"THE VERY LATEST"

Evening Post, Volume CXII, Issue 97, 21 October 1926, Page 14

"THE VERY LATEST"

INFRADYNE RECEIVER.

"The last word in new circuits is the infradyne." This statement, quoted from another paper, is calculated to start another wave of excitement among the "circuit-hounds, ". but, fortunately perhaps, the so-called infradyne is one of the luxury arrangements, as, costly and elaborate as the superheterodyne. Actually it is a special type of superheterodyne, and a little discussion of its main points will illustrate to what lengths the craze for circuit designing will take some people. * The argument upon -which the superheterodyne based its claims to attention is primarily the difficulty of securing efficient radio-frequency amplification of short waves. The apparatus is designed therefore to convert the received signals into new signals of a fairly long wave-length—the same wave-length whatever station is being received —and pass them through an amplifier designed specifically to give good amplification of that wavelength. Whether the amplifier, in the general run of superheterodyne receivers, actually does give efficient amplification is very much open to question. The success of the superheterodyne actually rests not so much upon its efficiency as an.amplifier, valve for valve, when compared with other modern receivers, as upon the fact that it provides a multi-stage amplifier of great power, sensitivity, and selectivity, with only two tuning controls. It has been abundantly proved that the fundamental argument mentioned is wrong, and that it is quite easy, by means of balanced circuits, to get very efficient direct amplification of waves at least as short as those used in broadcasting, and even shorter. Here conies in the infradyne. The Lupcrheterodyne uses an oscillator valve, whose oscillations are combined with those of the incoming signal to produce a new, lower frequency by heterodyne action. This frequency is the difference between the frequency of the signal waves and that generated by the oscillator. But when such a combination of waves is made, there is, in addition to the difference frequency, a sum frequency as well. It is possible, therefore, by using an oscillator which generates short wave, to produce by heterodyne another shortwave signal ready for amplification. "We are immediately up against the problem of providing an amplifier which will deal efficiently with this new short-wave signal —the very problem which the superheterodyne was invented to solve. From this it «an be judged whether the infradyne principle is worth pursuing. The infradyne receiver, as described, generates a new wave of 90 or 10,0 metres, which is passed through a three-stage amplifier. The original signal goes through two stages of radiofrequency amplification before conversion to the now frequency. The set uses ten valves, seven of them preceding the main detector.