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1 Armstrong, Edwin Howard
[br]b. 18 December 1890 New York City, New York, USAd. 31 January 1954 New York City, New York, USA[br]American engineer who invented the regenerative and superheterodyne amplifiers and frequency modulation, all major contributions to radio communication and broadcasting.[br]Interested from childhood in anything mechanical, as a teenager Armstrong constructed a variety of wireless equipment in the attic of his parents' home, including spark-gap transmitters and receivers with iron-filing "coherer" detectors capable of producing weak Morse-code signals. In 1912, while still a student of engineering at Columbia University, he applied positive, i.e. regenerative, feedback to a Lee De Forest triode amplifier to just below the point of oscillation and obtained a gain of some 1,000 times, giving a receiver sensitivity very much greater than hitherto possible. Furthermore, by allowing the circuit to go into full oscillation he found he could generate stable continuous-waves, making possible the first reliable CW radio transmitter. Sadly, his claim to priority with this invention, for which he filed US patents in 1913, the year he graduated from Columbia, led to many years of litigation with De Forest, to whom the US Supreme Court finally, but unjustly, awarded the patent in 1934. The engineering world clearly did not agree with this decision, for the Institution of Radio Engineers did not revoke its previous award of a gold medal and he subsequently received the highest US scientific award, the Franklin Medal, for this discovery.During the First World War, after some time as an instructor at Columbia University, he joined the US Signal Corps laboratories in Paris, where in 1918 he invented the superheterodyne, a major contribution to radio-receiver design and for which he filed a patent in 1920. The principle of this circuit, which underlies virtually all modern radio, TV and radar reception, is that by using a local oscillator to convert, or "heterodyne", a wanted signal to a lower, fixed, "intermediate" frequency it is possible to obtain high amplification and selectivity without the need to "track" the tuning of numerous variable circuits.Returning to Columbia after the war and eventually becoming Professor of Electrical Engineering, he made a fortune from the sale of his patent rights and used part of his wealth to fund his own research into further problems in radio communication, particularly that of receiver noise. In 1933 he filed four patents covering the use of wide-band frequency modulation (FM) to achieve low-noise, high-fidelity sound broadcasting, but unable to interest RCA he eventually built a complete broadcast transmitter at his own expense in 1939 to prove the advantages of his system. Unfortunately, there followed another long battle to protect and exploit his patents, and exhausted and virtually ruined he took his own life in 1954, just as the use of FM became an established technique.[br]Principal Honours and DistinctionsInstitution of Radio Engineers Medal of Honour 1917. Franklin Medal 1937. IERE Edison Medal 1942. American Medal for Merit 1947.Bibliography1922, "Some recent developments in regenerative circuits", Proceedings of the Institute of Radio Engineers 10:244.1924, "The superheterodyne. Its origin, developments and some recent improvements", Proceedings of the Institute of Radio Engineers 12:549.1936, "A method of reducing disturbances in radio signalling by a system of frequency modulation", Proceedings of the Institute of Radio Engineers 24:689.Further ReadingL.Lessing, 1956, Man of High-Fidelity: Edwin Howard Armstrong, pbk 1969 (the only definitive biography).W.R.Maclaurin and R.J.Harman, 1949, Invention \& Innovation in the Radio Industry.J.R.Whitehead, 1950, Super-regenerative Receivers.A.N.Goldsmith, 1948, Frequency Modulation (for the background to the development of frequency modulation, in the form of a large collection of papers and an extensive bibliog raphy).KFBiographical history of technology > Armstrong, Edwin Howard
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