Abstract: An optical undersea telecommunications system has a main cable (1) which branches (BU1) near a landfall to two separate stations. Each branch (71,81) supplies half the current of the main cable (1) for powering the regenerators. In the event of a fault in a branch (e.g. 81) caused by an anchor or fishing gear, the operations branch (71) regenerator (e.g 11) can supply the full current (I) via a zener diode power feed and bypass circuit and high voltage diodes (D1,D2) automatically prevent leakage of current back to the fault.

Abstract: An impulse noise source in a bidirectional submerged communications system is positionally located by detection apparatus at one end of the system which measures the time interval between the same impulse arriving twice at the one end of the system, firstly, via a shorter or faster path in the system (either the incoming path to the one end, or a reference frequency band in the incoming path) and, secondly, via a longer or slower path in the system (either the go path from the noise source, a go/return distant loop and the incoming path, or another frequency band in the incoming path). Group delay distortion of the system affects the location accuracy and is equalized by networks in the detection apparatus.