A lot vs. Alot: 9 Grammatical Pitfalls
(FSK) The use of frequency modulation to transmit digital data, i.e. two different carrier frequencies are used to represent zero and one.
FSK was originally used to transmit teleprinter messages by radio (RTTY) but can be used for most other types of radio and land-line digital telegraphy. More than two frequencies can be used to increase transmission rates.