Abstract: An impedance network used for ring trip or loopsupervision purposes in a telecommunications system. The network employs a multi-port impedance bridge with one set of opposed terminals (first port) coupled to the line loop being supervised and the opposed terminals (second port) coupled to an AC ringing source. A third port is coupled to intermediate points in the impedance of opposite bridge legs. The third port leads to a low pass filter network and ultimately to a DC detection circuit. The third port is also coupled through impedances to the AC source to receive an attenuated AC component signal to cancel any stray AC components entering the detection circuit.