150 years ago, on August 16, 1858, President of the United States James Buchanan received a congratulatory telegram from Queen Victoria and sent her a return message. The first official messaging over the newly laid transatlantic telegraph cable was marked by a parade and fireworks display over the New York City Hall. The festivities were overshadowed by the fire that happened for this reason, and after 6 weeks the cable was out of order. True, before that he did not work very well - the Queen's message was transmitted within 16.5 hours.
From idea to project
The first sentence regarding telegraph and the Atlantic Ocean was a relay scheme in which messages delivered by ships were to be sent by telegraph from Newfoundland to the rest of North America. The problem was the construction of a telegraph line along the complex relief of the island.
Seeking the help of the engineer in charge of the project subsequently attracted the American businessman and financier Cyrus Field, who became indispensable for the transatlantic cable project. In the course of work, he crossed the ocean more than 30 times. Despite the setbacks Field faced, his enthusiasm led to success.
The businessman immediately seized on the idea of ââa transatlantic telegraph transmission. Unlike terrestrial systems, in which pulses were regenerated by a relay, the transoceanic line had to do with one cable. Field received assurances of the possibility of transmitting a signal over long distances from Samuel Morse and Michael Faraday.
William Thompson gave this theoretical justification, in 1855, published the law of inverse squares. The rise time of a pulse passing through a cable without inductive load is determined by the time constant of an RC conductor of length L equal to rcL 2 , where r and c are the resistance and capacitance per unit length, respectively. Thomson also contributed to subsea cable technology. He improved the mirror galvanometer, in which the slightest deviations of the mirror caused by current were amplified by projection onto the screen. He later invented a device that records signals in ink on paper.
The technology of submarine cables was improved after the appearance of gutta-percha in England in 1843 . This resin of a tree growing on the Malay Peninsula was an ideal insulator because it was thermoplastic, softened when heated, and returned to solid form after cooling, facilitating the insulation of conductors. Under conditions of pressure and temperature at the bottom of the ocean, its insulating properties improved. Gutta-percha remained the main insulation material for submarine cables until the discovery of polyethylene in 1933.
Field Projects
Cyrus Field led 2 projects, the first of which failed, and the second ended in success. In both cases, the cables consisted of one 7-wire wire surrounded by gutta-percha and armored with steel wire. Corrosion protection was provided by tarred hemp. The nautical mile of the cable of the sample of 1858 weighed 907 kg. The transatlantic cable of 1866 was heavier, 1622 kg / mile, but since its volume was larger, it weighed less in water. The tensile strength was 3 tons and 7.5 tons, respectively.
All cables had one return water conductor. Although sea water has less resistance, it is subject to stray currents. Food was carried out using chemical current sources. For example, the project of 1858 had 70 elements of 1.1 V each. These voltage levels, combined with improper and careless storage, have led to the failure of the deep-sea transatlantic cable. The use of a mirror galvanometer made it possible to use lower voltages in subsequent lines. Since the resistance was approximately 3 ohms per nautical mile, currents of the order of a milliampere, sufficient for a mirror galvanometer, could be conducted at a distance of 2000 miles. In the 1860s, a bipolar telegraph code was introduced. The dots and strokes of the Morse code were replaced by pulses of opposite polarity. Over time, more complex designs have been developed.
Expeditions 1857-58 and 65-66
For the laying of the first transatlantic cable by issuing shares, ÂĢ 350,000 was raised. The American and British governments guaranteed a return on investment. The first attempt was made in 1857. Two steamers, Agamemnon and Niagara, were required to transport the cable. Electricians approved the way in which one ship laid a line from a coast station, followed by connecting the other end to a cable on another ship. The advantage was that it maintained a continuous electrical connection with the shore. The first attempt ended in failure when cable management equipment failed 200 miles from the coast. He was lost at a depth of 3.7 km.
In 1857, the chief engineer of Niagara, William Everett, developed new equipment for cable management. A notable improvement was the automatic brake, which worked when the tension reached a certain threshold.
After a severe storm that nearly sunk the Agamemnon, the ships met in the middle of the ocean and on June 25, 1858 began to lay the transatlantic cable again. The Niagara moved west, and the Agamemnon moved east. 2 attempts were made, interrupted by damage to the cable. The ships returned to Ireland for his replacement.
On July 17, the fleet set off to meet each other again. After minor failures, the operation was successful. Walking at a constant speed of 5-6 knots, on August 4, the Niagara entered Trinity Bay about. Newfoundland. On the same day, Agamemnon arrived at Valentia Cove in Ireland. Queen Victoria sent the first welcome message described above.
The 1865 expedition ended in failure 600 miles from Newfoundland, and only the attempt in 1866 was successful. The first message on the new line was sent from Vancouver to London on July 31, 1866. In addition, the end of the cable, lost in 1865, was found, and the line was also successfully completed. The transfer rate was 6-8 words per minute at a cost of $ 10 / word.
Telephone communications
In 1919, the American company AT&T initiated a study on the possibility of laying a transatlantic telephone cable. In 1921, a deep-sea telephone line was laid between Key West and Havana.
In 1928, it was proposed to lay a cable without repeaters with a single voice channel across the Atlantic Ocean. The high cost of the project ($ 15 million) in the midst of the Great Depression, as well as improvements in radio technology interrupted the project.
By the beginning of the 1930s, the development of electronics made it possible to create an underwater cable system with repeaters. The design requirements for intermediate link amplifiers were unprecedented, since the devices had to run uninterruptedly on the ocean floor for 20 years. Strict requirements were imposed on the reliability of components, in particular electronic lamps. In 1932, there were already electric lamps that successfully passed the test for 18 years. The radio elements used were significantly inferior to the best models, but they were very reliable. As a result, the TAT-1 worked for 22 years, and not a single lamp failed.
Another problem was the installation of amplifiers in the open sea at a depth of 4 km. When the ship stops to reset the repeater, kinks may appear on the cable with spiral armor. As a result, a flexible amplifier was used, which could be stacked with equipment designed for telegraph cable. However, the physical limitations of a flexible repeater limited its throughput to a 4-wire system.
Britain's Post has developed an alternative approach with rigid transponders of much larger diameter and throughput.
Implementation of TAT-1
The project was resumed after the Second World War. In 1950, flexible amplifier technology was tested by a system linking Key West and Havana. In the summer of 1955 and 1956, the first transatlantic telephone cable was laid between Oban in Scotland and Clarenville on about. Newfoundland, far north of existing telegraph lines. Each cable was about 1950 nautical miles long and consisted of 51 repeaters. Their number was determined by the maximum voltage at the terminals, which could be used for power supply without affecting the reliability of high-voltage components. The voltage was +2000 V at one end and -2000 V at the other. The system bandwidth, in turn, was determined by the number of repeaters.
In addition to repeaters, 8 submarine levelers were installed on the east-west line and 6 on the west-east. They corrected the accumulated shifts in the frequency band. Although the total loss in the 144 kHz bandwidth was 2100 dB, the use of equalizers and repeaters reduced this value to less than 1 dB.
Getting started TAT-1
In the first 24 hours after the launch on September 25, 1956, 588 calls were made from London and the USA and 119 from London to Canada. TAT-1 immediately tripled the capacity of the transatlantic network. The cable bandwidth was 20â164 kHz, which made it possible to have 36 voice channels (4 kHz each), 6 of which were divided between London and Montreal and 29 - between London and New York. One channel was intended for telegraph and service.
The system also included land communications through Newfoundland and submarines with Nova Scotia. These two lines consisted of a single cable 271 nautical miles long with 14 rigid repeaters designed by the UK post. The total capacity was 60 voice channels, 24 of which connected Newfoundland and Nova Scotia.
Further enhancements to the TAT-1
The TAT-1 line cost $ 42 million. The price of $ 1 million per channel stimulated the development of terminal equipment that would use bandwidth more efficiently. The number of voice channels in the standard frequency range of 48 kHz was increased from 12 to 16 by reducing their width from 4 to 3 kHz. Another innovation was Temporary Speech Interpolation (TASI), developed by Bell Labs. TASI doubled the number of voice circuits thanks to pauses in speech.
Optical systems
The first transoceanic optical cable TAT-8 was put into operation in 1988. Repeaters regenerated pulses by converting optical signals into electrical signals and vice versa. Two working pairs of fibers worked at a speed of 280 Mbps. In 1989, thanks to this transatlantic Internet cable, IBM agreed to fund the T1 level line between the University of Cornwall and CERN, which greatly improved the connection between the American and European parts of the early Internet.
By 1993, more than 125 thousand km of TAT-8 were in operation worldwide. This figure almost corresponded to the total length of the analog submarine cables. In 1992, the TAT-9 entered service. Fiber speed has been increased to 580 Mbps.
Technological breakthrough
In the late 1990s, the development of erbium-doped optical amplifiers led to a quantum leap as submarine cable systems. Light signals with a wavelength of about 1.55 Ξm became possible to amplify directly, and the bandwidth was no longer limited by the speed of the electronics. The first optically amplified system across the Atlantic was the TAT 12/13 in 1996. The transfer rate on each of the two pairs of fibers was 5 Gb / s.
Modern optical systems allow the transfer of such large amounts of data that redundancy is critical. Typically, modern fiber optic cables, such as TAT-14, consist of 2 separate transatlantic cables, which are part of the ring topology. Two other lines connect the coast stations on each side of the Atlantic Ocean. Data is sent in a ring in both directions. In the event of a break, the ring is self-healing. Traffic is translated into spare pairs of fibers in the working cables.