Abstract: A communications terminal for transmitting and receiving communication signals over a power line communications network and including an interface circuit for coupling the terminal to the power line of the network is disclosed. One embodiment of the network includes a transformer for coupling communication signals between the power line and terminal. The coupled communication signals are measured from the secondary of the transformer and used to govern an amplifier circuit which generates matched signals, representative of the measured communication signals. The matched signals are inverted in polarity at the output stage of the amplifier and applied to the secondary winding of the transformer to cancel substantially the electromagnetically coupled communication signals from the power line, thereby providing a high bridging impedance to the power line communication signals without impeding substantially the coupling of the terminal's own communication signals.

Abstract: A loop current detector for detecting current flowing in a pair of telephone wires comprises:A. a saturable reactor having first, second and third windings, the first and second windings adapted to be connected in a loop circuit to pass DC current,B. resistance connected with the third winding to form therewith a voltage divider, and an oscillator having an AC output connected with the divider, characterized in that the AC voltage drop across the third winding is relatively high when no DC current flows through said loop circuit, and said drop is relatively low when DC current flows through said circuit, andC.