![]() ![]() The heterodyne worked better but had to await the development of suitable low-power RF sources: small alternators, arc generators, or vacuum-tube oscillators. For its detector Federal interrupted the incoming signal at a radio-frequency rate with a rotating commutator. Cyril Elwell followed with his development of the arc generator, the basis of the Federal Telegraph Co. Fessenden himself coined the term, from the Greek heteros (other) and dynamis (force).įor years Fessenden was the lone proponent of continuous waves, and possessed the only such transmitter, the radio-frequency alternator later perfected by E.F.W. Later a local oscillator was substituted for one of the transmitter-receiver combinations and the heterodyne as we know it was born. Originally both radio frequencies were to be transmitted, received with two antennas, and combined in a detector. The principle of "beats" or difference tones between simultaneous audio pitches was well known since antiquity, but Reginald Fessenden in 1901 was the first to apply the principle to radio transmissions. In view of this apparent misappropriation of credit, it is worthwhile to take a careful chronological look at the superheterodyne, to see precisely how it was invented and how it was introduced into practice. ![]() Lévy did not publicly press his claims outside of France, and even there, Armstrong was often credited with the invention. Since AT&T was in the same patent pool as Westinghouse and RCA, this transfer had no effect on the industry and attracted little notice. In 1928 Armstrong lost his superheterodyne patent in an interference proceeding within the Patent Office, when most of its claims were transferred to a Lévy patent owned by AT&T. So, if the superheterodyne was his most valuable invention-and it is fundamental to essentially every radio and television made since 1930-it would be surprising if Armstrong had not had his priority disputed. FM had been gathering dust on theoreticians' shelves for decades before Armstrong took it up, but as soon as he had made it worth fighting over, he was beset from all sides. John Bolitho had discovered much of the superregeneration principle before Armstrong, who prudently bought Bolitho's patent before negotiating with RCA. Lee de Forest got legal credit for regeneration (and others might have, with better counsel, notably Robert Goddard ). Some Frenchman named Lévy claimed he was first, but whoever heard of him?Īll of Armstrong's inventions were involved in controversies. He devised it during World War I, patented it shortly afterward, sold his patent to Westinghouse who cross-licensed RCA and the radio industry, and that was that. ![]() "Everyone" knows that Armstrong invented it. Armstrong's four principal inventions-regeneration, superregeneration, the superheterodyne, and frequency modulation-the superheterodyne has always seemed one of the least controversial. "The Legacies of Edwin Howard Armstrong." Originally published in the Proceedings of the Radio Club of America, Nov. ![]() Support This Site: The Souvenir Shop :: Contributors :: Advertise Support This Site: Contributors :: Advertiseįorums :: Resources :: Features :: Photo Gallery :: Archives :: Chat :: Clubs :: Books :: Value Guide Forums :: Resources :: Features :: Photo Gallery :: Vintage Radio Shows :: Archives :: Books ![]()
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