| 摘要 |
A read amplifier generates pulses in response to the transitions of a phase encoded signal and selectively gates the pulses to an output and to a retriggerable one shot multivibrator under the control of inhibit pulses produced by the multivibrator. During a preamble of the data signal in which a known sequence of zeros is produced, a decade counter prevents generation of pulses in response to the polarity return transitions between the zeros and prevents the inhibit pulses from being applied to gate the pulses produced by the data signal until a predetermined number of zero pulses has been counted. During the preamble the inhibit pulses at the output of the multivibrator are averaged and compared with a reference so as to adjust the duty cycle of the multivibrator to produce inhibit pulses which are 70 percent of the duration of the bit intervals of the data signal. Thereafter, the system is self-adjusting with the multivibrator responding to each pulse at the beginning of a bit interval to begin generation of an inhibit pulse and the averaging circuit being operative to adjust the multivibrator duty cycle as the bit intervals change so as to maintain the duration of the inhibit pulses at a selected ratio of the length of the bit intervals.
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