Abstract: A loop-circuit for a telephone line is provided that includes a transistor having a first electrode directly connected to one of the wires of the line, a second electrode connected to the other of the wires of the line by means of a resistor, a gate electrode thereof being connected via a resistor to one of the wires of the line, and by means of a capacitor to the other wire of the line, wherein a switch is arranged to cut-off the transistor and another switch is arranged or provided to disconnect one of the plates of the capacitor from the rest of the circuit.

Abstract: An additional line coupling circuit to an intercom telephone set having inserted between the additional line and the intercom telephone set, a d.c. line uncoupling circuit as well as means coupled to one of the wires of the line for transmitting signals on the line and means connected to one or the other line wires for receiving the signals transmitted on the line.