FM Radio and RDS
Frequency Modulation brought pristine audio quality to radio broadcasting. Combined with Radio Data System (RDS), FM became more than just audio—carrying traffic alerts, station names, and now hybrid digital signals.
Edwin Armstrong's FM
Edwin Armstrong invented frequency modulation in 1933, proving that FM dramatically reduced static and interference compared to AM. His FM system offered near hi-fidelity audio that AM could never match.
FM Frequency Bands
- 88-108 MHz: Standard broadcast FM worldwide
- 76-90 MHz: Japan FM band
- 65.8-74 MHz: Former Soviet/OIRT FM band
- Channel spacing: 200 kHz (US), 100 kHz (some countries)
RDS: Data on FM
Radio Data System (EN 50067:1989) embeds digital information within the FM broadcast signal at 57 kHz:
- PI: Program Identification (station identity)
- PS: Program Service name (8 characters)
- RT: RadioText (64 characters, scrolling info)
- TP/TA: Traffic Program/Traffic Announcement flags
- AF: Alternative Frequencies list
- CT: Clock Time (synchronized time)
Modern FM Features
- HD Radio: In-band on-channel digital audio
- FMeXtra: Digital subcarriers on analog FM
- RDS2: Enhanced data capacity
- Digital Audio Broadcasting (DAB): Competing digital standard
Timeline
1933Edwin Armstrong patents FM radio
1939First FM broadcasts begin in US
1941FCC allocates 42-49 MHz for FM
1958RDS (Radio Data System) developed in UK
1961FCC moves FM to 88-108 MHz band
1980sRDS adopted widely in Europe
1990sHD Radio begins US deployment