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 message in return. The first official exchange of messages over the newly laid transatlantic telegraph cable was marked by a parade and fireworks display over New York City Hall. The festivities were overshadowed by a fire that happened for this reason, and after 6 weeks the cable failed. True, even before that he did not work very well - the message of the queen was transmitted within 16.5 hours.
From idea to project
The first telegraph and Atlantic Ocean proposal was a relay scheme in which messages delivered by ships were to be telegraphed from Newfoundland to the rest of North America. The problem was the construction of a telegraph line along the difficult terrain of the island.
The request for help from the engineer in charge of the project attracted the Americanbusinessman and financier Cyrus Field. In the course of his work, he crossed the ocean more than 30 times. Despite the setbacks Field faced, his enthusiasm led to success.
The businessman immediately jumped at the idea of a transatlantic wire transfer. Unlike terrestrial systems, in which the pulses were regenerated by relays, the transoceanic line had to get by with a single cable. Field received assurances from Samuel Morse and Michael Faraday that the signal could be transmitted over long distances.
William Thompson provided the theoretical basis for this by publishing the inverse square law in 1855. The rise time of a pulse passing through a cable without an inductive load is determined by the time constant RC of a conductor of length L, equal to rcL2, where r and c are the resistance and capacitance per unit length, respectively. Thomson also contributed to submarine cable technology. He improved the mirror galvanometer, in which the slightest deviations of the mirror caused by the current were amplified by projection onto a screen. Later, he invented a device that registers signals with ink on paper.
Submarine cable technology was improved after gutta-percha appeared in 1843 in England. This resin from a tree native to the Malay Peninsula was an ideal insulator because it was thermoplastic, softened when heated, and returned to a solid form when cooled, making it easier to insulate the conductors. Under the conditions of pressure and temperature at the bottom of the ocean, its insulating propertiesimproved. 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 a single 7-core wire surrounded by gutta-percha and armored with steel wire. Tarred hemp provided corrosion protection. The nautical mile of the 1858 cable weighed 907 kg. The 1866 transatlantic cable was heavier, at 1,622 kg/mile, but because it had more volume, it weighed less in the water. The tensile strength was 3t and 7.5t respectively.
All cables had one water return conductor. Although sea water has less resistance, it is subject to stray currents. Power was supplied by chemical current sources. For example, the 1858 project had 70 elements of 1.1 V each. These voltage levels, combined with improper and careless storage, caused the deep sea transatlantic cable to fail. 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, at a distance of 2000 miles, currents of the order of a milliamp, sufficient for a mirror galvanometer, could be carried. In the 1860s, a bipolar telegraph code was introduced. The dots and strokes of the Morse code have been replaced with pulses of opposite polarity. Over time, developedmore complex schemes.
Expeditions 1857-58 and 65-66
£350,000 was raised through the issuance of shares to lay the first transatlantic cable. The American and British governments guaranteed a return on investment. The first attempt was made in 1857. It took 2 steamships, Agamemnon and Niagara, to transport the cable. The electricians approved a method in which one ship laid the line from a shore station and then connected 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 the cable-laying equipment failed 200 miles offshore. It was lost at a depth of 3.7 km.
In 1857, Niagara's chief engineer, William Everett, developed new cable-laying equipment. A notable improvement was an automatic brake that activated when the tension reached a certain threshold.
After a violent storm that nearly sank the Agamemnon, the ships met in the middle of the ocean and on June 25, 1858, began laying the transatlantic cable again. The Niagara was moving west, and the Agamemnon was moving east. 2 attempts were made, interrupted by damage to the cable. The ships returned to Ireland to replace him.
July 17, the fleet again set off to meet each other. After minor hiccups, the operation was a success. Walking at a constant speed of 5–6 knots, on August 4, the Niagara enteredin Trinity Bay Newfoundland. On the same day, the Agamemnon arrived at Valentia Bay in Ireland. Queen Victoria sent the first greeting message described above.
The 1865 expedition failed 600 miles from Newfoundland, and only the 1866 attempt was successful. The first message on the new line was sent from Vancouver to London on July 31, 1866. In addition, the end of a 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 communication
In 1919, the American company AT&T initiated a study into the possibility of laying a transatlantic telephone cable. In 1921, a deep water 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) at the height of the Great Depression, as well as improvements in radio technology, interrupted the project.
By the early 1930s, developments in electronics made it possible to create a submarine cable system with repeaters. The requirements for the design of intermediate link amplifiers were unprecedented, since the devices had to operate uninterruptedly on the ocean floor for 20 years. Strict requirements were imposed on the reliability of components, in particular vacuum tubes. In 1932, there were already electric lamps that were successfully tested infor 18 years. The radio elements used were significantly inferior to the best samples, but they were very reliable. As a result, TAT-1 worked for 22 years, and not a single lamp failed.
Another problem was the laying of amplifiers in the open sea at a depth of up to 4 km. When the ship is stopped to reset the repeater, kinks can appear on the cable with helical armor. As a result, a flexible amplifier was used, which could fit equipment designed for telegraph cable. However, the physical limitations of the flexible repeater limited its capacity to a 4-wire system.
UK Post has developed an alternative approach with hard repeaters of much larger diameter and capacity.
Implementation of TAT-1
The project was restarted after World War II. 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 the island. Newfoundland, well north of existing telegraph lines. Each cable was about 1950 nautical miles long and had 51 repeaters. Their number was determined by the maximum voltage at the terminals that could be used for power without affecting the reliability of high-voltage components. The voltage was +2000 V at one end and -2000 V at the other. The bandwidth of the system, in itsqueue was determined by the number of repeaters.
In addition to repeaters, 8 subsea equalizers were installed on the east-west line and 6 on the west-east line. 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 to less than 1 dB.
Getting Started TAT-1
In the first 24 hours after launch on September 25, 1956, 588 calls were made from London and the US and 119 from London to Canada. TAT-1 immediately tripled the capacity of the transatlantic network. The cable bandwidth was 20-164 kHz, which allowed for 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 a land connection through Newfoundland and a submarine connection to Nova Scotia. The two lines consisted of a single 271 nautical mile cable with 14 rigid repeaters designed by UK Post. The total capacity was 60 voice channels, 24 of which connected Newfoundland and Nova Scotia.
Further improvements to TAT-1
The TAT-1 line cost $42 million. The $1 million per channel spurred the development of terminal equipment that would use bandwidth more efficiently. The number of voice channels in the standard 48 kHz frequency range has been increased from 12 to 16 by reducingtheir width from 4 to 3 kHz. Another innovation was temporal speech interpolation (TASI) developed at Bell Labs. TASI doubled the number of voice circuits thanks to speech pauses.
Optical systems
The first transoceanic optical cable TAT-8 was put into operation in 1988. Repeaters regenerated pulses by converting optical signals into electrical ones 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 a T1 link between Cornell University and CERN, which significantly improved the connection between the American and European parts of the early Internet.
By 1993, more than 125,000 km of TAT-8s were in operation worldwide. This figure almost corresponded to the total length of analog submarine cables. In 1992, TAT-9 entered service. The speed per fiber has been increased to 580 Mbps.
Technological breakthrough
In the late 1990s, the development of erbium-doped optical amplifiers led to a quantum leap in the quality of submarine cable systems. Light signals with a wavelength of about 1.55 microns can be directly amplified, and the throughput is no longer limited by the speed of the electronics. The first optically enhanced system to fly across the Atlantic Ocean was TAT 12/13 in 1996. The transmission rate on each of the two pairs of fibers was 5 Gbps.
Modern optical systems allow transmission of such large volumesdata that redundancy is critical. Typically, modern fiber optic cables such as TAT-14 consist of 2 separate transatlantic cables that are part of a ring topology. The other two lines connect coast stations on each side of the Atlantic Ocean. Data is sent around the ring in both directions. In the event of a break, the ring will self-repair. Traffic is diverted to spare fiber pairs in service cables.
