Edwin Armstrong Regenerative Feedback (1913), Superheterodyning (1918), FM (1933)

Aug 18, 2006 3:19 PM


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Born December 18, 1890, Edwin Armstrong developed an interest in wireless technology as a teenager. He later entered Columbia University's Electrical Engineering program, where he investigated practical applications for Lee De Forest's Audion triode tube. In 1913, in an effort to improve radio reception, Armstrong fed the output of the triode back into its input, a process he called “regenerative feedback.” It greatly amplified the signal and, if enough feedback was applied to the input, it also acted as an oscillator. Armstrong eventually raised the funds to patent the circuit, which became the basis for today's continuous-wave radio transmitters.

In 1918, he invented superheterodyning, which used the principle of heterodyning (combining two frequencies to create new signals equal to the sum and difference of the original pair), and applied it to radio receivers. Ironically, one of his most notable developments was frequency modulation (FM) in 1933, which didn't make its mark until decades later. To promote the technology, he built the first FM radio station in 1940, but despite the band's improved sound, he was unable to convince networks and broadcasters to support FM. After years of legal battles and despondence over FM's lack of success, he committed suicide in 1954.

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