In radio, **frequency deviation** is the result of frequency modulation. In the FM band for broadcasting, deviation is normally 150kHz total, which is ±75kHz of the carrier frequency. Excessive deviation is the result of overmodulation, and causes interference to adjacent channels.

Phase modulation has the same net effect as FM, but **phase deviation** is measured in degrees or radians, compared to the umodulated carrier wave. The modulation index is equal to the phase deviation in radians.

See also: standard deviation in mathematics