THE WIRELESS WORLD.

Otago Daily Times, Issue 19969, 10 December 1926, Page 5

THE WIRELESS WORLD.

NOTES AND NEWS, By Magna Vos. 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. Wireless operators on duty at the commercial station VIS, Sydney, recently held direct communication with a ship in the Bay of Biscay, almost 10,000 miles distant. While listening to Australian broadcasting, which is regarded by New Zealand listeners as being of a remarkably high standard, one is struck by the fact that a large portion of the programme consists of the relaying and broadcasting of concerts, band recitals and dance music from various sources outside the studio. The extensive use of relaying has the feature of being advantageous, both to the listener-in and to the broadcaster in providing variety at no great cost, but in New Zealand there is the difficulty that public entertainments suitable for relaying are not of nightly occurrence. Connection to a number of the local picture theatres would provide variety in this typo of orchestral music and, while such relaying is already conducted by 4YA from one or two theatres, other theatres should be linked up to exploit all the possibilities DONT’S FOR VALVE USERS. Don't over-run your valve, especially if it is a dull emitter. Don’t employ a higher anode voltage then that for which the typo of valve is designed. Don’t forget that a power valve is advisable for good loud-speaker work. Don’t throw de-sensitised dull emitteis away, as sensitivity may frequently be restored. Don’t forget that dull emitters can be used as bright emitters if sensitivity has been lost. Don’t keep tapping your valve with your finger. ... . don't if you want satisfaction, use a rather rnicrophonio dull emitter as detector without special valve-holder. Don't forget to clean valve-legs occasionally. , Don’t ignore the advantage to be obtained from separate lI.P. tappings. Don’t forget to use the valve specially designed to work in a certain position in the circuit. Don’t omit to use valves of low vnterolectrode capacity for ultra short-wave work. Don’t forget that valve bases may bo removed and special mountings made to reduce capacity effects. Don’t buy unnamed cheap valves if good results and economy arc desired. Don’t forget that many small receiving valves will function satisfactorily in small power transmission. Don’t forget that valves can be run in series to limit the current consumption, where it is desired to use dry batteries for filament heating purpose*. . Don’t pull varies out of their sockets by taking a grip on the bulb. DO NOT ABUSE YOuxt VALVES. One of the chief causes of distortion in a receiver which may appear to be functioning otherwise than correctly is the overloading of the tubes. In many of the earlier-built receivers comparatively high ratio' audio frequency transformers were used somewhere in the region of five to 'one and perhaps as high as seven or eight to one. Many people will still buy high ratio intervaive transformers- It has been found, as a result of long experiments, that the tendency to use the transformers m amplifiers by giving them a step up, ratio has been very much overdone. It is the job of the valvos to amplify and not the transformers, and frequently when high ratio transformers are being used, the valve which is being fed by the output side of the transformers is being asked to do too much, with a result that it docs not .produce the clear round tone which is desired, but rather tends to introduce a rattle, which is very often mistaken for a fault in a loud-speaker, or, as frequently expressed, blasting of the microphone at the broadeast studio. In nine case® out of 10 this can bo traced to the overloading of valves. The chances of faulty transmission from a station such as, for example, IYA, are remote. The control engineer, in addition to controlling the musical pick up arrangements, actually receives the programme on a. loud-speaker in his room so that he is able to immediately detect and check any fault that may appear. It is safe to say, then, that all trouble taking the form of distortion is caused within the receiver. In cases where receivers already have high ratio transformers installed the listener should take some steps to limit the effect caused by their “step up.’ 1 have noticed that many attempt this by. placing across the secondary winding of their transformers fixed condensers of a value of from 001 to perhaps .005. This procedure should never be adopted. A condenser may with advantage bo placed across the primary windings of a transformer, but never across the secondary. A resistance of about half a megohm placed across the secondary winding will act aa a limiter and will greatly improve reproduction. For those who contemplate building audio frequency amplifiers 1 would say—keep in mind the fact that the audio frequency transformer is not an instrument to amplify the signals, that is the function of the valve, but should merely be used to transfer energy from one valve to the next. It is, therefore, deairable to use transformers having a ratio of one to one or nofe more than two to one. It will still be advantageous to use a resistance as a limiter to prevent occasional overload of the valves and consequently the rattling form of distortion. It should be clearly understood that a valve of the 201 A typo, for example, is not intended to produce enormous volume, and should it be forced to do to »t almost surely follows that distortion will result. If big volume and good reproduction are desired the ordhary general service valve should be replaced by .power valves whose function jt is tc handle largo amounts of energy without distortion. .. Set owners should never be satisfied until thev have overcome all causes of distortion. Reproduction of broadcast music and voice can be made perfect, and it is only by attaining such results that the best can be had from a wireless programme. AMERICAN RADIO CENSUS. Since 1980 over 1400 broadcasting stations have been licensed in America, And no fewer than 870— over 62 per cent, have gone out of the business (states the N*'' - Yo*rk Radio. Two mam reasons are given for these defections. The first is the financial difficulties experienced by the broadcasters in running the stations. ixoariy 50 per cent, of thS STQ statious that c osod un disappeared from the air on this ac count. It was found that to broadcasting service was a costly business, and as no return was received from the listeners, the proprietors of tho stations decided to cut their losses and close down. It only goes to show that broadcasting is not a business that everyono can manage, there must be an understanding of the re quirements of listeners and of the |*P C " to bo incurred m providing a service that will last. The second main reason advanced for the failures also proves this. About 20 per cent, of the proprietors of stations retired from the business because they realised that they were, not giving as -satisfactory a service as their competitors. They found that the “Message they doIfeirecl to put over, could be don©, better by people who understood the bllsln f-*?’ who consequently had many more u * te n® rs ’ It was more economical to pay another station to broadcast then advertisements an The Pr decrea”o a in the number of stations pars to y havo had the other effect. There arc probablv too many stations now operating in the various cities, especially, as only a portion of them can afford to give good services. A census was conducted recently to ascertain the number of bstenors. It was conducted in a very thorough manner bv the American Telephone and Telegraph Company, which operates 18 of the principal stations in the Eastern and Middle West of the State®. A questionnaire was sent out and the answers wore very interesting Over 3,750,000 people answered the questions, and it was estimated that the listeners numbered over 15,000,000. (A more recent return gives the. number of Bets in u Q c fis 5,500,000; Qiid as ifc estimated from the replies to the former questionnaire that five persons listened at each set the radio audience in the United States can be set down at over 87.000.000 people.)