Abstract: Signal monitoring apparatus in which a baseband signal including noise is compared at timed intervals with a reference signal and an estimated noise signal from an estimated noise signal generator. Indications of whether the estimated noise signal is higher or lower than the noise level present in the signal are applied to a digital accumulator in the estimated noise signal generator. Certain of the most significant bits in the accumulator are employed to generate the analog estimated noise signal. An arrangement for preventing or permitting the passage of indications to the accumulator approximates the Rayleigh distribution of differential error probabilities about the estimated noise signal being generated. The result is that the estimated noise signal is an rms value averaged over a large number of measurements. Certain of the most significant bits in the accumulator are decoded and converted to an analog voltage which is a measure of the signal-to-noise power ratio of the baseband signal.

Abstract: Receiving apparatus for processing differential quadrature phase shift keyed (DQPSK) signals. Received 70 MHz IF signals are mixed with a 70 MHz reference frequency to provide quadrature components of each received signal. The resultant of the quadrature components of each signal is converted to a digital representation. The digital representations are sampled at sixteen times the baud rate. Samples are subtracted by two's complement addition and the difference produced by samples from two successive received signals is read out as the data encoded in the signal. The resultant of each two's complement addition is monitored to determine if there is no difference indicating that the samples are from the same received signal or if there is a difference indicating that the samples are from different received signals.