Multiple frequency-shift keying
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Multiple frequency-shift keying (MFSK) is a variation of frequency-shift keying (FSK) that uses more than two frequencies.
[edit] Types
Defined examples of a multiple frequency-shift keying system include dual-tone multi-frequency (DTMF), which is used in touch tone phones and the Multi-frequency trunk signals used in Twentieth Century telephone exchanges.
MFSK or "polytone" modes used for shortwave communications
- COQUELET
- PICCOLO
MFSK modes used for VHF, UHF communications
- DTMF, mainly for telemetry control
[edit] Spectrum efficiency versus other HF modes
RTTY and packet spectrum efficiency comparted with respect to {bits/second} thruput
