Self compensating spread-spectrum hybrid

Abstract

A communications station (10) couples a bidirectional input-output signal path (16') to two unidirectional signal paths; a transmit signal path (12') and a receive signal path (14'), using a controllable hybrid (20). A feedback control system in the station minimizes the amount of transmit signal appearing at the receive output port (24) of the hybrid (20). The control system spreads the spectrum of a pilot signal (40) by means of a biphase modulator (46) and a pseudorandom generator (42) to produce a spread-spectrum pilot, which is added, in a summer 30, to the transmit signal. The spread-spectrum pilot signal covers the bandwidth of the information signal, and is reflected in an amount and with a phase which depends upon the relative impedance presented to the hybrid (20) by the bidirectional signal path (16'). The receive signal, which arrives at the station bidirectional port (16) from the bidirectional path, is coupled from the hybrid (20) to a spread-spectrum demodulator (56), which regenerates the own-station pilot signal with a phase which depends upon the impedance presented by the bidirectional signal path to the hybrid. The pilot signal is phase-detected (64), processed, and applied to the hybrid to degeneratively minimize the amount of transmit signal coupled to the receive port (14).