FM band
In most of the world, the
FM band goes from 87.5~108.0
MHz, while in the Americas it starts at 88.0, at the top end of
TV channel 6. In
Japan the FM broadcast band is 76-90MHz, unlike any other country in the world. The name "FM band" is slightly misleading, as one can transmit
FM on any frequency, but this band is primarily used for frequency modulation broadcasting. All of these bands mentioned are considered to be in the
VHF band.
While most countries use frequencies ending in .1, .3, .5, .7, or .9, some use .0, .2, .4, .6, and .8. Still others use .15, .35, .55, .75, .95, or .05, .25, .45, .65, .85 instead. This offset helps to prevent co-channel interference, and take advantage of FM's capture effect.
In North America, each channel is numbered from 201 (88.1MHz) to 300 (107.9MHz) in increments of 1 (0.2MHz). 87.9MHz is technically part of TV channel 6 (82.0~88.0MHz), but is used by class D LPFM stations in the U.S as channel 200.
The basic formulas determining channels for North America as mentioned is as follows:
(MHz - 47.9) * 5 = ch#
(ch# / 5) + 47.9 = MHz
Normally, each
channel is 200
kHz (0.2
MHz) wide, and can pass
audio and
subcarrier frequencies up to 100kHz.
Deviation is up to 200kHz total, or ±100kHz, but is typically limited to 150kHz total (±75kHz) in order to prevent interference to adjacent channels on the band. Stations may go up to 10% over this if they use stereo or other subcarriers, increasing total
modulation by 1% for each 2% used by the subcarriers.