WIRELESS NEWS.

Press, Volume LXII, Issue 18680, 1 May 1926, Page 10

WIRELESS NEWS.

CRYSTAL CONTROL. FOB BROADCASTING STATIONS. (srzcuLLi: fcsiniH ros "ths tbsss.") (By "Electra.") Station WGY in U.S.A. i 9 the first super-power station to utilise crystal control for the transmitter, and reports froru the International Week tests state that the wave held its frequency uiideviatingly. In fact, the best available measuring instruments failed to record even a fractional departure from 790 KC frequency assigned to the station. A piece of quartz crystal less than an inch square, ground to a thickness a shade less than an oighth of an inch, controls the frequency of tho 50 kilowatt output of WGY's giant developmental transmitter. Crystal quartz has been utilised for frequency control on the regular 5 k.w. transmitter of WGY for several months. Special conditions had to be met in adapting this form of control to fix tlu> frequency'of 50 k.w. output. Besides the General Electric Company's development transmitter with its bank of eight 20 kilowatt waterrooled valves, are two small coppercovered cabinets with dials, switches, and meters built in the faces. On© of these boxes contains the crystal and a single exciting tube. In the second box is a single amplifying valve. Successive stages of amplification up to one kilowatt are placed in separate panels. The small slab of quartz is enclosed in a metal chamber which is connected to work directly on a five-watt valve. Tho crystal and valve in combination act as a high-frequency generator, whoso output is determined by the contraction and expansion of the crystal. This particular crystal is ground to provide a frequency or pulsation period, of 790 kilocycles. The interaction of vntvo and crystal may bo described as the setting up of a mechanical force, which is converted into an electrical force of a definite fixed frequency dependent upon the dimensions of the piece of crystal used—the thinner the crystal the higher the frequency.

Valve and Crystal. The five watt valve, directly connected to,the crystal, works into a fifty watt valve, resulting in the amplification of the original energy at the fixed frequency. . Still further amplification is obtained by connecting the fifty watt valve to a 250 watt valve, arid then a/ourth stage is secured by connecting tho output of the 200 to a 1000 watt valve. _ All valves used up to this point are air-cooled. .In the next stage a metal watercooled valve rated at 20 kilowatts is introduced. This valve is part-of the transmitter, and formerly was used as tho master oscillator. This valve, before the introduction of the crystal, was a self-excited generator. Now it is excited by the proceeding stages of crystal amplification". The 20 k.w. tube then excites the banjj: of eight 20 k.w. power tubes of tho transmitter. The average listener may not know how a broadcasting station maintains its frequency, and he may hot be inters ested in the method. However, he strongly advociates a strict adherence to frequency, because stations are spaced so closely in tho broadcast'band that interference is almost. sure to occur if. a station wavers periodically from its .frequency. There is also fairly good evidence that faditag tends to decrease when the frequency is held 'constant., Radio; engineers of the .General Electric Company have certainly demonstrated that crystal control may be' successfully adapted to any practical power. '

Air Navigation. The accuracy of radio compasses and direction' finders is daily being demonstrated. In th©' recent flight across the Atlantic from Palos to Perntimbuco Major Franco ■ and Captain' Ruiz do Alda, used a Marconi direction finder to keep them on the right - course. In a letter, Captain do Alda, who was navigator, states thit; on parts of theflight^it would have.been impossible to carry on without this aid, .for they kept below the'clouds for great'distances and were therefore uhable to eiiijploy astronomical navigation. Above the clouds, cf course, it was impossible, to measure the deviation due to wind or even to find the direction of; that deviation. deferring'to'one stage of the. flight, he. says: "We perceived indistinctly a very far island on the port sido, and Franco decided to' make for it. I told hhn that it was, Lanzarote, and ashe, was apparently not convinced, I gave him his bearings, obtained by the radio direction finder, and they showed mathematically the degrees by which we were diverging from the route. Then Franco, convinced, got back on to the route, and we continued without seeing Las Palmas." s .. . It wjll be remembered, that' at the of the flight over the ocean ,of 1-440 miles,, th§ aviators , unerringly made the small island of Fernando Noronlia. '' This is only one case where tho radio direction finder was. of great use. Anyone who. has Bpoken to somo of the operators off tho larger ships will no doubt have'heard of cases where,- in times of heavy fogs, it has been possible to the correct boaringa by the radio direction finder bo that the ship can proceed in safety.

Here and There. I noticed in a recent local radio publication that since, the four, radio inspectors hare been in business, the Vhowling" valve-nuisance has been considerably reduced; Personally, I cannot agree with this. To my mind for everyone they, "fix" another , one springs ii p in its place. If one gives it a tew moments' thought, he will 6ee that the present situation cannot bo improved upon. A radio inspector locates a "howler," pays him a visit, and gives the necessary instruction for working the set in order to obtain. a minimum of interference. He spends, perhaps, half an hour, with the offender, and then departs, feeling that lie has done a good turn to other listeners. Next evening that same "bowler" Can be heard. I know of one case where he was on the air agaiu within fifteen minutes after tho inspector's departure. Some may ask, "Why should that be?." I think the following reason fully answers • this question: A man who has built a set froln instructions received and has been operating' it for two or three months, has been getting'good results,, but has never learnt how. to tune tho various stations in without causing interference. The point which arises is., can learn within half an hour? He, tries out the method shown him by the inspector, but finds that he can pick up the stations much easier and quicker, bv his old method, and in tho majority of cases ho gpes back to it. There are many other reasons why "howling valves'* can never be cured. One of the best ways to greatly ,reduce the trouble is-'the- erection of high power broadcasting stations. I have' just ; received advice from 3AR, Melbourne, of a filight alteration in their transmission times. The new times are as follows (New Zealand tiroe^: —1-0 p.m. to 2.30, 4.0 to 6.30 p.m., 8.15 p.m. to 12.10 a.m.; Sundavs, 12.0-to 2.0 p.m., 4.-30 to 5.30 p.m.! 8.0 to 11.50 p.m Everybody is wondering what is going to happen to the Dunedin broadcasting statitjn, VLOX. when the Exhibition closes. Arrangements .have been made to carry on with the elation

at a different situatioh, and it is hoped that it will be possible to make the shift without missing a programme. Mr J. Bingham, of tho New Zealand Broadcasting Co., is at present in Auckland, in connexion with the. erection of the new 500 watt, station.