Structure features of minimum frequency shift keying signal modems

The article discusses specific features of constructing modems for minimum frequency shift keying signals using various schemes with high noise immunity levels. An analysis of the formation of these signals and frequency modulation signals, which are orthogonal if enhanced, is provided, including quantitative indicators and comparative characteristics. Two schemes of minimum frequency shift keying signal demodulators (coherent and autocorrelation) are examined, including their comparative features. Operation principles of these demodulator circuits with the use of timing diagrams are described, requirements for the reference oscillator generators included in coherent demodulators are formulated, as well as the requirements for minimum frequency shift keying signals, which ensure the greatest noise immunity in autocorrelation demodulators of minimum frequency shift keying signals with binary signals quantization.