[rakesh777]

The first applications of electron tubes were in radio communications. Guglielmo Marconi pioneered the development of the wireless telegraph in 1896 and long-distance radio communication in 1901. Early radio consisted of either radio telegraphy (the transmission of Morse code signals) or radio telephony (voice messages). Both relied on the triode and made rapid advances thanks to armed forces communications during World War I. Early radio transmitters, telephones, and telegraph used high-voltage sparks to make waves and sound. Vacuum tubes strengthened weak audio signals and allowed these signals to be superimposed on radio waves. In 1918, Edwin Armstrong invented the "super-heterodyne receiver" that could select among radio signals or stations and could receive distant signals. Radio broadcasting grew astronomically in the 1920s as a direct result. Armstrong also invented wide-band frequency modulation (FM) in 1935; only AM or amplitude modulation had been used from 1920 to 1935.



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