Abstract: A line interface apparatus includes a line coupling transformer having first and second windings, and an impedance matching circuit connected to the first winding. The impedance matching circuit includes a first section characterized by a first impedance, a second section characterized by a second impedance, and a switch circuit, connected to the first and second sections and to the first winding of the line coupling transformer, for switching either the first or the second section in series with the first winding of the line coupling transformer. An echo of a transmitted signal is replicated and subtracted from a composite signal comprising a received signal and the echo of the transmitted signal. The result of the subtraction is compared to a threshold value to indicate whether a loop connected to the second winding of the line coupling transformer has an impedance about equal to a first impedance or about equal to a second impedance.

Abstract: An adjustable balancing circuit (900) for an adaptive hybrid is suitable for use with a two-conductor transmission line in full duplex communications. In a preferred example, the adjustable balancing circuit (900) includes a first impedance structure (902), a second impedance structure (904), a plurality of N resistor-inductor-capacitor (RLC) networks (908), a first plurality of N switch circuits (912), and a second plurality of N switch circuits (914). The first plurality of N switch circuits (912) switchably cascadingly couples the first plurality of N RLC networks (908) to a first end of the first impedance structure (902). The second plurality of N switch circuits (914) switchably couples a first end of the second impedance structure (904) to a first end of each RLC network. When properly configured, the adjustable balancing circuit (900) cancels reflected transmit signals caused by the presence of short bridged taps on the two-conductor transmission line.