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Radio Schools in Honduras

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Radio Schools in Honduras APRIL197735p Aboweeftioi Radio schools in Honduras Australia $A1.20 Canada 51.50 Denmark Kr. 11.00 Finland Fmk. 6.50 Germany Dm. 4,50 Greece Dr. 45.00 Holland Df1. 4.50 Italy L. 900 Malaysia M$3.25 New Zealand SNS1.40 Norway Kr.10.00 incl. moms Portugal Esc. 40.00 South Africa R. 1 10 'rain Ptas. 80.00 eden Kr. 6.90 incl. moms 51.50 www.americanradiohistory.com wireless world Electronics, Television, Radio, Audio APRIL 1977 Vol 83 No 1496 Contents 35 Time, gentlemen, please Front cover, showing the 36 NRDC surround -sound system by M. A. Gerzon medium wave aerial at Radio - lándia, Comayagua, Honduras, 39 News introduces the article on edu- 40 Characteristics and load lines -5 by S. W. Amos cation by radio in that country 44 Wireless World amateur radio station (page 57). 45 Sensitive metal detector by D. E. O'N. Waddington Photographer Paul Brierley 48 H.F. predictions 53 New of the month IN OUR NEXT ISSUE Bullock's boardroom and the engineer Britain pioneered the integrated circuit Electrolytic capacitor tester. Vmos devices "middle of this year" Enables the value of an electro- 57 Education by radio in Honduras by M. K. Bates lytic capacitor to be measured 60 Literature received. 100 years ago automatically and the result displayed directly by meter. 61 Circuit ideas Leakage is also indicated. Simple noise generator Variable band -pass filter Ripple eliminator Two -stage linear amplifier. A 65 Viewdata -3 by S. Fedida discussion of the design of 70 World of amateur radio solid -state 50W and 300W linear amplifiers for the h.f. band 73 Electronic rhythm unit -2 by A. Battaiotto and G. Ronzi (1 .6- 30MHz). 76 Letters to the editor The Warden Report Current dumping amplifier Radio in the '80s, a look Advanced pre -amplifier design forward to sound receiver design 79 Broadcast stereo coder by T. Brook and the ideal set of the future by 83 Power semiconductors by M. R. Sagin the BBC's chief engineer of radio 93 New products broadcasting. 96 Just for the record by A. D. Foster APPOINTMENTS VACANT INDEX TO ADVERTISERS ISSN 0043 6062 Current issue price 35p, back issues (if available) 50p, at Retail and Trade Counter, Paris Garden, London SEI. By post, current issue 55p, back issues (if available) 50p, order and payment to Room 1,1, Dorset House, London SEI 9LU. Editorial & Advertising offices: Dorset House. Stamford Street. London SEI 9LU. Telephones: Editorial 01 261 8620: Advertising 01 261 8339. Telegrams /Telex. Wiworld Bisnespres 25137 London. Cables. " Ethaworld. London SEI. Subscription rates: 1 E7.00 year: UK ana overseas ($l8.20 USA and Canada). Student rate: 1 year. l3.50 UK and overseas ($9.10 USA and Canada). ibpa ABC Distribution: 40 Bowling Green Lane. London EC I R ONE. Telephone 01 837 3636. Subscriptions: Oakfield House. Perrymount Rd, Haywards Heath, Sussex RH I6 3DH. Telephone 0444 59188. Subscribers are requested to notify a change of address. C 1.P.C. Business Press Ltd, 1977_' www.americanradiohistory.com 34 Wireless World, April 1977 f r 1 Ili MNIIIIIIIM>« ANIIWNINI710/4141/701r 11O11 mow AM 1 4/.111110li 1W1\11111l4110l1.If11111f 1A1MA11[1/J\Il11/1I`1y 1NINIII:/i11\!\\st'I.1!\dill ram r/ia isi I111=r : oZ/111..' yW117 WWM NMAMR MIMI 1r 10N1 I r'I ...., 7f r11w1111111111r...111JrM 1 81. .Ya ' 1 t airy J /111w lAt as JA M.u..amY..,r u....rr J ítá1'ie\ äs0 s+i 1= -_ v,¡!r 011111... .410'%11.110in L4ulf= i ? 1"S iti ' 1_. ri w1. - 01l:-+Ir- \-_rYSoru_ 1r-+. 1V1Ulls\t1ti ft `Ìl1iÁ1\151.I!'11f7 I r i t >'............... _± - t\/!!J 1r1MfM1J1 7Ñ1rr17f...UV_.i i S AwSJ =MON I_r t/ls1 7i\! Ji/ris /f'A IU.11o!/7t1AI% -..!'911 ft7 t:et' ,tal WPM tlftl SA1 -t'\/.W'a!,r V11Y Jt (¡' Jr i rii- IìIA` f 7 ..JAa.ll5N/11\ The Test of Time Critics were most generous in their praise when the Shure V -15 Type III pickup cartridge was introduced. The ultimate test, however. has been time. The original engineering innovations, the uniquely uniform quality and consistent performance reliability of the V -15 Type Ill have made it THE classic choice as the source of sound for the finest music systems, both here and abroad. Consider making the relatively modest investment of a new cartridge to upgrade the performance of your entire hi -fi system. Why not ask Shure Electronics Na' Limited for their recommendation? Addre..s Shure Electronics Limited Eccleston Road. Maidstone ME15 6AU Telephone: Maidstone (0622) 59881 d > best The original manuscript by J. S. Bach shown is repro- by of The British Library. HLJRE duced kind permission j WW -010 FOR FURTHER DETAILS www.americanradiohistory.com Wireless World, April 1977 35 wireless world Time, gentlemen. Please! Editor: TOM IVALL, M.I.E.R.E. When this issue of Wireless World appears on the news stands the deadline for submissions to the Home Office on British policy on frequency reallocations for the 1979 WARC will be only six weeks away. (See News of the Month, March Deputy Editor: p.37). Yet a few months ago even this much PHILIP DARRINGTON consultation seemed out of reach. Phone 01 -261 8435 The Home Office is to be congratulated on reversing its policy of selective consultation and giving the public a chance to have their say. It could be argued, indeed, that the process might have begun much earlier had the electronics Technical Editor. GEOFFREY SHORTER, B.Sc. industry and its representatives been less acquiescent in the Home Office's Phone 01-261 8443 reluctance to encourage public intrusion. Even though the discussions to which the discreet trusties we referred to in December found they had an exclusive Assistant Editors: entrée were on matters of public concern far beyond their immediate interests, MIKE SAGIN they made, at first, no effort to press for a programme that might dilute their own Phone 01-261 8429 RAY ASHMORE, B.Sc., G8KYY bargaining strength. Phone 01 -261 8043 But it is for the electronics industry, singly and collectively, to put its own JOHN DWYER Phone 01- 261 8620 house in order. The immediate need is to make sure that the 1979 package is a fair reflection of the views of all those with an interest in the allocation of frequencies. The Home Secretary's statement is only a beginning. Indeed it Production: a I). R. BRAY contains surprising admission of the inadequacy of what he has craftily called "the preliminary phase" of the work for the conference: although, he says, a substantial measure of consultation with users and manufacturers has already Advertisement Controller. taken place, during the next phase "those known to have an interest will be ROWELL G. BENTON specifically invited to comment." One wonders how "substantial" the measure of consultation during the preliminary phase could have been. Advertisements: One hopes, too, that equal weight will be given to the public's views as to-those PHILIP NOSSEL (Manager) invited." This be if is Phone 01- 261 8622 "specifically can only the case the public as well informed as those "known to have an interest," yet we have not received any details of the Home Office proposals for disseminating the contents of the Warden reports and LEO KEMBERY any others relevant to the WARC. If the "wider programme of consultation" is to Phone 01 -261 8515 be anything more than an empty political gesture these reports must be made public. OWEN BAILEY (Classified Advertisements) The ten days following the publication of the next issue of Wireless World will Phone 01 -261 8508 or 01- 261 8423 not give enough time to read the available material, to consult colleagues, and to draft a considered proposal. The consultation period should be extended, just as the Annan committee extended theirs. An extension to the end of the year would JOHN GIBBON (Mahe -up and copy) Phone 01- 261 8353 give officials a clear year to collate and prepare the British case. Is that so much to ask? Publishing Director: GORDON HENDERSON www.americanradiohistory.com 36 Wireless World, April 1977 NRDC surround -sound system Michael Gerzon reveals the thinking behind system 45J by Michael Gerzon, M.A Mathematical Institute, Oxford This article gives a feel for how it has are in -phase or out -of -phase with the (divided by the pressure amplitude) proved possible to evaluate the whole pressure signal components are used by should be one for real -world sounds, range of possible methods of encod- the ears. In practice the 90° -phase and so decoders should be designed ing and decoding surround -sound components of figure -of -eight pick -up with a pressure -to- velocity ratio assur- based on fundamental psychoacous- do affect localization quality toward the ing this requirement for all reproduced tic principles. Although the full top end of this low frequency range, and sound directions at low frequencies, in development was highly mathemati- produce an effect called "phasiness." addition to ensuring correct Makita cal, the basic principles underlying In practice, the head may rotate, so localization. It is an incorrect velocity - the Ambisonic or NRDC 45J system' that the forward -pointing figure -of- vector length that makes the side image of surround -sound are described eight pick -up of sound information is reproduction so poor in conventional without mathematics, this new sys- also used to determine sound direction. "discrete" quadraphonics. tem being the best possible according The relative intensity of in -phase If there is too high a phasiness, it is to the methods used.
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