Acoustic telegraphy

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As acoustic telegraphy (also harmonic telegraph or Stimmgabeltelegrafie ) are different developed in the 19th century multiplexing method called that made it possible at the same time more than a telegraphic message to be transmitted over a single telegraph line.

Procedure and history

Acoustic telegraphy uses different low frequencies or communication channels for each message . A telegraph operator used a conventional Morse code key to tap the message in Morse code . The button switched the transmission of direct current pulses in the frequency of deep sound waves of a certain frequency on or off. On the receiving end there was a specially tuned device that only resonated at a specific resonance frequency and ignored other frequencies transmitted over the same telegraph wire.

The word acoustic comes from the Greek ακουειν akuein "to hear". Acoustic telegraphy devices worked electromechanically and produced humming or humming noises that could be heard over a distance of a few meters. The main function of these devices, however, was not to generate sound waves, but to use direct current pulses at the frequency of sound waves as a carrier signal for Morse code.

Among the inventors who were concerned with the acoustic telegraphy include Charles Bourseul , Thomas Edison , Elisha Gray and Alexander Graham Bell . Their efforts to develop acoustic telegraphy, which would reduce the cost of telegraph services, eventually led to the invention of the telephone .

Some of Thomas Edison's devices used multiple synchronized tuning forks that were tuned to select a frequency in order to open or close an electrical circuit that way. Acoustic telegraphy was conceptually similar to today's frequency division multiplexing method .

Essential patents

  • AG Bell: Transmitter and Receiver for Electric-Telegraphs . U.S. Patent 161739, April 6, 1875, PDF .
  • E. Gray: Electrical Telegraph for Transmitting Musical Tones . U.S. Patent 166095, July 27, 1875, PDF .
  • TA Edison: Acoustic Telegraph . U.S. Patent 182996, October 10, 1876, PDF .
  • TA Edison: Acoustic Electric Telegraphs . U.S. Patent 186330, January 16, 1877, PDF .
  • TA Edison: Acoustic Telegraph . U.S. Patent 200993, March 5, 1878, PDF .
  • TA Edison: Circuits for Acoustic or Telephonic-Telegraphs . U.S. Patent 203019, April 30, 1878, PDF .
  • TA Edison: Acoustic Telegraph . U.S. Patent 235142, December 7, 1880, PDF .

Edison's patents were acquired by the New York City- based Western Union Telegraph Company .

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