| 摘要 |
A system for decoding a PSK signal comprising a constant amplitude carrier whose phase shifts 180 DEG each time a logical signal is transmitted. The decoder system includes a phase-locked loop including a first phase detector, a loop filter, and a voltage-controlled oscillator. The incoming PSK signal is supplied to the input of the phase-locked loop and through a 90 DEG phase shifter to one input of a second phase detector. The other input of the second phase detector is taken from the output of the voltage-controlled oscillator and the output of the second phase detector will indicate whether a carrier or data is detected. The output of the second phase detector is connected to the inputs of first and second comparators. One comparator has its inputs biased so that it normally outputs a low signal until the second phase detector indicates the detection of a carrier. This output can be used as a source of reconstructed data. The second comparator responds to the detection of data by outputting a gating signal. A switching element located in the phase-locked loop is normally conductive to allow the loop to operate but the switching element is responsive to the gating signal from the output of the second comparator indicating that data is present to switch off the loop so as to enable the present decoder to be used with even relatively long data pulses even though the time constant of the loop filter is relatively fast for a quick lock-up time.
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