SpectrumWiki

 
FM Broadcast Band

FM broadcast stations operate in the 88-108 MHz band, on a 200 kHz channel raster beginning at 88.1 MHz and ending at 107.9 MHz. A total of 100 channels are available, but the FCC maintains an allotment table specifying which channels are available in a given geographic market. The calculations are based on propagation considerations, local population, frequencies being used in adjacent and other nearby markets, and other factors.

The 88-92 MHz portion of the FM band is reserved for non-commercial educational stations. Both commercial and noncommercial stations may be licensed in the 92-108 MHz portion.

All FM stations broadcast in wideband analog FM mode (approximately 200 kHz bandwidth), but some stations also operate a companion digital signal by the use of digital (OFDM) sidebands above and below the analog signal. This method is called In-Band On-Channel (IBOC) digital, as opposed to the concept of providing for an additional channel or band in which to provide digital service. The total power allowed in the digital sidebands is presently 10% of the power transmitted in the analog signal, to help avoid interference to adjacent FM channels.

As of March 2012, there were 6,555 commercial FM stations and 3,712 non-commercial educational FM stations licensed in the U.S. (10,267 total stations, or, on average, about 103 stations per channel).

Interesting factoid: The audio signal for analog TV channel 6 falls just below the FM broadcast band, at 87.75 MHz. This frequency is tunable by many FM receivers. In many cities, TV channel 6 is used more as a "bootleg" FM broadcast station than as a TV station. However, as all TV stations, including low power and Class A stations, must convert to digital by the end of 2013, such bootleg operations will disappear.