A rule defining 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. Note 1: The Carson bandwidth rule is expressed by the relation CBR = 2 (f + fm) where CBR is the bandwidth requirement, f is the carrier peak deviation frequency, and fm is the highest modulating frequency. Note 2: The Carson bandwidth rule is often applied to transmitters, antennas, optical sources, receivers, photodetectors, and other communications system components.