Armstrong, Edwin Howard (1890–1954)

US radio engineer who developed a system known as superheterodyne tuning for reception over a very wide spectrum of radio frequencies and frequency modulation (FM) radio transmission for static-free reception.

Armstrong was born and educated in New York, and became a professor at Columbia University. He was involved in much litigation over patents and eventually killed himself.

The superheterodyne receiving circuit was developed by Armstrong during World War I in an attempt to make a receiver that could detect the presence of enemy aircraft by means of the electromagnetic (radio) waves given off by the sparking of the ignition systems of their engines. In 1919 he introduced the superheterodyne principle that allowed the the triode valve to be used for amplification and tuning in radios.

At that time, radio broadcasting used amplitude modulation (AM), which is susceptible to static interference. In 1933 Armstrong, with US physicist Michael Pupin (1858–1935), developed and patented the FM method of radio broadcasting, in which the transmitted signal is made to modulate the frequency of the carrier wave over a wide waveband. FM is unaffected by static and is capable of high-fidelity sound reproduction; it remains the basis of quality radio, television, microwave, and satellite transmissions, although the high frequencies used are generally limited to line-of-sight distances. FM broadcasting did not gain ground until after World War II.