FM broadcast
The wide FM used by music and talk stations on the FM dial.
What does it sound like?
High-quality music or speech, often stereo.
Who uses it?
FM broadcast stations.
Where and when can I hear it?
88-108 MHz in the Americas (similar ranges elsewhere).
The science
An FM broadcast station gets a channel 200 kHz wide, and at full (100%) modulation its frequency swings as far as 75 kHz either side of center. Stereo is carried by a clever stack: the main signal holds left plus right, so mono radios still work, while left minus right rides on a 38 kHz subcarrier. A faint 19 kHz pilot tone, exactly half that frequency, tells the receiver how to rebuild the two channels.
Why use it?
The wide swing gives FM much of its resistance to static and room for full-range, high-fidelity sound, which made it attractive for music. Adding stereo without breaking older mono radios let the system grow without leaving listeners behind.
Lore
Edwin Howard Armstrong received four patents on his FM techniques in 1933. The FCC approved the combined General Electric-Zenith stereo system in April 1961, and on June 1, 1961 WGFM in Schenectady, New York became the first station to broadcast in FM stereo.
Easily confused with
- AM voice, from the same family
- Single-sideband voice (SSB), from the same family
- Narrow FM voice, from the same family