IN RADIO—The Signal Must Be Good
MUCH pioneer work in the propagation of directional radio waves and in the transmission of programmes in foreign janguages has been done by the General Electric Company of New York. The following article, which is the text of a te‘k given by Boyd W. Bullock, Assistant Manager of Broad¢a.ting, gives some indication of the work that has been done by this company in an endeavour to further the science of tadia for peaceful purposes.
yee of the vital considerations in international shortwave broadeasting-without question the most fundamental --is the problem of providing the intended foreign audience with a signal which is sufficiently good to enable consistent and satisfactory. reception’ of programmes, . L. A good signal, of course, is of primary importance in the regular broadcast band at home-but when operating in the shortwave, or high-frequency, portion of the radio spectrum-over great distancesthe problem is more complex. , In the first place, radio waves the characteristic.of jumpig ing off into space from the. trans--Initting antenna and not returning to earth. until -considerable distance has been traversed. This behaviour becomes more _ pronounced and the effective distance greater as the frequency is increased, until, in the shortwave broadcast regions, "skip distance," as it is called, becomes a very important. factor. If "skip distance" for a given frequency remained constant, the problem of picking a fre-~ quency to reach a given area would be relatively simple. But "skip .distance" varies widely for a given frequency-being affected by daylight and darkness, by the seasons, by such remote phenomena as sunspots, and by the direction (geographical bearing) of the line between transmitter and receiver.
All these seemingly unrelated factors resolve themselves into one basic influence, and. that is the ionisation of the atmosphere, the degree of which is governed by the amount and quality of sun radiation through the atmosphere. Thus do daylight and darkness, the seasons, and sunspots enter the problem. Also direction of propagation of the radio waves-for, travelling east and west, they may traverse both daylight -and darkness, while on a north-south circuit; they may move entirely in either day or night. All other directions involve varying conditions between. these extremes. The general situation is that daylight decreases skip distance-and therefore effective range. a A frequency such as 15,330 k.c. (19 metre band) is good for broad-’ easting service to South America from Schenectady, N.Y., in the daytime-afternoon especially-but © is not very suitable after dark. At night, frequencies in the 5000 k.c. {31 metre band) are much more effective. In the morning, the > 21,000 kc. (18 metre band) is * best. " "Moreover, the portions of the day during which the above frequencies are most ~ Suitable vary with the seasons of the year, since with the changing seasons, not: only do the hours of sunrise and sunset change, but also the angle at which sunlight passes through the atmosphere. Even these fairly predictable variations occurring with the seasons. have been upset somewhat, in the last several years, and the deviation ascribed to the influence of coincident sunspot phenomena. ° The fove-oing, with the. exception of the'l eal technical: problems eornnecica wi.t the transmitter, are tits oturo! physical, conditions encountered by ‘the broadcaster who is desirous of providing a good international shortwave signal on a consistent, year round basis. At the same time, he is up against another problem-also fixed by the laws of Nature-but a problem only because there are many other stations, at home and
abroad, who ultilise the shortWave and send their signals out ‘into the same atmosphere. Allocations ADIO waves vrecognise no international boundaries, so in order to prevent utter contusion, the matter of allocation and register of frequencies is an organised international function handled by the International Radio Convention at Berne, Switzerland. This does not mean that broadcasters deal direct with the Berne Convention. In the United States, such matters are the province of the Federal Communications Commission. Broadcasters-and all other radio enterprises--must apply to the F.C.C, for frequency assignment and licensing. But the F.C.C. can assign only those frequencies made available to the U.S., and must register such assignments at Berne. Both the Convention at Berne and the F.C.C. maintain engi-
neering: sections which. continually study the complex and changing problem of frequency (and’ power) assignments-the pur--pose ,being to permit as -many stations as possible to operate. within the relatively limited ‘bounds of the radio spectrum, without undue interference with ‘each: other. This is no arbitrary matter, but one ‘fixed by thé laws of Ndature-so-man ‘is obliged to conform or spite his own face if he fails to heed. « ‘Many stations, of. course, may be assigned the same frequeney, but in such a case it has been deemed that geographical separation and limited power {and perhaps restrictions on the hours of operation) are suflicient to prevent
interference and confusion harmful to the services of the individual stations, In numerous instances, such happy lack of interference has failed io result. In these cases, the authorities attempt to rearrange assignments to correct the trouble. Nearly everyone is familiar with cases of station interference in the "regular" broadcast. band, and, if he has been sufficiently interested, can recall that certain steps were taken to prevent this interference. It is not always possible, with so many stations clamouring for their place in the ether, to completely solve the interference problem. ~ From the fact that the higher frequencies-those falling within the so-called shoriwave region (1600 k.c. and up) and particularly those above 4000 k.c.-exhibit remarkable distance-covering ability, it is apparent that the problem of interference prevention becomes world-wide in scope. Power Increase
gO much for a generalisation of the difficulties which must be overcome in providing foreign listeners ‘with the necessary good shortwave signal. The experiences of one broadcaster who has been furnishing consistent shortwave transmissions to Latin America. for thirteen years will provide specific illustration. In February and September of 1925, W2XAF and W2XAD were first licensed to the General Blectric Company as experimental shortwave broadcast stations. Ever since that time, both stations have transmitted programmes for the benefit of listeners in other countries. During this period, their schedules have grown heavier, and more and more programme features have been presented which were specifically designed for particular foreign audiences-especially our LatinAmerican neighbours. In 1928, the assigned frequency of W2XAF was raised slightly to 9530 k.c., its present frequency. In 1929, W2XAD was dropped from 15,340 k.c. to 15,330 kc. and at the latter figure its frequency has remained. ; Both changes were required by ‘the Federal Radio Commission (antecedent of the Federal Communications Commission) in order to conform with international agreements, During recent years, W2XAF has operated with a power output of 25 kilowatts, while about — a year ago, W2XAD went to 20° kilowatts from. its previous 10. By means of direct listener response: and through such agencies as the offices of the International} General Electric Company located in the foreign countries, a continuous and reliable cheek on programme reception has. been possible. This study of reception has not- only given data on signal strength and quality but. has. also provided information on. the, types of programme liked by the foreign audiences. Particularly have .these studies been concerned with sig-. nal and programme -for patio America. ai Interference YNTHL the latter part of 1936, the broadeasting: from W2XAPF and W2XAD brought constant evidence. of strong, ‘consistently received signals in Central and South" America. Then reports began to come in of . interference by a growing number of other shortwave broadcast stations. Some ofgmese were locai Latin-American’ -stations, while others were Buropean. The most consistently complained of was DIN, a station in Berlin, Germany, operating on 9540 ke-10 kc. higher thea "we KAP.
The wvature of this interference was "side-band"’ interference-a form of trouble which oceurs when two powerful signals are received which, although they may be working 10 ke. apart on adjacent channels, still become mixed. This
effect occurs because the modulating or voice frequency which is superimposed on the carrier frequency tends to widen out the carrier by an amount plus and minus the modulating frequency. Technically, a modulated carrier wave can
he resolved into three component freauencies-one the fundamental earrier frequency, one this fundamental minus the moduiating. fre queney, and the third the fundamental plus the modulating: frequency. It can be seen readily that when modulating frequencies go above 5000 cycles (5 k.ec.), carriers separated by only 10 k.c. will tross up. Modern high-fidelity modu ation involyes frequencies at lcast as high as or 9 kc. Then what could be done to ‘reduce the-new interference and restore the consistent programme reception which many letters from South America begged for? Because of the difference in ‘direction, DIN could caver South Ameri¢a eiiectively by using a narrow. beam--only 15 degrees wide. Right away, the DIN signal was powerful, because most of its energy. appeared to be crowded into this narrow beam. As for the roatcasts : from Schenectady, a much avider beam had to be used to preperly spread out and cover the South American coltinent-with corresponding loss in signal strength even though higher power might be used in the antenna. (To be continued.). eee a
N.Z. DX Club Representatives Northiand: R-. -A- Roycroft, : H.Q., 21 Anzac Road, Whangarei, Auckland: fF. Newing, 316A., 50 . Bannerman Road, Marningside, Mount Aibert, AuckJand, S.W.1. . i Waikato: W. 620A,, Christopher St., Tauranga. Poverty Bay: A. Towers, 148 H.B., 4099 Ormond Road, Gisborne. ; Hawke’s Bay: V. bk. 119 H.B., 4 Railway Espianade, Waipukurau. Napier: 0. N. Hailett, 143 H.B., ; 16 Selwyn Road, Napier, Taranaki: A. Maule, 87T. «c/o Fire Station, Patea. . Wairarapa: H. Campbell, 542W., 812 Queen Street, Masterton. Wanganui: Frank Carr, 150W., ° 21 Lowther St., Wanganui. Manawatu: C. J. Morgan, 143W., .: 401 Main Street, Palmerston. North. Foxton: J. Bennett, 437W., Union Street, Foxton. Marton: J. R. Bain, 217W., 97 Princess Street, Marton Junction. Wellington: -H. Wickens, 503W., ‘* "92 Endeavour Street, Lyall Bay, Wellington. ; . Marlborough Canterbury: A. Simpson, 246M.-C., Sunleigh Flats, Grafton Street, Sum-., >: mer, Christchurch. Nelson: M, G. Neighbours, 39N., Waimangaroa, Westport. . "Westland: W. A. Reynolds, 34 Wa Waitaha, South South- _ ¢. land, Otage:.P. R. King, 1430t,, To- _* Karahi, Oamaru. Southland: C.-F. Ludiow, 87S., 101 Robertson Street, Inverci gargilly a Tasmania: Miss V. Dowling, 990., ‘Table Cape, Road, Wynward. South Australia: J. H. Moody, 460., 395 Glen Osmond Road, Gien Osmond. West Australia: H. Stephens, 400., c/o Railway Station, Katanning. . England: L. Orton, 140., thorpe, Willov/ybank, Ux. .. + bridge. ;. ¢ ftw ft United. .States: Irving H. Levy, "910., Box 18, Cherckee Station, Louisville, Kentucky.
Meetings HAWKE'S BAY. jn the Club Room, above Woosd’s Tearooms, Waipukurau, at 7.45 mm. on Wednesday, January 41. , : Vv. L. KING (119H.B.), Branch Secretary. NORTHLAND, | At 21 Anzac Road. Whanaaret, | at 7.30 p.m. on Monday, January | R. A. ROYCROFT (2H.Q.), | Branch Secretary. AUCKLAND. ; In the Society of Arts. Hall, Kitenener Street. at S p.m., on Wednesday, January 11. F. NEWING (316A.), Brancn Secretary. | WELLINGTON. in the Club Ficoms of the ist Wellington City Rover Crew, 8rd floor’ "Times" Building, Kelburn Averue, at 8 p.m. on Monday, January 9 H. WICKENS (503W.), Branch Secretary. WAIKATO, In. Hamilton on Saturday, January 14, 1939, W. NORRIS (620A.), Branch Secretary,
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Radio Record, Volume XII, Issue 29, 30 December 1938, Page 39
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1,850IN RADIO—The Signal Must Be Good Radio Record, Volume XII, Issue 29, 30 December 1938, Page 39
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