THE WIRELESS WORLD

Otago Daily Times, Issue 23672, 2 December 1938, Page 2

THE WIRELESS WORLD

NEWS AND NOTES By Magna Vos Items ot local interest are invited' Dy '■ Magna Vox ’’ for publication In this column It is necessary that such matter should reach this office by Tuesday of each week for Insertion In the following Friday IYA Auckland. —BSO k.c.. 461.3 metrei 2YA Wellington.—s7o k.c.. 526 metre: 2BL Sydney.—74o k.c. 405 metres 2FC Sydney. k.c., 478 metres 3AB Melbourne.—77o k.c. 390 metres SCL Adelaide.—73o k.c. 411 metres 4QG Brisbane.—Boo k.c. 311 metres 3YA Christchurch -720 k.c. 416.4 metres 4YA Dunedin.—79o k.c., 370.5 metres 4YO Dunedin —ll4O k.c. 261 metrei ANSWERS TO CORRESPONDENTS "Interference.” Lawrence.—(l) It probably would, but signal strength would be reduced as well. However, if you have the cable on hand, the experiment would be well worth trying. (2) The only possible alternative is to erect a noisereducing aerial with a high, flat top running at right angles to and as far as possible from the source of interference. The use of a transposed, shielded, or twisted lead-in will prevent interference ’on the lead-in itself. B. N. L., Dunedin.—The trouble you are having with this aerial is certainly unusual, The switch seems to be reversed for one thing. Unfortunately, you have not supplied full enough details for me to form any idea of the cause of the fault. I would suggest that you refer your trouble to the dealer from whom you bought the set. STILL A MYSTERY Extraordinary as it may appear, the German mystery station which radiates anti-Nazi views remains undetected, although it has been operating for about a year. It transmits on 29.8 metres from 10 till 11 p.m. daily, and in spite of detective sets, remains a mystery. AN ANOMALY The United States, the world’s leading radio country, has over 600 stations licensed on the broadcast band, but only 17 on short wave. South America, on the other hand, has more than 150 short waves in operation. FOR THE DEAF A new instrument known - as the mutitone has been installed in the Deaf and Dumb Institute at Melbourne. The teacher speaks through atransmitter and the children hear through earphones and light receivers slung over their shoulders. One inmate, a little girl, recently heard a human voice for the first time—and it was the voice of a crooner moaning “ If I Had a Girl Like You.” WEIRD AND VARIED A few years ago aerial construction took a wide range, zeppelln, cage, ball, sausage, and other contrivances being popular. To-day one seldom sees a new aerial other than a single straight wire erected, though doublet lead-ins. claimed to cancel out static and interference, are occasionally installed. Another novelty that has lost favour, except in portable sets, is the built-in antenna. On a mains-operated receiver this picked up all manner of noises, and was often of little use unless a line filter wak fitted. A MOBILE UNIT 8.8. C, engineers have overcome the delays which used to be experienced in erecting an aerial for its mobile television unit by the use of apparatus resembling the portable fire escape. The “ escape ’’ can be extended to a height of 80 feet, and is surmounted by a transmitting mast aerial 20 feet high. The use of the new apparatus saves practically a day each time the television unit is set up. DAYLIGHT AND DARK New listeners are usually curious to learn why there is such a difference between signal strength from mediumwave stations between daylight and dark, and why short-wave stations have so much the longer range during the day. It has become an accepted fact that medium waves need darkness in order to bridge long distances, whilst short waves vary according to 1 wavelength, some coming through in the daytime and others at night. Investigation has shown that an important part is played by the KenellyHeaviside layer, an ionised layer of air situated about 100 k.m. (60 miles) above the earth. lonisation means that the atoms of the component gases of the atmosphere receive an electrical charge, due chiefly to the ultra-violet rays of the sun. Medium waves, when traversing long distances, can reach us only by reflection from this layer, which in turn requires sunlight £oi its existence. So it will be understood why medium waves exhibit a different behaviour by day and by night. Whilst medium waves are thus influenced by the Heaviside layer, short waves pass right through this layer and are not reflected until they encounter another layer, the Appleton layer, which is situated at a distance of 240 k.m. (150 miles) from the earth. This Appleton layer is subject to variations in height and characteristics under the influence of sunlight, as is shown by the existence of daytime and night-time waves in short-wave reception. Up to now we have been discussing ether waves that reach us by reflection, but besides these waves (known as “ space waves”) a broadcasting station radiates waves which follow the earth's curvature and are called “ ground waves.” ’ These ground waves are independent of the ionised layers, and can be received at practically the same strength by day and night. The shorter a wave is, the smaller is the region in which the ground wave can be received at ample strength. In the case of short waves this phenomenon is so pronounced that practically no reception is obtained beyond a few kilometres from the station. Not until the reflected wave is a thousand kilometres (about 600 miles) further away does it return to earth and become receivable. Ether waves, like the waves of the sea, have cres.ts and troughs. When these waves reach us from different directions, the paths by which they travel will never be of exactly the same length. The result Is that while at one moment several crests (or several troughs, as the case may be) happen to reach the aerial simultaneously, producing greater reproduction strength, another moment occurs when a wave-crest and a wave-trough are picked up together. The two are in direct opposition to each other, so that however powerful the station is it will die out entirely at that moment. Action thus alternates with counteraction, giving rise to the fading effect. In the case of long-wave and nearby medium-wave stations the waves we receive are practically always ground waves, so that these stations hardly ever fade. The propagation of ether waves is greatly influenced by the sun. as shown by the difference in daytime reception, and it is also a fact that the varying position of the sun during different seasons of the year gives corresponding seasons in the ether, the effect of which is distinctly manifested on short waves.