Why Do FM Frequencies End in an Odd Decimal Number?

The FM broadcast in the United States starts at 88.0 MHz and ends at 108.0 MHz. The band is divided into 100 channels, each 200 kHz (0.2 MHz) wide. The center frequency is located at 1/2 the bandwidth of the FM Channel, or 100 kHz (0.1 MHz) up from the lower end of the channel. For example, the center frequency for Channel 201 (the first FM channel) is 88.0 MHz + 0.1 MHz = 88.1 MHz.

Below 88.0 MHz lies TV Channels 5 and 6.
Above 108.0 MHz the frequencies are used for aeronautical operations.

So the lowest FM center frequency, for the first channel, is
88.0 MHz + 0.1 MHz = 88.1 MHz
88.2 MHz + 0.1 MHz = 88.3 MHz
88.4 MHz + 0.1 MHz = 88.5 MHz
.
up to
.
107.8 MHz + 0.1 MHz = 107.9 MHz

Every FM center frequency ends with a decimal extension of .1, .3, .5, .7, or .9. To convert FM channel numbers to/from a corresponding frequency, you may use the conversion tool at http://www.fcc.gov/fcc-bin/audio/findvalues.html.

In the AM band, each AM station has a maximum bandwidth of 10 kHz, extending 5 kHz above and 5 kHz below the assigned center frequency. The AM band in the United States covers frequencies from 540 kHz up to 1700 kHz, in 10 kHz steps (540, 550, 560 ,,, 1680, 1690, 1700). 530 kHz in the United States is not available for broadcast use, but is reserved for the use of low powered Travellers' Information Stations. AM band stations do not have assigned channel numbers.

AM and FM station assignments in other countries may not be made according these procedures. In some countries, an FM station may be assigned a frequency with an even decimal such as 106.2 MHz. In many places, AM broadcast stations are assigned on frequencies with a 9 kHz bandwidth (531 kHz, 540 kHz, 549 kHz, etc.). (Links to other countries' regulatory agencies are listed at http://www.fcc.gov/fcc-bin/world-govt-telecom.html.) There are a few AM stations assigned in the United States in this manner, in Guam, the Marianas Islands, and American Samoa.