Radio broadcast .. (1922-30)

A Super-Sensitive Long-Range Receiver Another Invention of Edwin H. Armstrong Which He Calls the "Rolls-Royce" Receiver By PAUL F. GODLEY A ^STRONG, of radio receiver fame, called it a "Rolls-Royce." He named one after the "flivver," too. It was his single-tube superregenerative receiver. But, notwithstanding the marvels which are to be unearthed from beneath the intricacies of the super-regenerative scheme, the real "bug" on radio reception methods— super supersensitive radio reception methods — has a very keen and long unsatisfied hankering to know all about that most sensitive receiver, the super-heterodyne. That long-to-be-remembered sporting proposition so spectacular and successful in its outcome, the bridging of the Atlantic last winter by American amateurs, brought the superheterodyne receiver into the limelight. Armstrong's phrase, "the Rolls-Royce receiver" —a phrase which he coined at the time of his disclosure of the superregenerative receiver, added considerable prestige to that intriguing and mystifying word, " super-heterodyne. " And, when, in starting to learn about the super-heterodyne, the reader finds the statement that it is a method of radio-frequency amplification, he is not for one moment to jump to the conclusion that radio-frequency amplification by the super-heterodyne method is by any means an ordinary method. It is perhaps the simplest of receivers in operation. At the same time it is, no doubt, the most complicated of receivers to construct because of the care which needs to be taken with it. Let it be said for the benefit of those few who The Super-Heterodyne Here, again, we find the practical genius of Edwin H. Armstrong, inventor of regeneration and super-regeneration, applied to a receiver designed to help America terminate the World War. Again we find a war development of great peace-time value. For many years Armstrong and the author of this article have been close friends. It is not surprising, therefore, that Godley knew of the super-heterodyne receiver and used it in his tests at Ardrossan, Scotland, in December, 1921, when he proved its value by copying signals from about thirty amateur stations located in various sections of this country. — THE EDITOR. may not yet have learned it, that the threeelement vacuum tube as a detector of radio oscillations has an adjunct which is known as its "threshold value." To be specific, the three-element vacuum tube will not function as a detector until the incoming oscillatory currents are of a certain disappointingly large value. As a result of this defect (we are sorely tempted to call it that), many, many surging signal currents come to dwell in our antenna and receiver circuits, unannounced and unknown. Long ago their presence there had been suspected and, even in early times, methods which we would now consider quite crude were employed in an attempt to make their acquaintance. Primarily, most of these attempts had to do with amplifying the audible signal currents in the belief that after the weaker signals had operated the vacuumtube detector, they were so nearly exhausted as to be below audibility. Further study disclosed the fallacy of this, and then it was that the great value of employing the three-element vacuum tube in their amplification prior to their detection was discovered. Radio-frequency amplification has been used for several years, quite successfully, at long wavelengths where the frequency of oscillations is comparatively low. It was not until the World War that any great attention was given to finding out the reasons for the difficulties encountered when radio-frequency amplification was attempted on very short waves. Here the oscillatory currents are of comparatively high frequency. Up to this