Abstract: A system for decoding a PSK signal comprising a constant amplitude carrier whose phase shifts 180.degree. 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.degree. 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.

Abstract: A system for transmitting and receiving serial data over a pair of differential lines so that relatively large differences in ground potential will not affect the integrity of the transmitted data. Each differential line has a first switch for pulling the line high and a second switch for pulling the line low. Logical gates hold all switches off to allow the lines to float in response to a first control signal. A second control signal enables the logical gates to pull the first differential line up and the second differential line down whenever true data is to be sent and for pulling the second differential line up and the first differential line down whenever data is true. Associated with each switch is a protective diode and cold filament lamp for protecting the respective switch and insuring system operation even if large swings in ground potential occur.