THE WIRELESS WORLD

Otago Daily Times, Issue 23718, 27 January 1939, Page 2

THE WIRELESS WORLD

NEWS AND NOTES By Magna Vox Items ot local Interest are invited ov •* Magna Vox ’’ for publication in this column It is necessary that such mattei should reach this office by Tuesday ot each week for insertion in the ''ollowme Friday IYA Auckland -650 k.c.. 4(51.2 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. 300 metres SCI-. Adelaide.-730 k.c.. 411 metres 4QG Brisbane.-800 k.c. 311 metres 3YA, Christchurch - 720 k.c 416,4 metres 4YA Dunedin.—79o K.c., 379.0 metres IYO Dunedin.—ll4o k.c. 261 metres ANSWERS TO CORRESPONDENTS •• Amplifier," Tomahawk.—Youi transformer specification shows that it is more than ample for an extra tuner, even if the field supply be taken from the powei pack. The circuit shows a variable resistance between the 250 volt and 400 volt terminals li this is to regulate the voltage, then a voltage divider would be much better, more especially as you have plenty of milliamperage ' Four-valve, Waikouaiti.—The lauti that you describe is certainly not normal, and Is probably caused by one of two things; Either the I.F is oscillating, or the aerial is too long 1 should say thai it is the aerial that it too long, as a receiver of this type works well on a short aerial Not having an R.F stage ahead of the frequency changer, however, the selectivity can be made too small if a long aerial Is used Check through for faulty bypass condensers and try dropping the plate voltage on the oscillator and screens a little to see if that will effect an improvement. EARTHS FOR BATTERT SETS The earth is important with a battery set in the country It is essential to have a good earth, with a short lead. Most people in the country find it easy to hunt out an old kerosene tin, to which they can solder an earth lead The tin should have holes punched in the sides and the bottom, and be buried in the ground for a couple of feet If the spot is on the damp side, so much the better Some people bury a length of pipe so that it projects into the tin and pour water down it from time to time Others find that if they drive the pipe into the ground, with the earth wire attached to it with an earth clip, this works as a good earth. If you have a water pipe system in which the pipes run into the ground, you can make the earth direct to such a pipe Make sure that the pipe doesn’t run under the house for some distance before it goes into the ground, as this isn’t the same as earthing it closer to the set ANOTHER QUESTIONNAIRE The Australian Broadcasting Commission recently conducted an “ investigation ’’ into the likes and dislikes of listeners to radio drama. This was carried out on the 8.8. C “panel’ system. 100 selected persons agreeing to give attention to all plays broadcast by National stations over a oeriod of three months and then to fill in a questionnaire submitted to them This system is open to criticism, as the listeners are selected and they are required to answer set questions. One can easily imagine the N.B.S by this method obtaining favourable reports on its own productions although these find favour with only a minority of New Zealand licensees. For what they are worth the Australian conclusions were that comedy is preferred to other types of plays, but that there was a distinct aversion to anything suggestive to “ outback.” The thriller was listed only fifth in popularity, and preference was expressed for plays lasting not longer than 30 minutes. CORRECT ALIGNMENT Although the greatest care is taken in the design and construction of modern all-wave radio receivers to ensure that the “ alignment,” on which depends both sensitivity and selectivity shall remain correct, after a period in service variations are apt to occur The first indication of misalignment is a lack of the usual ability to receive distant stations, and this defect may be apparent on only one or perhaps two of the bands, or it may extend over the whole range. Misalignment is readily corrected, requiring only the proper adjustment of some half-a-dozen “ padding condensers.” To make such adjustments. however, minutely-exact and rather complicated electrical apparatus is required, and the job is essentially one for a properly equipped technician, who will make a very modest charge for realignment. PROGRESS OF TELEVISION Strenuous efforts were made at the 1938 Kadiolympia to stimulate interest in television. So far there are only about 3000 viewers within the service area of the Alexandra Palace 8.8. C television transmitter As actual reception of 8.8. C. programmes is not possible in a building where so many electrical appliances are in operation recourse was had to two special transmitters feeding into co-axial cables for speech but the many viewers which were demonstrated under actual working conditions were fed from an aerial above the roof of Olympia The quality of the images shown was very high, (he light and shade variation good and there was, moreover, a complete absence of flickering. With all these improvements prices of viewers were substantially reduced.

HIGH FIDELITY In a receiver high fidelity simply means that the loudspeaker reproduces very faithfully the programmes put over the microphone. For a number of reasons exact reproduction has not yet been achieved, but a good set is little short of the absolute, and does, in fact, so render speech and music that the most discerning ear cannot detect the slightest shortcoming. To ensure high fidelity the set must have what is called an overall linear response from 50 to 8000 cycles or higher. This simply means that the speaker will react properly to every note from the lowest to the highest. The demand for selectivity causes side band attenuation, but compensation after detection largely replaces the tones lost through the necessity for selectivity Many modern receivers employ automatic lone and volume expanders to secure the utmost in fidelity of reproduction The manual tone control on many sets is simply a moans of boosting the reproduction of any desired group of frequencies at the expense of other tones thus giving treble or mellow reproduction at will THE RADIO TELEPHONE The radio-telephone circuit which was brought into use recently between Australia and the United States will be a useful addition to the Australian oversea radio-telephone channels Besides providing a direct link with North America, il will provide an alternative circuit to practically all parts of the world Until a few weeks ago the Australian Post Office network could be connected directly through a radio-telephone circuit with London Wellington Bandoeng (Javal Rabaul and certain ships at sea Through these points, hut mainly through London il could be connected to telephone networks with a total of about 35 million subscribers. A number of these connections could be made from London through trunk land lines but a still greater number have t be made through other radio circuits The whole o( North America for example could only be reached through London and one or other of the Atlantic channels. The new circuit will avoid this extra step and put the Australian and American networks in direct contact. This will greatly improve the reliability of the communications because, no matter how good radio-tele-phone circuits may be when two or more are connected in series the chance of an imperfect result i? correspondingly increased This no doubt will have been noticed in some oi the 8.8.C.’t Christmas broadcasts of past years. The new circuit will play an important part in providing an alternative circuit to any part of the

world. A country which has direct service from the United States will be brought if not in closer touch probably in more certain communication with. Australia when conditions are poor than by existing channels. It may hapnen that when the Anglo-Aus-tralian circuit is not good, better communication with England may be established by way of America, a facility, which may be of great benefit in times of stress. The advantage of more than one path was shown during the Coronation broadcasts. Radiotelephone circuits are fairly complex undertakings Between anv two points two wavelength must be used simultaneously and a transmitting and receiving station must be supplied at each end. These are generally miles apart, and there is the additional necessity of combining the circuits of each so that they may be connected to the usual two-wire telephone circuit. Delicate and ingenious apparatus is inserted at the combining points This apparatus, according to the presence and direction of speech currents, connects the telephone instrument to the transmitter or receiving equipment. It is operated entirely by speech currents, and no matter how fast the direction of transmission of words may change, it works so that there is never a complete circuit round the incoming and outgoing radio circuits Without it all sorts of singing and howling conditions would be established There are also the scrambling or inverting arrangements for ensuring secrecy. These change the character of speech so that it is unintelligible, complementai’y apparafus at the other end reversing the treatment and making it intelligible.