Carson bandwidth rule

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In telecommunication, 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 R. Carson's 1922 paper [1].

(Note: John Renshaw Carson was born in 1886. He worked in AT&T. He died in 1940. He had a twin brother, Joseph Robb Carson.)

Carson's bandwidth rule is expressed by the relation CBR = 2(Δf + f _m) where CBR is the bandwidth requirement, Δf is the peak frequency deviation, and f _m is the highest frequency in the modulating signal.

For example, an FM signal with 5kHz peak deviation, and a maximum audio frequency of 3kHz, would require a approximate bandwidth 2(5+3) = 16kHz.

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

Theoretically any FM signal will have an infinite number of sidebands and hence an infinite bandwidth but in practice all signicificant sideband energy (98% or more) is concentrated within the bandwidth defined by Carson's rule.