Abstract: The problem of noise enhancement is eliminated in communications systems by predistorting the amplitude of the transmitted information signal in a manner which compensates for the amplitude distortion introduced in a portion of the communications channel. In the disclosed embodiments, the communications system includes two signal transceivers which communicate with one another through a communications channel. The communications channel includes two-wire subscriber loops adjacent to each signal transceiver with a four-wire transmission path disposed between the subscriber loops. Each transceiver transmits an information signal which, depending on the system noise characteristics, is predistorted to compensate for all or a portion of the amplitude distortion introduced in a subscriber loop adjacent to that signal transceiver. The predistortion necessary to provide such compensation is determined at each transceiver in response to a received narrowband signal at that transceiver.

Abstract: A phase-lock loop includes a scaling element whose scale factor is adaptively adjusted as a function of the value of a state variable in the loop--illustratively, the magnitude thereof. That function is such that, after the adjustment has been made, the value taken on by the state variable is within a predetermined range. In particular embodiments, the scale factor and the state variable are simultaneously adjusted reciprocally, rather than simply adjusting only the scale factor and waiting for the normal operation of the loop to change the state variable, advantageously minimizing any transient degradation in loop performance that may occur as a result of the adjustment.