Frequency modulation

In telecommunications, frequency modulation (FM) conveys information over a carrier wave by varying its frequency (in contrast with amplitude modulation (AM), in which the amplitude of the carrier wave is varied while its frequency remains constant). In analog applications, the difference between the instantaneous and the base frequency of the carrier is directly proportional to the instantaneous value of the input signal. Digital data can be sent by shifting the carrier's frequency among a set of discrete values, a technique known as frequency-shift keying.