In telecommunications, the Carson's bandwidth rule defines the approximate bandwidth requirements of communications system components for a carrier signal that is frequency modulated by a continuous or broad spectrum of frequencies rather than a single frequency. Carson's rule does not apply well when the modulating signal contains discontinuities, such as a square wave. Carson's rule originates from John Renshaw Carson's 1922 paper.

where:

• is the bandwidth requirement;

• is the peak frequency deviation; and

• is the highest frequency in the modulating signal.

For example, a typical VHF/UHF two-way radio signal using FM mode, with peak deviation, and a maximum audio frequency of , would require an approximate bandwidth of .

Standard broadcast stereo FM, with a peak deviation of , has a highest modulating frequency (which combines and ) of (assuming no RDS or other subcarriers). Most of the energy therefore falls within an approximate bandwidth of . (Geographically close FM broadcast transmitters are almost always assigned nominal center frequencies at least apart).

Carson's bandwidth rule is often applied to transmitters, antennass, optical sources, receiverss, photodetectors, and other communications system components.

Any frequency modulated signal will have an less than the carrier inside, therefore more information is needed for spectrum planning.

References

• Leon W. Couch II, "Digital and Analog Communication Systems, 6th Edition", Prentice-Hall, Inc., 2001.

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