RADIO TOPICS.

New Zealand Herald, Volume LXII, Issue 19141, 6 October 1925, Page 7

RADIO TOPICS.

BT THEHJCOK. STABILISING WAVE LENGTHS. ■ The shifting of wave length of a transmitting station has been,, found difficult to prevent, as it may be caused 'by such seemingly trivial things as a sagging of the aerial and a variation of the amount of current used in the transmitter. Frequent checks with a wave meter, the only possible way until recently of determining whether the station was near its assigned wave length, were unsatisfactory. Recently, however, a method of automatically regulating the wave length has been, discovered and is providing a simple solution of an awkward problem. In the device practical use is made of the phenomenon of piezo-electricity. This is an effect exhibited by certain crystals which become electrically charged when subjected to pressure on their ends. Further, such crystals, of which quartz is an example,, when placed between two charged plates change slightly in length. When a quartz crystal suitably cut is placed between two metal plates connected in an oscillating circuit the crystal will alternately elongate and contract, vibrating at radio frequency. Any crystal has its own natural frequency of vibration bo that a crystal of definite size may be cut which will vibrato at a frequency corresponding to a definite wave length and at no other frequency. It has been found that by using a .crystal in a specially-constructed circuit and building the oscillation up through the high-power transmitting set, the wave length of the radiated waves is exactly the same as that of the crystal. .No ordinary change in the adjustment of the transmitting set can cause any appreciable change in the wave length. There is an additional advantage in the use of the quartz crystal in that there is said to be an improvement in the quality of the transmission by a reduction of the amount of distortion. CRYSTAL DETECTORS. Whatever be the secret of the detecting action of a crystal, it is reasonably certain that this action is accomplished within a thin film, possibly some scores of atoms deep, on the surface of the crystal. The main body of the crystal serves merely to support this surface film. It has no more to do with the detecting action than the main structure of . a house has to do with the paint on its rocf. Why not make use, then, of a mere film of crystal material, of lead sulphide (which is the same as galena), or of something else? That this can be done with considerable success is claimed by an English experimenter, Mr. James Strachan, who has done valuable work on various phases of crystal detection. Mr. Strachan reports, for example, that a piece of lead, a piece of silver or a piece of copper may be exposed to moist sulphuretted hydrogen gas and will acquire a thin film of the respective sulphide, which film is then quite efficient as a detector. It works best, he reported, when used with an applied potential. Similar effects may be obtained with oxide films on copper or brass. The mere tarnish which forms naturally in the air on brass articles will serve quite well for radio detection. These film detectors are worthy of the attention of those who experiment with crystal detectors. THE BROADCASTERG SITUATION. At a recent meeting of the Wellington Philosophical Society Professor R. Jack, of the University of Ota go, during the coarse of a lecture on radio telegraphy and telephony, expressed his views on broadcasting in New Zealand. "The broadcasting position in New Zealand is not satisfactory,'' said the lecturer. This class of work had been started in New Zealand before anything was done in Australia, but s.t the present time Australia was away ahead. This was a great pity. A great deal of dissatisfaction had been caused and he felt there would be & good deal more. New Zealand ought to have the very best broadcasting stations that could be got, for the results would be of the utmost importance. In addition to having weather and mukei reports the stations should provide high-class musical entertainments. It was an important point that receiving apparatus haci now reached a stage of development which made it possible to reproduce fine music, so that great enjoyment ccold be derived from the transmitted programmes. He did not know what the policy of the present promoters of broadcasting was, but it was imperative that a big view should be taken of the matter, so as to provide stations capable of giving transmissions of the highest quality. Dr. Jack has been keenly interested in wireless for a long time and conducted the first experimental work in wireless telephony in New Zealand a few years ago at the University of Otago, with" what were at that time phenomenal results so far as distant reception was concerned. In fact the history of broadcasting shows that Dr. Jack was one of the world pioneers in applying the young art of radio telephony to broadcasting. NOTES AND HINTS. The Auckland Radio Association is holding a public meeting of Auckland listeners to-morrow evening at 8 o'clock in the Y.M.C.A., so that the present broadcasting situation may be discussed and reviewed. Every listener should in his own interests make it his, business to attend. The world's largest broadcasting station, SXN, has been erected at Daventry, England, and although the station at present operates with a power of 25 kilowatts, provision has been made for a rating up to 60 kilowatts. The station met with its first mishap during the August bank holiday period, when one of its famous £BO valves burnt out and the station was put out of action for some five minutes. Valve maintenance is one of the most expensive items for radio engineers and when the station was testing a comparatively small mishap occurred ; but tiie loss on valves ran up to £4OO within a quarter of an hour. Hie most expensive misfortune of this sort occurred just after the war when, at the one and only station which was then putting out a broadcast programme, an engineer inserted a switch the wrong way and burnt out nearly £SOOO worth of valves. The occurrence was tragic enough; but when repairs had been effected the engineer derived what consolation he conic? from the thought that during the burning-out he was spending more money per second than all the Allies combined were spending in the same period during the war. Unfortunately a hitch has occurred in the arrangements whereby a company was to erect and operate a broadcast station at the Dunedin Exhibition as stated last week in Radio Topics. It is now stated officially that a. license has not been granted for the erection of the station. "Aerial," writing in the Dominion, states that, "The suspension of the broadcasting service by tie Wellington station, 2YK, was due to a disagreementover the price to be paid the owners ■for it by the new broadcasting company. The Dominion Radio Company asked £IOOO for the full equipment and the new company offered £l6B. The owners of the station declined to agree to an arbiter fixing the' price." . All British passenger liners mast be fitted with at least one lifeboat equipped with radio transmitting apparatus, according to a recent rale of the London Board of Trade, These sets will be able to send tip to 50 miles and the receiving sets used in conjunction with them will receive signals from at least a thousand miles, according to tiio power of the sending station. The writer, as listeners' representative" lon the Radio Broadcasting Advisory Board, has received advice from Mr. A. Markman, secretary of the P. and T. Department, that a meeting of the board ' will be held next week in Auckland.