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Spark-gap transmitter

Low-power inductively coupled spark-gap transmitter on display in Electric Museum, Frastanz, Austria. The spark gap is inside the box with the transparent cover at top center.

A spark-gap transmitter is an obsolete type of radio transmitter which generates radio waves by means of an electric spark.[1][2] Spark-gap transmitters were the first type of radio transmitter, and were the main type used during the wireless telegraphy or "spark" era, the first three decades of radio, from 1887 to the end of World War I.[3][4] German physicist Heinrich Hertz built the first experimental spark-gap transmitters in 1887, with which he proved the existence of radio waves and studied their properties.

A fundamental limitation of spark-gap transmitters is that they generate a series of brief transient pulses of radio waves called damped waves; they are unable to produce the continuous waves used to carry audio (sound) in modern AM or FM radio transmission. So spark-gap transmitters could not transmit audio, and instead transmitted information by radiotelegraphy; the operator switched the transmitter on and off with a telegraph key, creating pulses of radio waves to spell out text messages in Morse code.

The first practical spark gap transmitters and receivers for radiotelegraphy communication were developed by Guglielmo Marconi around 1896. One of the first uses for spark-gap transmitters was on ships, to communicate with shore and broadcast a distress call if the ship was sinking. They played a crucial role in maritime rescues such as the 1912 RMS Titanic disaster. After World War I, vacuum tube transmitters were developed, which were less expensive and produced continuous waves which had a greater range, produced less interference, and could also carry audio, making spark transmitters obsolete by 1920. The radio signals produced by spark-gap transmitters are electrically "noisy"; they have a wide bandwidth, creating radio frequency interference (RFI) that can disrupt other radio transmissions. This type of radio emission has been prohibited by international law since 1934.[5][6]

  1. ^ "Radio Transmitters, Early" in Hempstead, Colin; Worthington, William (2005). Encyclopedia of 20th-Century Technology. Routledge. pp. 649–650. ISBN 978-1135455514.
  2. ^ Morris, Christopher G. (1992). Academic Press Dictionary of Science and Technology. Gulf Professional Publishing. p. 2045. ISBN 978-0122004001.
  3. ^ Champness, Rodney (April 2010). "The spark era - the beginning of radio". Silicon Chip Online: 92–97. Retrieved 14 March 2018.
  4. ^ Terman, Frederick Emmons (1937). Radio Engineering (2nd ed.). New York: McGraw-Hill Book Co. pp. 6–9. Retrieved September 14, 2015.
  5. ^ Individual nations enforce this prohibition in their communication laws. In the United States, Federal Communications Commission (FCC) regulations make it a felony to operate a spark transmitter: "Section 2.201: Emission, modulation, and transmission characteristics, footnote (f)". Code of Federal Regulations, Title 47, Chapter I, Subchapter A, Part 2, Subpart C. US Government Publishing Office website. 1 October 2007. Retrieved 16 March 2018.
  6. ^ Cite error: The named reference Schroeder was invoked but never defined (see the help page).

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