THE WIRELESS WORLD

Otago Daily Times, Issue 21300, 2 April 1931, Page 18

THE WIRELESS WORLD

NEWS AND NOTES By Magna Vox. Items of local interest are 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. Metres. 7ZL, Hobart 535 3AR, Melbourne .. .. .. 484 4YA, Dunedin '. .. 403 2EC, Sydney 442 2YA, Wellington 420 4QG, Brisbane 385 3LO, Melbourne 371 2AB, Sydney 310 2KY, Sydney 280 ANSWERS TO CORRESPONDENTS, “ Hummer,” Ranfurly.—There is no doubt that microphonia valves are causing the trouble. See that your valves are in shock absorber sockets, place the cabinet on corner felt of sponge rubber, and place sponge rubber under the speaker also. It is not a good practice to have the speaker on top pf the set, for, although microphonic noises may not always be prevalent, the vibration does not do the valves any good. “ Superhet,” Dunedin. —The trouble appears to be in your audio transformers. Try a change. Experiment with grid leaks and grid bias. Try .002 condensers across secondary of transformers, and if this does not fix it try a 100,000 ohm variable resistance across the transformer secondary. The main trouble is that the transformers are not matching, and this is a most important factor in a super-het. R. M. 8., Dunedin.— (1) I shall try to obtain the diagram you require, and will forward it on receipt of a stamped addressed envelope. (2) A fixed phone condenser would not make much difference to your crystal set. Sometimes it is found that the tone is improved by shunting a fixed condenser across the telephones. During the period when electricity flows through the detector the voltage is applied across the telephone receiver and also across the condenser in parallel with them. The short interval between the rectified halt waves of the high-frequency incoming signals is thus smoothed over by the condenser, which gives to the receivers energy received during the previous half-wave pulsation. The action of receivers is thereby strengthened, but in many cases no appreciable difference will be noticed. OTAGO RADIO EXHIBITION. The third annual radio exhibition is to be held in Dunedin towards the end of next month. The Otago Radio Association is again responsible for the venture, which promises to be even more successful than the two previous exhibitions held in 1929 and 1930. The Pioneers’ and Early Settlers’ Halls have been engaged, and arrangements are well in hand. The radio dealers are taking up space with enthusiasm, and are busily planning the individual displays. The Radio Broadcasting Company of New Zealand, Ltd., is co-operating with the exhibition executive, with the result that excellent programmes have been arranged for presentation at the exhibition, and some of the leading musical organisations and wellknown artists will be seen performing before the microphone. A big feature of the exhibition will be a 'Children’s party conducted by Big Brother Bill. MICROPHONE VALVE HOWL. One of the most annoying little troubles which can occur in radio is the gradually-building-up howl which is caused by a microphone valve, _ With many valves it can be cured by sticking a lump of plasticine on top of tbe valve, or by damping the glass in some other manner. Sometimes, however, practically any valve put in the detector position will start up a howl, all with their own particular note. This generally only happens when a very high degree of magnification is being obtained from the various stages of the sot, or when the set is working right on the edge of instability. It will also be found as a rule that in such cases a rather higher H.T. voltage than usual is in use on the detector valve, making it motje sensitive than it would be normally. If such is the case, the remedy is obviously to reduce, the voltage, when the trouble is almost sure to cease. It may be necessary to go as low as 30 to 40 volts, but the loss in sensitivity will not matter in a set with high-gain L.F. stages, DIAL ADJUSTING.

It will be found very handy to arrange the tuning dials bo that_ they give about the same reading for a given wavelength. Suppose when you have adjusted the two dials (assuming there are two) for proper reception of the desired station, and you tlien find that their readings are quite different, it is easy to shift the dial of one of the condensers until it reads the same as the other dial, but without shifting .the moving vanes. This necessitates loosening the dial on its spindle and keeping the moving vane system of the condenser stationary whilst the dial is shifted in relation to it. The dial is usually secured to the spindle by means of a tiny_ sunk screw, called a “grubscrew,” which can be manipulated by means of a very small screwdriver. It should be mentioned that when finding the settings for the two dials it is preferable to make your tests without using reaction, because if you use reaction you have a third complication, and every time you use either of the tuning dials you are liable to influence the amount of the reaction. The result is that you never know where you are, and you will never really be able to arrive at finality. But with reaction control turned down to zero it is quite a simple matter to tune in to a fairly powerful transmission (such as the local station) and then to adjust the tuning dials as mentioned above. AUSTRALIAN LICENSES. Although four of the six States showed an increase in the number of listeners' licenses issued during February, the total for the Commonwealth showed a decrease of 709. This falling-off is not nearly so serious as it was in January, when the total decrease for the six States was 1752. 'ln January the total for New South Wales decreased by 370; but last month an improvement took place, resulting in an increase for the State of 216, bringing the total number in force at the end of February to 118,971, or 4.77 per 100 of population. The decline in the figures for Victoria for January was not quite so serious last month. In January the State’s figures were reduced by 1324, compared with a reduction of 1224 during February. This left Victoria’s total at the end of February at 139,139, which is 7.79 per 100 of population. The only other State to show a decrease for February was Queensland, whose total was reduced by 103, which is three times as great as the lose in January—34. The total for Queensland at the end of last month was 24,281, or 2.57 per 100 of population. During January the figures of South Australia were reduced by 177; but last month they improved by 219, bringing the total to 28,489, or 4.90 per 100 of population. Western Australia and Tasmania both showed splendid improvement in their figures last month, Western Australia’s total being increased by 126 to 8290, and Tasmania’s by 57 to 7834. _ The total number of licenses in operation in the Commonwealth at the end of February was 327,004, compared with 327,713 at the end of January. Though the decerase in January and February have been so heavy, the gain for the Commonwealth for the eight months has been 14,812, the total'at the end of June last being 312,192. More than half of that gain has come to New South Wales, the total for the State at June 30 being 111,253. INTERESTING FIGURES. An authoritative analysis, based largely on official figures, places the total number of wireless receiving sets now in use at the astounding figures of 24,000,000. and their value at £200,000,000. Broadcasting estimates agree that a conservative figure would be three listeners to every set in use, so that on this basis the mhnber of listeners may be taken as 72,000,000. These figures enable some idea to be formed of

the colossal dimensions reached by the radio industry in something less than 10 years, and expert opinion declares that the peak is still far from having been reached. Evidence of this is found in the decision of the Radio Manufacturers’ Association to make the Olympia Exhibition of September next twice the size of that of last year. America continues, commer-cially-speaking, to be the most important radio country, absorbing 45 per cent, of the total production. England comes next, Germany third, and France fourth. Approximately 52 per cent, of the sets in use in the United States are electrically operated. European countries, inclusive of the British Isles, are represented in this analysis by approximately 11,000,009 sets. License fees range on the average from 10s to 20s per set, or, say, £8,000,000 per annum, bearing in mind the fact that the fees range from 15 pence in France to nearly £9 per set in Turkey. The important position occupied by the United States in respect of the wireless industry is not wholly due to its area and population. For one thing, broadcasting is not a Government monopoly. It is wholly in the hands of private and competitive enterprise. Mr M. H. Aylesworth, the president of the National Broadcasting Company, announces that his company alone will spend during this year a sum of nearly £2,500,000 on broadcasting talent. This, he explains, does not mean that artists already employed will receive more money individually, but that a greater array of talent will be marshalled before the microphone. FARNSWORTH TELEVISION. Further detais are now to hand concerning the remarkable claims of Mr P. 1. Farnsworth, the Californian radio enwho has invented a new valve for television transmission which abolishes the need of a revolving disc. A New York correspondent says that in a statement made to a body of experts in that city, Mr Farnsworth announced that he had in his laboratory a television system in operation which required a wave-length of only six kilocycles to carry the images from the transmitter to the receiver. The receiver itself is housed in a cabinet about 12 inches square, from which connection is made to an ordinary broadcast receiver at a point immediately following the detector stage. Even six kilocycles, Mr Farnsworth declared, is not the minimum wave-band needed for transmission. He is at work on a system which will reduce this to five kilocycles, so that images can be sent over the normal American wave-band used by the broadcasting stations. He foresees that television will be eventually combined with sound programmes over a single 10-kilo-cycle channel, one side of the carrier wave taking the image and the other side the voice and music. Mr Farnsworth was asked by one of the radio experts how ho could transmit television images, which require 900,000 light impulses per second, over a wave-band designed only lor five or six kilocycles. His reply was that the wave-band, corresponding to the 900,000 impulses generated per second, is cut into sections of five or six kilocycles by means of filters, and each station transmitted separately but simultaneously. A restoring network at the receiving end brings back the 900,000 impulses to form 300 line images at the rate of 20 per second. A further stage in the development of the Farnsworth system will, it is stated, make it possible, during the hours of sunlight, to transmit out-of-door scenes.