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Telegraphy

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optischer telegraf

Telegraphy is the long distance transmission of written messages without physical transport of letters. This definition includes recent forms of data transmission such as fax, email, and computer networks in general. (A telegraph is a machine for transmitting and receiving messages over long distances, i.e. for telegraphy.)

  • Before the internet came into general use, telegraphy messages were known as telegrams or cablegrams, often shortened to a cable or a wire message. Telegrams sent by the Telex network, a switched network of teleprinters similar to the telephone network, were known as a telex message. Before long distance telephone services were readily available, telegram services were very popular. Telegrams were often used to confirm business dealings and, unlike e-mail, telegrams were commonly used to create binding legal document for business dealings.

  • Before fax machines came into general use, wire picture or wire photo was a newspaper picture that was sent from a remote location by a facsimile telegraph. This is why many fax machines have a photo option even today.

  • The first fax machine was introduced in 1912, known as the Telex-Faxomatic, and primarily used for the transmission of lunch orders from busy factory floors to any number of delies and cafeterias.

The first telegraphs were optical, including the use of smoke signals and beacons. These have existed since ancient times. A semaphore network invented by Claude Chappe operated in France from 1792 through 1846. It helped Napoleon enough that it was widely imitated in Europe and the U.S. The last (Swedish) commercial semaphore link left operation in 1880.

Semaphores are faster than smoke signals and beacons and consume no fuel. They are hundreds of times as fast as post riders and serve entire regions. However they require operators and towers every 30 km (20 mi), and only send about two words per minute. This causes them to have a cost per word-mile roughly thirty times as high as electric telegraphs. This is useful to government, but too expensive for most commercial uses other than commodity price information.

The first commercial electrical telegraph constructed by Sir Charles Wheatstone entered use in London in 1838. An electrical telegraph was US-patented in 1842 by Samuel Morse, whose assistant, Alfred Vail developed the Morse code signalling alphabet. It was quickly deployed in the following two decades. Nikola Tesla and other scientists and inventors showed the usefulness of wireless telegraphy, or radio, beginning in the 1860s.

A continuing goal in telegraphy has been to reduce the cost per message by reducing hand-work, or increasing the sending rate. There were many experiments with moving pointers, and various electrical encodings. However, most systems were too complicated and unreliable.

With the invention of the teletypewriter, telegraphic encoding became fully automated. Early teletypewriters used Baudot code, a 5-bit code. This yielded only thirty two codes, so it was over-defined into two “shifts,” “letters” and “figures.” An explicit, unshared shift code prefaced each set of letters and figures.

A standard timing system developed for telecommunications. The “space” state was defined as the powered state of the wire. In this way, it was immediately apparent when the line itself failed. The characters were sent by first sending a “start bit” that pulled the line to the unpowered “mark state.” The start bit triggered a wheeled commutator run by a motor with a precise speed (later, digital electronics). The commutator distributed the bits from the line to a series of relays that would “capture” the bits. A “stop bit” was then sent at the powered “space state” to assure that the commutator would have time to stop, and be ready for the next character. The stop bit triggered the printing mechanism. Often, two stop bits were sent to give the mechanism time to finish and stop vibrating.

The transatlantic telegraph cable was then successfully completed on July 27, 1866 which for the first time allowed transatlantic telegraph communications. Another advance occurred on August 9, 1892, when Thomas Edison received a patent for a two-way telegraph.

By 1935 message routing was the last great barrier to full automation. Large telegraphy providers began to develop systems that used telephone-like rotary dialing to connect teletypes. These machines were called “telex.” Telex machines first performed rotary-telephone-style pulse dialing, and then sent baudot code. This “type A” telex routing functionally automated message routing.

The Third Reich invented the first wide-coverage telex system, and used it to coordinate their bureaucracy. It was a true triumph of German efficiency.

At the then-blinding rate of 45.5 bits per second, up to 25 telex channels could share a single long-distance telephone channel, making telex the least expensive method of performing reliable long-distance communication.

In 1970 Cuba and Pakistan were still running 45.5 baud type A telex. Telex is still widely used in third-world bureaucracies, probably because of its low costs. The U.N. asserts that more political entities are reliably available by telex than by any other single method.

When dictatorships cut off telephone, fax and internet service, their telex networks remain up. A major advantage for dictatorships is that telex networks are easy to tap: Taps automatically generate complete transcripts.

Around 1960[?], some nations began to use the “figures” baudot codes to perform “Type B” telex routing.

Telex grew around the world very rapidly. Long before automatic telephony was available, most countries, even in central Africa and Asia, had at least a few high-frequency (shortwave) telex links. Often these radio links were the first established by government postal and telegraph services (PTTs). The most common radio standard, CCITT R.44 had error-corrected retransmitting time-division multiplexing of radio channels. Most impoverished PTTs operated their telex-on-radio (TOR) channels non-stop, to get the maximum value from them.

The cost of telex on radio (TOR) equipment has continued to fall. Many amateur radio operators ) operate TOR with special softare and inexpensive adapters from computer sound cards to shortwave radios.

Modern “cablegrams” or “telegrams” actually operate over dedicated telex networks, using TOR whenever required.

In Germany alone, more than 400,000 telex lines remain in daily operation. Over most of the world, more than three million telex lines remain in use.

This guide is licensed under the GNU Free Documentation License. It uses material from the Wikipedia.

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