THE WIRELESS WORLD

Otago Daily Times, Issue 23499, 13 May 1938, Page 2

THE WIRELESS WORLD

NEWS AND NOTES By Magna, Vox Items af local interest are invited by “ Magna Vox ” for publication in this column. It is necessary that such mattei should reach this office by Tuesday o( each week for insertion in the following Friday. IYA, Auckland.-(ISO K.c., 4(11.2 metres 2YA. Wellington.—s7o k.c., 526 metres 2BL, Sydney —740 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 metros 3YA, Christchurch.—72o k.c. 416.4 metres. 4YA, Dunedin.-790 k.c.. 379.5 metres 4YO. Dunedin.—ll4o k.c.. 261 metres ANSWERS TO CORRESPONDENTS “ Speaker,” Tokarahi.—The marking on the speaker is merely the resistance in ohms of the windings. It has nothing to do with the loudness of the signals given by the speaker. The one that you have would be just as suitable as any of the others you mention. The best resistance to use depending on the type of valve used in the last stage of the set. J. McR.. Roslyn.—l am afraid you will have to lower that aerial, even if it does mean lowering the pole, as there is no other way to adjust the condensers except by having the twisted pair near the aerial. When doing this, by the way. make sure that the two ends of the twisted flex cannot touch each other and are well insulated there. THE COUNTRY BATTERY SET The outback listener’s battery problem is not nearly so acute as it was a few yeai's ago. No longer is it necessary to have an untidy box containing A, B and C batteries connected to the set by a confusing array of wires. The battery unit is housed unobtrusively in the cabinet. Many sets outback in Australia now run on an air-cell, which is guaranteed to give 1000 hours of service. Those who prefer wet batteries are able to install a windcharger—actually a windmill connected to an electric generator, which brings the spare up to full voltage again. Another device is a powercharger, a four-cycle single-cylinder, air-cooled petrol engine which drives the generator. The price of the windcharger outfit and of the powercharger is slightly over £2O. TECHNICALLY EFFICIENT Coincident with an announcement of extensions in telvision programmes Mr Gerald Cox, British Broadcasting Corporation director of television, said that the home was the place for television, because, in its present stage, programmes could not be designed for any other purpose. It was certainly impossible to suit both large theatre screens and the small home screens simultaneously. He urged that viewers should resist the temptation to compare television programmes too closely with the films or the stage, and pointed out that the excitement and charm of home television rested in its unique Qualities of intimacy and immediacy. He added that the scope and consequent progress of the British Broadcasting Corporation service hinges upon continual technical improvements at what one might call the camera or studio end, and that technically television is now a really efficient medium. Financial considerations had retarded progress to some extent, and until recently there had been but one fully equipped television studio, a room 70ft by 30ft. TELEVISION AND TELEPHOTO A great many people appear still to be confusing television with telephoto. In transmission of photographs a “ stu! picture is scanned by a pencil of light, which picks up lights and shadows and, acting on i a photo-electric cell, produces corresponding fluctuations in an electric current. This current (sent by land line, cable, or by radio for shorter distances) operates a light at the receiving end and reproduces the original picture fairly well on photographic film. This occupies anything from two to ten minutes, dependent upon the size of the picture and the fineness of the screen or number of lines in which it is scanned. Television requires the complete picture to-be transmitted at least ten times per second, to produce the illusion of motion. That is why television is still round the corner. A NEW 2FC The Pennant Hills transmitter, which has operated for many years under the call sign 2FC Sydney, is to be replaced by new plant, which is being erected on a 120-acre site at Liverpool, New South Wales. While only one 10 k.w. transmitter is to be installed at the outset, the single storey brick building will be large enough to accommodate another plant of like output, which is, incidentally, about three times that of the present aerial power of the old station. The new equipment will come on the air toward the end of June or early in July, and will provide virtually undistorted, signals over a range of 35 to 10,000 cycles. The aerial system will be similar to that of IYA, but the mast top will be 730 ft above ground level, and will thus be the tallest structure in Australia. The ground system will consist of buried wire, very much like that employed *t the Henderson site. INTERFERENCE PROBLEMS In a recent announcement, Mr H. P. Brown, the official of the Australian P. and T. Department who controls the radio service—made some remarks on the interference problem. Among other things he declared that parasitic interference (developed by commercial electrical equipment) can be almost entirely eliminated by proper attention to the design and maintenance of such equipment, and by the interpolation of certain devices in the circuits of electrical systems. Mr Brown declared that the Post Office last year investigated and disposed of about 10,000 cases of interference which had been brought under its notice. It would be interesting to know what “ disposed of ” means, and whether 10,000 sources of interference were eliminated. New Zealanders have learned to regard official announcements on this problem with a good deal of derision. RENEWING THE AERIAL Once an aerial is erected, it receives ro attention from The average owner until a gale blows it down or until it falls from corrosion. The engineers of a big American factory point out that the elements (sun, wind, rain, etc.,) have such a damaging effect upon the aerial system over a period of time that they strongly advise thal a new aerial be erected every year or so to ensure efficient operation of the -e----coiver. Rapid deterioration of the aerial is more noticeable in some sections of the country than m othe'rs, particularly in and around industrial centres, where smoko and soot are extremely heavy and contain chemicals which collect on the insulators, aerial wire, lead-in and antenna transformer causing leakage, corrosion, and the changing of the original characteristics of the aerial system. This results ni weak pickup of the radio signal One of the most common causes of weak reception, when the aerial becomes defective, is leaking insulators. Dust and soot collect on the insulators, resulting in the aerial wire being partially shoried to ground. This condition causes what is known as loading of the antenna circuit, and replacement of the insulators is the only remedy. Change in weather conditions causes the glaze of the insulator to crack. Dust and soot collect on the surface, resulting in the insulator absorbing moisture and thus allowing the radio waves to leak to the ground. This causes weak reception on both broadcast and shortwave. Corrosive elements are present in the dust in the air and in the rain in some localities. These elements attack the joints and wires of the aerial system, causing corrosion, with resulting noise and weak reception. The lead-in line will be affected by weather conditions. -The life of the line depends Entirely upon the materials used, but even with the nest of materials some deterioration occurs. ' Eventually the insulation between the wires breaks down, and there is m Elfcct only a single-wir« lead-in

between the radio set and the antenna Such deterioration reduces the noise eliminating ability of an aerial system and greatly affects overall efficiency The conditions outlined above will have an even greater effect upon short-wave reception than on broadcast. It is important therefore that the aerial be renewed after a reasonable period of use.