FASHIONS IN RECEIVERS

Evening Post, Volume 137, Issue CXI, 10 June 1926, Page 14

FASHIONS IN RECEIVERS

THE POPULAR NEUTRALISED TYPE.

It is very interesting to notice how favour moves in wireless receiving practice from one type of receiver to another. In the days when .only the wealthy and the forjunate could obtain valves and everyone else had to use crystal detectors, there was not very much latitude, but the enthusiasts managed, nevertheless, to create fashions and crazes for different "hookups/ all of which gave practically the same results. It has remained for these later days for laboratory experts to work out crystal receivers which are considerably more efficient, that those used before such appliances became practically useless, except to beginners. All experimenters with valve receivers can think up a little list of circuits, each of which was sworn by as the best that ever was, labelled with the names of Armstrong, Weagaut, Cockaday, Rciuartz, "S.T. 100," and so on, and all of them more or less back numbers, though as. a matter of fact they are all effective arrangements. They can remember, too, the short enthusiastic flurry of the horrible super-regenera-tive arrangements of Armstrong and Flewelling; horrible, that is, for broadcast reception, though undoubtedly extraordinarily effective for certain purposes. Most of these came from American sources. Britain's chief contribution was not so much in the shape of a specific circuit as in the adoption of radio-frequency amplification, which was taken very seriously in hand and developed to a. high point, especially in the form of the, tuned anode circuit and reflex arrangements. Later came two really big departures, which are still dominant—the neutrodyne and its varieties, and the superheterodyne or supersonic circuits, both highly developed on both sides of the. Atlantic. The neutrodyne ■is actually one of a class of several varieties of which the characteristic is that they include one or more stages of radio-frequency amplification which, properly adjusted, cannot oscillate and are thus able to give maximum amplification but are unable to cause any interference by radiation. Eeeeivers of this class are at the present time the mose efficient known for use with an out-door aerial, and with five valves will perform any practicable feat of broadcast reception. The super-het-erodyne, for the same output, requires more valves, because it is not intended for use with a big aerial, beinjS?in general a source, of continual interference; but used with a loop, it is in the highest rank as a long distance receiver. These two big classes are both in high'favour just now; but owing to the fact that the super-heterodyne is considerably more costly—and if it is to be really good, is by no means, easy- to design and build—it still figures as rather a luxury.

Out of the neutrodyne has come a smaller neutrodyne type, using only one stage of radio-frequency amplification, neutralised as in the parent type, but feeding a regenerative detector circuit. This again has two sub-types, the reflexed (of which the Roberts is the best-known example) and the unrcflexed, populaviscd under the name of Browning-Drake. ' In these receivers the use'of regeneration on the detector virtually makes up for the absense of the second radio-frequency amplifier, so that a well-constructed Roberts of three valves is not far behind a fivevalve neutrodyne, if the latter has been so adjusted that there is no regeneration. As, however, it is difficult to get rid of regenerative effects altogether, and most operators naturally adjust tlieir sets to get as much as possible consistent with stability, the big neutrodyne has rather the advantage. " „ . As a satisfied user of a neutralised receiver, and being convinced by bitter experience of the bad effects of most other receivers in creating interference, "Grid-Bias" strongly advises anyone who can do so to use some form of neutralised amplifier, and some further note on tho subject will be given shortly-