THE WIRELESS WORLD

Otago Daily Times, Issue 23202, 28 May 1937, Page 2

THE WIRELESS WORLD

NEWS AND NOTES

By Magna Vox

Items of local interest arc invited by " Magna Vox" for publication in this column. It is necessary that such matter should reach this office by Tuesday of each week for insertion on the following Friday. IYA, Auckland.—6s K.C., 52(5 metres. 2YA, Wellington.—s7o K.C.. 526 metres 2BL, Sydney.—74o K.C., 405 metres. 2FC, Sydney.—6lo K.C., 476 metres. 3AR, Melbourne—77o K.C., 390 metres. SCL, Adelaide.—73o K.C., 411 metres. 4QG, Brisbane.—Boo K.C., 311 metres. 3YA, Christchurch.—72o K.C., 416.4 metres. 4YA, Dunedin.—79o K.C., 379.5 metres. 4YO, Dunedin.—ll4o K.C., 261 metres.

ANSWERS TO CORRESPONDENTS "Amateur," Clyde.—As the diameter is increased the number of turns must be reduced. The exact valves, however, cannot be determined without full knowledge of all the factors, including the length of tho winding, but, approximately, you would get what you require by using the same length of wire. "All-wave," Mataura.—(l) The station would probably,- be OLR4A, Prague. Czechoslovakia, which transmits on a wavelength of 11.84 m.c. I should say that with such a log you have little cause for complaint. (2) If it is operating as well as you say, why try to improve it? I am continually advising contributors to leave their sets alone when they are functioning satisfactorily. (3) No aerial will have any effect on the surge you hear, which is one of the many vagaries of shortwave reception. (4) Yes, that is quite right, as you will find if you try it.

" Super-six," Owaka,—lt is sometimes the case that a low-powered station of low wavelength can, at night, rise to very high signal value in certain localities. This, however, may not last over a period of time. It should be remembered, moreover, that some sets are not so efficient at the low-frequency end of the dial, with the result that a high-powered station in the near vicinity may not seem so loud as it should when compared with a low-powered transmitter much further away.

J. F. M., Dunedin.—(l) A faulty IC6 valve will frequently give trouble such as you describe. Can you not borrow one and try it out? If this does not remedy the fault I would suggest that you have a chat with the agents. If your receiver is still covered by a guarantee, it would be wiser to let them fix it in any case. (2) No, it is still on the air. (3) That would be a matter for the proprietors of the station. If I were to interfere they would be justified in telling me to mind my own business. SHORTER WAVES Coincident with the trend towards still shorter wavelengths for long-dis-tance broadcasting are announcements that manufacturers are redesigning their sets so as to secure reception on wavelengths down to 12 metres, in place of the previous lower limit of 18.5, or occasionally 16.4 metres. A few manufacturers have gone even further and resorted to five bands, so as to gain coverage to 4.5 or 5 metres, thus taking in the ultra short-wave broadcasts which will accompany television programmes, as well as the myriads of portable radio telephones which clutter up the hundreds of channels around 5 metres. 2YA'S STRENGTH "The most powerful station in the southern hemisphere," 2YA has been in operation for several months, quite long enough for it to be run in and to have been brought to its maximum efficiency. Instead of giving the complete coverage of the Dominion that was promised, it is often received in parts of the South Island at lower strength than IYA—much further away and of much lower power. It might be supposed that geological factors are responsible for the disappointing performance of 2YA with its 60 kilowatts, but that theory is exploded when a comparison is made with the one-kilo-watt commercial station in Wellington (comments an exchange). 2YA's impotency is probably due to the antifading aerial system installed. MECCA CALLING Considerable difficulties were encountered in the-building of the broadcasting station which has just been completed in the Holy City of Islam. Since the station stands oh holy ground, to which unbelievers are not admitted, only Moslem engineers could be permitted to erect the station. Four natives were therefore sent to London to study radio engineering. All the material for the station had to be taken to Mecca on camels owing to the absence of railway facilities. The station will be used chiefly for broadcasting the prayers and ordinances of the prophet and disseminating his teaching. It will also be employed for the spreading of Arabian culture generally. EMPIRE ARTISTS Are there no New Zealanders in London who can offer their services to the Empire station, or are Australians more pushing? (asks a writer in an exchange). Whatever the facts it is curious that the pre-Coronation Empire programmes featured very few New Zealand artists and very many Australians. Except for Vera Moore, pianist, and Arnold Trowell, violoncellist. New Zealand has had very few of her citizens in the Empire programmes recently. In comparison Australians have outclassed all-comers. In a brief fortnight no fewer than 19 items were interpreted by Australian artists. Brian Lawrence, it must be admitted, appeared in six of the items. Nevertheless, New . Zealand artists visiting England might well attend to the laurels of their Dominion, which, from an Empire programme aspect, require a little renovating. SUNSPOTS AND RADIO For the first time anywhere a scientific record has been obtained by experts of the Radio Research Board at Sydney University of phenomena that occur when disturbances in the sun are followed by wireless fade-outs. Radio reception has been affected by a group of sun spots, and at one period all Australian short-wave radio services were interrupted. Dr D. F. Martyn (research physicist of the board) said recently that measurements of electrical changes in the ionosphere or ionised layer of the atmosphere had been made while fade-outs in radio reception were occurring, and these results would be correlated, if possible, with information of solar disturbances received from the Mount Stromlo observatory, near Canberra. "There are two theories of the cause of solar interference with wireless reception on the earth," Dr Martyn said. "According to one, it is due to particles emitted from the sun, which travel much more slowly than light, and would require 26 hours to reach the earth. The other theory, held by observers in Britain and America, is that fade-outs in commercial wireless services are connected with eruptions (not sunspots) on the surface of the sun, consisting of large movements of gases. These fade-outs are simultaneous with the eruptions, or at least follow with the speed of light (which at 186,000 miles a second takes about eight minutes to travel from the sun to the earth). Signals sent out from Sydney University in the usual way, for reflection from the ionosphere and reception at the Liverpool field station, did not come back on some wavelengths, and othevs were much weaker." Dr •Martyn added that usually the effect of sunspot activity was to improve short-wave radio. Complete fade-outs seemed to be connected with eruptions rather than sunspots. THE BEAM SYSTEM High-speed commercial services by means of short-wave transmissions concentrated in the form of a beam have been so well proved that for longdistance systems between fixed points no other systems are now considered. Marconi, in his earliest experiments in 1896, made the first beam transmissions, directing short waves upon the receiving point by means of a reflector, but for twenty years after that short waves were entirely neglected. They were known to attenuate rapidly, and it was impossible with the apparaLus then available to provide high-power radiations of this type. In 1916 Marconi, thinking that a concentrated transmission of short waves would be of value for war purposes, returned to the investigation of this kind of radiation.

He still had to make use of the comparatively imperfect apparatus of the day, spark transmitters and crystal receivers, but he was able to obtain good results over a distance of six miles using a wavelength of three metres. Next year, C. S. Franklin, an engineer of the Marconi Company, who had been assigned the task of developing the idea, covered 20 miles. Work then progressed steadily in England, and distances of 78 miles were covered on 15 metres and then 97 miles. The advantage of reflectors at both ends of the link was adequately realised when it was shown by measurement that with them the signal was about 200 times stronger than without them. The next step was the construction of a special transmitter of 12 kilowatts at Poldhu, and a parabolic reflector hung from the masts over 300 feet high, valves having then come into use. Marconi, in his yacht, the Eleltra, steamed away from the station to the South Atlantic, and the 97-metre signals were picked up 1250 miles away in daylight, and 2230 miles away at night, the limit of that voyage. The power of the transmitter was then increased, and in February, 1924, without a reflector, 92-metre signals were picked up at 1400 miles in daylight, and at convenient times of the day the signals were heard in Australia. Marconi was so certain that short waves would be the means of providing economical long-distance communication that, using the same wavelength, he transmitted speech to Australia on May 30, 1924. In the meantime Franklin was going thoroughly into the matter of reflectors. The parabolic type used in the early experiments was an unwieldy and expensive structure, and Franklin sought other means of obtaining the required concentration of radiation. He found that parallel grids, one acting as the aerial and the other as a reflector, would serve the purpose. This scheme is the basis of all " beam " systems of communication. At this stage of development a bold decision was made. The British Post Office was anxious for an Imperial system of communication to be established and long-wave highpower stations were being erected or on the point of being erected in England and the Dominions. Marconi and his engineers were so optimistic of the possibilities of the short-wave " beam " system that although the Franklin type of aerial had not been thoroughly tried and little was known of the behaviour of waves below 100 metres or of the design and operation of short-wave equipment, they accepted the responsibility of installing a scheme with severe technical requirements as to test and guarantees. The Marconi Company's associates in Australia, South Africa, and Canada were entrusted with the establishment of the stations at the other ends of the circuits. When the proposals were accepted the station at Poldhu -and the yacht Elettra commenced a series of tests on wavelengths of 92, 60, 47, and 32 metres. Other problems were also strenuously attacked, and as a result of intensive research much knowledge was quickly gained. Ultimately the services were opened at various dates in 1926 and 1927 with immediate success, the standards so freely accepted in 1924, although nothing like them have been required before, being surpassed without any trouble. Since then two or more services have been dealt with on a common aerial without any interference, and telegraph and telephone circuits have been operated through the same transmitter and receiver without mutual interference.