THE WIRELESS WORLD

Otago Daily Times, Issue 22835, 20 March 1936, Page 2

THE WIRELESS WORLD

NEWS AND NOTES

By Magna Vox.

Items of local interest are invited by “Magna Vox" for publication in tins column. It is necessary that such matter should reach this office by Tuesday or each week for insertion on the following Friday. 2BL, Sydney.—74o K.C., 405 metres. 2FC, Sydney.—6lo K.C., 402 metres. 3AR. Melbourne. —630 K.C., 476 metres. 3LO, Melbourne.—77o K.C., 390 metres. SCL, Adelaide.—73o K. 0., 411 metres. 4QCJ. Brisbane.—Boo K.C., 811 metres. IYA, Auckland.—6so K.C., 461.3 metres. 2YA, Wellington.—s7o K.C., 526 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. "Control,” Waitati.—lf the removal of the aerial makes no difference, it would appear that the set is fitted “with a most efficient system of automatic volume control. If the specifications of your set state that it has a.v.c., then everything may be in order, but if a.v.c. is not intended, then there must be some fault, such as a broken connection m the aerial coil unit or something like that. If, however, the serviceman says it is 0.K., I should not like to contradict him without something more definite to go on. “ All-wave,” Oamaru. —You could quite easily use an R.F. stage with this set, making the coils plug in, with duplicate in the aerial and R.F. sockets, except, ot course, for reaction winding, which would be on the detector coil, and the larger primary for the R.F. transformer. Resistance coupling would be quite in order. The end of the grid resistor for the pentode would be connected to the same point as the transformer secondary is now connected for the bias. D. S. O’C., Dunedin. —It might, and it might not. It should improve your reception to erect an aerial about 40 feet high and about 70 feet in length, but it ia doubtful whether you would get such a good log as your friend. He is evidently in a very good location for reception, as are moat of the places in that district. If you can manage it, you should get much better result* with the improved aerial.

THE BOARD’S QUESTIONNAIRE. The broadcasting authorities have already compiled, printed, and issued a questionnaire on the subject of radio programmes. It has been sent to moat ot the poet offices already, and listeners can obtain it either in the near future or when they renew their radio licensee at the end of the month. In its own way the filling in of the answers is important, because there is little doubt that the aggregate opinions of the public do influence the board. Judging by the popularity of recordings dealing with “ Vienna,” the last questionnaire, issued some years ago, must then have indicated a Vienna complex among listeners. Possibly by now they have changed. Unfortunately the new questionnaire does not ask this specific question. It asks for a cross to be placed against one in a list containing the most popular of the national stations, and the fifth question deals with the popularity of various types of entertainment. “Do you dance to broadcast music?” is the seventh and last question.

AUXILIARY STATION CHANGES. From Monday next the evening programmes of the auxiliary stations IYX, 2YC, 3YL, and 4YO arc to be extended by half an hour, and if the shortly-to-be-taken listeners’ questionnaire is to be regarded at all seriously, the Broadcasting Board is prepared to consider prolonging the breakfast sessions of the main stations. This is very nice, indeed, but most listeners would appreciate, instead, more careful attention to the breakfast and other “ popular ” sessions, which appear to receive Cinder-ella-like consideration. Insufficient care is exercised in the choice of the records, many of which ate repeated so often as to amaze one aware of the huge library of recordings available. Every endeavour should be made to improve the, brightness and popular appeal of the breakfast sessions, which warrant the best efforts of the staff. COMING ATTRACTIONS. In addition to Florence Austral, the noted Australian vocalist, John Lcmone (flautist), Sydney de Vries (baritone), and Browning Mummery (operatic tenor), whose projected tours were announced some time ago, the Broadcasting Board has arranged for Dorothy Helmrich, an Australian vocalist, who has done much singing for the British Broadcasting Corporation, and Gladys Lorimer, a New Zealand soprano, who has recently completed a season at Covent Garden, to tour the main stations. The whole group is to broadcast in July, and the present intention is to form the artists into a company to present charity concerts at each of the main cities. It is understood that the board is negotiating with other instrumentalists and vocalists, and that a further announcement will be made shortly. TELEVISION IN GERMANY. The new television service in Berlin consists of a daily programme of one hour’s duration from 8 to 9 in the evening, repeated from 9 to 10 p.m. Apart from this extension —the old service provided entertainment on only three evenings a week —the broadcasters have now obtained direct television facilities enabling them greatly to vary the programmes which, in the past, had been limited to films. Sight is broadcast on 6.72 metres and sound on 7.06 metres, definition remains at 180 lines, and the number of frames is still 25. It would not have been possible in so short a time to build suitable transmitters for higher definition. Inaugurating the programme, the deputy director of German Transmissions, Herr Boeso, stated that the service was experimental. Public televiewing rooms in various parte of Berlin have been provided to permit the public to follow the service in its experimental stage and to become accustomed to it. The programmes of light entertainment consist of direct television by well-known artists, of excerpts from the latest film releases, and of a newsreel film specially made for television. Tip; programme is changed each week. METAL TUBES. Manufacturers of radio receivers arc not united in their acceptance of the new all-metal tubes, quite a few having adopted n, (i wait-and-see ff attitude, a nd others arranging for the use of either glass or metal types at the user’s option. Apart from a few types that are special to the metal series, the metal tubes are, so far as the essential elements are concerned, the counterparts of the glass series. The main advantage claimed for the metal lubes is that the improved base design permits easier insertion ot the tubes into the special sockets, and at the same time reduces the inter-elec-trode capacities, thus resulting in improved operation, particularly on the short-waves, where even minute capacity decreases result in much higher sensitivity. The manufacturers pinning their faith to the older glass type envelope, have secured this latter advantage by redesigning the tube ba/ses to thfit used for the metal tubes. SHORT-WAVE STATION FOR PERTH. A short-wave experimental broadcasting station is being established at Perth by Amalgamated Wireless (A/sia), Ltd. The elation, which will have a wave range of from 20 to 50 metres, will be located at Applecrose, the radio centre of the west. The apparatus, which is under construction in Sydney, will bo in operation about tiic middle of April. It is intended to conduct this station in a manner similar to those of VK2ME, Sydney, and VK3ME, Melbourne, which have been transmitting programmes of music and talks on Australia for over five years. RADIO INTERFERENCE. At the request of the Institution of Electrical Engineers the British Electrical Research Association undertook some time ago to conduct an extensive investigation involving tests and countrywide experiments of the measurement ot

the intensity of interference from various sources, and also the development of methods of suppression. In dealing with interference from trolley buses, mercury arc rectifiers, and lifts, preliminary work was carried out on the long and medium wavebands with a voltmeter arranged to read the audio output. Automobile ignition systems presented a different problem, ns this type of disturbance is mainly confined to the short wavelengths, including the band at present in use for television. For preliminary measurements at these frequencies a super-regen-erative receiver and valve voltmeter were employed. Using the foregoing simple methods of measurement, it was found possible to determine the relative merits ‘of the various methods of suppression and the actual degree of suppression effected. It was quickly recognised, however, that information obtained in this way. whilst valuable for immediate use, would not prove sufficiently quantitative for future needs, such, for example, as the basis of any restrictive proposals, since the latter, to be effective, must define the level at which a given disturbance or noise must be suppressed. The desirability of arriving at measurements on an absolute basis having been agreed, the E.R.A. proceeded to design and construct a 3-HF radio noise-measuring set covering the 200-2000-metre band, sufficiently sensitive to measure a disturbing field of 1 microvolt per metre, and also a short-wave set covering the 5-80 metre band with the same sensitivity. Investigation of trolley bus interference showed that the most efficient combination of suppression arrangements consists of the use of Jow-current control circuit filters, together with condenser suppressors fitted at intervals on the overhead lines. This method not only gives greater suppression than the original trolley arm chokes alone, but avoids the fitting of a considerable weight on the roof of the bus. There is the further advantage that this method is not likely to be regarded as unworkable on the grounds of expense. This research has established that radiated disturbance from a given trolley bus system can be reduced to a level where it will no longer interfere with a local broadcasting service. Investigation of interference from ignition systems has been confined mainly to the short-wave band, extendi/ig from 60.3 megacycles. At these frequencies strong interference is experienced. Methods of suppression have been devised, the more efficient being resistances of the “distributed” type, whose selfcapacity is low, inserted at the sparking points (the plug and the distributor) in order to prevent high-frequency currents from reaching the high-tension leads, which act as radiating aerials. Carefully conducted investigations have shown that interference from electric lifts is transmitted along the supply mains and radiated by the wiring of the lift equipment, in particular from the unscreened trailing leads running from the car to the halfway box situated in the lift shaft. Mains-borne lift interference can be effectively suppressed_ by the use of chokes and condensers in combination. The foregoing survey will serve to show that the major technical difficulties associated with the problem of radio interference have not only been overcome, but in a satisfactory manner, as the methods of suppression indicated involve very little expense.