FSK=Frequency Shift Keying

Larry Gauthier (K8UT) wrote:
No, FSK is not CW. Although others have provided a technical definition of
FSK (Frequency Shift Keying), from a practical standpoint FSK is one of two
methods that hams use to transmit in RTTY mode.

Unlike CW, where characters are constructed by sending combinations of short
(dot) and long (dash) signals all on one transmit frequency, RTTY characters
are sent by shifting your transmit frequency back and forth between a higher
(mark) and lower (space) frequency. In most ham circumstances, those two
frequencies are 170 cycles apart.

Hams use two popular techniques to create those 170-hertz shifted
frequencies:

- FSK, in which the VFO of the transmitter "knows" to shift its frequency
hi/lo in response to an input signal on the rear panel. FSK mode functions
when the transceiver is in RTTY mode.

- AFSK, in which a computer, using software that controls its sound card,
generates the correct tones and those tones are fed into the microphone
input of the transceiver. AFSK mode functions when the transceiver is in SSB
mode