Reimagining Edwin Armstrong

A new biography reassesses the invention of FM

Reviewed by Michael Riezenman

image of Armstrong cover
Early FM Radio: Incremental Technology in Twentieth-Century America
By Gary L. Frost; Johns Hopkins University Press; 2010; 208 pp.; $60.00; ISBN 978-0-8018-9440-4

The tragedy and triumph of the invention of frequency modulation (FM) is well known: Major Edwin Howard Armstrong, in a tour de force of insight into mathematics, realized that wideband FM would work better than narrowband; RCA, with which he had long been associated, refused to pay him royalties; and in 1954, during the sixth year of the resulting lawsuit, he jumped to his death from his 13th-floor New York City apartment.

In 1990 his law firm donated his legal files to his alma mater, Columbia University, in New York City, making possible a more realistic picture of what happened. What the files revealed was that Armstrong stood on the shoulders of other, earlier workers in FM; that RCA and its head, David Sarnoff, weren’t so much greedy as uninterested; and that, in the beginning, no one—including Armstrong—realized FM’s two biggest advantages over AM: its abilities to suppress static and to reject interstation interference. In those days, communications companies were concerned more with fading than static, and FM was promoted more as a cure for the former than as a way of reducing the latter.

Early FM Radio is the first serious biography to benefit from the newer documents. Author Gary L. Frost finds that while Armstrong wasn’t a particularly good theoretician, he was a practical, gifted engineer whose convictions never stood in the way of progress. If a belief or idea didn’t work, he was quite ready to abandon it in favor of an alternative with a better chance of success. Armstrong gave up on narrowband FM not so much because of John Carson’s brilliant theoretical proof that it couldn’t work but because he could never get it to work in practice. His breakthrough invention was not simply FM but wideband FM.

Unfortunately, Frost, an engineer and historian, perpetuates the common misconception that FM is superior to AM because noise is a phenomenon more of amplitude than of frequency. As the late Professor Samuel J. Mason of MIT once explained, a radio signal is best visualized as a vector with a ball of fuzz at its tip. The instantaneous value of the signal component represented by the fuzz ball can be along the length of the vector, at right angles to it, or at any angle in between—all with equal probability. The noise added to a radio signal will affect its amplitude or phase (or frequency) with equal probability. The noise reduction of FM comes about because the wide bandwidth occupied by the signal during transmission is reduced in the receiver, and when it is reduced, the noise is reduced along with it.

Other than this important but common error, the book seems a valuable addition to the history of electronics, not least because it relieves Armstrong and Sarnoff of their mythological status as angel and devil and considers them instead as differently gifted practitioners.

About the Author

Michael Riezenman retired from IEEE Spectrum as a senior editor in 2003, after 11 years at the magazine.

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