Abstract: A clock setting circuit is provided at a receiving modem for adjusting the phase of a timing signal defining the signal sampling instants. The received signal is filtered in two filters to derive a first signal having a phase .phi..sub.1 and a frequency f.sub.1 equal to f.sub.c - 1/2T, f.sub.c being the carrier frequency and 1/T being the transmission baud rate, and a second signal having a phase .phi..sub.2 and a frequency f.sub.2 equal to f.sub.c + 1/2T. The first and second derived signals are combined to derive an error signal indicative of the phase difference .phi..sub.2 - .phi..sub.1 which difference is used for adjusting the phase of a phase locked oscillator which provides the timing signal.

Abstract: A data transmitting and receiving system in which data is transmitted by varying the phase and amplitude of a carrier, including a receiver which detects the data in a received signal while reducing the effects of noise components which alter the phase and amplitude of the received signal. An in-phase component and a quadrature component are derived from the received signal and are then rotated an angular amount which is a function of an estimated value of the phase error in the received signal. The rotated components are then compared with two sets of reference coordinates for selecting a pair of reference coordinates which have values closest to the values of the rotated in-phase and quadrature components, respectively. The estimated value of the phase error is derived as a trigonometric function of the rotated components and selected reference coordinates. The selected reference coordinates are indicative of the transmitted data.

Abstract: A digital phase filter including two decision filters connected in cascade or parallel for minimizing the noise components in a received phase modulated digital signal. The first decision filter cancels the residual noise component representing the phase intercept component and the phase shift component introduced by frequency shift, and the second decision filter minimizes the random noise component representing phase jitter and white noise.