Edwin Howard Armstrong was an American electrical engineer and inventor, who developed FM radio and the superheterodyne receiver system.
Sketch of Armstrong, c. 1954
Armstrong's boyhood home, overlooking the Hudson River in Yonkers, New York, c. 1975
Armstrong explaining the superregenerative circuit, New York, 1922
Armstrong arranged for the construction of a transmission tower in Alpine, New Jersey, near New York City, and financed demonstration operation of W2XMN, the first FM radio station. W2MXN's antenna is mounted between the top two tiers, visible as a vertical line at the far upper right.
Frequency modulation (FM) is the encoding of information in a carrier wave by varying the instantaneous frequency of the wave. The technology is used in telecommunications, radio broadcasting, signal processing, and computing.
FM has better noise (RFI) rejection than AM, as shown in this dramatic New York publicity demonstration by General Electric in 1940. The radio has both AM and FM receivers. With a million-volt electric arc as a source of interference behind it, the AM receiver produced only a roar of static, while the FM receiver clearly reproduced a music program from Armstrong's experimental FM transmitter W2XMN in New Jersey.
Frequency spectrum and waterfall plot of a 146.52 MHz carrier, frequency modulated by a 1,000 Hz sinusoid. The modulation index has been adjusted to around 2.4, so the carrier frequency has small amplitude. Several strong sidebands are apparent; in principle an infinite number are produced in FM but the higher-order sidebands are of negligible magnitude.
An American FM radio transmitter in Buffalo, NY at WEDG
