Phantom circuit

In telecommunication, a phantom circuit is a third circuit derived from two suitably arranged pairs of wires, called side circuits, with each pair of wires being a circuit in itself and at the same time acting as one conductor of the third circuit.

Note: The side circuits are coupled to their respective drops by center-tapped transformers, usually called "repeat coils." The center taps are on the line side[?] of the side circuits. Current from the phantom circuit is split evenly by the center taps. This cancels crosstalk from the phantom circuit to the side circuits.

Source: from Federal Standard 1037C and from MIL-STD-188