Teletypewriter message

Telegraphy (from Greek: τῆλε , "at a distance" and γράφειν , "to write") is the long-distance transmission of textual or symbolic (as opposed to verbal or audio) messages without the physical exchange of an object bearing the message. Thus semaphore is a method of telegraphy, whereas pigeon post is not.

Telegraphy requires that the method used for encoding the message be known to both sender and receiver. Many methods are designed according to the limits of the signalling medium used. The use of smoke signals, beacons, reflected light signals, and flag semaphore signals are early examples. In the 19th century, the harnessing of electricity led to the invention of electrical telegraphy. The advent of radio in the early 20th century brought about radiotelegraphy and other forms of wireless telegraphy. In the Internet age, telegraphic means developed greatly in sophistication and ease of use, with natural language interfaces that hide the underlying code, allowing such technologies as electronic mail and instant messaging.

The word "telegraph" was first coined by the French inventor of the Semaphore line, Claude Chappe, who also coined the word "semaphore".

A "telegraph" is a device for transmitting and receiving messages over long distances, i.e., for telegraphy. The word "telegraph" alone now generally refers to an electrical telegraph.

Wireless telegraphy is also known as "CW", for continuous wave (a carrier modulated by on-off keying), as opposed to the earlier radio technique of using a spark gap.

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