Abstract: A system for data pulse transmission through a single-wire, water-return cable payed out from a coil in an open pack to any selected length over a predetermined wide range (e.g., 4K to 16K feet) employing a toroidal core around the cable near the pack and a multiturn primary winding on the core. The single-wire cable constitutes a single turn secondary winding terminated at the receiver end by a resistor and coupled to the water (circuit ground) at the transmitting end by stray capacitance between the cable remaining in the pack and the surrounding water. The receiver employs an equalizing network to compensate for the amplitude-frequency characteristic of the cable of nominal length within the predetermined range resulting in only slight over-compensation for a shorter cable length and slight under-compensation for a longer cable length.