Frequency modulation (FM) radio, developed by Edwin Howard Armstrong in 1933, revolutionized radio broadcasting by enabling static-free, high-fidelity sound transmission. Despite fierce corporate resistance, FM became the dominant medium for music broadcasting and the foundation for numerous modern communication technologies.
Background
Early radio used amplitude modulation (AM), encoding information by varying the strength (amplitude) of the radio signal. AM had a fundamental problem: electrical interference, lightning, and other sources of “static” manifested as amplitude variations indistinguishable from the intended signal, degrading sound quality.
Engineers assumed noise was an inherent limitation of radio. Armstrong proved otherwise[1].
The FM Breakthrough
Rather than varying signal amplitude, FM encodes information by varying the frequency of the carrier wave. Armstrong discovered that wide-band FM offered dramatic advantages:
- Noise immunity: Static and interference cause amplitude variations, which FM receivers simply ignore
- High fidelity: FM can faithfully reproduce frequencies across the entire audible range
- Consistent quality: Signal strength variations don’t affect sound quality
- Capture effect: FM receivers lock onto the strongest signal, reducing interference
Armstrong demonstrated FM to RCA in 1933, but the company—having invested heavily in AM infrastructure—saw FM as a competitive threat rather than an improvement.
Technical Principles
In FM, the frequency of the carrier wave varies in proportion to the amplitude of the audio signal:
- When the audio signal is high, the carrier frequency increases
- When the audio signal is low, the carrier frequency decreases
- The amplitude of the carrier remains constant
This simple principle, combined with wide bandwidth (about 200 kHz per channel vs. 10 kHz for AM), enabled FM’s superior performance[2].
Resistance and Adoption
Armstrong faced determined opposition from established interests:
- RCA lobbied the FCC against FM spectrum allocation
- The FCC repeatedly changed FM’s assigned frequencies, obsoleting existing equipment
- AM broadcasters opposed a technology that threatened their investments
Despite these obstacles, FM gradually gained acceptance:
- 1941: FCC authorized commercial FM broadcasting
- 1945: FCC moved FM to its current band (88-108 MHz), delaying adoption
- 1961: FCC authorized FM stereo
- 1970s-1980s: FM surpassed AM in audience share for music
Beyond Broadcasting
FM technology extends far beyond radio broadcasting[3]:
- Television audio: FM carries the sound for analog television
- Two-way radio: Police, fire, and emergency services use FM
- Space communication: NASA used FM for Apollo mission communications
- Wireless microphones: Professional audio equipment relies on FM
- Analog cellular: Early cellular systems used FM for voice transmission
Legacy
Armstrong’s FM system demonstrated that fundamental problems in communications could be solved through innovative engineering. The principle of trading bandwidth for noise immunity influenced subsequent technologies including:
- Spread spectrum communications
- Digital modulation techniques
- Satellite communications
FM radio remains the primary medium for music broadcasting worldwide, testament to a technology that overcame both technical challenges and corporate opposition to become a cornerstone of modern communications.
Sources
- Britannica. “FM Radio.” Technical principles and history.
- Wikipedia. “Frequency modulation.” How FM works.
- National Inventors Hall of Fame. “Edwin Howard Armstrong.” FM applications beyond broadcasting.