CRYSTAL CONTROLLED FREQUENCY SHIFT KEYING SYNCHRONOUS GENERATING SYSTEM

摘要

An FSK transmitter includes a crystal controlled generator which includes a counter which when cycled provides a number of output signals which are logically combined to produce pulse waveforms having different repetition frequencies. The generator counter is arranged to be cycled in accordance with the state of bilevel signals applied to a plurality of input selection lines to apply pulse waveforms of the appropriate repetition frequencies to an output circuit for transmission over a communications channel. The transmitter further includes a ramp generator which is synchronized with cycling of the crystal controlled generator and which is also operative in response to the state of input selection lines to produce pulse waveforms whose repetition frequencies approximate those produced by the crystal controlled generator. During a shift in frequency, the transmitter uses the ramp generator waveforms to establish the cycle time of the counter so as to provide a nominal time period for the pulse waveforms being applied to the output circuit during the time of frequency shift thereby minimizing distortion of the waveforms at the time of crossover.