Armstrong´s invention of noise-suppressing FM [History of Communications]

Edwin H. Armstrong is well known as the inventor of wide-deviation or wideband FM. His patent on this invention was granted December 26, 1933, followed soon thereafter by demonstrations of his system before engineers, papers on the subject of wideband frequency modulation (FM) and its noise-suppression property, and eventually, of course, after World War II, widespread acceptance of FM by the radio industry and the public at large. The years in between were devoted to a bitter court fight between Armstrong and RCA, leading eventually to Armstrong´s tragic suicide in 1954. This is well documented in the book by Lessing devoted to Armstrong´s life (1969). What is not clear is precisely how and when Armstrong had the intuitive leap, his Eureka! moment, that led to this truly momentous invention. Armstrong was notorious for leaving very little documentation on his inventions. Lessing does note that Armstrong was fully occupied with his FM work, carrying out thousands of experiments, from 1928 to 1933, but no attempt to further narrow this interval of time down or discuss how he came to develop the wide-deviation FM concept is offered. We try, in this brief note, using documentation available in the Armstrong papers housed at Columbia University, to come to grips with these questions.