Frequency Modulation Using Digital Filtering Techniques

A simple unstable second-order digital filter with one variable multiplier can provide a source of frequency-modulated signals. This modulator is readily time-shared and should prove attractive when a large number of transmitters are required. A system consisting of a multiple installation of identical binary frequency-shift keying data transmitters is described and analyzed. A refinement which totally eliminates amplitude and phase discontinuities is also presented.