AC telegraphy

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The Wechselstromtelegrafie (abbreviation WT ) is an analog method of frequency division multiplexing , the economic multi-channel transmission by telex signals , via telephone lines, microwave is used, or radio links. The amplitude or frequency modulation was mainly used as the type of modulation . The individual carrier frequencies are modulated separately with the message content of the telex signal and transmitted together over a transmission channel and demodulated again separately at the end of the channel.

As early as 1922, six telegrams could be transmitted simultaneously on telephone cables over a line pair with audio frequency alternating current telegraphy with carrier frequencies.

The bandwidth of the available transmission channel is usually divided into frequency bands of equal size. The number of teletype channels possible at the same time is determined by the maximum transmission speed and the individual teletype channels (in baud ).

According to the speed of the teletype channels are on a telephone channel:

  • 24 channels with 50 baud or
  • 12 channels with 100 baud or
  • 6 channels with 200 baud possible.

It is also possible with the help of alternating current telegraphy that telephony in a reduced bandwidth and telex connections can be transmitted simultaneously without interference via a voice channel.

AC telegraph device of the NVA MWT 1/2

With the mobile AC telegraphy device of the NVA "MWT 1/2" it was possible to transmit two additional WT channels (channel 8 and channel 10 according to CCITT ) in a telephone channel with reduced bandwidth (1.8 kHz; normally 3.1 kHz) .

Successor to AC telegraphy

As part of the digitization of transmission networks, alternating current telegraphy has often been replaced by digital time division multiplexing . Since the characters are temporarily stored here before the joint transmission, data manipulation, such as e.g. B. the removal of start and stop bits, the conversion of unsecured transmission procedures into secure with a fixed frame and corresponding block protection and data compression as well as the implementation in other systems.

literature

  • Harald Schumny: Signal transmission. Textbook of communications engineering with remote data processing, 2nd revised edition, Friedrich Vieweg & Sohn Verlag, Braunschweig 1987, ISBN 3-528-14072-0 .
  • August Jipp: Modern Telegraphy. Teletype technology with the associated line and auxiliary technology, Springer Verlag, Berlin / Heidelberg 1934.
  • Gerhard Dressler, Heinrich-Karl Podszeck: High-frequency communications technology for power plants. 2nd edition, Springer Verlag, Berlin / Heidelberg 1952.
  • Julius Wallot: Introduction to the theory of weak current technology. 4th edition, Springer Verlag, Berlin / Heidelberg 1944.

See also

Web links