FSK stands for Frequency Shift Keying. It is a modulation scheme where a specific source transmits digital information through discrete changes in a carrier wave frequency.

FSK has a number of classifications. BFSK, or Binary Frequency Shift Keying, is the simplest among these classifications. As its name suggests, BFSK makes use of two distinct frequencies to transmit binary information: 0s and 1s. The 1 refers to the mark frequency while the 0 refers to space frequency.

The other forms of FSK are:

  • Minimum Shift Keying, also known as MSK, is believed to be a more efficient form of FSK. This is because in FSK, the difference betwe en the lower frequency and higher frequency is the same as half the bit rate. This results to the 0 and 1 waveforms having half a carrier difference.
  • Audio Frequency Shift Keying, otherwise known as AFSK, is another form of FSK. In AFSK, digital information is represented as changes in the frequency or pitch of a particular audio tone. This yields a signal suitable for radio or telephone. The transmitted audio normally shifts between two tones: the mark and the space.

FSK is implemented in many systems and applications. The early telephone modems, for instance, use FSK to transfer and receive data. Caller ID systems also use FSK to register the necessary information.

In addition, FSK plays a major role in storing data on audio cassettes used for recording. Also, FSK is used in amateur radio that usesdata transmission via unmodified voiceband equipment.