Submarine Communications Cable

a long-distance communications cable laid on the sea or ocean bottom, to depths of several thousand meters.

The first sea cable for telegraphy was a one-conductor cable with gutta-percha insulation. It was laid in 1850 across the Strait of Dover between Dover and Calais. A transatlantic telegraph communications cable with a length of 3,750 km was laid in 1858 between Ireland and Newfoundland. Regular telegraphic communications via a submarine cable between Europe and America were initiated in 1866. The first low-frequency submarine telephone cables of the symmetric type were laid during the early 20th century. The use of intermediate repeaters in submarine communications cables began in 1943. The introduction of repeaters made it possible to lay submarine communications lines of practically unlimited length. In addition, high-frequency multiplexing increased the number of communications channels to 1,000 and more. The first transatlantic high-frequency telephone trunk cable line began operations in 1956. A transpacific trunk line between Canada and Australia (15,000 km long) was introduced in 1962–63.

Cable ships are used to lay submarine communications cables. By the early 1970’s, 30 oceanic telephone cable lines had been laid, with a total length of 140,000 km and with 4,170 intermediate repeaters. In addition, dozens of cable lines have been laid in the North, Baltic, Mediterranean, Black, and other seas. Submarine communications cables and communications satellites are now the basic means of intercontinental communications. A number of currently used submarine cables have the capability of transmitting 720 simultaneously conducted telephone conversations—that is, they provide for 720 communication channels that occupy a total frequency bandwidth of approximately 6 megahertz (mHz). The widening of the frequency spectrum and the increase in the number of communications channels are characteristic trends in the development of submarine cable trunk lines. For instance, the first transatlantic line to have 1,840 communications channels with a total frequency bandwidth of approximately 14 mHz started operation in 1974 between Great Britain and Canada.

A modern submarine communications cable is a coaxial cable with solid, usually polyethylene, insulation. Deepwater cables, laid in depths of 700 m or more, have no armor. A steel cable serves as the load-carrying component. It is balanced so as to prevent twisting and is located in the center of a tubular inner conductor. Such cables, which were invented in 1951 by the English engineer R. Broadbank, are classified as medium cables (diameter of the inner conductor is 8 mm and of the outer conductor, 25 mm) and large cables (8 mm and 38 mm, respectively). The latter type involves much less loss and has the potential for a significantly higher number of communications channels. A direct electric current is supplied to the repeaters through the inner conductor of the cable; seawater serves as the second conductor. Shallow-water, coastal, and shoreline cables have steel armor. It protects the cable against breaks that might occur from being hooked by trawlers and by ships’ anchors and from being dragged along the rocky sea bottom by the tide.