fsk

FSK, or frequency-shift keying, is a form of digital modulation in which information is conveyed by shifting the instantaneous frequency of a carrier between discrete values. In binary FSK, two frequencies represent the binary symbols 0 and 1; more generally, M-ary FSK uses M distinct frequencies to encode symbols. Some implementations use continuous-phase variants to improve spectral efficiency and reduce abrupt phase changes.

Key parameters of FSK include the center frequency, the frequency deviation (the separation between the frequencies used for different symbols), and the data rate or baud. The occupied bandwidth depends on both the frequency deviation and the data rate; practical designs may employ shaping filters to control spectral leakage. Variants such as Gaussian frequency shift keying (GFSK) filter the modulating signal to curb bandwidth, while minimum-shift keying (MSK) imposes continuous phase to improve efficiency.

Demodulation of FSK can be achieved with a frequency discriminator, a phase-locked loop, or coherent and non-coherent detectors, depending on implementation. Its strengths include robustness to amplitude variations and relatively simple receiver design, making it suitable for radio links, telemetry, paging systems, and other environments with fading or noise. A trade-off is that FSK typically requires more bandwidth than some phase-modulation schemes at the same data rate.

Common applications include traditional radio data transmissions and older dial-up modems, wireless telemetry, and broadcast paging. Variants like MSK and GFSK are chosen to optimize spectral efficiency and performance under specific channel conditions. Compared with amplitude-shift keying or phase-shift keying, FSK offers competitive reliability in non-ideal environments but may occupy more spectrum.