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Frequency modulation (FM) is the changing of the frequency of an oscillating signal's carrier. In communications that use a continuous sinusoidal signal, information can be encoded in a pattern of changes to the frequency. In FM radio, the encoded pattern is represents the pattern of air-pressure changes that constitute the sounds being communicated.
Frequency modulation is used in radar, such as in chirps and in continuous-wave frequency-modulated (CWFM) radar. The latter has some of the advantages of using chirped pulses plus the advantage of having no gaps in the received information.