Editing Spark-gap transmitter (section)

{{Short description|Type of radio transmitter}}[[File:Morseapparat-2.JPG|thumb|upright=1.7|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 [[transmitter|radio transmitter]] which generates [[radio wave]]s by means of an [[electric spark]].<ref name="Hempstead">"Radio Transmitters, Early" in {{cite book
| last1= Hempstead
| first1= Colin
| last2= Worthington
| first2= William
| title= Encyclopedia of 20th-Century Technology
| publisher= Routledge
| pages= 649–650
| date= 2005
| url= https://books.google.com/books?id=2ZCNAgAAQBAJ&q=encyclopedia+%22spark+transmitter%22&pg=PA650
| isbn= 978-1135455514
}}</ref><ref name="Morris">{{cite book
| last1= Morris
| first1= Christopher G.
| title= Academic Press Dictionary of Science and Technology
| publisher= Gulf Professional Publishing
| date= 1992
| pages= 2045
| url= https://books.google.com/books?id=nauWlPTBcjIC&q=%22spark+transmitter%22&pg=PA2045
| isbn= 978-0122004001
}}</ref> 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.<ref name="Champness">{{cite journal
| last1= Champness
| first1= Rodney
| title= The spark era - the beginning of radio
| journal= Silicon Chip Online
| pages= 92–97
| date= April 2010
| url= http://www.siliconchip.com.au/Issue/2010/April/The+spark+era%3A+the+beginning+of+radio
| access-date= 14 March 2018}}</ref><ref name="Terman">{{cite book |last=Terman |first=Frederick Emmons |title=Radio Engineering |edition=2nd |url=https://archive.org/stream/RadioEngineering/Terman-RadioEngineering#page/n19/mode/2up |access-date=September 14, 2015 |year=1937 |publisher=McGraw-Hill Book Co. |location=New York |pages=6–9}}</ref> 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 wave (radio transmission)|damped wave]]s; they are unable to produce the [[continuous wave]]s used to carry [[audio signal|audio]] (sound) in modern [[AM broadcasting|AM]] or [[FM broadcasting|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 [[Titanic|RMS ''Titanic'']] disaster. After World War I, [[Vacuum tube oscillator|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 (signal processing)|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.<ref name="FCC">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: {{cite web
| title= Section 2.201: Emission, modulation, and transmission characteristics, footnote (f)
| work= Code of Federal Regulations, Title 47, Chapter I, Subchapter A, Part 2, Subpart C
| publisher= US Government Publishing Office website
| date= 1 October 2007
| url= https://www.gpo.gov/fdsys/pkg/CFR-2007-title47-vol1/xml/CFR-2007-title47-vol1-sec2-201.xml
| access-date= 16 March 2018}}</ref><ref name="Schroeder"/>