Communications satellites are used for military communications applications, such as Global Command and Control Systems. Examples of military systems that use use communication satellites are the MILSTAR, the DSCS, and the FLTSATCOM of the United States, NATO satellites, United Kingdom satellites, and satellites of the former Soviet Union. Many military satellites operate in the X-band, and some also use UHF radio links, while MILSTAR also utilizes Ka band.
Submarine communications cable
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 optical fiber technology to carry digital payloads, which are then used to carry telephone traffic as well as Internet and private data traffic. They are typically 69 millimetres (2.7 in) in diameter and weigh around 10 kilograms per meter (7 lb/ft), although thinner and lighter cables are used for deep-water sections.[1]
As of 2003, submarine cables link all the world's continents except Antarctica.
The first submarine communications cables carried telegraphy traffic. Subsequent generations of cables carried first telephony traffic, then data communications traffic. All modern cables use optical fiber technology to carry digital payloads, which are then used to carry telephone traffic as well as Internet and private data traffic. They are typically 69 millimetres (2.7 in) in diameter and weigh around 10 kilograms per meter (7 lb/ft), although thinner and lighter cables are used for deep-water sections.[1]
As of 2003, submarine cables link all the world's continents except Antarctica.
Trials
After William Cooke and Charles Wheatstone had introduced their working telegraph in 1839, the idea of a submarine line across the Atlantic Ocean began to be thought of as a possible triumph of the future. Samuel Morse proclaimed his faith in it as early as the year 1840, and in 1842 he submerged a wire, insulated with tarred hemp and India rubber,[2][3] in the water of New York harbour, and telegraphed through it. The following autumn Wheatstone performed a similar experiment in Swansea bay. A good insulator to cover the wire and prevent the electric current from leaking into the water was necessary for the success of a long submarine line. India rubber had been tried by Moritz von Jacobi, the Prussian electrical engineer, as far back as the early 1800s.
Another insulating gum which could be melted by heat and readily applied to wire made its appearance in 1842. Gutta-percha, the adhesive juice of the Palaquium gutta tree, was introduced to Europe by William Montgomerie, a Scottish surgeon in the service of the British East India Company. Twenty years earlier he had seen whips made of it in Singapore, and he believed that it would be useful in the fabrication of surgical apparatuses. Michael Faraday and Wheatstone soon discovered the merits of gutta-percha as an insulator, and in 1845 the latter suggested that it should be employed to cover the wire which was proposed to be laid from Dover to Calais. It was tried on a wire laid across the Rhine between Deutz and Cologne. In 1849 C.V. Walker, electrician to the South Eastern Railway, submerged a wire coated with it, or, as it is technically called, a gutta-percha core, along the coast off Dover.
The first commercial cables
In August 1850, John Watkins Brett's Anglo-French Telegraph Company laid the first line across the English Channel. It was simply a copper wire coated with gutta-percha, without any other protection. The experiment served to keep alive the concession, and the next year, on November 13, 1851, a protected core, or true cable, was laid from a government hulk, the Blazer, which was towed across the Channel. The next year, Great Britain and Ireland were linked together. In 1852, a cable laid by the Submarine Telegraph Company linked London to Paris for the first time. In May, 1853, England was joined to the Netherlands by a cable across the North Sea, from Orford Ness to The Hague. It was laid by the Monarch, a paddle steamer which had been fitted for the work.
The first commercial cables
In August 1850, John Watkins Brett's Anglo-French Telegraph Company laid the first line across the English Channel. It was simply a copper wire coated with gutta-percha, without any other protection. The experiment served to keep alive the concession, and the next year, on November 13, 1851, a protected core, or true cable, was laid from a government hulk, the Blazer, which was towed across the Channel. The next year, Great Britain and Ireland were linked together. In 1852, a cable laid by the Submarine Telegraph Company linked London to Paris for the first time. In May, 1853, England was joined to the Netherlands by a cable across the North Sea, from Orford Ness to The Hague. It was laid by the Monarch, a paddle steamer which had been fitted for the work.
Transatlantic telegraph cable
The transatlantic telegraph cable was the first cable used for telegraph communications laid across the floor of the Atlantic Ocean. It crossed from Foilhommerum, Valentia Island, in western Ireland to Heart's Content in eastern Newfoundland. The transatlantic cable bridged North America and Europe, and expedited communication between the two. Whereas it would normally take at least ten days to deliver a message by ship, it now took a matter of minutes by telegraph.
Five attempts to lay it were made over a nine-year period—in 1857, two in 1858, in 1865, and in 1866—before lasting connections were finally achieved by the SS Great Eastern captained by Sir James Anderson with the 1866 cable and the repaired 1865 cable. Additional cables were laid between Foilhommerum and Heart's Content in 1873, 1874, 1880 and 1894. By the end of the 19th century, British-, French-, German- and American-owned cables linked Europe and North America in a sophisticated web of telegraphic communications.
Cyrus West Field was the force behind the first transatlantic telegraph cable, attempted unsuccessfully in 1857 and completed on August 5, 1858. Although not considered particularly successful or long-lasting, it was the first transatlantic cable project to yield practical results. The first official telegram to pass between two continents was a letter of congratulation from Queen Victoria of the United Kingdom to the President of the United States James Buchanan on August 16. The cable was destroyed the following month when Wildman Whitehouse applied excessive voltage to it while trying to achieve faster telegraph operation. The shortness of the period of use undermined public and investor confidence in the project, and delayed efforts to restore a connection. A next attempt was undertaken in 1865 with much-improved material and, following some setbacks, a connection was completed and put into service on July 28, 1866. This time the connection was more durable, and increased public confidence resulted when the 1865 cable was repaired and put into service shortly afterwards.
Whereas previously communication could only happen over ship, the transatlantic telegraph cable sped up communication to within minutes, allowing communication to happen within the same day. In the 1870s, duplex and quadruplex transmission and receiving systems were set up that could relay multiple messages over the cable. In cross-Atlantic currency trading, the pound sterling came to be referred as "cable" and to this day a cable in financial jargon is one million pounds[1]. The great utility of the cable built on itself, and multiple cables were established soon afterward.
Five attempts to lay it were made over a nine-year period—in 1857, two in 1858, in 1865, and in 1866—before lasting connections were finally achieved by the SS Great Eastern captained by Sir James Anderson with the 1866 cable and the repaired 1865 cable. Additional cables were laid between Foilhommerum and Heart's Content in 1873, 1874, 1880 and 1894. By the end of the 19th century, British-, French-, German- and American-owned cables linked Europe and North America in a sophisticated web of telegraphic communications.
Cyrus West Field was the force behind the first transatlantic telegraph cable, attempted unsuccessfully in 1857 and completed on August 5, 1858. Although not considered particularly successful or long-lasting, it was the first transatlantic cable project to yield practical results. The first official telegram to pass between two continents was a letter of congratulation from Queen Victoria of the United Kingdom to the President of the United States James Buchanan on August 16. The cable was destroyed the following month when Wildman Whitehouse applied excessive voltage to it while trying to achieve faster telegraph operation. The shortness of the period of use undermined public and investor confidence in the project, and delayed efforts to restore a connection. A next attempt was undertaken in 1865 with much-improved material and, following some setbacks, a connection was completed and put into service on July 28, 1866. This time the connection was more durable, and increased public confidence resulted when the 1865 cable was repaired and put into service shortly afterwards.
Whereas previously communication could only happen over ship, the transatlantic telegraph cable sped up communication to within minutes, allowing communication to happen within the same day. In the 1870s, duplex and quadruplex transmission and receiving systems were set up that could relay multiple messages over the cable. In cross-Atlantic currency trading, the pound sterling came to be referred as "cable" and to this day a cable in financial jargon is one million pounds[1]. The great utility of the cable built on itself, and multiple cables were established soon afterward.
Cable to India, Singapore, Far East and Australasia
An 1863 cable to Bombay provided a crucial link to Saudi Arabia.[4] In 1870 Bombay was linked to London via submarine cable in a combined operation by four cable companies, at the behest of the British Government. In 1872 these four companies were combined to form the mammoth globespanning Eastern Telegraph Company, owned by John Pender. A spin-off from Eastern Telegraph Company was a second sister company, the Eastern Extension, China and Australasia Telegraph Company, commonly known simply as "the Extension". In 1872, Australia was linked by cable to Bombay via Singapore and China and in 1876 the cable linked the British Empire from London to New Zealand.
