FM RADIO BROADCASTING

by R. J. Reiman, Historian

FM or frequency modulation, differs from AM or amplitude modulation, in that the frequency, rather than the amplitude is varied or modulated in accordance with the audio signal being transmitted. FM consists of both narrow-band and wideband types. Narrow-band systems are used for radiotelephone communications, and wide-band,which requires high-fidelity sound reproduction for broadcasting.

Edwin H.Armstrong, born in New York City in 1890, became an inventive genius in the field of broadcasting and conceived of the regenerative receiver circuit while still an undergraduate at Columbia University, and obtained a patent in 1913 for his invention. Unfortunately, this was bitterly disputed by Lee DeForest, Irving Langmuir, and Meissner, and the debate dragged on until 1934 when the United States Supreme Court decided in DeForest's favor. Armstrong, highly embittered, offered to return the IRE's medal he had received from the Institute for this invention.

Many of the radio engineers believed that the honor belonged to him.

During World War I,Armstrong entered the Army as a Signal Corps Officer and invented the superhetrodyne circuit to improve communications systems, an activity only indirectly related to his official duties. His patent application for this invention was challenged, but successfully withstood, and the patent was granted on June 8, 1920. His sale of the invention to Westinghouse, and a later invention of an improved regenerative circuit to RCA, made him wealthy. He met his wife, Secretary to David Sarnoff, during visits to discuss this invention.

The culmination of his career as an inventor came with his development of FM. He received a patent for FM in the early 1930's, but again bitter patent battles were to follow, this time with his old friend, David Sarnoff.

FM's advantages over AM included virtual freedom from atmospheric interference, arcing power lines and electrical appliances, greater immunity to interference from stations broadcasting at the

same frequency, and the capability for higher fidelity reproduction. Armstrong became a missionary for FM, risked and lost his fortune in his battle with the substantial AM interests, mainly Sarnoff, and ended his life on January 31, 1954 as a concluding act over the bitter conflict over FM broadcasting.

The battle for FM became a battle over allocation of the VHF range (88 to 108 MHz) to television and the idea of quality radio transmission with FM superior to AM. Television was still in the experimental stage, but David Sarnoff staked RCA's fortunes on TV and opposed Armstrong and

allocation of VHF to Armstrong's FM. It became a personal battle between Sarnoff and Armstrong,

and RCA finally conceded that Armstrong had invented FM, in a settlement to his estate long after his death.