Abstract: An eye opening monitor for a binary waveform such as provided as the video output of a demodulator. At the decision sample time, the video is compared to -V.sub.th and +V.sub.th reference voltages to determine if it falls in the range defined therebetween. If it does, a counter is reset. Because the carry-out pulses of the counter are used to produce -V.sub.th and +V.sub.th, the range defined therebetween is decreased by the additional time required to count to the carry-out after the counter is reset. The loop stabilizes with the range from -V.sub.th and +V.sub.th being quantitatively indicative of the eye opening. A voltage derived from V.sub.th is visually displayed.

Abstract: A multiplexer system providing a transmission frame field containing information derived from the cumulative total of stuff bits used over a plurality of frames. The stuff bits which also have assigned positions in the transmission frame are generally used in asynchronous systems to compensate for the input data rate of a group not being a fixed submultiple of the transmission rate. The demultiplexer system uses the information derived from the cumulative total to improve the bit count integrity performance of data channeled out to a user device. Also, during transmission fade conditions, the demultiplexer uses information derived from the frequency of past stuff operations to maintain group bit count close to its expected value.

Abstract: A digital data communication system employing quaternary phase-shift keying for transmission by a microwave radio link. The digital modulation of the quadrature channel is delayed from the in-phase channel by one-half the time duration of a bit so that the transmitted phase does not experience a quantum shift in excess of 90.degree.. This permits the use of an injection locked oscillator as an amplifier of the microwave transmission.