Multiple Frequency-Shift Keying

What Does Multiple Frequency-Shift Keying Mean?

Multiple frequency-shift keying (MFSK) is a method of signal modulation that extends the radio teletype (RTTY) two-tone technique to multiple tones, producing fewer errors. MFSK signal modulation technique involves discrete audio tone bursts of different frequencies, which deliver digital data. This technique was originally used by British and other European government agencies during the mid-1900s.


MSFK is a variant of frequency-shift keying (FSK), which makes use of more than two frequencies to transmit digital data.

At the time of its invention, MSFK was referred to as Piccolo, which is a high-pitched musical instrument that sounds much like an MFSK signal over a radio receiver speaker.

Techopedia Explains Multiple Frequency-Shift Keying

MFSK works by using comparatively narrow tone spacing. This helps to achieve significant data rates for a given bandwidth. For example, 64 bps in a signal bandwidth of 316 Hz is common.

The first MFSK mode was MFSK16, which was designed by Murray ZL1BPU. MFSK16 was first coded by Nino IZ8BLY, and was released in 1999. It featured full-time error correction and was built for long-path DX.

The benefits of MFSK include:

  • Error rate is reduced as the quantity of tones is increased.
  • High rejection of broadband noise and pulse caused by narrow receiver bandwidth per tone.
  • Low band rate for multi-path rejection and sensitivity.
  • Tolerant to ionospheric effects like multi-path, doppler, and fading.
  • Constant transmitter power – phase continuous for minimum keying noise.
  • No requirement for a linear transmitter.

Drawbacks of MFSK:

  • The individual tone detector’s narrow bandwidth and narrow spacing could make tuning complex.
  • Low TX/RX offset and good transceiver stability are crucial.
  • MFSK utilizes more bandwidth for a given text speed when compared to a PSK system; however, it is more robust.


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Margaret Rouse
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Margaret is an award-winning technical writer and teacher known for her ability to explain complex technical subjects to a non-technical business audience. Over the past twenty years, her IT definitions have been published by Que in an encyclopedia of technology terms and cited in articles by the New York Times, Time Magazine, USA Today, ZDNet, PC Magazine, and Discovery Magazine. She joined Techopedia in 2011. Margaret's idea of a fun day is helping IT and business professionals learn to speak each other’s highly specialized languages.