B =18.

To establish the accuracy of (4), calcula-tions were made using (4-7), shown in Fig.2,from which it is obvious that the proposedmodel accurately represents the normalizedinput-output characteristic of the long-tailed pair.

HARMONIC AND INTERMODULATIONANALYSIS

Consider the case of a long-tailed pairexcited by a multi -sinusoidal signal of theform.

Ve=IVk sin wkt

iVkNTI

Substituting (8) into (4), the output currentcan be expressed by

in=Lin sin n'r(-Vk)sin okt. (9)

n = 1.3.5 B VT

Using the identity

sin (x sin tut)=2/ hm+ I(X) sin (2m+ 11 wt,

12=IL-111211..i tTry Tr2

Fig.1.pair.

The basic circuit of the long-tailed

-6 -4 -Vn

Calculated, eqn 14)

a a = 3 0b a = 1 .5

c a =00

Fig.2. Graphs resulting from the applica-tion of equations (4) to (7).

Fig.3. Variation of the third -order interceptwith varying 0,.

the normalized output current can be ex-pressed as

n=1.3.5 m=0(10)

J2m+1(1-3- TT- sm (2m + 1) 641rya Vk)

By noting that

L,(x)=(-11m4(x),it can easily be shown that the amplitude ofthe output current component, of frequency

111kwk

and order imki = odd integer,

where rnl., is a positive or negative integer orzero, will be given by

.m9=91f'Yn

n=1,3.5

IT Ira Vk, ( I (11)k= k B VT/

Special case. To illustrate the use of equa-tion (11), consider a two-tone, equal -amplitude input signal of the form

V,(0=SIsinw it +sinw20. (12)

Using (11), the amplitude of the fur.-damental output current component of fre-quency oil (or w2) will be

/1=2V inTrS1 /n1(.51n I BVT I) BVT

n =1,3.5

and the amplitude of the third -order inter -modulation output current component offrequency 2w2± oil (or 2w1±(02) will be

(11BITvTS) Ji(11B7rvrS).

n=1.3.5

For 57rS/18VT4 1, the Bessel function can beapproximated by

1n(x) = (x/r/n!

and (13), (14) reduce to

I =BV -1"1'n=1,3,5

3121= 18(kST)I 03'Yn (16)

n = 1,3.5

Using (15), (16) the ratio of the unwantedthird -order intermodulation product to thefundamental will be

2R=I41_8(B-

nayn=1,3,5

/nynn=1,3,5

Using (5-7). (17) reduces to

R-1 TrS 216.72514-5.68576a8 131/T) 2.35346-0.42496a (18)

The third -order two-tone input interceptcan be obtained by equating (17) to unity.giving

S 12 r 2.35346-0.42496a 1/2(19)

VT- Tr 116.72514-5.68576a]

A plot for (19) is shown in Fig.3, from whichit is evident that, as a increases, the inter-cept level increases. Qualitatively, this resultis in agreement with the observations ofIrvine.

In this paper an empirical formula has beenpresented for the current -voltage character-istic of the long-tailed pair. Using thisformula, closed -form expressions have beenobtained for the amplitudes of the harmo-nics and intermodulation current compo-nents resulting from exciting the long-tailedpair by multisinusoidal large -amplitude sig-nal. The results obtained using the presentanalysis are, qualitatively. in good agree-ment with results published previously andcan be used to study the performance ofanalogue circuits using long-tailed pairs.

References1. J. Lidgey, The tale of the long -tail pair. Electro-nics & Wireless World. Vol. 91, No 9. 1985.pp.74-76.2. 1. Lidgey. The tale of the long -tail pair - part 2.Electronics & Wireless World, Vol. 91. No 10,1985, pp.27-31.3. R. J. Irvine. How linear is linear? Electronics &Wireless World, Vol. 92, No 12. 1986. pp.97 and109.4. I. A. Dodes. Numerical analysis for computerscience, Elsevier North Holland. New York. 1978.

Dr Abuelma'atti is in the Department ofElectrical Engineering and Computer Scien-ce of the Faculty of Engineering at theUniversity of Bahrain.

Sinewave oscillator usingc-mos inverters

Since the inputs of the inverters sinkhardly any current, according to equations 6and 7 we have

V4( 5)-VI(S) VI(51-V2(S)Z2(S) Z1(S)

With both resistors and capacitors equal, weget a new expression corresponding to equa-tion 9,

(RCS)2+ 12 - ( I a-1)-1'RCS+ 1 = 01-a(12)

From this we have the new formula for A

A- 2a,2 -5a +3

a' +2a -3

We see now that the gain A should not be-2 but a little higher. For example, whena=-20 the gain should be adjusted to-2.53. Referring to Fig.1 we find that Ra" =

Continued from page 1 87

5.4ki1, near the middle of the potentio-meter.

EXPERIMENTAL RESULTS

The circuit has been tested over the wholesupply voltage range of 4049 inverters and itworks well if A is appropriately adjusted:inverter gain varies a little with supplyvoltage. Thus to fulfil condition 12 (with animaginary 5) we must fit A. This problem isnot serious if we use a stable supply. A moreimportant problem arises from the fact thatis not easy to ensure that RI =R2 and CI =C,

over the whole frequency range. The sine -wave amplitude depends on the active com-ponent's (here, the inverter's) non -linearity.This problem is present in all RC sinewaveoscillators and it can be tackled in severalways. Here the amplitude was adjusted byadjusting A manually (with potentiometerRa"). The adjustment was only 2-3% withrandomly chosen components in the ranges391d1-1MS1 and 200pF-1 µF.

The temperature of the inverters waschanged independently of the temperatureof the resistors and capacitors, and it wasfound that the frequency was practicallyindependent of it over a wide temperaturerange.

References1. Landee R.. Davis D. and Albrecht A.. ElectronicDesigner's Handbook. McGraw-Hill 1957 (Grad-jevinska Knjiga 1965. 6-501.2. Ben -Zion K., Rami S. and Beny Z.. Analyticaland experimental approaches for the design oflow -distortion Wien bridge oscillators. IEEETransactions on Instrumentation and Measure-ment IM -30 no. 2, 147 (1981).3. ObradoviC M. and Milk A., generation ofsinewave signals containing very low distortions,XXVIII Yugoslav conf. of ETAN. Split 4-8 June1984.11.97.

Dr Damljanovie is with the electronics de-partment of the Boris Kidric Institute ofNuclear Sciences - Vinca in Belgrade.Yugoslavia.

low-cost PC based logic analysis - from Thurlby

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Now you can use your IBM-PC or compatible computer as thebasis of a sophisticated logic analyser system.

LA -PC Link is an interface package which links your computerwith the low-cost Thurlby LA -160 logic analyser to provide facilitiesnormally associated with only the most expensive analysers.

Sophisticated data state listingsUp to 32 words per screen in multiple data formats.Scrolling by line, page or word, plus random page access.Rapid screen compare facility. Full repetitive word search. High resolution timing diagramsSixteen channels of 64, 256 or 1024 samples per screen.Instantaneous par and zoom. Moveable channel positions.Dual cursors with automatic time difference measurement. 16 or 32 channels, clock rates to 20MHzOperates with all versions of the LA -160 with or without LE -32. Comprehensive data annotationEach data and control input can be allocated a user -defined label.Data files are date time stamped and can be fully annotated. Full disk storage facilitiesData files can be saved to disk and recalled for comparison.Data includes the analyser's set-up conditions and all annotation. Versatile printing facilitiesState listings and timing diagrams with annotation can be printed. Colour or mono display; keyboard or mouse controlColour, monochrome or text -only modes suit any display adaptor.Parts of the programme can be controlled by a mouse if required. Terminal mode for uP disassemblersActs as a terminal for use with Thurlby uP disassembler ROMs.

If you already have an LA -160 logic analyser the LA -PC Link inter-face package costs just £125. If you don't, an LA -160 with LA -PCLink costs from £520.

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STEW PRODUCTSSmart cardprogrammerGang programming of 'intelligent'credit -card -sized memory banks ispossible with a Stag 41M900 module.This adaptation of the PP41programmer is used to downloaddata from a master card or eprom, orfrom a host computer memorythrough the RS232 interface. Thestored data can be listed, edited anddeleted to update price lists, look -uptables, and similar information. Thecards have found use in providingplug-in font designs for use withcomputer printouts. StagElectronics Designs Ltd. TewinCourt, Welwyn Garden City, HertsAL7 IAU. Tel: 0707 332184.

Building-blockpower supplyPower supplies to almost anyspecification can be designed andbuilt using the InPower powerconverters and booster modules.which can be used as individual unitsor as basic building blocks toconstruct a p.s.u. for a specificapplication. Converter modules havea switching frequency of up to 1MHz,and are supplied in 30 to 150Wmodels with 10 to 400V inputs and 2to 90V outputs. Booster modules areconnected to the converters inparallel to extend the output to morethan 1 kW.

Multi -output, fault redundant anddistribution power systems can all heconfigured. Modules can be changedeasily if the specification is altered.

InPower supplies offers anefficiency of around 80% and a highm.b.t.f: low standby power and lownoise figures are also claimed. Smalland light, the modules fit onto p.c.bs.InPower, Ballysimon Road,Limerick. Eire. Tel: +353 6149677.

Eprom emulator runs through RS232Any computer with an RS232 portcan be used as an epromdevelopment system. An epromemulator, the DCA-EM08 from D.C.Allen, accepts all the regular epromformats and also permits access toallow bytes to be enteredindividually. Command sequencesenable the user to configure andcontrol the unit. 28 -pin eproms from8K to 64K are emulated with access

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The main control unit issupplemented by a high-speed podwith a 28 -pin header plug. Power isprovided through a mains supply toavoid overloading the target. D.C.Allen (Engineering) Ltd, 27 NuffieldRoad, Poole. Dorset BH17 7RA.Tel: 0202 671666.

Optical source and meterTwo hand-held instruments areintended for field-testing of opticalfibres. Wandel & Goltermann'sOLP-2 is an optical power meter foruse with the 850, 1300 and 1550nmwavelengths. It has a high sensitivityand is capable of both absolute andrelative measurements. Thereference setting is controlled by apotentiometer and is thereforeretained when the instrument isswitched off. Adaptors enable theinstrument to be matched to all thecommonly used optical systems.

OSL-2 is a compact light sourcewhich can be switched between 850and 1300nm. A method of thermalcompensation allows the instrumentto produce a stable output levelwithout any warm-up period.Nominal output levels are achievedwithin a temperature range of -10°Cto + 50°C. Such an ability is claimedto have been possible only inlaboratory equipment hut is now

available for precision field use.Wandel & Goltermann Ltd. ProgressHouse, 412 Greenford Road.Greenford, Middlesex UB6 9AH.Tel: 01-575 3020.

Protection varistorsThe protection ()tiered by connector -pin varistors guards equipment fromphysical damage and improvesreliability in components that may beupset by low -amplitude voltagesurges and transients. A range of CPvaristors from GE offers differentsizes and a wide selection of voltageranges for both direct andalternating currents. Maximumratings are 25 to 130V r.m.s. or 31 to150V direct. Energy dissipation is 1.5to 5 joules at peak currents of 250 to500A. Available through GothicCrellon Ltd. 3 The Business Centre,Molly Millars Lane, Workingham,Berks RG11 2EY.Tel: 0734 788878.

Flash a -to -d forspace video signalsA fast, low-cost analogue -to -digitalconverter is manufactured by ITT.Tv scramblers, digital teletextdecoders, video memory applicationsand D2 -MAC satellites are amongstthe uses of the 20MHz device. Itmainly consists of 127 comparatorsand operates as a seven -bit converter.or by toggling the I.s.b. it is possibleto create a pseudo 8 -bit mode withhigher video resolution. It isdesigned to be compatible with ITT'sDigit 2000 tv system. ITTSemiconductors, 145 Ewell Road,Surbiton, Surrey KT6 6AW.Tel: 01-390 6577.

Analogue data radiolinkRadio data links in the u.h.f. band areavailable with a range of analogueinputs, thought to be of particularuse in process control. ADL800transmitters from Micromake areprimarily intended as extensions tothe p.s.t.n. telemetry systems andmake possible the use of remoteoutstations or for temporarymonitoring.

The single -channel versionconverts the incoming analoguesignal to a stream of ASCII characterswhich are transmitted and can bereceived and then decoded on almostany desktop computer or terminal.Each sensor package includes signalconditioning circuits. a -to -dconverters and a c-mos processor togive 15 -bit measurement resolutionand eight samples/s. A half -duplexversion to be released soon will allowthe user to interrogate the remotesensors and adjust or re -program theconversion process. The outstationswill be addressable and will thereforeoffer random access by the centralprocess control computer.

All links are type -approved for usein the UK. They operate in the485MHz band with a maximum r.f.power output of 500mW. MicromakeElectronics, 1 The Holt. Hare Hatch,Upper Wargrave, Reading, BerksRGIO 9TG. Tel: 073 522 3522.

Modem for STE-busBritish Telecom claims to have madethe first STE-bus compatiblemodem. System designers are thusprovided with a means of building asystem for remote control and datagathering through the telephonenetwork. Operation to V21(300/300baud) or V23 (75/1500baud)standards and built-in processingallow control by a high-levelcommand protocol.

Model 4300 comes on a singleEurocard and, in addition to theusual modem functions, includes aloudspeaker for line monitoring.High speed bidirectional datatransmission can be achieved by theinclusion of a 1500/75baudconfiguration. British Telecom,Microprocessor Systems,Martlesham Heath. Ipswich 1P5 7RE.Tel: 0473 643101.

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NEW PRODUCTSAudio distortionanalyser and levelmeterAn auto -tuning rejection filter stageis a feature of the Crotech 2017distortion analyser and level meter.enabling it to eliminate thefundamental from a signal and thenmeasure the remainder; presentingthe result as signal distortion. Theinstrument functions between 30Hzand 300kHz.

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Signal voltage levels can bemeasured between 1mV and 300V,equivalent to +50dBm to - 60dBm.Levels are displayed by the meter toan accuracy of ±5%. Residual noiseis <2001.LV r.m.s. and an output ofthe level signal gives about 150mVinto an open circuit.

Crotech also makes a low -distortion signal generator and apower meter and the threeinstruments can be rack -mountedfor a comprehensive audio testsystem. Crotech Instruments Ltd, 2Stephenson Road. St. Ives.Huntingdon, Cambs PE I7 4W./.Tel: 0480 30181.

Pin -grid zif sockets.1 lever is used to close the contactson the Robinson Nugent PGZ rangeof pin -grid array sockets. This isintended for test and burn -inpurposes and reduces the contact -wiping action which causes wearwithin test sockets and can reduceelectrical contact. Tests have shownthat the sockets can withstand10.000 open/close action with noadverse effect on the beryllium -copper contacts. Available throughHunter Electronic Components Ltd.Unit 3 Central Estate. DenmarkStreet. Maidenhead. Berks S1.6 7BN.Tel: 0628 75911.

Any -mains powersupplyFitting an Onan Spec II power supplyto electronic equipment will allow itto he used anywhere in the world.claims Gresham Powerdyne. Inputsfrom 90 to 264V with frequenciesfrom 47 to 6311z can he acceptedwithout the need for transformertaps, range switching or jumpers andregulated outputs of ±5. 12.15 and+ 24 are provided with ratings of 50Wand 140W.

An additional advantage of thesystem is that it is suitable for use inareas where the voltage may dropthrough excessive cable length orwhere the mains voltage/frequency ishighly variable. Gresham PowerdyneI.td. Osborn Way. Hook. Hants RG279X11. Tel: 025 672 3939.

Demonstration servoAn instructional d.c. servo has beenspecifically designed to beanintroduction to the principles of d.c.control. The high engineeringstandard adopted permits advancedlevels of study where quantitativemeasurements are needed.

The system includes a control unitwith power supplies. A detailedmimic diagram on the front panel

shows how the system is working.The servo motor, with an integral

tachometer, drives a potentiometerthrough a gearbox. Variable Icadingis provided, acting directly on themotor shaft. Two manuals.introductory and advanced, areprovided. Feedback Instruments Ltd,Park Road. Crowborough. EastSussex TN6 2QR. Tel: 08926 3322.

Video studio on a PCPlug-in cards for an IBM ATcomputer combine 8 -bit frame storeswith 8 -hit video input channels.Images can be grabbed in real-timedirectly from a video camera orrecorder.

Colour look -up tables allow up to256 levels of grey scale or 256 coloursto be displayed simultaneously.selected from a palette of 16 million.By installing three cards in thecomputer, the user can generate afull colour system which will graband display 24 -hit true colour imagesin real time.

Display resolutions conform toEuropean or US broadcastingstandards. In addition to thestandard image display, a separateoverlay plane is provided for keyingtext or other computer -generatedimages. It is possible to view theactive frame through windows in theoverlay plane.

Primagraphics' Virtuoso PCsystem is to be supplemented by anumber of software packages whichwill include an MS-DOS version ofthe VCS image processing programfrom Vision Dynamics.Primagraphics Ltd. MelbournScience Park. Melbourn. Royston.Herts SG8 6E.I. Tel: 0763 62041.

RedesignedaccelerometersMiniature accelerometers have beenmade by Entran which use a newsensor design which have fewermoving parts and are machined to ahigh pr. :ision by spark erosion.

Egacy transducers are small butrobust: the mechanical stoparrangement allows them towithstand an overrange of up to10,000G. Measuring ranges vary

from ±5G up to ±2500G. Having amass of only one gram, the device isespecially suitable for vibrationtesting of small components and theoverrange allows leeway foraccidental impact or mishandling.Entran Ltd, 5 Albert Road,Crowthome, Berks RG11 7I.T.Tel: 0344 778848.

Board -mounted heatsinksA comprehensive range of board -mounted heat sinks is available fromMarston Palmer. Three profiles andfour lengths can be specified. with orwithout solderable pins or springclips, and with a number of standardhole patterns. Depending on thelength. thermal resistance is isn therange 7 to 12°C/W. The companyproduces over 100 different heat sinkprofiles. Marston Palmer Ltd.Wobaston Road. Fordhouses,%Volverhampton %W10 6%Tel: 0902 7s:61.

Inspection tool fordrillingThe integrity and accuracy of c.n.c.drilling in p.c.hs can be checked byusing Chek-Rite. This is a stable.colour -contrasting, translucent filmwhich is cut and drilled in the sameway as a prototype hoard. Placing thefilm over subsequent productionhoards makes it easy to spot incorrecthole locations and tolerances, missedor extra holes, or misorientation.Because the film is dimensionallystable, it can also be used to producesolder mask patterns. Two colours.bright green or darkroom -neutralorange are available. Intertronics.Allvalve House. 159 BrookwoodRoad. Southfields. London SW185BD. Tel: 01-871 2735.

STE-bus card runsCP/M+A single -board computer combinesthe 64180 processor with an STE-businterface and is thought to be ideallysuited to running CP/M+ bankedapplications.

The single -chip c.p.u.incorporates a Z80 -like 8 -bitprocessor with memorymanagement, two uart channels anda two -channel direct -memory -accesscontroller. Its 1Mbyte addressingspace is similar to that used in theSTE-bus. This allows the CP/M+operating system to run directlywithout the need for switched

memory hanks and give immediateaccess to the STE-bus extensionmodules such as hard and floppy discdrivers, memory and i/o cards.

All these features are combined inArcom's SC180 computer boardwhich includes four 28 -pin memorysockets and interrupt handling withcontrolled priorities. It can be usedfor both data processing and real-time systems applications forsoftware development or as a targetcontrol board. Arcom ControlSystems Ltd. Unit 8. Clifton Road,Cambridge CBI 5W'H. Tel: 0223411200.

Low -noise filteredD -connectorsBuilt-in filtering and steel shells onthe 'Silent -D' range of D connectorsmake them suitable for 90% of allapplications that need to meetstandards of electromagnetic noiseelimination. Online. the distributorof the ITT Cannon range. claims thatthe 10 to 15dB attenuation offeredmeets most requirements. whereasthe 40dB designed into many filterconnectors is only needed formilitary applications.

Plugs and sockets come in 9. 15.25. and 37 -way, right-angle p.c.h.-mounting versions. They featuregold -over -nickel contacts. OnlineDistribution Ltd. Melbourne House.Kingsway. Bedford MK42 9AZ.Tel: 0234 217915.

rN-Ew PRODUCTSSpace -saving i.c.designerLayout of v.I.s.i. circuits usuallyinvolves much manual work, but anew system from Caeco can produceresults automatically that are similarto those crafted manually. LayoutSynthesis generator uses a newtechnique that requires no presetlibraries of components. The systemcreates functional blocks of designusing an input logic diagram or a textfile describing the logical function ofthe device. The user specifies thedesired block shape. pin locationsand design rules and the programwill return a completed i.e. layoutwith detailed circuit and electricalparameters. The format of the outputis standardized so that the user caneasily edit a block and connect it withother blocks.

A further program. Caeco Blocks.can automatically place andinterconnect blocks prepared by thelayout system. designed by hand,imported from previous designs.standard cells or even blocksdesigned by other automatic tools.

The layout program follows theconventions used by most c-mosdesigners. N and p transistors aregrouped in separate regions.Transistors are lined up in rows toallow efficient power and signalconnections and long source/draindiffusion chains are formed fortransistors having commonconnections. This optimizes thediffusion areas and reduces space.

The system is claimed to offersimilar tools to the fully custom i.c.designer as are available to thosemaking application -specific i.cs.while offering speed and space -efficiency. Caeco Inc, PO Box 240,Beaconsfield. Bucks HP9 2QN.Tel: 04946 77706.

Mixed analogue anddigital simulatorSimultaneous running of ananalogue and digital simulator isnow possible through the co-operation of Viewlogic andMicroSim. Each of their simulationprogrammes. Viewsim and PSpice.have been linked by an interfacewhich transfers information betweenthe simulators and synchronizestheir operation. Accurate simulationis assured for circuits with feedbackloops or circuits with different timeconstants between the sections.

The system was developed byViewlogic and the resultantwaveforms. both analogue anddigital, can he displayed by theirViewWave waveform processor.These simulators run on a standardVAXNM X workstation. Availablethrough Instrumatic UK Ltd, FirstAvenue. Globe Park, Marlow, BucksSL7 1YA. Tel: 06284 76741.

Testing video monitorsA range of signal outputs is availableon the Grundig MT700 to make itsuitable for the testing andadjustment of virtually anymonochrome or colour tv monitor.All the standard European and USline and frame frequencies arecatered for and it is possible toprogramme the tester to cope withnon-standard formats.

In addition to the usual standardtest patterns for setting up

convergence. linearity. colouradjustment and frequency -response.there are a number of text testswhich are particularly suitable forcomputer monitors. Outputs are incomposite video signal form as wellas RGB and RCB/t.t.l. Interlace canhe switched out to reduce jitter ontests. Available through ElectronicBrokers Ltd. 140 Camden Street.London NW1 9PB.Tel: 01-267 7070.

Three-phase energy analyserA new ye! stun of the :%hcrovip energyanalyser can be used on a three-phasesystem with unbalanced loads. Itincludes integral phase andcontinuity indicators, and providestotal current, power and power -factorMicroprocessor controlled, theinstrument is claimed to be easy touse and gives a print-out of datacollection. Direct measurements

include: true instantaneous voltage.current, power -factor and activepower: reactive and active energyconsumption since the last zerosetting: leakage current to earth:voltage frequency and mean powerfactor. Alpha Electronics Ltd. Unit 5.Linstock Trading Estate, WiganRoad, Atherton. Manchester M29OQA.Tel: 0942 873434.

Inverters increase display lifeThe Endicott range of d.c. to a.c.converters are designed for use withelectroluminescent lamps. Appliedvoltage and frequency areautomatically adjusted by theinverter to give the display a constantlight level. And e.l. display acts like alossy capacitor and brightnessdiminishes in time. This is oftencompensated for by stepping up thevoltage and/or frequency. SmartForce inverters incorporate a tuned

resonating circuit that adjustsautomatically as the capacitance ofthe lamp changes. Versions of theinverters have input d.c. voltagesranging from W to 48V with nominaloutputs of 60, 80, 100 and 120V. Theycan provide power for up to 375cm'as used for backlighting I.c.ds inportable computers. GreshamPowerdyne Ltd. Osborn Way. I look.I lants RG29 911X.Tel: 025 627 4246.

Miniature tantalumcapacitorsA range of miniature mouldedtantalum chip capacitors conformsto a new E IA world standard for sizesIt is particularly designed for surfacemount applications. Four standardsizes are catered for by the Sprague293D range. which coverscapacitance values from 0.1RF to100ILF with working voltagesbetween 4 and 50V. Sprague ElectricUK Ltd. Airtech 2. Fleming Way.Crawley. West Sussex RI115 2YQ.Tel: 0293 517878.

Relays galoreMagnacraft makes relays in theUnited States. They are particularlystrong in solid-state and high -powerdevices. Keyswitch Varley makes acomplementary range. especially ofcradle and octal -based relays and hasnow become the UK stockists forMagnacraft, thereby offering a verycomprehensive range of relays.Keyswitch Varley Ltd. Tom CrihbRoad. Thamesmead, London SW28OBH. Tel: 01-3171717.

MOSO'-MOOla

Miniature 15W d.c.convertersThe new d.c.-to-d.c. converters fromRifa are the size of a credit card andnot much thicker. They are designedto he mounted on a p.c.b.. when theyhave a height of 10.7mm, hut mayalso be mounted with the base fittinginto a cutout on a p.c.b.. thenprotruding only 8.5mm.

PKC-series converters offer 500Vd.c. isolation and one, two or threeoutputs. Input voltages can rangefrom 24V to 48 or 60V and theoutputs are 5, 12 or 15V within2..5%. The design is particularlysuited to parallel connection and. forexample, has a negative temperaturecoefficient. Internally, they use300kHz p.c.m. switching: the highfrequency contributing to their smallsize. Rifa AB Power Products. MarketChambers, Shelton Square,Coventry CV1 1D1.Tel: 0203 553647.

THE ETL 68000PROCESSOR

32 bit processing, 10MHz Clock, 512K STATIC RAM and512K EPROM, the ETL 68000 is a powerful stand-alonesingle -board computer, based on the Motorola 68000 CPU.

TWO SERIAL PORTS CENTRONIC PRINTER PORT 1 MHz BUS PORT EXPANSION BUS (Fully Buffered)

Wide range of user configurable options including Serial Port Baud -rate Word Length/Parity Handshaking Configurations ROM/RAM Access time Programmable timer/counter Many EPROM/RAM typesAPPLICATIONS SOFTWARE: Monitor Software, including Assembler/Disassembler. Floating Point 32 bit Calculator software including:

sin, cos, tan, arctan, square root, log, exp, and many more Cross Assembler for PCs, BBCs and CPM machines. Easy to use 'C' Cross Compiler.

ELECDATA TECHNOLOGY LTDPulton Place. London SW6 5PRTel: 01-731 4146 Telex: 296501

ETL 3100A"FUNCTIONS BETTER"

The ETL 3100A Function Generatoris a new compact and versatile instrument with a comprehensiveset of waveforms and functions for your laboratory requirements.

Features: 2 x 1MHz Sine/Square Waveform Generators with amplitude

control. Hardware Adder with gain control. Hardware Multiplier with offset control. Pseudo Random Sequence Generator (PRSG) with variable

bit rate. Pu'se Generator with seven preset pulse widths and

separations, ideally suited for investigating impulse respon-ses of systems.

II 4 or 8 Pole Low Pass and Band Pass Tuneable Digital Filtersfeaturing accurate display of the 3dB or centre frequency(500Hz-50kHz).

Power Supply (+15V 0-15V and +5V) with high current rating.

For further information contact:

ELECDATA TECHNOLOGY LTDPulton Place. London SW6 5PRTel: 01-731 4146 Telex: 296501

ENTER 71 11). REPLY CARD

ELECTRONICS& WIRELESS WORLD

INDUSTRY INSIGHTCOMMUNICATIONS

APRIL ISSUEThe second in the series is concernedwith the explosively developing field ofelectronic communication of voice anddata, using radio or cable techniques.We look at private mobile radio, localarea networks and the facilities offeredby video services such as Prestel.The way ahead in p.m.r. is not alwaysclear, in view of political and spectrumconsiderations: industry experts pre-sent their views.

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Miteyspice provides AC and DC simulation (the DC may be usedto establish the operating point in a non-linear circuit at which asmall -signal AC analysis may then be performed). Miteyspiceincorporates numerous powerful features including 20parameter Ebers Moll transistor models and comes with a 50page manual full of useful hints including how to obtain illusiveparameters from manuafacturers' data.

Miteyspice is now in use in.education and industry throughoutthe U.K. and with its SPICE compatible syntax, is fast becomingthe teaching standard fpNanaltigile_dircuit simulation.

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BOOKSMicrowave Processing and Engineering,edited by R. V. Decareau and R. A. Peterson.Ellis Horwood series in food science andtechnology, 224 pages, hard covers, £37,ISBN 3-527-26210-5. Microwave here means60kW pasta driers at 915MHz (which shouldcertainly wipe out the managing director'scellular telephone) and steam processinglines for cut-up poultry parts on 2450MHz -in other words, mostly the large-scale in-dustrial uses of microwave heating. Besidesapplications, the text covers microwavetheory and techniques, magnetrons, klys-trons and special waveguide components.Further chapters illustrate the design ofmicrowave systems step-by-step and explainthe regulatory requirements in both and USand Europe.

Waveforms: a history of early oscillography,by V. 1. Phillips. Adam Hilger, 259 pages,hard covers, £35. Electronics is not so new adiscipline as to lack a past, and works such asthis and the splendid history of technologyseries from the IEE do a service by remind-ing us of it. The history of man's attempts tosee electricity stretches back further thanone might imagine and embodies devicesmore fantastical than now seems possible.But it is no part of Dr Phillips's purpose tomake fun of early travellers along blindalleys. Instead, he provides an informativeand extensively researched account, tracingout with the help of over 200 contemporaryillustrations the tangle of threads whicheventually came together in the cathode-rayoscilloscope. It is interesting to note howimaginative our 19th century forebears wereat naming their apparatus: some of theirefforts could well do with reviving, when werun out of three -letter abbreviations for newelectronic devices. Rheotome, for example,(Charles Wheatstone's word for a currentchopper) might have been an apt substitutefor s.c.r.

Electronics & Electronic Systems byGeorge H. Olsen. Butterworths, soft covers,406 pages, £19.95. Text for first and secondyear undergraduates or for higher -level TECcourse students. The analogue electronicssection is noticeably larger than the digital,which will please those who think theemphasis has been going too far the otherway.

Advanced Semiconductor Fundamentals byRobert F. Pierret (Purdue University).Addison-Wesley, soft covers, 228 pages,£17.95. Volume VI of a series on solid-statedevices, with sections on semiconductorproperties, quantum mechanics, energyband theory, equilibrium carrier statistics,recombination -generation processes andcarrier transport. The author intends thebook as a supplement to the graduate -leveltext Physics of Semiconductor Device.s byS.M. Sze (Wiley-Interscience, New York) andas a reference work for engineers and scien-tists.

Application -specificintegrated circuits

In volume production of both analogue and digital designs, application -specific i.cs reduce component count and hence inventory, assembly and

testing costs; they also increase reliability and reduce p.c.b. area. Generally,using an asic starts to become financially attractive when production

quantities reach a thousand or more.

1984 1486 1988 1990

NEC's asic production output trends show c -

Five years ago, the scope of asics was limited.Most asic devices were based on uncommit-ted logic arrays, resulting in wasted siliconand a relatively high degree of inflexibility.But now asics are available in many con-figurations - even microprocessor macros -and in semiconductor technologies rangingfrom t.t.l. to bipolar/c-mos combinations.

Software for asic simulation is so ad-vanced now that breadboarding can be un-necessary. Nevertheless, the full require-ments of the final asic must be defined beforethe design work starts to minimize costs.Changes in an asic design become moreexpensive as the design work progresses,reaching very high proportions once the firstiteration (samples) is produced.

Most manufacturers can supply a range ofasics with various numbers of gates. Ofcourse the functional requirements of thefinal device mainly determine which asic ischosen but the number of i/o pins neededalso has to be taken into account. It can benecessary to choose an asic with more gatesthan are needed in order to satisfy i/orequirements. Good design reduces the

Asic semiconductor technologies available from NEC

Type ProcessSpeed/geometry Gates

C-mos gate CMOS-3 2um 800.11000arrays CMOS-4/4A/4R 1.5um 30020000

CMOS-5 1.2um 200045 000

BiCmos gatearrays

BICMOS 4/4A 12µm 600.10000

Bipolar gate ECL-2 500MHz 300.2000arrays ECL3 200MHz 1200-3000

ECL-3A 450MHz 600-1200Cmos standard-cell arrays up to

64K ram256K rom

25 000 gates Mega macros

mos replacing by 1990.

number of gates required.Choosing a technology is quite easy, being

decided by cost, performance, power con-sumption and output current. Now thatc-mos devices out -perform t.t.l., the choiceis mainly between c-mos and e.c.l.

Total design time is a major considera-tion. Time scales for most of the designstages are difficult to determine, dependingon the capacity and efficiency of both thedesign centre and buyer as well as thecomplexity of the device. During the initialstage, designers have access to their paper-work logic design and can make alterations.At this stage also, the designer needs toconsider which tests are required for thefinal asic. Subsequently, the program for atest tape will be produced.

Generally, only the time between com-pleting the design and producing the firsttest devices is fixed; a few weeks is usual. Atone time, buyers relied solely on the speed ofdesign centres but now that asic-designworkstations and software are becomingreasonably priced, asic buyers can havemuch more control over design time.

Packaging also has to be considered.Power dissipation and chip layout can res-trict the types of packaging available andusing a high proportion of gates can affectpin out. In such complex i.cs, power -supplyand ground pins can be important. Withc-mos technology for example, the numberof outputs that can switch state simul-taneously is limited by the number ofground pins.

Nowadays, selling asics is a service indus-try. Success of an asic supplier depends asmuch on support as on the range of devices.

Advanced f.s.k. modem i.c.A high degree of integration offers the prospect of

intelligent auto -dialling modems with an unprecedentedlylow component count.

dvanced Micro Devices has announcedn enhanced version of its Am7910.s.k. modem chip, the device which in

the last couple of years has become virtuallystandard in low -speed asynchronous datamodems.

Like its predecessor, the new Am79101provides transmission and reception at ratesof up to 1200 bits per second, both in theCCITT V.21 and V.23 standards and on Bellstandards 103.113, 108 and 202. In Bell 202and CCITT V.23 half -duplex modes a hackchannel of up to 150 bit/s is possible, makingthe device suitable for split rates such as the1200/75 commonly used by viewdata sys-tems such as Prestel. But in addition, theAm79101 includes full support for autodiall-ing and auto -answer: it has a built-in d.t.m.Igenerator and call progress tone detection,which can identify dial tones and number -engaged signals.

8051-ocroconfroller

Modulation, demodulation, filtering,digital -to -analogue and analogue -to -digitalconversion are all implemented within thechip using digital signal processing techni-ques. Transmit signals are digitally -generated sine -waves: when the modulatorswitches from one frequency to the otherduring phase -shift keying, it does so in aphase -continuous manner. Data inputs andoutputs are serial signals at t.t.l.-compatible5V levels, which can easily be converted toRS -232 levels.

Connection to the telephone network maybe either via an acoustic coupler or via anexternal data access arrangement, whichprovides the necessary isolation. But a two -wire to four -wire hybrid is provided withinthe chip, simplifying the design of theinterface. The Am79101's high degree ofintegration will make it possible to designfull -featured modems with a very low com-

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ponent count. Very compact arrangementsfor portable use should be easy to achieve.

As a design illustration, AMD suggests the1200/75 modem shown below. For this splitdata rate, a second uart is needed in the formof an 8530; at non -split rates such as 300/300V.21. the Am79101 can be driven by the 8051on its own, using its built-in uart. Automaticanswering of incoming calls is handled by aninterrupt routine in the 8051. If d.t.m.f.dialling is not available on the telephonenetwork, the 8051 can pulse the relay togenerate loop -disconnect dialling pulses.Power supplies are +5V at up to 170mA and-5V at up to 25mA. Sample quantities of theAm79101 "World -Chip" are already avail-able; production quantities will be ready inFebruary. The device is to be produced in28 -pin d.i.l. and p.l.c.c. versions. Details,and a preliminary data sheet, can be suppliedby AMD at Woking on 04862-22121.

ON -HOOK

Am79101

BCDCD Vbb --5VDGND AGND

600one line

Hcto access urrongement

Cmos buffer

RING IND

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2.501.001.9S

1.700.951.751.7S

1.751.002.35

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STK415STK433STK435STK437STK43951K461STK463STK0015STK0029STK0039

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VIDEO SPARES 8 MEADS

recorder model PO For ourquota,on

3HSSV for fergusoni1VC 27303450016 for NationalPanasonic/Philips 29303HSS3N for Notional PanasonicNV777/330 39.503HSSN/4HSS for NotionalPanasonic 29.503HSSH for Hitachi 35.003HSSU3N for NOTIO01:0Panasonic 35.003HSSP for Sharp 35.003H5S6NA for NationalPanasonic Industrial 75.003HSSU2N for NotionalPanasonic 39303HSS5f for Fisher/Fidelity 35.003HSSR for Amstrad/SaishoTriumph 35.00PS3BS for Sony SLC5 6 7 etc

35.0015301 for Toshiba 39.50554075 for Sony SIC 7030 etc

3930PS5B3S for Sony SLC8K9 etc

4930Philips V7000 65.00

VIDEO BELT KITSAka, 8593009500 9800 2.75Amstrad 7000 'So. '

Triumph 1.50Ferguson 3816 2.75Ferguson 3822 1VCHR3360/3660 2.9SFerguson 3V23,1VCliR7700 ISOFerguson 3V711VCHR 7200 2.75Ferguson 3831,1V(H07650 2.75JVC HR3330/360G 2.75Hitachi VT I I '33 2.75

Hitachi 1/15000Hitachi VT8000National PanasonicNV300 333,340National PanasonicNV2000BNotional PanasonicNV777Notional PanasonicNV300013

National PanasonicNV7000National PanasonicNV86008610,8620Sanyo VT(5000Sanyo V105300Sanyo VT( 5500Sanyo V1(9300Sanyo VT(9300PSharp 6300Sharp 7300Sharp 8300Sharp 9300Sony (6Sony C7Sony T9Sony 5130008Sony SL80008080Toshiba 7540Toshiba 9600

2.951.25

3.751.501.75

3.753.903.503.503.503.502.753.502.953.754.503.501.50

T MULTIPLIERSUNIVERSAL 101PLER

DECCA 30DECCA 80DECCA 100DECCA 120DECCA 1730GEC 2040GEC 2110ITT CVCI-9ITT (V(20/25/30ITT (0(45PHILIPS 6815501PHILIPS G9PYE 697

6.356.956.9S

6.956.355.456.956.356.356.956.95

6006.50

PYE 713 4 LEADPYE 713 5 LEADPYE 731/25RANK A774RANK A823RANK T20ASIEMENS TVK76, ISIEMENS EUROPATHORN 1500THORN 1600THORN 3500THORN 8000THORN 8500'HORN 9000

19 9600. 5'10C

SUCK1V18 STICK1V20 STICK

8.508.508.506.356.9S6.9S6.9S7305.455.457.956.9S7.158.508300.901.251.101.40

VARICAP TUNERS15(1043 05 MULLARD 8.65EL(1043/06 MULL ARD 8.6S0321 8.25U322 8.2S0374 11.00

THERMISTORSVA10.10VA1056SVA8650VAI097

0.230.230.450.25

PUSH BUTTON UNITSDECCA/ITT 6 WAY 7.95DECCA 4 WAY 1.95HITACHI 4 WAY 11.95PYE 6 WAY 10.35GEC 213 6 WAY 9.50GEC 21106 WAY 10.50GEC 6 WAY 10.50G8 MATE) 6 WAY 14.50ITT 7 WAY 1030NEONS 7 WAY 1230RANK 4 WAY 10.50RANK 6 WAY 10.50

42 6 WAY 11.00

FUSES SPECIAL OFFER100 PER TYPE

2MM CliOB (a 006 ,ach E4.50100MA 200MA 150MA 500808'Amp 1 25Amp I 5Amp1 6Arnp?Amp 2 5Amp 3 15Arnp 4Arnp

?OHM /DS Dr 0 15 each 11130100MA 150MA 160MA 250MA500MA 800MA 1 2iArnp?Amp 3 I5Arnp SArnp

I 15 inch 0,8 (a 006 each34.00

250MA 500MA 750MA lAmpI 5Amp 2Amp 3Arnp 7Amp10Amp

125 inch A'S (a 0 15 eoch110.00

SOMA 60MA 100MA 150MA250MA 500MA 750MA 1 5Arnp3Amp 4Amp 5Amp

SUNDRIESMONO TAPE HEAR 2.50AUTO REVERSE TAPE HEAD 3.95STEREO HEAD 3.311PYE IF GAIN MODJLE 6.994 433 MHZ CRYSTAL (PAL) 0.455 5 MHZ CRYSTAL ISOUNDIG.45

DELAY LINE D5513 TAU82 1.15FOCUS CONTRIDIGEC1110 130FOCUS CONTROL PYE 731 130FOCUS STICK 0.95SAW FILTER 0.10ANODE CAP 27Kv 049SOLDER MOP 0.64TV MAIN SWITCJIESMAINS SWITCH 1.8(5 1.00MAINS SWITCH DECCA/GEC 1.00G8 SWITCH 1.00GI I SWITCH 0.95

GI 1/12 WITH REMOTE 1.15G11/12 WITH REMOTE ANDMAINS OFF 130

WIREWOUND RESISTORS

1207 WA 0.20II WATT 0.2517 WATT 0.30

LINE OUTPUT TRANSFORMERSMark 80 7.95DMA 100 7.95DECCA 1700 MONO 9.95DECCA 1730 8.25DECCA 2230 8.25GEC 1040 7.50GEC 1110 14.50GRUNDIG 1500 15.45GRUNDIG 510 60102222, 5011 6011 13.45111 (8(70 8.20ITT CVC/S 30 32 8.20PHILIPS G8 8.50PHILIPS G9 8.95PHILIPS GI I 13.95POE 691,697 11.50PIE 713'715 1130DYE 725 10.95DYE 731 9.95RBM 110A 12.40RANK MURPHY T18A 10.00

920A 12 50

A640 8 50A823 I1 50

TANDBERGE 90 I I.15TELEFUNKEN 711A 11.15

THORN 1500115KVI 1545THORN 1590 9.50THORN 3503 ((HT) 9.50THORN 8000 23.50THORN 8500 17.50THORN 9000 19.50THORN 9800 22.40THORN MAINSTRANSFORMER 3000135: 9.70

AAI 19

881150814504148015400156

BA3I8BA37884521BAY?'ElAW62HA51308016001050811510912689177891330916409176091790118709184BY 187

0919989700BY 71,BY 21

DIODES

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0.11.', 0.908929A : 0.2280299 6, 0.7289010 0.20BY075 61X1 1.75

81036 11iiiO 20

BYX38 60,10.60

BYX55 60 0.3009071 60. 1.7581061 0.1581088 11001995(30 0.35(548 8.00(SLOB 16.50MR5I0 0.65MR517 0.65°AA? 0.150090 0.100091 0.150095 0.100A702 0.20187100 5.0016138 2951N23( 4.951923ER 4.9516.9WE 2.95

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0.1501 010

7ENER DIODES

81061 Seri, I 0/988 S.,0.15 0 20

CATHODE RAY TUBESA small selectionfrom our stock of10,000 tubesPlease odd C3

oddMonolcorrioge (ME -1523Wper tube CME 2074W

C3BPEI

15.00 (ME 313268-1322W 10.00 0,6 710tHM

CME 1428W 35.00 7'97.H

29.00 D13'61068 MOO DI I 73GM 53.00 DG7 32 45.00 F31 1 3GR35.00 013 61168 59.00 DI 1816M 13.00 DH3 91 45.00 F41 147LC35.00 D13 63068 59.00 014 7006M 7510 F16 1016M 55.00 M7 I 7066145.00 D13 630GM 59.00 016 100GH/97 &SAO F21 13060 75.00 MI4 ICOGM35.00 014 I SOGH 75.00 D113 16060 69.00 F31 12LD 75.00 M17 1512600

7S.00 M13 112GV180.00 1 M24 120(C

10.00 4014 1 22WA45.00 M28 135G

175.00 M31 18768

55.00 M31 .184W591, M3I 190GRKA M31 1916849.00 M3I 195W53.00 M3132568

65.0055.00

55.0065.0035.00

PHONE0474 60521

4 LINES

P. M. COMPONENTS LTDSELECTRON HOUSE, SPRINGHEAD ENTERPRISE PARK

SPRINGHEAD RD, GRAVESEND, KENT DA11 8HD

A selection from ourstock of branded valves

A I 714 24.50A1834 7.5062087 11.50A2134 14.9582293 6.50A2426 39.50A2599 37.50A2792 27.50A2900 11.50A3042 24.00A3283 24.00A3343 35.95A( PI 5.50AC SP3A 4.95

S2PE N 8.50AC WP1 4.50AC 122 59.75AH221 39.00AH238 39.00A160 6.00ANI 14.00ARPI7 2.50ARP34 1.25

ARP35 2.00AZ1 1 4.50AZ31 2.5085894 250.00EIT513 55.00BT 17 25.00BT 113 35.00(1K 27.50C3M 17.95C1134 32.00C1149/I 195.00(1150/1 135.00(1534 32.00(CA 3.50

CD24 6.50CK 1 006 3.50C K5676 630CV Nos PRICES

ON REQUEST

f 288(C 17.501810F 25.0011148 1.00

EA50 1.00

1A52 55.001876 1.95

1A79 1.95

180(80 1 50

10(91 2 SO

EAf42 1.20EAF801 2.001834 1.501841 3.9S1891 0.8S18(33 2.5018(41 1.95EBC81 1.50

EBC90 0.9018(91 0.9018E80 0.9518E83 0.95113189 0.70

18193 0.951815 23018121 2.00EC52 0.75EC 70 1.751(81 7.95E(86 1.95EC88 1.95EC90 1301(91 530EC92 1.95EC93 130FC95 7.00EC97 1.10EC8010 12.00ECC32 330ECC33 3.50ECC35 3.50ECC81 1.501(181 SPECIAL

D3A 27.50 QUALITY 2.25

541 4.50 ECC82 0.115

D63 1.20 1(182

DA41 22.50 PHILIPS 1.95

DA47 17.50 ECC83 0.95

DA90 4.50 ECC83

DAF 91 0.70 BRIMAR 2.15

DAF96 0.65 ECC83

DC70 1.75 PHILIPS 1.95

DC90 3.50 ECC83

DC X 4-50(X1 SIEMENS 2.50

25.00 ECC83S 330

01116 28.50 ECC85 1.00

DE 18 28.50 ECC86 2.75

DE T20 2.50 ECC88 1.00

DE T22 3500 ECC89 130

DE123 35.00 ECC9 1 2.00

DE T24 27.50 EC( 189 1.95

DE T25 22.00 11(8015 6.9S

DE129 32.00 ECC8035 6.9S

DF91 1.00 1(1804 0.60

DF 92 0.60 ECC807 3.95

DF96 1.25 ECC2000 7.95

DF97 1.25 ECF80 1.15

DG1OA 8.50 ECF82 1.15

DH63 1.50 ECF86 1.70

D1177 090 ECF200 1.85

DK91 120 ECF 202 1.15

CIK92 1 50 ECF801 0.85

0135 250 EC8805 2.50

5163 100 ECF806 10.25

DL 70 2.50 ECH3 2.50

0173 2.50 ECH4 3.00

0191 3.95 ECH35 3.50

D192 1.25 ECH42 130

DL93 1.10 EC981 1.75

0194 3.50 1(883 1.00

51510 13.50 ECH84 1.00

01516 1000 101200 1.50

DM70 2.50 10.80 0.60

DM160 4.50 1(182 0.79

DOD 006 79.50 EC183 2.50

DYSI 1.50 1(184 0.74

0186/87 0.75 1(185 0.9S

DY802 0.85 1(186 0.95

1551 49.50 FC 805 0.95

E80CC 19.50 EF37A 230180CE 12.50 EF39 1301801 18.50 EF 40 4301801 29.50 1142 330E8 ICC 5.50 MO 2.50

1811 12.00 1f54 4.50

E82CC 4.50 18 55 4.95

183CC 4.50 1170 1.20

183F 5.50 EF 73 3.50

E86C 9.50 EF 80 0.55

E88( 7.95 EF83 3.9S

F88CC 3.50 EF85 0.50

F88CC 01 6.95 EF86 2.2S

188(C EF86

MULLARD 4.95 MULLARD 4.50

F90(C 7.95 EF86,CV4085

E9OF 7.95 5.00

191H 4.50 Ef 89 1.50

192CC 3.95 FF91 135

199F 6.95 EF92 215

11301 18.50 EF93 1.50

E180CC 9.50 1194 1.50

1180F 6.50 EF95 1.95

1182CC 9.00 EF97 0.90

1186F 830 EF98 0.90

1188C( 7.50 11183 0.75

12351 12.50 EF184 0.85

1280F 1930 11731 4.50

1283CC 12.00 51800 11.00

EF8045 19.50EF805S 25.00EF1306S 25.001E812 0.65EF1200 130EFP60 330EH9G 0.72(1(90 1.50

1132 0.95

1133 5.00EL34 2.95EL34 MUI L A.,

PHILIPS 4.50E136 2.508136MULLARD 3.9S1137 9.00(138 5301141 3.501142 2.00(1.71 4.501181 6.95

1183 7.S0

1184BRIMAR 0.9S

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11.91 6.001195 1.7511152 15.0011360 6.7S11500 1.95EL504 1.9511506 S.95

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11821 6.9S

11822 12.9511180 22.50EM34 1230EM83 1.65

EMB4 1.65

EM85 3.9SFM87 2.50EN32 15.00EN9 I 1.95

1997 4.50EY5i 0.801970 7301181 2.35EY82 1.151983 1.50EY84 5.951186/87 0.501188 035EY91 5.50E15006 1.5011802 0.701/35 1.00

1/40 2.75EZ4 I 2.7S1/80 0.7S1/81 0.751190 130FW4 300 2.95655/1K 9.00G I 802M 6.9S6240/20 9.00GC1013 17.50GC I OD 17.50GC10/48 17.506C10/41 17.50GC I 2/4B 17306D86W 6.00GDT 120M S.00GN4 6.00GNIO 15.00GRID6 4.00GS10( 163065108 12.006512D 12.00GT IC 14.00GU20 35.00GUSO 17.50GXU I 13.506503 24.00GXU5055 1430GY501 1.50GY802 1.506132 2.506/33 4.50GZ34 2.50GZ37 4.50HABC8.. 1.50FIBC90 1.95

88C9' 1.95

HF93 1.50HF94 1.95HK90 1.95H141 3.50H190 3.50.192 1.50f.,8( 7.004.133( 3.50

136 2.00s144 4.00s 145 4.00K161 5.004163 2.00P.166 USA 9.95K166 GEC 18.50K167 9.004.177

Gold 1 Km 11.9SK181 7.00KT88 USA 10.95KT88Selection 15.00KT88Gold 1101' 2230KTW6 I 2.50K1W62 2.50

KTW63 2.00

KT/63 2.50

107 20 95.0013913 6.95

M508 195.00M5143 155.00M5199 295.00M8079 6.00

M8082 7.50

M8083 3.25

M809' 7.50

M8096 3.00

M8098 5.50

M8099 5.00

woo 5.50M8136 7.00M8137 7.95

M8161 6.50M8162 5.50

M8163 5.50

M8190 4.50M8195 6.50M8196 5.50

M8204 5.50

M8273 4.50M8274 2.00

M8225 3.95M11404 3.50M11401 29.50ME 1402 29.50MHL D6 4.00MP25 195.00MS4B 5.50MUI4 3.50N37 12.50

N78 9.85

082 1.50

OA2WA 2.50003 2.50

082 1.S0

082WA 2.500C3 2.50OD3 2.500M4 2.500M58 3.00

0RP43 2.50

00850 3.95P61 2.50P41 2.50PAB030 0.75

PC86 0.7S

P08 0.75PC92 3.50P(97 1.10P(900 1.25PC(84 0.40PC(85 0.55

PC(88 0.70PCC89 0.70Iff(C189 0.70Pt( 80' 0.70PC(806 0.80PCE82 0.808C180 0.65

PCF82 0.60P(f 84 065PCF86 1.20

PCF87 1.25

P(F20C 1.80

PCF20 1.80

PCF801 1.35

PCF80. 0.85PUEstik 1.25

PCF806 1.00

PC180s 1.25

10420f 1.50

PC182 0.85

P(L83 2.50

P(1.84 0.75

11(1.85 0.80PC186 0.85

PCL805 0.90PD500 5.95

PEI 100 69.00PEN25 2.00

PF N4OD 3.00PEN45 3.00

PEN450D 3.00PEN46 2.00PE06 40N 42.00P11200 0.95

PL 36 1.75

P138 1.50

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425.004CX15008

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85.004032 125.004657 2.2546V7 2.25416A 2.95016 1.5040150A 35.004X5006 350.00SA/ I 02D 9.505A152'. 9.0056' 50.00

SAIIUK 6.255A -180M 9.0056 206K 10.00SAM8 2.15SAN8 1.2058 110M 10.0058-254M 14.5058-255M 19.50

5B 256M 15.005B 257M 15.0058258M 14305(22 125.005(L 8A 2.50

511801 2950.005)18 2.9S5R4GB 5.505R4GY 4.95514 5.95

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681(4 1.00 6SA7 1.35

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6818 1.15 6SG7 2.50

68M6 115.00 6587 1.35

6BN6 1.65 651767 1.20

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6E88 5.95 2017 3.95

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6166C 311 14500

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30E112 0.95 5675 28.00301113 1.10 5678 7.50

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5085 130 6057 3.75

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-TELEVISION BROADCASTAn industry

wake?An IEE discussion meeting."What is happening to the UKbroadcast manufacturing indus-try?" brought together a paneland audience of manufacturersand users, many at managing -director level. It was a pity thatthe overall attendance, like thatat so many recent IEE profes-sional group meetings, ratherreflected an industry in decline,with the manufacturers' nameplates on equipment in the tele-vision and radio studios of theUK now very different from thoseof only ten years ago and with anumber of familiar names com-pletely gone. Nevertheless, it iswidely recognized that the UK isstill a vigorous and successfulcompetitor in transmissionequipment and in the equip-ments developed and marketedby a number of small Britishspecialist firms, many of themformed only recently.

But there is no denying thatthe final withdrawal a year ago ofBritish industry from the designand manufacture of high-gradeelectronic cameras and otherflagship products has had asobering effect on both industryand broadcasters. It has alsobeen a decade of mergers andacquisitions, sometimes withsuccessful companies losingtheir own identities in the pro-cess: in other cases with a num-ber of small production unitsgrouped under the umbrella of alarge group.

Some members of the largepanel were keen to deny anyillness. let alone demise or awake. With Stuart Sansom aschairman and panellists RichardEllis. John Jefferies, Peter Rain-ger. John Wills, John Jarvie. Jer-ry Ventham. Granville Cooper,Mike Cox. Richard Taylor andKen Barrett. and contributionsfrom Peter Wayne. Tom McGannand Bill Dennay. as well as tel-exed comments from PeterMothersole there was no lack ofdiverse and often conflictingviews on what has gone wrong.what has gone right and what theprospects are for the future.

Do British firms spend enoughon r&d? Are they sufficientlymarketing -led or technology -led? Have we lost the pioneeringspirit in which engineeringgiants such as Alan Blumlein

(see page 184) also possessed theability to be first-rate adminis-trators? Do the City and theincreasingly influential accoun-tants concentrate too much onshort-term results? Can UKfirms successfully co-ordinatetheir efforts while retaining theircorporate independence? Hasthe EEC a diode in circuit thatencourages European countriesto sell into the UK white largelyblocking exports into the moreprotected markets of France andGermany?

To almost all of such ques-tions, except perhaps those ondeficiencies in engineeringtraining, almost directly con-trary answers were given. Some,but perhaps insufficient, atten-tion was given to the profoundeffects of Japanese marketingstrategies that concentrated firston attacking the mass consumerand component sectors by offer-ing improved reliability that sig-nificantly reduced the differ-ences between consumer andprofessional equipment, thengaining and holding specificmarket sectors. if necessary bywhat John Wills (Varian-TVT)described as "kamikaze -pricing"that can still put their equipment30 to 40 per cent below thecompetition despite dramaticchanges in the value of the yen.

But it was depressing to hearone panelist trotting out the dis-credited idea that the Japanesebroadcast industry is derivativerather than innovative. Were thisreally the case, more of thoseBritish name plates would still beseen in our studios!

Componentvideo for film

storageIt could be argued that the singlemost important current trend intelevision is the increasing use ofcomponent waveforms. withluminance and chrominance sig-nals kept separate rather thanthe long-established compositepicture waveforms with 'mixedhighs'. Component techniquesare being used in digital ICCIR601) and analogue form. includ-ing MAC (multiplexed analoguecomponents). Analogue compo-nent techniques have made prac-ticable the use of half -inchmetal -particle tape for studio asyell as field operation in the

form of the M.II and Betacam SPformats. Granada's Liverpoolcentre became one of the first tooperate on a component basisand the BSB UK d.b.s. play -outcentre being planned nearSouthampton will operate en-tirely with component video.Thames Television is already us-ing its new M.II component edit-ing suites at the Euston Roadcentre.

Thames is also using a novelfrom of 'Studio -Mac' in a newapproach to long-term storage ofarchival material on 35mm(possibly later 16mm) black -and -white film with a technique itterms "Cinemac". This is basedon telerecording a black -and -white display of time -compressed MAC colour pic-tures.

In support of this system,Thames engineers argue thatsome of their 20 000 massivereels of two-inch archival quad-ruplex recordings, althoughmostly less than 20 years old,have already begun to show se-rious signs of deterioration. in-cluding gradual disintegration ofthe cardboard packaging, lead-ing to mould growth on the tapeitself. Very long term storage ofbroadcast -quality colour tapesstill remains to some degree anunknown quantity. Similarly.conventional telerecording ofarchival material on to colourfilm would not only be rathermore costly and subject to pro-cessing flaws. but would alsorequire careful temperature con-trol to ensure that the film isstored at under 10°C. Black -and -white film can tolerate storagetemperatures up to 25'C and arelatively wide humidity range.Furthermore film material, un-like video tape. is independent oftelevision standards and can beplayed out for any system with-out standards conversion.

Thames are using the agreedS -MAC standard with the addi-tion of line marker pulses and adigital time -code track that iden-tifies individual frames. PALcomposite signals from thearchival tape are decoded with ahigh -quality comb -filter decoderand the analogue luminance andcolour -difference componentsare sampled digitally (CCIR 601digital standard). The stored13.5MHz luminance and6.75MHz colour -difference sig-nals are read out at 27MHz toprovide a MAC -type black -and -

white display and then tele-recorded, for later reproductionwith the aid of a MAC -decoder ashigh -quality colour pictures.

Avoiding on-screen ovens

The second annual report of theRadiocommunications Divisionof the DTI provides an interest-ing example of the efforts of thedivision's Kenley radio technolo-gy laboratory to look ahead andanticipate potential electro-magnetic compatibility le.m.c.)problems rather than waitinguntil it is too late to do muchabout them.

The laboratory is already pre-paring to meet complaints aboutinterference from the fifth har-monic of 2.3GHz microwaveovens to d.b.s. reception (recep-tion of low -power distributionsatellites by home viewers is notprotected). The unstabilizedmagnetron power generators.despite the decreased leakage ofsignals through oven doorsbrought about by public concernat possible biological hazards,are still capable of interferingwith weak incoming satellite sig-nals. and this problem could beenhanced by the smaller dishantennas with poorer sidelobeperformance, possibly locatedinside a house window only a fewfeet from an oven.

The DTI laboratory has de-veloped an improved method ofmeasuring the level of radiationfrom ovens and other microwavesources. To quote the DTI report:"A screened room is equippedwith two or three paddle wheels.Rotation of the paddles producesa time -varying pattern of nodesand antinodes in the electro-magnetic field generated by theequipment under test. By wait-ing 10 to 20 seconds a receivingantenna will give a maximumoutput which is related to thetotal power of the equipmentunder test. The technique is use-ful for frequencies above 1GHzand has now been accepted as aninternational standard methodof measurement. Work is nowcontinuing to determine whatlimits should be used with thismethod in order to protect thereception of satellite television."

Television Broadcast is compiledby Pat Hatwker.

RADIO COMMUNICATIONSUniversitiestackle e.m.c.

\ number of UK university de-partments, where research in va-rious aspects of electromagneticcompatibility le.m.c.) is underinvestigation, have recentlycome together in an effort tcform a grouping similar to thatwhich has existed for a numberof years in the field of mobileradio research. These include:Bradford (Dr P. Excell), Bristol(Dr. R. Burbridge), City Uni-versity London (S. Wilkinson),Hull (Professor M. Darnell), Not-tingham (Professor P.B. Johns)and York (Dr A.C. Marvin).

As an opening shot, Dr AndyMarvin sent out some 200 invita-tions to industry, Governmentdepartments, research establish-ments etc. for a meeting at CityUniversity. The organizers ex-pected that about 20 peoplewould show interest, but about70 accepted the invitation. Themeeting provided firm evidencethat there is a growing recogni-tion of the importance of e.m.c.and r.f.i. in many branches ofindustry - although this has notprevented many problems fromremaining undiscovered untilproducts are in use.

Surveys by Dr Peter Excell andDr Andy Marvin, plus poster pre-sentations, gave an overview 'ofwhat is currently being achievedby university research in suchareas as biological and r.f. igni-tion hazards; user-friendly soft-ware packages for the computa-tion of pick-up on metallic struc-tures; e.m.c. measurements;crosstalk and harmonic genera-tion by the 'rusty bolt' effect;miniature and superconductivecavity resonators for filtering;parallel plate and Crawford celltechnique for testing the degreeof immunity of equipment; re-search into intermodulation pro-ducts generated in materials andstructures; h.f. systems withadaptive frequency selection; theapplication of transmission -linemodelling to computer simula-tion of electromagnetic fieldsand couplings to circuits; thedevelopment of test methodsenabling measurements to becarried out in screened rooms orwith computer simulation; andinvestigation of radiation leak-age from screened cables and thecoupling between coaxial cables.

It was evident from the lively

discussion period that there is adichotomy in respect of industryand academic expectations. Uni-versity research is increasinglyhaving to wear the clothes ofmarketplace in attempting to sellits expertise in order to obtainfunding support from industry.Industry looks on the universi-ties primarily as academia fromwhere it would like to receivegraduates with a better basicknowledge of the increasinglyimportant thermal and e.m.c.design factors.

When I drew attention todigital e.m.c. problems that havebeen exacerbated by the longdelay in limiting, by regulation,the radiation from desk -top com-puters and other consumersdigital equipment, AnthonyNieduszynski. divisional head ofDTI's Radiocommunications Di-vision, expressed confidence thatthe draft EEC directive on e.m.c.will be implemented within thenext 18 months.

It was admitted that most uni-versities still find it difficult, ifnot impossible, to squeeze thestudy of e.m.c. into degreecourses in electronics engineer-ing. Too many firms producingconsumer or even professionalproducts still show little aware-ness of the problems that theycan give rise to, or conversely theproblems imposed on others bybasic lack of immunity to r.f.fields. Some unease was express-ed that the merging of the IEEand IERE could result in a reduc-tion of activities in the e.m.c.field, since the IEE, it was sug-gested, pays less attention toe.m.c. than the IERE.

City University drew attentionto the keynote address by RearAdmiral R.J. Crick, USN, at a1987 e.m.c. conference, when hesaid in conclusion: "There is asignificant and growing problemof global proportions in the abil-ity to employ new technologywithout paying undue perform-ance penalties. Electromagneticenvironment considerationsneed to be organized and syste-mized into an engineering disci-pline, taught in our engineeringcurricula and applied in designand production to help reducethe unexpected performancepenalties."

The London meeting express-ed the hope that the universityresearchers will agree to staytogether on a more formal basisto encourage e.m.c. studies. But

whether industry will agree tofund much university e.m.c. re-search remains to be seen.

One UK educational establish-ment where e.m.c. studies arealready being encouraged is theCambridgeshire College of Artsand Technology. John Worsnop,a senior lecturer and also radioamateur G2BAO, has been con-cerned with a project that in-volves the recording of v.h.f.meteor -burst signals using aBBC microcomputer. He en-countered e.m.c. problems ema-nating not only from this com-puter but from several hundredother computers around the col-lege campus. He has describedmethods of reducing r.f.i. byabout 30dB by having the plasticcase of the BBC micro platedwith a conductive zinc com-pound and by decoupling andfiltering the interface and mainsleads. CCAT has two HND stu-dent projects in this area: oneconcerned with the suppressionof r.f. pickup in public addresssystems, the other studying theuse of fibre -optic cable to replacecopper in RS232 computer ter-minal wiring.

In -car securityThe vulnerability of in -car enter-tainment (i.c.e.) and two-wayradio equipment to car thievesand/or vandals has led a numberof manufacturers to incorporatesecurity devices in models at thetop end of their ranges. It hasbeen claimed that, in the U.K.

Car antenna

alone, one i.c.e. unit is stolen onaverage each minute of the day,often with damage to the vehicle.

Communications equipment,including cellular, p.m.r. andamateur radio, has proved asattractive to the thieves as enter-tainment systems. Some modelshave been designed to be re-moved from their housings whenthe car is left unattended, withthe added bonus that they canthen be used as hand -portableunits.

Another useful step is not tohave an attention -attractingantenna on the car. The backwindow heater antenna de-veloped at Bangor ( E&WWFebruary 1985, pp64-67) andnow fitted as standard on a num-ber of cars is much less vulner-able to casual vandals than theusual external car antenna andhas been shown to work reason-ably effectively as a communica-tions antenna with the aid of amatching unit.

The Dutch engineer amateurDick Rollema, PAOSE, has foundthat a standard car radio antennamounted on the front side of theroof immediately above thewindscreen provides also an en-tirely acceptable antenna for his144MHz, lOW transceiver, withthe aid of a simple matching -

filter. This provides adequateprotection for the front-end ofhis car radio.

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I0 BROADCASTMSC digital

stereo at256kbitis

A decade ago, in the short-livedflurry of interest in the possibil-ity of broadcasting 'surroundsound' (quadraphony) based onAmbisonics technology, the IBAdeveloped. field-tested andpatented a '21/2 -channel' systemcalled MSC, standing for monostereo compatible.

Curiously, the same set ofinitials has emerged again. thistime from Germany, and nowstanding for 'Multiple adaptiveSpectral audio Coding' - usingadaptive transform coding toprovide Compact Disc digitalquality over transmission chan-nels at a data rate of 256kbit/sinstead of the normal CD rate of1.4Mbit/s.

MSC has come from the jointefforts of E.F. Schroeder and H.J.Plate of Thomson consumer r&dlaboratories at Hanover and D.Krahe of the University of Duis-burg (IEEE Trans. on ConsumerElectronics November 1987.pages 512 to 519). It is pointedout that whereas codingmethods based on delta modula-tion or differential p.c.m. seemincapable of preserving CD quali-ty at data rates below about300kbit/s, this is not the casewith a form of adaptive trans-form coding described by R.Zelinski and P. Noll in 1977 forlow bit -rate speech transmis-sion.

Transform coding itself re-duces redundancy of a signal andit is claimed that despite thelarge bit -rate reduction only ab-out 15 per cent of the transmit-ted data. containing the sideinformation on the global shapeof the spectrum, needs to beerror -protected. High quality au-dio is maintained with randomerrors of the order of 10-3 in theunprotected 85 per cent of data.Fora 44.1kHz sampling rate, thesignal representation is only ab-out 2.9 bits per sample with, it isclaimed, the overall annoyanceof transmission errors much lessthan with straight p.c.m. en-coding.

Detailed testing of the systemon many different types of musicand sounds has still to be carriedout. Dedicated hardware is beingconstructed as the next step to-wards an I.s.i. solution.

On radio, on CD: classic 78srevived by Robert Parker.

Recordingsrestored

In his several Jazz Classics inStereo series on BBC Radio 2, theAustralian sound engineerRobert Parker has shown conclu-sively how effective can be theuse of digital signal processing inremoving the surface noise andclicks from the 78 r.p.m. discrecordings of the 1920s and1930s - revealing in the processhow much better some record-ing companies were than othersin achieving good standards ofacoustic and early electrical re-cordings - even though not ev-erybody would agree that addingdigital pseudo -stereo effects al-ways offers significant advantageto playing out a mono channelon spaced loudspeakers.

It is thus widely recognizedthat digital signal processingoffers many advantages in restor-ing archival material over ana-logue processing, particularly interms of flexibility and the easewith which complex operationscan be implemented. With ana-logue processing. it has beenpointed out, separate equipmentis required for operations such asfiltering, spectrum analysis andthe more specialized operationsspecific to restoration of re-corded material; whereas, withdigital processing, the systemcan be completely reconfiguredunder program control from akeyboard.

Likely to be marketed this yearis the Cedar (computer enhanceddigital audio restoration equip-ment to a design developed bythe National Sound Archive ofKensington, London (where aunit has been installed) in col-laboration with Cambridge Elec-tronic Designs. As shown at the1987 BKSTS film and televisionexhibition at Brighton, this hasbeen developed specifically for

the restoration of damaged orimperfect archival recordings byeliminating thumps, bangs,scratch noise etc. from disc,cylinder, acetate or film record-ings with the aid of softwaredesigned for IBM or compatiblecomputer systems.

The effectiveness of digital sig-nal processing was also demons-trated in conjunction with a pre-sentation by S.V. Vaseghi. P.J.W.Rayner and L. Stickler at the1987 Congress of FIAF at Berlin.

They emphasized that many ofthe more advanced processingtechniques are virtually impossi-ble to realise with analogue sys-tems. Operations requiring sig-nal delay, such as correlation,are difficult to achieve in ana-logue form, but straightforwardin digital form since signal datacan be stored in memory.

They demonstrated an exam-ple of a disc which had beenbroken and the two halves gluedtogether, resulting in two diffe-rent forms of click on each re-volution as the stylus jerked up-wards and dropped downwards.It was shown that scratch tem-plates could be obtained andboth these forms of large clicksvirtually suppressed.

Digital processing also offerspromise for removing periodicinterference with slowly varyingfrequency, echo removal andpossibly distortion correction.

Sailing underfalse colours

The tendency for American uni-versity authors to produce long,exhaustive studies, pepperedwith references to a multitude ofpublications, on ever more spe-cialized topics was evident longbefore the growth of compute-rized library information -retrieval systems. But electro-nics will surely exacerbate thesituation.

I have no idea whether Lawr-ence C. Soley and John S.Nichols plus five acknowledged"researchers" used computer re-trieval in compiling 'ClandestineRadio Broadcasting - a study ofrevolutionary and counter-revolutionary electronic com-munication' (Praeger, 1987) butit includes some 270 publica-tions in its 12 -page list of refer-ences, rather than any referenceto first-hand involvement. Even

so. the information given on theBritish operation of 'black'broadcasting by the PoliticalWarfare Executive from "Simp-son's" recording centre inWavendon (Milton Keynes)appears to have been drawn sole-ly from Sefton Delmer'smemoirs. The authors haveapparently missed the more de-tailed and more objective bookby Ellic Howe, 'The Black Game- British subversive operationsagainst the Germans during thesecond world war' (MichaelJoseph). They concentrate main-ly on the many post-war 'black'and 'grey' radio stations thathave broadcast highly politicaland subversive programmes inCentral and South America, EastAsia. Africa and the Middle East,including a number of opera-tions funded by the CIA in the 25years or so since the days of theCIA's anti -Castro station onSwan Island in the Caribbean.

Political broadcasting hasspawned its own vocabulary andSoley and Nichols provide someuseful definitions. 'White' sta-tions are those that operatelegally and openly identify them-selves in their propaganda broad-casts (e.g. Radio Liberty, RadioFree Europe). 'Grey' stations areclandestine stations attributed toor purportedly operated by dissi-dent groups within a country(e.g. Free Voice of Iran). 'Black'implies broadcasts by one sidethat are disguised as broadcastsby the other.

In practice there is a range ofshades between white, grey andblack. 'Snuggling' implies oper-ating a station on the same oradjacent frequency as a legalbroadcast station. 'Ghosting'consists of interruptions to alegal station on the same fre-quency.

In some useful appendices, thebook lists well over 200 clandes-tine stations that have operatedin the periods 1948 to 1967 and1971 to 1985, identified by ideol-ogy or source. The number mayseem large, until it is remem-bered that Howe identified noless than 48 different operationsby the PWE between 1940-45 inthe UK alone, mostly on h.f. butalso using the 600kW 'Aspidistra'medium -wave transmitter atCrowborough, Sussex.

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Award -winningposition sensor

An additional feature of the re-cent Testmex exhibition was theinstitution of the Testmex awardfor a project connected with testand measurement. The winnerwas a system for sensing thepositions of the edges of objects,using a single linear -arraycharge -coupled device tc.c.d.).

The target is back -lit and thec.c.d. is focussed onto its imagein a system very similar to aphotographic camera. Thecharge accumulated on each ele-ment of the c.c.d. is sampledsequentially at a frequency of upto 33kHz. Sampling frequencycan be varied by the user. Theprototype device can identify theposition of an edge to a resolu-tion of one part in 256.

The advantage of the system isthat it does not contact the mate -

UPDATErial and does not depend on ithaving any electrical or magne-tic properties. Intended to solve aspecific problem in textilemachines. the edge sensor is

suitable for measurements onfilaments, threads and wires andis likely to find applications in anumber of different areas.

Receiving the award was AmirRezaie, an electronics student atBristol University where the sen-sor was developed as a jointproject between the mechanical,and the electrical and electronicsengineering departments.

Teletext for thecity

News and prices from the inter-national foreign exchanges,financial and futures markets areto be broadcast, like Oracle. us-ing spare capacity on the IBA tvsignals. Reuter's Citywatch ser-vice comes from its central data-base obtained directly from over1000 financial institutions, near-ly 2900 subscribers in 79 coun-tries and from a network of 1100journalists.

Improvingairport radar

Two study contracts have beenawarded to Marconi by the CivilAviation Authority to investigatemethods of improving the per-formance and operational effec-

tiveness of primary and secon-dary radar systems.

The first study concerns theintegration of primary andsecondary surveillance radar onthe display of an approach con-troller. At present the primarysystem uses the familiar ana-logue display with a rotary sweepon a circular screen. The s.s.r.receives, from an automatictransmitter on the aircraft, itsidentity and height.

The proposal is to use airfieldsurveillance radar plots in placeof the analogue data, reinforcedby the s.s.r. This could provide aclear clutter -free display and re-move the need for the dark en-vironment now needed for ana-logue displays. Additional advan-tages accrue from the variety ofradar data sources that couldthen be used. The study willconcentrate on making the dis-play accurate, immediate andunambiguous.

Secondary surveillance radaris the specific area of the secondstudy which will investigate thereplacement of rotating anten-nas with electronically -scannedarrays le.s.a.).

The advantage of an e.s.a. isthat it can be programmed totake up any direction immediate-ly, and so is not dependent on theintermittent sampling or dwelltime (i.e. beamwidth) of a rotat-ing antenna. This will be espe-cially useful when the s.s.r. mes-sages are expanded into the ex-tended messages of 'Mode S'. Thestudy will consider many aspectsof antenna design and beam -forming techniques

Torch rescuedby Australians

Torch Computers. which nowspecializes in Unix workstations,has received a 'substantial' capit-al injection from Catsco, an Au-stralian computer and com-munications group. Catsco hassupplied a number of systems,based on Torch equipment, tothe New South Wales and Victor-ia state telecom companies, so ithas a vested interest in keepingTorch going. Its directors alsosee Torch as an entry into theEuropean marketplace and theopportunity to launch "a numberof new and exciting productsfrom the development teams ofhot h companies."

Changes atNimbus recordsNimbus Records was the first UKcompany to build its own com-pact disc mastering and manu-facture plant. Its first commer-cial CD-rom is a world atlas.commissioned for use by oilcompanies. Each CD stores550Mbyte of mapping data and isrun by a personal computer withoutput to a digital plotter. Threescales and two projections arebuilt into the disc images butaccompanying software fromClarinet Systems allows the userto zoom in and out with a choiceof 26 projections. Colour displayand plotting of specific features,boundaries, towns, landmarks ispossible.

The largest information display in the world using liquid crystals is Racal's claim for the arrivals anddepartures board at London's Euston station. Eight thousand display modules are arranged in 20 lines.Each module uses a 12 by 6 dot matrix to allow upper and lower case characters. All is controlled froma desk -top computer.

The company's expansionplans include further manufac-turing facilities in Wales and inthe USA while the pilot plant inMonmouth will concentrate onlaser mastering (for which thecompany won a Queen's Award)and other pre -production ser-vices. A new research and de-velopment centre is being pro-vided for work on new productsand improvements and a soundand vision studio for recordingCDs and CD videos.

Maxwell Communications hasacquired a majority share in thecompany for £24M. A particularthrust of the investment is thedevelopment of electronic pub-lishing on CD-rom.

Hopping relayBattlefield communicationsoften use frequency -hoppingradio systems which are resistantto jamming and eavesdropping.Now Ericsson has come up with afrequency -hopping radio relay toenable the use of flexible net-works with anti -jamming per-formance. Pseudo -randomswitching across the full band-width is used to protect thenetwork from high -power pulsedjamming as well as partial bandjamming.

Prize forhelpingdisabled

The third IEE prize for helpingdisabled people will be awardedin November, six months after31st May which is the closingdate for entries. Applications arewelcomed from any part of theworld for electrical or electronicsdevices or techniques which helpovercome any type of disability.

Winners of the three -yearlycompetition include John Feav-er, for a system to operate a carfrom a joystick manipulated bythalidomide victims and otherseverely handicapped people. In1985 there were two winners:Andrew Downing of the Universi-ty of Adelaide, for an eye -gazeoperated computer: and PeterDonaldson of the MRC for anelectronic bladder control devicefor paraplegics.

rUPDATE1104710"wroilo71071107.70.440-it.,40000001011010

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A fly's leg is used to demonstrate the size and precision of amicrostructure produced by Degussa, Frankfurt Such galvano-forming processes are used in the preparation of i.cs.

Only devices actually in useare eligible. Devices will havebeen developed or significantlyimproved since June 1985.Awards are made to individualsand not to companies or institu-tions: though the prize may beshared. Applicants need not bemembers of the Institution. De-tails from the Institution of Elec-trical Engineers, Savoy Place,London 11'M? OBL.

Award foryoung

designersElectronics engineers under theage of 25 are invited to enter forthe 1988 Young Electronics De-signers Awards. To enter, stu-dents must produce an electro-nic device of their own which isoriginal, effective and has a use-ful application in every day life.Trophies and cash prizes arepresented to winners in each ofthree categories: junior (under15), intermediate (15-18). andsenior (19 to 25). Entrantsshould be students in UK educa-tional establishments and thesenior category has the increasedincentive of the possibility ofemployment in electronics andcourse sponsorship.

Finalists will also receiveprizes from the sponsoring com-panies, Cirkit and Texas Instru-ments. The awards are adminis-tered by a charity. The YedaTrust. 24 London Road, Hor-sham, West Sussex RH12 lAY:the closing date for applicationsis 31st March.

Ferranti sellssemiconductor

businessFerranti has sold its semicon-ductor division to Plessey for£30M. At the same time it hasmerged with, i.e. bought, theInternational Signal and ControlGroup. This marks a shift inemphasis for the company, awayfrom components and towardsfurther expansion into inte-grated systems. During the re-cession Ferranti has found itincreasingly difficult to keep upwith the growing demands fornew devices. Rationalizing itspriorities has resulted in thecurrent moves. A Ferrantispokesman told us that similarmoves have taken place betweenGEC and Plessey, with PlesseyTelecommunications going toGEC and some of GEC's manu-facturing facilities transferred toPlessey. Plessey and Marconi,followed closely by Inmos, willthus be the only remaining ma-jor semiconductor manufactur-ers in the UK.

In briefIBM are to buy high -resolutioncolour c.r.ts from Mullard fordisplay terminals. The contractis thought to be worth millionsof pounds. Mullard's plant inDurham will supply the tubes toIBM in Greenock where termin-als and personal computer sys-tems are produced in large num-

bers for Europe. the Middle Eastand Africa.

The prestigious Fellowship of theSociety of Motion Picture andTelevision Engineers. SMPTE,has been awarded to a BBC en-gineer. Michael Stickler is depu-ty head of BBC tv planning andinstallation and was awarded thefellowship for his work with re-mote control and digital videointerface standards. Over recentyears Mr Stickland has beenchairman of the EBU committeewhich has investigated andagreed with the SMPTE interna-tional standards for such sys-tems.

Those who forget to turn their tvoff at night may be surprised tosee scrambled pictures on theirsets. The BBC is carrying outexperiments for a closed user -group system which could trans-mit programmes overnight to,for example doctors, which couldbe recorded for subsequent view-ing. The trials involve scramb-ling the pictures by pseudo-random line delays, while thesound is frequency inverted.There is no plan to institute sucha system since it would need anew broadcasting act. A similarsystem, Discret 12, is used inFrance.

Desktop weather maps are nowavailable to subscribers of Micro -Link, whose WeatherLink ser-vice receives images from thegeosynchronous Meteosat whichtransmits true -colour picturesrather than the infra -red imagesavailable from NOAA in polarorbit. The images are distributedthrough the telephone line andcan be received by most desktopcomputers with a modem.

Power transistors from SiliconTransistor Corporation are to betested and packaged in the UK bySemiconductor Supplies Inter-national. This joint venture pro-vides an alternative Europeansource for 2N, Jedec. MJ and SDTdevices under the trade nameSilicon Transistor Europe. It alsomakes possible custom packag-ing and special selection of pow-er devices for up to 100A.

Two PDP11 computers havebeen bought by the BBC for usewith Radio Data Services. Initial-ly, channel identification will bebroadcast, with traffic flashes onsome local stations.

PINEAPPLE SOFTWAREPrograms for the BBC model 'IT, B+, Master and Master Compact with disc drive

DIAGRAM IIDiagram II is a completely new version of Pineapp , ; ir Diagram' drawing software The newversion has a whole host of additional features which make it into the most powerful and yet quick touse drawing program available -for the BBC micro The new features mean that 'Diagram II' can now beused for all types of drawings. not lust circuit diagrams Scale drawings are possible and the facilitiesfor producing circles and rubber banded lines together with the pixel drawing routines make any typeof drawing possible This advert has been produced completly using Diagram II

Summary of Diagram II features:1 Works on all model BBC computers and makes use of Shadow memory if pass2 Rapid line drawing routines with automatic loins for circuit diagrams.3 Rubber band line and circle drawing modes4 Makes use of the Acorn GXR rom to produce ellipses, arcs, sectors. chords and flood filling5 Pixel drawing mode allows very fine detail to be added6 Defined areas of screen may be moved, copied. deleted or saved to disc7 On -screen cursor position indication allows scale drawings to be made8 Keyboard keys may be defined to print User defined Characters allowing new character sets to be

used9 Wordprocessor files may be loaded and formatted into defined areas

10 Up to 880 UDC's if shadow memory available, 381 without shadow11 Compatible with Marconi Trackerball and most makes of 'mouse'

.12 All 'Diagram Utilities' are included13 Completly scaleable print routines allow any area of the diagram to be printed either horizonta

or through 90deg. in scales that may be varied in 1% steps allowing up to 18 mode 0 screens to B.printed on an A4 sheet (still with readable text)

14 Smooth scrolling over the whole area of the diagram

Diagram II consists of a set of disc files and a 16k Eprom. The disc is formatted 40T side 0and 80T side 2. Please state if this is unsuitable for your system, or if you require a 3.5Compact disc

DIAGRAM II f55 VAT p&p free

MARCONI TRACKERBALLFor Model 13' and B+ (with Icon Artmaster)For Master 128 (with Pointer Rom)Bare Trackerball (no software)Pointer Rom (available separately)Trackerball to mouse adaptersPostage and packing on Trackerballs

f60 00+ VATf60 00 +VAT(49.004 VATf 12 50 + VAT

f8 00+ VATf 1.75

All orders send by return

PCBPineapple's now famous PCB drafting aid pr,,,I.. ipiex double sided PCB's very rapidly using anymodel BBC micro and any FX compatible dot-matrix printer.

The program is supplied on Eprom and uses a mode 1 screen to display the two sides of the board inred and blue either separately or superimposed Component layout screens are also produced for asilk screen mask.

The print routines allow a seperate printout of each side of the board in an expanded definition highcontrast 1.1 or 2,1 scale. Toe print time is typically about 5 minutes, for a 1 1 print of a 7- * 5" boardThis program has too many superb features to adequalty describe here, so please write or 'phone formore details and sample printouts

Price f85.00 r' VAT

PCB PLOTTER DRIVERi'w adtht,rri to the PUB suttwdre .s me PUB plotter drverrame. This enables files produced by PCB to be used inAction with most types of plotter to produce plotted output

er than the normal dot-matrix printer output The program is de for use with most makes of plotter including Hewlett,ard. Hitachi and Plotmate M The program can also be

',figured to work other plotters by entering suitable plotterinstructions.

All the features of the printer driver are included, such as theautomatic thinning down of tracks between roundels Mirror imageplots are also available

Price f35.00 VAT

ADFS UTILITIES ROMADU is an invaluable utility for all * sto the ADES filing system aswell as providing an extensive LL 1, r covering areas such asrepeated disc compaction. saving and loading Rom images. auto booting of files and many more

Copying of DFS discs onto ADFS discs can be made in one pass with automatic creation of therequired directories on the ADFS disc All functions are fully compatible with Winchester drives.including * BACKUP which allows backing up of Winchesters onto multiple floppies

New *commands are as follows: *ADU. *BACKUP, *CATALL, *CHANGE, *DFSADFS, *DIRALL.*DIRCOPY. *DIRDESTROY. *DIRRENAME. *DISCEDIT. *DRIVE. *FILEFIND, *FORMAT.*KILLADU. *LOCK. *MENU. *PURGE, *PWRBRK, *UNLOCK, *VERIFY, *VFORMAT

Price £29.00 + VAT

MITEYSPICE- Powerful AC & DC, circuit analyser package with Graphics output. Sendfor more details - L119.00 + VAT

39 Brownlea Gardens, Seven Kings, Ilford, Essex IG3 9NL. Tel: 01-599 1476 [A w1

VALVES SPECIAL Prices are correc at time of press Du may fluctuateQUALITY Please phone for tarn quotation V A T included

A1065 1.40A2293 7.00A2900 12.75AR8 1.15ARP3 1.15ARP35 0.70ATP4 0.90612H 6.90CY31 1.40DAF 70 1.75DAF96 0.90DET22 32.80DF92 0.650F96 0.85DH76 0.750L92 1.850186 87 0.6501802 0.70E92CC 2.80E18000 11.5051148 0.58EA76 1.601634 0.70E691 060EBC33 1.85EBC90 0.90EBC91 0.90EBF80 0.95EBF89 0.80EC52 0.65EC9i 4.40EC92 1.85ECC81 0.95ECC82 0.95ECC83 0.75ECC84 0.60ECC85 0.75ECC88 1.10ECC189 0.95ECC804 0.65ECF80 0.95ECF 82 0.95ECF802 1.80ECH42 1.20EC1-181 0.70ECH84 0.80ECL80 0.65ECL82 0.75ECL85 0.75ECL86 0.90EF9 3.50EF22 3.90EF37A 2.15E F 39 1.10

E1-80 0.65EF83 3.90EF85 0.60EF86 1.25EF 89 1.60EF91 1.60EF92 215EF95 0.95EF96 060EF 183 0.75E F 184 0.75E F812 0.75EF1,200 1.8511390 0.85E L32 0.85EL34 2.101L34' 5.15EL82 0.70EL84 0.95EL86 0.95EL90 1/5EL91 6.50E L95 125EL504 2.70E L509 5.85EL519 7.70EL821 8.45EL822 9.95ELL8OSE 4.50EM80 0.80EM87 3.00E151 0.90E Y81 0.75518687 0.60E188 0.65EZ80 0.70EZ81 0.70GM4 89001501 1.30GZ32 1.40GZ33 4.20:GZ34GZ34' 3.80GZ37 3.951066' 15.50K T77" 14.006188 17.006188" 25.00ML4 3.20ML6 3.20MX120 01 29.50N78 9.900A2 0.70062 0.80

PCL82 0.95PCLE14 0.85PCL86 0.80PCL805 85 0.9510503510 4.30PFL200 1.10PF L200" 290PL36 1.10PL81 0.85PL82 0.70P1,83 0.60PL84 0.90PL504 1.25PL508 2.00PL509 5.65PL519 5.85PL802SE 3.45P180 0.70PY81 800 0.85P182 0.75P188 0.60PY500A 2.1000003 10 5.950000310' 7.5000V03 20A 27.5000006400 28.5000V06404' 49.50OV0312 5.75SP61 1.80T 121 37.50T T22 37.50000080 0.75UBF80 0.70UBF89 0.70UCC84 0.85UCC85 0.70UCH42 2.50UCH81 0.75UCL82 1.60UF41 1.85UF805 1.60UF8 1-20UL84 0.95

UMB° 0,90,,UM80' ''..um, 0.70UY82 0.70UY/35 0.85vR105 30 1.4550115030 1.80X61M 9.70X66 180Z749 0.752759 19.00ZBOOU 3.45

2801U 3.75Z803U 21.1529007 2.45103 2.75114 0.651R5 0.80154 0.651S5 0.751T4 0.751U4 0.802X2A 3.803A4 0.703012 3.403828 12.003828' 19.503D6 0.603E29 21.85304 1.654032 18.255R401 3.355040 1.855V4G 0.7551301 0.955Z3 2.805Z4G 1.255Z4GT 1.15630LS2 0.806A67 0.706AC7 1.156AG5 0.606AK5 0.95601(6 2.856AL5 0.606AL5W 0.856AM5 6.506AM6 1.606AN8A 2.506005 1.756A05W 2.306AS6 1.156AS70 4.956AU6 0.9060X4GT 1.30600501 1.306606 0.856BA6' 1'856E1E6 09560E6' 1.8560060 1.606606 1.306007A 0.85613R7 4.806BW6 6.106BW7 1.65

6C4 1.106CH6 7906CL6 2.756CW4 7.406CX8 4.608cy5 1.156D6 2.506F6G 1.956F6GB 1.106F7 2.80

6F8G 0.856F12 1...,-6F14 1.156F15 1.30....,,

6F17 ....6F23 0.656F24 1.136F33 10.506FH8 18.806GA8 1.956GH8A 0.906H6 1.606,14 1.956J4WA 3.10605 2,3061501 0.90616 0.856.16W 2106.JE6C 8.106JS6C 8.1061U6 6.3561(7 1.4561(06 7.406L6 4.606L6GC 6.256L60T1C 2.556118 0.706LD20 0.706L06 8.106070 1.306SA7' 1.806SG7 1.806SJ7 1.806SK7 1.856SL7G7 0.856SN7G I 1.506S07 0A56SR7 4.606V6G 1.506V601 1.406X4 1.5060501 0.756160 2.806Z4 1,307Z4 1.00

90811E212A612AT612AT712AU712AX7t 2BA6128E612E11-17

12E112J512K7GT

12K8GTt 207GT12SC712SH712SJ7t 2SK712S07GT12Y413031306190051903190619H520D1

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ENTER 48 ON REPLY CARDENTER 45 ON REPLY CARD

QuarthandDEC Bought and SoldCOMPUTER EQUIPMENT

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DN- I I £450LP 11 Printer I/' £200R501 + Controller E350RX-211 RX02 Controller 0210

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Marconi T12162 Attenuator 0 111dB £100Marconi TF2430 Freq Counter 80MHz £200Racal Dana 9500 Counter Tuner £250HP5004A Signature Analyser £395HP1056 Quartz Oscillastor C150HP6)2A UHF Sig Generator £375HPI602A logic Analyser £450Solartron 3430 Portable Data Logger £850Rodford DMS2 C275Marconi C1452A Siq Gen (250

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LINSLEY-HOOD SUPER HIGH QUALITY AM/FM TUNER SYSTEMA combination of his ultra high quality FM tuner and stereo decoder described in ET!'and the SynchrodyneAM receiver described in "WW- Cased to match our 300 Series amplifiers this kit features a ready builtpre -aligned FM front end. phase locked Stop IF demodulator with a response down to DC and an advancedsample and hold stereo decoder This tuner sounds better than the best of the high-priced exotica but thanks*o HART engineering, remains easy to build0400 -FM FM Only Kit Complete C134 61K400A6CFM Full AM/FM Kit 0205 92

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LTD.1AA.

DINERS

CLUBVISA

_2/01-953 6009SPECIAL OFFER PCB CARDS Card No 1 I /80A DMA. I . 2130A CPU.

1 D8255 AC5 in holders. I .' 5MHz Xtal. 8 . MB8264 15.1 x SN74198Nr 53 various chips, rew ex -equip £16.50

16,Inda7 Cu opr,ue /AI Mender Clid,SIS J ,4 50 GreerThandar Composite 7511 Monitor Chassis ' 1.,4 50I3 WhiteThandar Composite 7511 Monitor Chassis I. 14350 GreenThandar Composite 7511 Monitor Chassis, 12 £43.50 B WhiteMonitors are new and boxed 12 volt DC £4.00 c p

Che-. 11- 11;.,r-u!s_r r . .,,, _,,e3 Keyboard incirl.:u; 0 - u].,.. ..:Jedgraphic keys 108 keys form X -V mate, full cursor control keys6 encode keys 9 graphic control keys 517 rail teak and black aluminium case.diagram 52,5 ,i 36 3. 10 circuit diagram supplied new and boxed £24.95 3+122.00 ehCard No 2 I x WD1933B-01 in holder F 16 various new ex equip £1225

Card No 3 2. 08255 AC 5. 2 .HLCD0437P in holder n 10 various chips, newex -equip 14.95

12" 7511 Comp. Video 22MHz bandwidth monitor 230V AC input new andboxed, green phosphor In case and data £59.95 c p 500 Wavetek. VGC Model I I 1 L75.00

Wavetek. VQC. Model 131 178.00E H Resea- oh Labs Model 139L Pulse General. £80.00Schaffner MSG 200C NSG223 interference Gene -at, - £650.00Singer Gert Phase Angle Voltmeter c with 4001-1: mois, , 125000Dalton 100.1 Multifunction Meter £250.00Patron 1058Digital Multi Meter £250.00Dacron 1013 RMS Voltmeter 1115.00Marconi Sanders Microwave Oscilloscope 27-40GHz 11.150.00Siuers Lab Rotary Vane Attenuator 8 2 12 4GFiz Cal to 22 8-88 £215.00Tektronix 111 Constant Amplitude Signal Generator 350KH: to 100MHz£175.00dryans 626000 A3 Pen Recorders complete from 1175We have a large selection of Pen RecordersOatron 103/A RMS Voltmeter £145.00KSM 0-248 0.156 Metered PSU new £500.00Tektronix 133 Linear IC Test Fixture £375.00HML411 0 .206V Capacitor Charger £1.000.00 newTektronix 2101 Pulse Generator 2 5Hz to 25MHz Repetition ./k/.. £115.00Ballantine 323-01 True RMS Voltmeter £115.006SAF Veneer 7737A Digital Counter £150.00Miles High \ion Insulation Tester IT30 c -with probe 3065 L31600Krohn, Hite Sideband 10 watt Amp DC IMC Model DCA: £200.00General Radio slotted line recorder type 1521-SLQ1 120000Farnell F unc ion Generator EG1 190.00Philips 3212 25MHz D Beam Oscilloscope £350.00h'ewlett Packard 181A Oscilloscope Mainframe storage c with 18016 el chit

vertical amp 50MHz. 1820A time base with manual £375Hewlett Packard 62605M DC PSU 5V DC : Si 100A £125.00Hewlett Packard 301 Carrier Amplifier Recorder £150.130Hewlett Panlard 33308 Synthesiser £1.500.00Hewlett Packard 331 A Distortion Analyzer 1230.00Hewlett Packard 43IC Power Meter £69.00Hewlett Packard 34508 Multifunction Meter 1150.00Hewlett Packard 116IA Logic Slate Analyzer c w 8085 Module & 80 Moduleclock probes 6 bit data probe E850.00 c p 115 00Hewlett Packard 5000A Logic State Analyzer 1230.Hewlett Packard DC PSU amp t 500 IA /75.00

Card No 4 LCD 6 digit display 12 momentary plain keyboard rocker switch 4bar LEDs Green, yellow. red Flat top type 16.95

power supplies All 240V AC input unless stated 5V 20A s mode 118.50. 5V40A s,mode £25.00. 5V 606116.40 12V 60A £70.00 Farnell SM , 5V 106.i 24v 46. I 120 500M - 5V IA. new data £28.50. Farnell SM I2V 2 56 ultrasmall £38.00, Farnell Fan Cooled SM . 5V 106

5V IA.. I28 3A. 120. 1A13250. 12V 3A Linear 11725. Farnell SM 6V406126.50. Solartron metered PSU 2.0 - 600 0 --IA £51.75. 10 5V 30A SM£26.50.5V :A PC Card Regulated £8.60. 0-36V. 0-3A metered £50.00. Gould379.5v 40k I 2V 46. 150 11A. s mode £59.00 Power supply makes areFame!! Advance Gould Coutant AC DC Aztek. SolartronSpecial Offer AC DC Electronics 5V 60k 12V. 2. 2 5A 2400 ort 115V inputL50.00

Card No 5 Peripheral Communication Controller 8 . MC686618* MCI4891 8. MC1488P 13 Ass Chips all in holders 118.95

Card No 6- 64.646 16 pin Ram 15Ons Access time . 2964 controller IC4-14 various chips £19.95

Card No 7 Hard disk floppy disk controller card S100 series IncludingD765AC D8237 AC5 8253 8085A 2764 646 [prom SN74L240N 224N etcinc. block diagram £26.50

Tektronix Plug In Units. 111 D 'trace DC to 50MHz £43 I A2 Dlrace DC to50MHz 1.35 IA4 41race DC to 50MHz £75 165 Cc omparator DC to 50MHz£39 CA cal. pre amp £45 Many more in stock please ring

Card No 8 Infra red Remote Controller I AY -3-8470A Encoder IC I Infra Red

Emitter 16 Keyboard membrane 1.3.50

Card No 9 1 . MC68.300L12 CPU Motorola ceramic gold planted I ' 16MH:Xtal oscilloscope i 37 various chips irc block diagram 129.95

SEW Panel Meters First band meters MR52P. size 60.60 MR45P size50.50. MR65P 80. 80, MR38P 42.42. accuracy 2%

Card No 10 I MC68000L8 CPU Motorola ceramic gold plated. I .16MHzXtal oscilloscope 041 various chips. inc block dia £10.95

MR52P (SR) 30A AC Movolg Iron £7.00MR52P (SRI 106 AC Movng Iron £7.00MR45P IA DC M 'Coil £6.00MR65P 26 DC 16.00MR65P 5V DC M Coil 15.75MR45P 300V ACM Coil with reel £625MR45P I MA DC M Coil 15.75MR38P (CR) 3000 AC M Coil with 'ea £6.00MR52P (CR) 3000 AC M Cr r vett, re, t £625.MR52P 5CW DC M Co, f575MR38P DC

MR45P 250000VDC M-Ciii, L5 75M , £5 00

MR45P 50-0-508 DC 162550830 82.110 56 DC M C" 1700SC/830 -11 - VU Meter £625MR65P 50A DC M 11011E7.00Many more panel meters quantity discount

Shugart 56400 51/4" full height disk drives. single sided. single density.ex equip tested. 120.60 data supplied 2. £37.50

CDC Wren 36 meg Winchester 5IV"hard disk drive. new ex equipment c -withuser manual 1145.00 cep 3 60

Newbury Wyndsor 9412 80 Meg hard disk drive, 8"" new ex equipment£135.00c 'p 5.75. c with manual CODY

Tabor Micro floppy, single sided

Hewlett Packard 989541010 8" disk drive cased power supply manuals etcNew and boxed discount for quantities S.295.00. VAT carriage and packingat cost, please ring

Hewlett Packard 86A Personal Computer with built in interfaces for 2 discdrives and centrum, ciinoatible printer. 641s built in user memory. 14 userdefinable keys. dispir. .. it by 16 or 24 hi,i mO characters. c 'with systemdemo disk user prof:' - riser manual I - imide. complete new inr.- ii,,,i b.,,,,,, £350 On .- iiiri i1 r , , ' ',1 4,,,,,,t '" 7

Motorola TTL Monitor Chassis. 7' green phosphor. 22MHz bandwidth 120 DCinput 1 2A new and boxed. complete with circuit diagram and data compatibleto BBC. IBM computers. diagram supplied for connection to BBC. 751/ compvideo circuit diagram supplied. discount for 10 4' £20.60

We would like the opportunity to tender for surplus equipmentOfficial Orders/Overseas Enquiries WelcomeiOrder by phone or post. Open 6 days. half day Thursday. Please ring for C/P details not shown Postal rates apply U K.mainland only. All test equipment carries warranty. All prices including 15% VAT 8 c/p unless stated. Save time phone your order for quick delivery with Access. Amex.

Diners or Visa cards. Remember all prices include VAT and c/p unless stated

ELECTRONICS Sr WIRELESS WORLD 211

TRAINEERADIOOFFICERSAre you looking for a secure shore-uased job whicl . otrura rewording career in the forefront of modern Tele-

communications technology... then considerjoining GCHQ as o Trainee Radio Officer.

Training involves a 32 week residential

course, (plus 6 weeks extra if you cannottouch type) after which you will be

appointed RADIO OFFICER and undertakea varlet. '.-pecialist duties covennc ....hole

of the 'n of DC to lightWe offer you: Job Security GoodCareer prospects Opportunities

for Overseas Service AttractiveSalaries and much more.

To be eligible you must hoid or hopeto obtain on MRGC or HNC in aTelecommunications subject with an

. ability to read Morse at 20 wpm.(City and Guilds 7777 at advanced

level incorporating morse transcription would be advantageous). Anyonewith a PMG, MPT or 2 years relevant radio operating experience is also eligible.

The Civil Service is on equal opportunity employer.

Salaries: Storting pay for trainees is age pointed to 21 years. For those aged 21or over entry will be of £7,162. After Training an RO wit start at £10,684 rising by 5

annual increments to £15,753 inclusive of shift and weekend working allowance.fffff . d weft, Wnte or telephone for an application....................."

brrn to:-........... : saw

APPOINTMENTSAdvertisementsaccepted up to

12 noon January 30for March issue

DISPLAYED APPOINTMENTS VACANT: £25 per single cul. centimetre min. 3cm).LINE advertisements (run on): £5.50 per line, minimum £45 (prepayable).BOX NUMBERS: £12 extra. ( Replies should be addressed to the Box Number in theadvertisement, c/o Quadrant House, The Quadrant, Sutton, Surrey SM2 5AS).PHONE: PETER HAMILTON, 01-661 3033 (DIRECT LINE)

Cheques and Postal Orders payable to REED BUSINESS PUBLISHING and crossed.

I CH THE RECRUITMENT OFFICE, GCHQ, ROOM A/1108fIO7THE

ROAD, CHELTENHAM, GLOS GL52 5.-UOR TELEPHONE 0242) 232912/3

Hardware/Software/SystemsL9,000-05,000

Asa leading recruitment consultancy we have a wide selection of opportunitiesfor high calibre Design, Development, Systems and supporting staff throughout the UK

If you hove experience in any of the following then you should be talking to us for.i career move

ARTIFICIAL INTELLIGENCE IMAGE PROCESSING ANALOGUE DESIGNMICRO HARDWARE 8. SOFTWARE GUIDED WEAPONS C PASCAL

ADA * RF &MICROWAVE ELECTRO-OPTICS SIMULATION C'IREAL TIME PROGRAMMING * SYSTEMS ENGINEERING ACOUSTICSSONAR * RADAR SATELLITES AVIONICS * CONTROL ANTENNA

VLSI DESIGN

Opportunities exist with National, International and consultancy companies offeringexcellent salaries and career advancement

To be considered for these and other requirements contact John Spencer orStephen Morley or forward a detailed CV in complete confidence quoting Ref. WW/66.

Recruttmern

STS Recruitment, 85 High Street, Winchester,Hants 5023 9AP. Tel: (0962) 69478 (24 hrs).

Sinclair House, 74 Willoughbytilmil.P.I.111mIlml Lane. London N17 OSFAPPOINTMENTS Telephone 01-808 3050

THE UK's No. 1 ELECTRONICS AGENCYELECTRONICS ENGINEERS if you are looking for a

job in DESIGN, FIELD SERVICE, TECHNICAL SALESor SOFTWARE ENGINEERING.

Telephone NOW for one of our FREE Jobs lists orsend a full cv to the address below.

Vacancies throughout the UK to £18000 pa.

Co we EN - -- - on

Capital Appointments Ltd., FREEPOST London N17 OBR.

Please send me your list for Engineers

Name (ww)

Address

Post Code

01-808 3050 - 24 HOURS

Due to its continuing successes the Waverley Division of DowtyMaritime in,ftems lid ha, requirements for the fallowing staff

ENGINEER/TECHNICIANSCommissioning EngineerPreparation of sonar systems and peripheral equipments to enableFactory kceptance Tests to be conducted Prime responsibilities willbe to establish operational systems, spares, equipments, and PBC's AnliNC/D qualification is expected, together with experience gainedpreferably at system level Fault finding ability an advantage

Prided !won TechnicianPrimarily setting -to -work of Thermal Printers which are state of the artproprietary Waverley products Assistance with sea trials, otherproducts and customer field service is required from time to timeApplican s should hold a minimum of ONC, ideally HNC/D in electronicswith three years' experience

Repairs -.clinicianThe succnsful candidate will be capable of diagnosing electronic faultsto component level, setting -to -work, calibration and final inspection ofrefurbished items In addition, the capability to conduct comprehensiveelectronic and mechanical surveys returned for repair will be expectedQuaid icctions sought are ONC/TEC III or equivalent together with aminimum of three years' experience.

Vacancies also exist in our Production Area forPrototype WirepersonsTo work on the wiring of electronic cabinets and sub -assemblies.Applicants must have the ability to work directly from drawings andschedules 2/3 years' experience of working to the high standardsrequire( is essential

Salaries offered will depend upon ability and experience Somerelocati )n assistance will be paid where appropriate.

Immediately for an (wok a,

Terri Houghton, Personnel Officer, Dowty Maritime Systems,Waved!), Division, 10 Cambridge Rood, Granby Industrial Estate,

\..Weymauth DT4 9TJ. Tel: 0305 784738, ext 174. 507

1)0W5717

212 1:1.1:0 I It( \ I s cE 11 1121. LESS WORLD

Wanted urgentlyPractical people for the Third World.Builders &BricklayersGhana. Kenya. Papua NewGuinea

Carpenters &JoinersNigeria. Papua New Guinea

Clerk of WorksMalawi

Civil EngineersNigeria, Sri Lanka

Machinists, SheetMetal Workers,Fitters & WeldersNigeria

Foundry Engineers,MetallurgistsGhana. Sierra Leone

Petrol/DieselMechanics &AgriculturalMechanicsBelize. Tanzania, Sierra Leone.Ghana, Liberia. Nigeria,Vanuatu

ElectronicsEngineers-including Hospital/Radio equipmentBelize, Nigeria

Many people want to help the Third World.But only a few are in a position to offer the kind of helpwanted most: the handing on of practical skills tohelp others help themselves.VSO has urgent requests from developing countriesfor people to work in the skill areas listed here.You need the appropriate experience and a technicalqualification. You will be paid a local wage. You willhave the opportunity to live and work within a ThircWorld community for at least 2 years (so you should bewithout dependants). You will experience a completelydifferent way of life.If you feel you could fill any of these posts (rememberthat much of your work would involve training others)please contact us NOW.Tick you skill area and post to: Enquiries Unit, VSO.9 Belgrave Square, London SW1X 8PW.I am interested. I have the following qualification.

Address

EWW 2 88

VHelping the Third World help itself.24pS A E appreciated Chaityno.313757.

lhoirPo'

Electronic Engineers-What you want, where you want!TJB Electrochemical Personnel Services is a specialised appointmentsservice for electrical and electronic engineers. We have clients throughoutthe UK who urgently need technical staff at all levels from Junior Technicianto Senior Management. Vacancies exist in all branches of electronics andallied disciplines - right through from design to marketing - at salarylevels from around £8,000 - £25,000.

If you wish to make the most of your qualifications and experience andmove another rung or two up the ladder we will be pleased to help you.All applications are treated in strict confidence and there is no danger ofyour present employer (or other companies you specify) being made awareof your application.

TJB ELECTROTECHNICALPERSONNEL SERVICES,12 Mount Ephraim,Tunbridge Wells,Kent. TN4 8AS.

Tel: 0892 510051(24 Hour Answer: ',rvice)

INIHIMIHIPUIll 18401M4140004,1110411881841~1104111141HIN811.11081

Please send me a TJB Appointments Registration form.

Address

ARTICLES FOR SALE

CLIVEDENTechnicalRecruitment

MWMOIR.F. DESIGN ENGINEER 1111. HantsDetailed design and development circuitryfor hand held communications systems.

£14,000

FIELD SERVICE ENGINEER BerksRepairservice and install electroniclocking systems. Extensive overseastravel. CNegotiable - carTEST ENGINEER SurreyFinal test and assembly of marineequipment using digital andmicroprocessor techniques £10,000

APPLICATIONS ENGINEER SurreyHardware/software design of local areanetworks. Extensive travel and customerliaison. £14,000

CUSTOMER ENGINEERC10,000 - car

Installation and commissioning of complexdatacommunication networks

f 10.000- carR&D TECHNICIAN SurreyDigital and microprocessor experience.bread boarding of circuits for videoequipment. £12.500

Hundreds of other Electronic vacancies

Roger Howard. C.Eng, M.I.E.E.. M.I.E.R.E.CLIVEDEN TECHNICAL RECRUITMENT

92 The Broadway. Bracknell. Berks RG12 1ARTel: 0344 489489 (24 hour)

163 Bitterne Road. Southampton SO2 4BH.Tel: 0703 229094

TO MANUFACTURERS. WHOLESALERSBULK BUYERS. ETC.

LARGE QUANTITIES OF RADIO. TV ANDELECTRONIC COMPONENTS FOR DISPOSAL

SEMICONDUCTORS, all types. INTEGRATED CIRCUITS. TRANSISTORS.DIODES, RECTIFIERS. THYRISTORS. etc RESISTORS. C/F. M/F, W/W, etc.

CAPACITORS, SILVER MICA. POLYSTYRENE, C280, C296. DISCCERAMICS, PLATE CERAMICS, etc.

ELECTROLYTIC CONDENSERS, SPEAKERS. CONNECTING WIRE. CABLES,SCREENED WIRE. SCREWS. NUTS. CHOKES. TRANSFORMERS. etc.

ALL AT KNOCKOUT PRICES - Come and pay us a visit ALADDIN'S CAVE

TELEPHONE: 445 0749/445 2713R HENSON LTD

21 Lodge Lane, North Finchley. London. N.12IS nutns from Tal'y Hn Crum-, 1161,

173 MHZ FM TELEMETRYTELECOMMAND RADIO

LINKS Remote Switching Voltage Monitoring Serial Data Transm;ssion

ADENMORE LTD27 Longshott Estate, Bracknell RG12 1R)

TeL (0344) 52023

REDUCE TELEPHONE BILLSThe Corne Call Monitor is a BT

approved device which allows youto watch the cost of a call whilst

you are making d Simply attachesto your phone

£15.00 75p&p

From Corrie Communications Ltd,PO Box 8. Accrington. Lancs 8EI5 1RJ.

TEST EQUIPMENTGOOD USED EQUIPMENT /AM AVAIIAILE

Amfm synthesized.signal generators type 2019 keyboardentry digital readout programmable £2500Hewlett Packard 1741A 100Mhz.

storage scope £1.000.Tektronix 2215 Dual trace 60MHz

scope £500Hewlett Packard 17108 Portable

200MHz. Dl' with delay £650.Solartron 11 72 frequency response

analyser £1250.Considerably more always in stock

send for lists.BUYING OR DISPOSING

ContactCOOKE INTERNATIONAL

Unit 4. Fordingbridge Site. Main Road.Barnham. Bognor Regis.West Sussex P022 0E8

Tel: 0243 68 5111/2

VUTRAX 5CAD software (full

package) + 14" highresolution monitor.

£7,500 + VATTel: 0371 830083

Oscilloscope. rechargeable battery/mains.20MHz. portable. Z -mod. square wavecalibrator. batteries FOC. £145. Tektronixdual -trace. dual time -base. time delay etc.£125. Weyhill Precison Generator withlive decimal place counter £55. Muirheaddecade standards: R -C12. C8L £18Dual -beam electronic switch. single to dualtrace scope £35. Hatfield Video Modulator£15. AWL VHF/UHF FM Radio Test -Setwith plug-in £65. Precision twin -drive tapecassette mechanism with stereo head £10Combination workstation comprising vari-able 27V. PSU, 2 amp. transistor tester.transistor voltmeter. audio generator £75.Fractional hp motors £7112 60W ICamplifiers £6.50 ea. Micro Spot -Weldinghead £59 GEC 20.000 ohms/volt. indust-rial grade BSS89/Super 50 testmeter £4540W RF Power Meter £29. Marconic AudioMicrowatt meter £18. Vacuum Diffusionpump £39. Large reels fibreglass 10- dram.10" high £25. Oscilloscope probesvarious. 5 dig counter £18 Weld tester andleads £30. Motor dnven co -axial switch£25.

040-376236. 2016

When replying to classifiedadvertisement readers are

I recommended to take steps to protectI their interest before sending money.

FIGOLLEDGEI

L ELECTRONIQSJ-I

QUARTZ CRYSTALS OSCILLA-TORS AND FILTERS of all types.Large stocks of standard items. Spe-cials supplied to order. Personal andexport orders welcomed - SAE for listsplease. OEM support thru: designadvice, prototype quantities, produc-tion schedules. Golledge Electronics.Merriott, Somerset YA16 5NS. Tel:0460 73718. 124721

IMHOF CASES - large range at halfprice! 16 page cat FREE. 1988 Compo-nent and surplus catalogue out now. 88pages of bargains - only £1. Green -weld, 443G Millbrook Road. South-ampton, SO1 OHX. Tel:107031772501.

BRIDGES waveformn transistoranalysers. Calibrators, Standards.Milli voltmeters. Dynamometers. KWmeters, Oscilloscopes. Recorders.Signal generators - sweep. lowdistortion, true RMS. audio. RM.&vim ion. Tel: 040 376236. 12616)

ARTICLES WANTED

WANTEDTest equipment, receivers,valves, transmitters, com-ponents, cable and electro-nic scrap and quantity.

Prompt service and cash.

M & B RADIO86 Bishopsgate Street

Leeds LS1 4B60532 435649

WANTED

PLATINUM, GOLD, SILVERSCRAP. Melted assayed and paid forwithin 24 hours relay contacts, thermocouples. crucibles. Also printed circuitboards, plugs, connectors, palladium,rhodium, tantalum and ruthenium. Wehave the technology to do the difficultrefining jobs that others can't handle.Totally free sampling service. Sendsamples or parcels (Regd post) orcontact Eric Henderson, 0773 570141.Steinbeck Refineries (UK) Ltd.Peasehill Industrial Estate, Ripley,Derbyshire DE5 3JG. No quantity toolarge or small 495

SERVICES

STEWART OF READING110 WYKEHAM ROAD.

READING RG6 1 PLTEL: 0734 68041

TOP PRICES PAID FOR ALLTYPES OF SURPLLS TESTEQUIPMENT, COMPUTER

EQUIPMENT, COMPONENTSetc. ANY QUANTITY

NEW PROJECT?VOXAGE LTD will design and develop prototype equipmentto specification. Expertise in analogue and digital hardware.high-level and low-level software with particularspecialisation in test equipment.For a competitive quotation, callFRASER BLACK on 0203 22799.63 St Nicholas Street, Radford,Coventry CV1 4BN.

PCB ARTWORK DESIGN. CAD Sys-tem. Outputs, Penplot or Photoplot,Driumap or Excellon Tape. Conven-tional PTH or Multilayer. SMD and/orstandard parts. Contact ACL, PendrePontrhydygroes, Dyfed SY25 6DX. Tel:(1974 22670

QUICK BOARD DESIGNS A speedyprinted circuit design service to getideas into practice, Circuit Design,PCB Artwork, Prototypes. Everythingfrom concept to production Tel: 01 4040020

CIRCOLECTHE COMPLETE ELECTRONIC SERVICE

Artwork, Circuit Design, PCB Assembly, Test & Repair Service, Q.A.Consuiancy, Prototypes, Final Assembly. Full PCB Flow SolderingService.Quality workmanship by professionals at economic prices.Please telephone 01-646 5686 for advice or further details.

TAMWORTH MANOR302-310 COMMONSIDE EAST, MITCHAM

1139114=111111

SERVICESP.C.B's DESIGNED. Artworkcapacity available fin single doublesided. P.T.H. and multi -layer PA:13:s,also silk screens, solder masks, labelsetc. For C.A.D. Photoplot, artwork &photography, contact Mr. Williams. 49West bourne. Honeybourne. Evesham.W. ircs, WR I I 5PT. Tel? 0:386 832152.

EXPORTS OF USA SATELLITEAND MICROWAVE communicationequipment, microwave components,microwave test equipment. manufac-turing processes, technology licensingand used microwave test equipment.Please send your enquiry to SEMEX,P.O. Box 26786, Tempe, Arizona85282, USA. Telex: 9102504420SEMEX UG. Fax: 602-829-0130. szs

TURN YOUR SURPLUS i.csransistors etc. into cash, immediate

settlement. We also welcome theopportunity to quote for completefactory clearance. Contact COLES-HARDING & CO, 103 South Brink.Wisher+. ca no 17,7,s I s=,

BUSINESSOPPORTUNITIES,

WANT TO RUN YOUROWN BUSINESS?

. title,copyright and goodwill of a well-known

on -going series of internationalsemiconductor reference manuals withworldwide circulation Established 10

years with standing order subscriber lists

Requires good (but not extensive)knowledge of semiconductor usage with

minor graphic and word processing Runson desktop micro Sales E35 -40k pa.

Easily expandable Good profit marginOperational location unimportant

£20,000 all -in for this going concernYour premises.

Tel: 0252 628526 551

3MAII SHICIION i MY IISIHINE I S toe YOUR RIBMIUMININ WHICH

MAY BE Is STOCK

Latest bulk Government release -Cossor Oscilloscope CDU150(CT531/3)£150 only. Solid state general purposebandwidth DC to 35MHZ at SMV/Cirt - DualChannel - High brightness display 18-10cm) full delayed time base with gatedmode - risetime IONS illuminated graticule- Beam finder - Calibrator 1 KHZsquarewave power 100 - 120V 200V - 250volts AC - size W 26CM - 14CM deepWT 12 5 KG - carrying handle. colour blue.protection cover front containing polarizedviewer and camera adaptor plate - probe111 - mains lead. Testec in fair condition:nth operating instructions - E150.CO.Racal RA17L CommunicationsReceivers. 500KC/S to 30MC/S in 30

As I MDS wide from £175. All receiversart tested and calibrated in our

,rkshop supplied with dust coveroration instructions circuit in her usednddion - Racal Ancillary Units for alle,vers mostly always in stock - Don 10

Telephone Cable I 2 mile canvas-tamers or wooden drum new tram £20 --

Army Whip Aerials screw type F sectionsand bases large qty available now P.O.R. -Test Equipment we hold a large stock ofmodern and old equipment. RF and AFSignal Generators - SpectrumAnalysers - Counters - Power Supplies- Oscilloscopes - Chart Recorders allspeeds single to multipen XV Plotters A4A3 - Racal Modern EncryptionEquipment Racal Modern MorseReaders and Senders - Clark AirOperated Heavy Duty Masts P.O.R. Allitems are bought direct horn H MGovernment being surplus equipment priceis ex -works. S.A.E. for enquiries. Phone forappointment for demonstration of anyitems. also availability or price changeV.A.T. and carriage extra.

DOW 11,41I AM %VIM 1111101111118011111, WERIMIL

14 W1111111011. MOM HUT, 1111011111141111,

WNW 1011 2011 TR MI. (0274) 11040117.

WANTED: 111111/111INT TED 111111PRIENT -VALVES - PUNTS - SOCKETS, STUNK

FTC. SEDIVING AND 11W4MITIMMHIUIPMENT

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ELECTRONICS & WIRELESS WORLD 2. I

MATMOS LTD, 1 Church Street, Cuckfield, West Sussex RH1 7 5JZ.Tel: (0444) 414484/454377

COMPUTER APPRECIATION, 111 Northgate, Canterbury, Kent CT1 1BHTel: Canterbury (0227) 470512. Telex: 966134 COMPAP GSPECIAL VALUEASTEC SWITCH MODE PSU. 5V ro 8A, 12V or 3A. 12V 0.3A to a total 65W. Compactcased unit. BRAND NEW £14.50 (carr. £3.00)DEC PDP 11-73 SYSTEM with DZVI 1 asynchronous multiplexor, DLVI 1 serial interface.BA11-SB 9 F 4 backplane. TANDON 8" floppy disc drive with DILOG Model RXV-21 controller.2. AMPEX PYXIS 27 5' 4- Winchester disc drives with DILOG D0614 controller. All containedin DEC cabinet with DEC power control. 512kb memory £2,250.00ITT SCRIBE III WORD PROCESSING SYSTEM. Professional system originally selling ataround C6.000 without printer. Now offered with software included and a variety of differentoptions (including hard disc. comms. etc.) available. This system is available from us ALLBRAND NEW at the cost of current budget systems. but with office -quality performance andfeatures. With dual processor workstation (TI 9995 8 Z8OH), 12" green display with slowscrolling. 128kbytes RAM. dual 500kbyte SHUGART 51/4" floppy disc drives and comprehensivesoftware. Various printers and options available 0290.00 (carr. £10.00)ITT SCRIBE III WORKSTATION. Monitor sized main unit of above system with high qualityhigh resolution 12" green screen monitor (separated video and sync). 5V and 12V casedswitchmode power supply, processor electronics as above incorporating TEXAS 9995 and Z8OHprocessors with 128kbytes and associated support chips. all BRAND NEW but with only monitorand power supply guaranteed working. Original cost at least £2,500 C39.95 (carr. £5.00)DATA GENERAL ECLIPSE CS/60 SYSTEM comprising: ECLIPSE processor with 512kbytesMOS memory. 5 line terminal 'ILA type 005-8599, 2, 50mbyte cartridge disc drives Model6067-4, DATA PRODUCTS lone printer, 8" floppy disc drive Model 6031-4 £1,650.00microNOVA Model MPT/100 SYSTEM with the following features: terminal sized desktop unit.mN602 processor with 64kbytes RAM, 2. RS232 interfaces, connector for microNOVA I/O bus.dual DSDD 5'4" floppy disc drives. 83 key keyboard, green screen 12"monitor, 25 80

£165.00(carr. £10.00)DATA GENERAL MODEL 6220 8 Winchester drive, 5 mbyte. Apparently suitable for above

£95.00 (carr. £5.00)DATA GENERAL Model 6041 DASHER TP1 printer. Serial interface 300/6006 £140.00DATA GENERAL Model 6052 DASHER VDU TERMINAL All Baud rates to 192006

£95.00 (carr. £10.00)MATMOS TERMINAL. MATMOS PC with Version 2 EPROM for terminal emulation. Probablythe lowest cost terminal available anywhere. With set-up menu and with data rates up to 9600Baud. Machine is easily modified for split Baud rate operation. 75/12008. EPROM plugs intoRom socket accessible from exterior. Emulation is VT -52 compatible for cursor addressing; andfor character attributes as far as the MATMOS PC allows. MICROSOFT BASIC is still availablefrom the keyboard. (EPROM card on its own. 020.00: EPROM card with socket only for user'sown EPROM. 08.00) BRAND NEW £69.00 (carr. £5.00)PLESSEY Model T24 V22/V22 bis 2400 Baud MODEM. Including free software disc for IBMor MATMOS PC. Compact automatic modem featuring the lastest technology and the highestpossible data rate over the ordinary phone system. Offers: both V22 and V22 bis compatibility,1200/2400 Baud operation with auto bit rate recognition, operation on both ordinary phone(PSTN) and private circuit (PC). auto call and auto answer, duplex operation allowingsimultaneous transmission and reception of data at 2400 Baud in both directions over a singlephone line. compact size (9" .9" 212"). BT approved and suitable for new PRESTEL V22bisservice. Price includes software for use with public domain comms packages for IBM PC and allmanuals. BRAND NEW. NEW LOW PRICE C169.00 (carr. £5.00)TRANSDATA Model 307 ACOUSTIC MODEM. Low cost self-contained modem unit allowingmicro or terminal connection to BT lines via telephone handset. V24 interface. up to 300 Baud.originate/answer modes etc. BRAND NEW with manu,-11 £19.95 (carr £3.00)

STOP PRESSVICTOR SPEED PAK 286

IBM PC accelerator x 6) with cachememory £139

TRANSDATA Model 307A ACOUSTIC MODEM. As above, but originate only£14.95 (cam £3.00)

DUPLEX Model 100 green screen 12 high resolution monitor with composite video input. Withtilt and swivel stand. BRAND NEW C39.50 (carr £5.00)PANASONIC Model JU-363 31/4" floppy disc drives. Double Sided Double Density 80 track 1megabyte capacity unformatted. Latest low component It height design. SHUGARTcompatible interface using 34 way IDC connector. Will interface to lust about anything. BRANDNEW. (We can offer at least 20% discount for quantities of 10 plus). Current model. We cansupply boxes of 10 discs for £15.95 plus £1.50 carriage 059.50 (carr. C3.00)HITACHI Model 305S/SX 3" disc drives. With SHUGART compatible interlace as for51/4"drives. Uncased. 125K (single density) or 250K (double density). 40 track: 100 tpi); softsector; 3ms track to track time; standard 34 way edge connector; 12V 8 5V powered (standardconnector) with overall 3.7W typical power consumption. These drives have been tested by uson the BBC with DFS. on the AMSTRAD 6128 and on the TATUNG EINSTEIN. and are alsoknown to be suitable for the AMSTRAD 664 and as a second drive for the AMSTRAD 464.Single sided. 250kb unformatted. BRAND NEW. Data cables are available from us for theAMSTRAD 6128 and BBC at 07.50. and an installation pack including data and power cableswith instructions is available for the TATUNG Einstein at 012.00 £24.95 (carr. C3.00)FUJITSU Model M2230AS 51/4" WINCHESTER disc drive. 6.66mbyte capacity unformatted.16/32 sectors. 320 cylinders. With ST506 interface. BRAND NEW 075.00 (carr. £3.00)DRIVETEC Model 320 high capacity 51/4" disc drives. 3.3Mbyte capacity drive - samemanufacturer and same series as KODAK 6.6Mbyte drive. 160 track, downgradable to 48 tpi. Nofurther info at present. BRAND NEW £45.00 (carr £3.00)SHUGART Model 405R 51/4' disc drive. Full height, single sided, 40 track, without guarantee

£16.95 (carr £3.00)DEC Model BAI IMF box, power supply and 8 slot backplane for 0 -bus. Easily upgraded forlatest 0 -bus boards. BRAND NEW £95.00 (carr. £5.00)ADAC Model 1822 128kbyte CMOS memory for 0 -bus. With battery backup

075.00 (carr. £3.00)HATFIELD INSTRUMENTS Type 2105 Ohm attenuator £40.00 (carr. £3.00)BRYANS Model 4500 UV recorder with 6. 45001 amplifiers 1mVicrn-50Vicm and chart speedsfrom 1 mm/min 500mm/s. Timing line interval is adjustable from 0.0025-10s and RecordDuration 0.5s -20s. With remote control facility C95.00 (cam £10.00)HEWLETT PACKARD Model 59370A dual VHF switch. DC to 599MHz 50 Ohm switch forHP -1E1 £185.00HEWLETT PACKARD Model 5045A digital IC tester with CONTREL Model H310 automatichandler. With IEE interface and print out of test results either pass/fail or full diagnostic includingpin voltages at point of failure. With full complement of pin driver cards and complete withsubstantial library of mag. card test programs for 74 series TTL and other Cs. CONTRELhandler allows fully automatic testing of ICs which are sorted into 2 pins. Price includes asecond HP5045A (believed fully operational) for maintenance back-up £1,250.00TIME ELECTRONICS Model 9810 programmable power supply £160.00TIME ELECTRONICS Model 505 DC current source. 0.05%. With leather case ex psu _145.00KRATOS MS30 DOUBLE BEAM MASS SPECTROMETER. Approximately 8 years old withnegative ion capability and fast atom bombardment (FAB). With gas and direct introductionsample probes and with gm chromatograph inlet system. Output spectra are available directlyvia a HEWLETT PACKARD storage display and a UV recorder. An on-line DATA GENERALDS60 computer system, which includes a graphics printer and two TEKTRONIX 4014 terminals.analyses output p.o.e.Please note: 'VAT & carriage (also VAT) must be added to all prices -'VISA and ACCESS orders accepted.

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INDEX TO ADVERTISERSAppointments Vacant Advertisements appear on pages 212-215

PAGEAirlink Transformers 194Anritsu Europe 145AntexIElectronics) IBC

Black Star Ltd 180

CAD Innovations 202Carston Electronics 121Cavendish Automation 131Cirkit Holding PLC 112Clark Mast 122Colomor Electronics Ltd 210Computer Appreciation 216Control & Display Tech 108Crotech Instruments Ltd 168

Data Acquisitions Ltd 166Dartington Frequency 106Dataman Design: - 163Design Consultant - 160

PAGEElecdata Tech 197Electronic Brokers Ltd. .138,0BCElectronic Source, The 122Engineering Solutions 106,207Field Electric Ltd 211GNC Electronics 192Gould Instruments 147Happy Memories 205Harcourt Systems 170la meg Oscilloscope 160larrison Elec 210cart Electronic Kits 211lenry's Audio Electronics 205lenson R, Ltd 194lilomast Ltd 170

loom (UK) Ltd 112Instrumentation '88 (Trident) 141I nstrumex I FC

Johns RadioKestrel Elect CompLI Electronics 152Langrex Supplies 182Level! Electronics 166MA Instruments 202MQP Electronics 108Marlow Marketing 170Marconi Instruments 148,149Microconcept 169Number One Systems 194PM Components 200/201PPM Instruments 155Pineapple Software 210Prism Instruments 165Quarthand Ltd 211Ralfe Electronics

PAGE PAGE215 Slee Electro Products 205210 Solatron Instrument 152

Solex International 207Sowter EA 180Stewart of Reading 194Surrey Electronics Ltd 122Taylor Bros 111Thandar Electronics 165Techni Rent 108Thoroughbred Direct Sales 202Those Engineers 122,152,197Thurlby Electronics 142,192Triangle Digital Sery 180Waverley Electronics 131Websters Elec 170Weka loose insertWithers R. Comm 207

112 Xen Electronics 202

OVERSEAS ADVERTISEMENT AGENTSFrance and Belgium: Pierre Mussard. 18-20 Place de la Madeleine, Paris 75008.United States of America: Jay Feonman, Reed Business Ltd.. 205 East 42nd Street. New York, NY 10017 - Telephone (212) 867 2080 - Telex 23827

Printed in Great Britain by E.T. Heron .Print, Ltd. Crittall Factory, Braintree Road, Witham, Essex CM8 :1Q0, and typeset by Graphac Typesetting, 181'191 Garth Road, Morden, Surrey SM4 4LL,for the proprietors. Reed Business Publishing Ltd. Quadrant House. The Quadrant. Sutton, Surrey SM2 5AS. (_) Reed Business Publishing Ltd 1988. Electronics and Wireless World can be obtainedfrom the following AUSTRALIA and NEW ZEALAND: Gordon & Gotch Ltd, INDIA: A. II. Wheeler & CO. CANADA: The Wm, Dawson Subscription Service Ltd., Gordon & Gotch Ltd. SOUTHAFRICA: Central News Agency Ltd: William Dawson & Sons ,S.A. I.td. UNITED STATES: Eastern News Distribution Inc.. 14th Floor, 11l Eighth Avenue, New York, N.Y. 10011.

SOLDERING KITFree `thry To Sofoe..0 book le r

and pack of wader

Soldering Kt

TC.CU-DTeriperature-Cont-olledSphering Unit

Model C- 15 Watts. Available for250, 220, 115, 100, 50 or24 volts.

Model XS- 25 Watts. Available for240, 220, 115, 100, 30, 24or 12 volts.

Model XS -BP- 25 Watts. 240 volts, fittedwith British Plug.

5T4 Stand- To suit all irons

Professional Precision for the Amateur Enthusiast.ANTEX has a worldwide reputation for quality & service & for many years

has been on? of the best known & mpst popular names in soldering. Alwaysat the forefront of technology, ANTEX is continually researching new andbetter ways Df achieving more accurate, reliable, and :ost effectivesoldering. Oi ANTEX Soldering Ircns the advanced design of the interfacebetween the e ement & the bit allows more efficient heat transfer to thebit and improved stability of the temperature at the point of contact withthe work. Indeed, experiments have !hown that an X45 watt iron can beused for tasks where a 40 watt iron would normally have been required.

ANTEX Soldering Irons exhibit exce3tionally low lealiage currents & henceare suitable tor use on Static Sensitive Devices. Sophist cated temperaturecontrolled scldering units have recn:ly been added to the ANTEX range.

SKS Soldering Kit. Containsmodel CS 240v iron, an ST4Stand and solder.

SK6 Soldering Kit. Containsmodel XS240v I -on, an ST4Stand and solder

SKS-BP and SK6-BPSoldering Kits as above withBritish Plug

Model CS-17 Watts Available for240, 220, 115, 100, 50, 24or 12 volts.

Model CS -BP- 17 Watts 240 volts, fittedwith Britisr Plug

- Very robust temperaturecontrolled Soldering Unit,with a choice of 30 Watt(CSTC) or 40 Watt (XSTC)miniature ironsRange 65°C to 420°C.Accuracy 2%.

TCSU-DElegant TemperatureControlled ScIdeing Unitwith 50 W Iron (XSD) andbuilt around FERRANTIcustom-made ULA. Range /Ambient to 450°C Acc-uracy ± 5°C. Zero /crossing switcning. / yak ,\

sDpeotancgheable4(b

(Z\'4'tray

ELECTRONIC BROKERS

OSCILLOSCOPES

TEKTRONIX 485B350MHz dual channel £4 250Hewlett Packard 1715A 200MHz dual channelHewlett Packard 1740A 100MHz dual channelTektronix 2445 150MHz 4 -channelTektronix 4656100MHz dual channelTektronix 475B 250MHz dual channelTektronix TM503, PG506, SG503, TG501

Oscilloscope calibrator

£1,750£1,350£2,250£1,550£2,350

£5,500

SIGNAL SOURCESHewlett Packard 3325A-001 Synthesised

Function Generator, 1µHz-21MHz £3,250Hewlett Packard 8640B-001-002 RF Signal Generator,

1024MHz-20Hz £4,250Wavetek 2001 R.F. Sweep Generator, 1-1400MHz £2,750

PROTOCOL ANALYSERSHewlett Packard 4951B 50bps-19.2Kbps £2,950Hewlett Packard 4951C As 4951B, plus 3.5" floppy £3,500Hewlett Packard 4953A 50bps-70Kbps £7,500All products fully refurbished and sold with fullone-year warranty.

OF SECOND USERTEST EQUIPMENTSPECTRUM ANALYSERS

141T, 8552A, 8555A10MHz-18GHz spectrum analyserHewlett Packard 182T, 8558B 0.1-1500MHz

Spectrum AnalyserHewlett Packard 3582A 0.02Hz-25.5KHz

Spectrum AnalyserTakeda Riken TR4132 100KHz-1GHz

Spectrum AnalyserMarconi 2371 50Hz-200MHz Spectrum Analyser

HEWLETTPAC KA R D

£7,250£6,100

£6,950

£3,750£5,950

NETWORK ANALYSERSHewlett Packard 8410C Analyser Mainframe, 1010MHz-40GHzHewlett Packard 8411A Harmonic Frequency ConverterHewlett Packard 84128 Phase/Magnitude Package Price

display 950£9Hewlett Packard 84148 Polar Display ,950SPECIAL OFFERSMarconi TF2173 Synchroniser for TF2016 Sig GenRacal Store 14D 14 Channel Instrumentation Tape

Recorder DeckTektronix 4041 System controller, complete with

option 30 file manager, graphics,plotting and signal processing, ROMS £4,500

Farnell SSG520 and TTS520 Radio comms test set,10-520MHz £3,500

Full range of Tektronix display and graphics products -call with your requirements FROM £650

Electronic Brokers

£4,500

El 140-146 Camden St,London NW1 9PB.

j Fax : 01-267 7363Telex: 298694Tel: 01-2677070_)

For further information contact our Sales Office. All prices exclusive of carriage and VAT.Prices correct at time of going to press. A copy of our trading conditions is available on request.

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