Edwin Howard Armstrong : biography
Edwin Howard Armstrong (December 18, 1890 – January 31, 1954) was an American electrical engineer and inventor. He has been called "the most prolific and influential inventor in radio history". He invented the regenerative circuit while he was an undergraduate and patented it in 1914, followed by the super-regenerative circuit in 1922, and the superheterodyne receiver in 1918. Armstrong was also the inventor of modern frequency modulation (FM) radio transmission.
Armstrong was born in New York City, New York, in 1890. He studied at Columbia University where he was a member of the Epsilon Chapter of the Theta Xi Fraternity. He later became a professor at Columbia University. He held 42 patents and received numerous awards, including the first Institute of Radio Engineers now IEEE Medal of Honor, the French Legion of Honor, the 1941 Franklin Medal and the 1942 Edison Medal. He is a member of the National Inventors Hall of Fame and the International Telecommunications Union’s roster of great inventors.
Even as the regenerative-circuit lawsuit continued, Armstrong was working on another momentous invention. Working in the basement laboratory of Columbia’s Philosophy Hall, he invented wide-band frequency modulation (FM) radio. Rather than varying ("modulating") the amplitude of a radio wave to encode an audio signal, the new method varied the frequency. FM enabled the transmission and reception of a wider range of audio frequencies, as well as audio free of "static", a common problem in AM radio. (Armstrong received a patent on wide-band FM on December 26, 1933.)
In 1922, John Renshaw Carson of AT&T, inventor of Single-sideband modulation (SSB modulation), had published a paper in the Proceedings of the IRE arguing that FM did not appear to offer any particular advantage.J.R. Carson, , Proc. IRE, vol. 10, no. 1 (February 1922),pp. 57-64 Armstrong managed to demonstrate the advantages of FM radio despite Carson’s skepticism in a now-famous paper on FM in the Proceedings of the IRE in 1936,E.H. Armstrong, , Proc. IRE, vol. 24, no. 5 (May 1936),pp. 689-740. which was reprinted in the August 1984 issue of Proceedings of the IEEE.E.H. Armstrong, , Proc. IEEE, vol. 72, no. 8 (August 1984),pp. 1042-1062.
Today the consensus regarding FM is that narrow band FM is not so advantageous in terms of noise reduction, but wide band FM can bring great improvement in signal to noise ratio if the signal is stronger than a certain threshold. Hence Carson was not entirely wrong, and the Carson bandwidth rule for FM is still important today. Thus, both Carson and Armstrong ultimately contributed significantly to the science and technology of radio. The threshold concept was discussed by Murray G. Crosby (inventor of Crosby system for FM Stereo) who pointed out that for wide band FM to provide better signal to noise ratio, the signal should be above a certain threshold, according to his paper published in Proceedings of the IRE in 1937.M.G. Crosby, , Proc. IRE, vol. 25, no. 4 (April 1937), pp. 472-514. Thus Crosby’s work supplemented Armstrong’s paper in 1936.
In 1934 Armstrong began working for RCA at the request of the president of RCA, David Sarnoff. Sarnoff and Armstrong first met at a boxing match involving Jack Dempsey in 1920. At the time Sarnoff was a young executive with an interest in new technologies, including radio broadcasting. In the early 1920s Armstrong drove off with Sarnoff’s secretary, Marion MacInnes, in a French sports car. Armstrong and MacInnes were married in 1923. While Sarnoff was understandably impressed with Armstrong’s FM system, he also understood that it was not compatible with his own AM empire. Sarnoff came to regard FM as a threat and refused to support it any further.
From May 1934 until October 1935, Armstrong conducted the first large scale field tests of his FM radio technology from a laboratory constructed by RCA on the 85th floor of the Empire State Building. An antenna attached to the spire of the building fired radio waves at receivers about 80 miles away. However RCA had its eye on television broadcasting, and chose not to buy the patents for the FM technology.