WAR ON REGENERATORS

Evening Post, Volume CVII, Issue 22, 26 January 1924, Page 22

WAR ON REGENERATORS

Although investigation of the acts has shown that-oscillating receivers are not responsible for most of the interference experienced by listener,™ in the United States, the trouble caused by such sets is very serious. America has never adopted any restriction on the use of receivers liable to cause interference, and the 'single-circuit" tuner is very popular there, owing to the-ease with which it can be tuned, and its efficiency in long distance reception, in which respect it is claimed by its adherents to be superior to the two-circuit tuner. On this point, however, issue is joined. New Zealand amateurs ar e not permitted to use the single circuit tuner with reac- j tion; and in Britain this type of receiver is forbidden for use on the broad- ' casting wave-lengths, though not' for other purposes. The object of the restriction is of course to prevent the pleasure of one listener being interfered with by the carelessness or over-enthus-iasm of another. It seems probable that the rather' small amount of interference experienced m America, where the circuit .banned xn New Zealand is so popular, is due to the great supply ofpowerful broadcasting, which makes it generally unnecessary to use strong regeneration. When, however, occasion colls for delicate listening, the American operator can object_as rigorously as anyone. The problem came into great prominence in connection with the great Trans-Atlantic broadcasting test held in November, when all the stations in Britain, and I s<? ve? :a", i" America, under a carefully arranged plim, transmitted programmes

could be heard in each others' territory. The test was a remarkable success, though the reception of British music, in America was rendered difficult •by the relatively low power of the British' stations, and was seriously, affected by the difficulty in preventing interference by transmitters whose owners did not recognise the importance of silence. The nights of the test were, in the circumstances, periods of almost ,chilly silence, in which the squeal of an oscillating receiver was liable to make the highly strung operator of a multi-valve set jump in his chair.. For. the time being; therefore, the agitation for the abolition of sets capable of oscillation was distinctly stimulated.

Merely to abolish single circuit tuners, does not get over the trouble. Anyone who listens-in in .Wellington' will know thattr-if !he assumes, as he is, in duty bound, to do, that nobody, here uses single-circuit tuners with valves. Reaction applied, to the ■ secondary of a tuner often causes radiation from the aerial. Apparently one' of the most satisfactory methods of reception avoiding radiation is to use one valve as a rjidio-frequency amplifier, coupled to the next valve by the tuned impedance and with reaction on the inductance of the plate circuit. Not only does this give all the advantages of regeneration j it gives the receiver longer "reach," due to the radic-freqnency amplification. It makes -re-radiation almost impossible if the.set is properly designed, because the first' valve chokes off the currents that tend- to flow back to the, tuning circuits. In this method, the tuner can be a single circuit without any risk or regrets. . '

Most of those who have been wguing against the radiative receiver in America appear at present to be setting their faces against regeneration in general, and assert that the1 proper remedy is in the direction of straight-forward amplification by a succession of valves. This doctrine has been given a powerful impetus by the development of the superhetrodyne and ,neutrodyne systems. -The first of these enables multiple stages of high-frequency amplification to be used without the tuning difficulties inseparable from the ordinary "cascade" arrangement ; and the neutrodyne has a specific arrangement which cancels the tendency of high frequency amplifiers to oscillate. Either of these arrangements thus facilitates the use of extreme high frequency amplification, which is, as a general rule, then* low frequency. Two stages of "tuned" radio-frequency amplification is as much as most people would cafe to manage in the ordinary way. During the' Trans-Atlantic Tests already mentioned, Paul Godley received the English broadcasts with 3" sixtube "tuned r.f. set. Two other prominent workers had seven-tube and ninetube super-helerodynes.