telegraph


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telegraph,

term originally applied to any device or system for distant communication by means of visible or audible signals, now commonly restricted to electrically operated devices. Attempts at long-distance communication date back thousands of years (see signalingsignaling,
transmission of information by visible, audible, or other detectable means. Since prehistoric times humans have sought and employed ever more effective means of communicating over distance. Signal fires on mountain tops announced awaited events.
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). As electricity came into greater use, various practical and experimental methods of signaling were tried. A method that came into general use throughout most of the world was based in large part on the work of Samuel F. B. MorseMorse, Samuel Finley Breese,
1791–1872, American inventor and artist, b. Charlestown, Mass., grad. Yale, 1810. He studied painting in England under Washington Allston and achieved some success.
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. In Morse telegraphy, an electric circuit is set up, customarily by using only a single overhead wire and employing the earth as the other conductor to complete the circuit. An electromagnet in the receiver is activated by alternately making and breaking the circuit. Reception by sound, with the Morse codeMorse code
[for S. F. B. Morse], the arbitrary set of signals used on the telegraph (see code). It may also be used with a flash lamp for visible signaling. The international (or continental) Morse code is a simplified form generally used in radio telegraphy.
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 signals received as audible clicks, is a swift and reliable method of signaling. The first permanently successful telegraphic cablecable,
originally wire cordage of great strength or heavy metal chain used for hauling, towing, supporting the roadway of a suspension bridge, or securing a large ship to its anchor or mooring. Today a cable often refers to a line used for the transmission of electrical signals.
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 crossing the Atlantic Ocean was laid in 1866. In 1872, J. B. Stearns of Massachusetts devised a method for "duplex" telegraphy, enabling two messages to be sent over the same wire at the same time. In 1874, Thomas A. EdisonEdison, Thomas Alva,
1847–1931, American inventor, b. Milan, Ohio. A genius in the practical application of scientific principles, Edison was one of the greatest and most productive inventors of his time, but his formal schooling was limited to three months in Port Huron,
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 invented the "quadruplex" method for the simultaneous transmission of four messages over the same wire. In addition to wires and cables, telegraph messages are now sent by such means as radio waves, microwaves, and communications satellites (see satellite, artificialsatellite, artificial,
object constructed by humans and placed in orbit around the earth or other celestial body (see also space probe). The satellite is lifted from the earth's surface by a rocket and, once placed in orbit, maintains its motion without further rocket propulsion.
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). Telex is a telegraphy system that transmits and receives messages in printed form. Today telegraphy is rarely used, having been supplanted by the telephonetelephone,
device for communicating sound, especially speech, usually by means of wires in an electric circuit. The telephones now in general use evolved from the device invented by Alexander Graham Bell and patented by him in 1876 and 1877.
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, facsimilefacsimile
or fax,
in communications, system for transmitting pictures or other graphic matter by wire or radio. Facsimile is used to transmit such materials as documents, telegrams, drawings, pictures taken from satellites, and even entire newspapers.
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 machines, and computer electronic mailelectronic mail
or e-mail,
the electronic transmission of messages, letters, and documents. In its broadest sense electronic mail includes point-to-point services such as telegraph and facsimile (fax) systems.
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, among others. Western Union, the American telegraph company whose origins date to 1851, stopped transmitting telegrams in 2006.

Bibliography

See J. W. Freebody, Telegraphy (1959); E. H. Jolley, Introduction to Telephony and Telegraphy (1970).

Telegraph

 

a device for transmitting and/or receiving electric signals in telegraph communication.

The first practical telegraph, an electromagnetic design, was invented by P. L. Shilling and demonstrated in 1832. In the early days of telegraphy, coded messages were transmitted by keyboard devices or telegraph keys. The received messages were recorded by a register in the form of broken lines, for example, with a siphon recorder, or as a series of dots and dashes, as with the Morse telegraph. With the Wheatstone telegraph and Creed printer, the received telegraph signals were recorded on a perforated paper tape; the Creed printer could also reproduce printed characters. Improved letter-printing telegraphs were developed by Iakobi (M. H. Jacobi), Hughes, and Siemens, and Baudot developed the multiplex telegraph. The “copying” telegraph, or teleautograph, which copies letters in script, was also invented.

Figure 1. Block diagram of a telegraph transmitter: (1) message source, (2) encoder, (3) selector, (4) distributor, (5) output device, (6) actuator, (7) control device, (8) service element sender

The first Soviet telegraphs were built by A. P. Trusevich (1921), V. I. Kaupuzh (1925), and A. F. Shorin (1928); Shorin’s telegraph was put into service in 1929. Other Soviet inventors and scientists who made important contributions to the development and design of the telegraph included L. I. Tremí’, S. I. Cha-sovnikov, E. A. Volkov, N. G. Gagarin, A. D. Ignat’ev, L. N. Gurin, G. P. Kozlov, and V. I. Kerbi.

Modern telegraphs use either an equal-length or an unequal-length code. The unequal-length code is rarely used in telegraphy because it is less economical and not suitable for use with a receiver’s teleprinter. In the equal-length code, each code combination contains the same number of elements, thus facilitating reception by a teleprinter. Depending on the transmission method used, telegraphs may be designed for start-stop or synchronous operation.

Modern telegraphs usually consist of a transmitter and a receiver, which are usually supplied with direct current from 60-volt rectifiers or with alternating current from a direct connection to electric power mains.

The transmitter encodes the characters being transmitted by producing combinations of elementary signals according to the given code. It then converts the parallel code combination into a serial combination. The receiver inserts service signals into the code combination for the synchronization and phase alignment of the receiver and transmits to the communications line a sequence of electrical signals of the required duration and amplitude. When the transmitter is operating (Figure 1), each character of the transmitted message passes from the message source to the encoder, where it is automatically converted to a code combination. The elements of the combination appear simultaneously at the encoder output and pass into a selector. The transmitting distributor successively converts each element of the code combination into an electrical signal of specific duration. The output device generates electrical signals of the required power, polarity, and wave form, and a sender produces the service elements for the code combination. The transmission speed is controlled by an actuator, and the method of transmission—start-stop or synchronous—is determined by the operational mode of a control device.

The telegraph receiver (Figure 2) receives the electrical signals of the code combination, determines the polarity of each elementary signal, decodes the code combination, and prints the received characters. The electrical signals of the code combination enter an input device, which determines the signal polarity and corrects distortions. From there the elementary signals of the code combination pass through the receiving distributor to a selector, where they are stored and passed on to the decoder. Signals from the decoder output are fed to the printer, where the message is recorded on a paper tape (in a tape telegraph) or on a roll (in a page teletypewriter). Synchronization and phase alignment of the receiver are carried out by the receiver’s distributor and control device operating together. The speed of operation is controlled by the actuator.

Figure 2. Block diagram of a telegraph receiver: (1) input device, (2) receiving distributor. (3) selector, (4) decoder, (5) printer, (6) actuator, (7) control device

Telegraphs may also have accessory equipment to perform automated functions, such as reperforators, transmitters, and automatic answering and shut-off devices. Such accessories provide automatic transmission and reception of messages, automatic verification of switching connections, and automatic on-off switching of the actuator.

Until the middle of the 20th century, all telegraphs were electromechanical devices. By the 1970’s, however, series production of electronic telegraphs was organized in the USSR and many foreign countries. Most of the devices used in such equipment usually have no contacts. In the transmitter such contactless components include the coding and output devices, the distributor, the actuator, the control device, and the service element sender. In the receiver they include the input device, the selector, the distributor, and the decoder. In comparison with electromechanical systems, the electronic telegraph has many advantages, including higher transmission speed, longer service life, lower power consumption, and provision for making rapid changes in transmission speed and code type. Work on an electronic telegraph with no mechanical elements is in progress.

REFERENCES

Balagin, I. Ia., V. A. Kudriashov, and N. F. Semeniuta. Peredacha diskretnoi informatsii i lelegrafiia. Moscow, 1971.
Printsipy postroeniia elektronno-mekhanicheskikh telegrafnykh apparatov. Moscow, 1973.

A. I. KOBLENTS

telegraph

A low-speed communications device that transmits up to approximately 150 bps. Telegraph grade lines, stemming from the days of Morse code, cannot transmit a voice conversation. In 1843, the U.S. Congress authorized USD $30,000 to build a telegraph line between Baltimore and Washington, DC. The wire was strung onto 700 poles which were placed approximately 300 feet apart. On May 24, 1844, at the U.S. Supreme Court in Washington, Samuel Morse tapped out "What hath God wrought" via telegraph to his assistant Alfred Vail who was waiting at a Baltimore railroad station, some 40 miles away.


The Days of the Morse Code
Data was transmitted at about four to six bits per second in the latter half of the 1800s, which was as fast as a human hand could tap out Morse code. The unit on the right is the telegraph key. A metal bar on the receiver (left) simply banged against another bar when the current passed through, creating a clicking sound.







Synonymous With Telegraphy
In the mid-1800s, Western Union consolidated long distance communications in the U.S. The first transcontinental line began in 1871. By the turn of the century, there were more than a million miles of telegraph lines.
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