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Data transmitting systems

  • US 4,066,841 A
  • Filed: 09/24/1976
  • Issued: 01/03/1978
  • Est. Priority Date: 01/25/1974
  • Status: Expired due to Term
First Claim
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1. In a frequency shift keying data transmission system for transmission of information in a binary coded pulse waveform in which the mark of the binary coded pulse waveform is represented by a half cycle of a first keying frequency and the space is represented by a half cycle of a second keying frequency, the improvement comprising:

  • means for the generation of a signal of an approximately sinusoidal waveform having a phase continuous at the transitions of said sinusoidal waveform and wherein the time lengths of the mark and space symbols thereof are matched to the half time periods of the respective keying frequencies and the slope of said approximately sinusoidal waveform is constant at the cross-over points, and means for measuring the time duration between the crossover points of the binary coded pulse waveform signal and comparing the time duration with a reference to determine whether the duration corresponds with that of the shorter half time of the higher keying frequency or that of the longer half time period of the lower keying frequency, wherein said means for measuring and comparing includes a source of clock pulses, a counter connected to said source of clock pulses, means responsive to the beginning of a half cycle of binary coded pulse waveform signal for starting the counter, means responsive to the end of a half cycle of received signal for stopping the counter, and comparator means for determining whether the count of clock pulses during each enabled period is greater or less than a predetermined count corresponding to a time duration greater than the half time of the higher frequency and less than the half time of the lower frequency.

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