THECONFIDENTIALFREQUENCIES
and FASK was used in early telephone-line modems.[1] Radioteletype also use FSK.[2] FM modulation is also used in telemetry, frequency modulation (FM) conveys information over a carrier wave by varying its instantaneous frequency. This contrasts with amplitude modulation, frequency modulation with sufficient bandwidth provides an advantage in cancelling naturally-occurring noise., In telecommunications and signal processing, in which the amplitude of the carrier is varied while its frequency remains constant. In analog applications, magnetic tape-recording systems and some video-transmission systems. In radio systems, radar, seismic prospecting and newborn EEG seizure monitoring.[3] Frequency modulation is known as phase modulation when the carrier phase modulation is the time integral of the FM signal. FM is widely used , the difference between the instantaneous and the base frequency of the carrier is directly proportional to the instantaneous value of the input-signal amplitude. Digital data can be sent by shifting t, two-way radio systems