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the branch of science and technology that studies the principles of establishing telegraph communication, develops methods for transmitting telegraph signals and the equipment required by these methods, and evaluates the quality of data transmission over telegraph channels.
As a scientific and technical discipline, telegraphy is divided into the following branches, corresponding to the principal areas of interest: telegraph codes, dealing with the optimum conversion of alphameric data into combinations of electrical signals during transmission and the reciprocal conversion of the signals upon reception; terminal equipment, dealing with design principles for telegraph equipment, transmitters and reperforators, methods of signal transmission and reception, and the development of electronic equipment; telegraph channels, dealing with the most economic use of expensive wire communications and the design of channels with specific characteristics; and telegraph networks, dealing with the choice of methods for connecting subscribers and terminal points, the most advantageous distribution of stations, and the quality of subscriber services.
In order to ensure high-quality transmission in telegraphy, studies are being conducted on signal distortions, the causes and laws governing these distortions, and errors that occur during data transmission and methods of eliminating such errors.
Unlike other forms of communication, telegraphy operates with discrete messages composed of a finite number of symbols—letters, numbers, and punctuation marks. The signals that transmit these messages are also discrete. The theoretical basis of telegraphy is the general theory of communications, information theory, and the theory of potential noise immunity. Probability theory and Boolean algebra also find application in telegraphy.
Phototelegraphy is a special branch of telegraphy and has historically been included in the discipline. It studies the principles of facsimile.