ABSTRACT
Frequency shift keying can be used in systems having very little to do with high data rate communications; for years it has been the method used in the simple modems one first used to communicate with remote computers. For binary systems, one just sent a pulse of one frequency for a logic one and a second frequency for a logic zero. The frequency variations due to the modulation will drive the signal up and down the resonant curve, producing simultaneous amplitude variations, which then can be detected using an envelope detector. A format for digital modulation in which the signal may vanish utterly at intervals is to be adopted with caution and with full cognizance of one’s sync problem. Several methods of digital modulation might be considered extreme examples of some kind of analog modulation. Probably the most commonly used type of digital modulation is some form of phase shift keying.
