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Submarine communications cable

From Academic Kids

A submarine communications cable is a cable laid beneath the sea to carry telecommunications between countries.

The first submarine communications cables carried telegraphy traffic. Subsequent generations of cables carried first telephony traffic, then data communications traffic. All modern cables use fiber optic technology to carry digital payloads, which are then used to carry telephone traffic as well as Internet and private data traffic.

As of 2002, submarine cables link all the world's continents except Antarctica.

It is designed to factor out general communications cable issues from transatlantic / telephone / telegraph special cases

Contents

History of submarine communications cables

The first submarine communications cable was a telegraph cable laid between England and France in August 1850 by the Anglo-French Telegraph Company. In 1852, a cable laid by the Submarine Telegraph Company linked London to Paris for the first time.

The first transatlantic telegraph cable was laid in 1858 (Cyrus Field), but was in operation for only a month. Subsequent attempts in 1865 and 1866 were more successful.

Transatlantic cables of the 19th century consisted of steel wire, wrapping india rubber, wrapping gutta-percha, which actually surrounded the multi-strand copper wire. The portions for a distance from each shore had additional protective armor wires. Gutta-percha, a natural polymer similar to rubber, had nearly ideal properties for insulating submarine cables, aside from a rather high dielectric constant which made cable capacitance high. Gutta-percha was not replaced as a cable insulation until polyethelene was introduced in the 1930's. Gutta-percha was so critical to communications that in the 1920's the American military experimented with rubber-insulated cables, since American insterests controlled significant supplies of rubber but no gutta-percha manufacturers.

Long-haul submarine telegraph cables had tremendous electrical problems. Unlike modern submarine cables, the technology of the 19th Century did not allow for in-line repeater amplifiers in the cable. The cables used huge voltages to overcome the resistance of their tremendous length. They also have extreme amounts of capacitance and inductive reactance. The distributed resistance, capacitance and inductive reactance operate in combination to slow down and disperse the telegraph pulses in the line, distorting them and limiting the speed of telegraph operation.

Early cable designs failed to correctly analyze these facts. Famously, there was a showdown between Dr. E.O. Wildman Whitehouse of the Atlantic Telegraph Company and Prof. William Thomson (Lord Kelvin). Dr. Whitehouse believed that with enough voltage, any cable could be driven. Because of the excessive voltages recommended by Whitehouse, Cyrus Field's first transatlantic cable never worked reliably, and eventually shorted to the ocean when Whitehouse increased the voltage beyond the cable design limit. William Thomson designed a complex electric field generator that minimized current by resonating the cable, and a sensitive light-beam galvanometer for detecting the faint telegraph signals. He became rich on the royalties of these and several related inventions. William Thomson was elevated to baron Lord Kelvin for his contributions in this area, chiefly an accurate mathematical model of the cable using Lagrange transforms, which permitted design of the equipment for accurate telegraphy. The effects of atmospheric electricity and the geomagnetic field on submarine cables also motivated many of the early polar expeditions.

Lord Kelvin had produced a mathematical analysis of propagation of electrical signals into telegraph cables based on their capacitance and resistance, but since long submarine cables operated at slow rates, he did not include the effects of inductance. By the 1890's, Oliver Heaviside had produced the modern general form of the telegrapher's equations which included the effects of inductance and which were essential to extending the theory of transmission lines to higher freqeuncies required for high-speed data and voice.

While laying a transatlantic telephone cable was seriously considered from the 1920s, a number of technological advances were required for cost-efficient telecommunications that did not arrive until the 1940s.

In 1942, Siemens Brothers, in conjunction with the British National Physical Laboratory, adapted submarine communications cable technology to create the world's first submarine oil pipeline in Operation Pluto.


TAT-1 (Transatlantic No. 1) was the first transatlantic telephone cable system. Between 1955 and 1956, cable was laid between Gallanach Bay, near Oban, Scotland and Clarenville, Newfoundland. It was inaugurated on September 25, 1956, initially carrying 36 telephone channels.

In the 1960s, transoceanic cables were waveguides transmitting frequency-multiplexed radio signals. The repeaters were the most reliable vacuum tube amplifers ever designed. A high voltage direct current wire powered the repeaters. Many of these cables still exist and are usable, but abandoned because their capacity is too small to make money. Some have been used as scientific instruments to measure earthquake waves and other geomagnetic events.

In the 1980s, optic fiber cables were developed. Modern optic fiber repeaters use a solid-state optical amplifier, usually an Erbium-doped fiber amplifier. A solid-state laser is powered by the voltage difference between the ocean and a wire carrying high voltage direct current. The solid-state laser excites a short length of doped fiber that itself acts as a laser amplifier. As the light passes through the fiber, it is amplified. This system also permits wave-division multiplexing, which dramatically increases the capacity of the fiber.

The optic fiber used in undersea cables is chosen for its exceptional clarity, permitting runs of more than 100 kilometres between repeaters to minimize the number of amplifiers and the distortion they cause.

The fibers are usually arranged in a self-healing ring to increase their redundancy.

The first transatlantic telephone cable to use optical fiber was TAT-8, which went into operation in 1988.

Technology of submarine communications cables

to be written

Economics of submarine communications cables

to be written

Owners and operators of submarine communications cables

to be written

Owners and operators of cable-laying ships

See also

External links


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