Forked telephone circuit separating call and receive paths - uses self-balancing FET controlled impedance bridge

摘要

The forked telephone circuit separates the 'call' and 'receive' paths in a two-wire connection (23). A bridge (19, 22, 23, 24, 25) is self-balanced in amplitude and phase by variable resistive (19) and reactive (22) impedances which are voltage regulated by a F.E.T. circuit. The phase sensitive detector (16) which uses the calling signal (18) as its reference, controls the resistive impedance. A second phase sensitive detector (20) controls the capacitive impedance using a reference signal 90 deg. out of the phase with the calling signal (21). This circuit can be extended for use with inductive components.