Editing Spark-gap transmitter (section)

===Obsolescence===
[[Image:Marconi Model P-4 2 kW ship spark transmitter.jpg|thumb|upright= 1.0|Marconi 2 kilowatt ship spark transmitter, 1920. ]]
All these early technologies were superseded by the [[vacuum tube]] [[positive feedback|feedback]] [[electronic oscillator]], invented in 1912 by [[Edwin Armstrong]] and [[Alexander Meissner]], which used the [[triode]] [[vacuum tube]] invented in 1906 by [[Lee de Forest]].<ref name="Hempstead"/> Vacuum tube oscillators were a far cheaper source of continuous waves, and could be easily [[modulated]] to carry sound. Due to the development of the first high-power transmitting tubes by the end of World War I, in the 1920s tube transmitters replaced the arc converter and alternator transmitters, as well as the last of the old noisy spark transmitters.

The 1927 International Radiotelegraph Convention in Washington, D.C. saw a political battle to finally eliminate spark radio.<ref name="Schroeder">{{cite book
| last1= Schroeder
| first1= Peter B.
| title= Contact at Sea: A History of Maritime Radio Communications
| publisher= The Gregg Press
| date= 1967
| pages= 26–30
| url= https://books.google.com/books?id=sEeaJC_y22EC&q=spark&pg=PA14-IA15
}}</ref> Spark transmitters were obsolete at this point, and [[radio broadcasting|broadcast radio]] audiences and aviation authorities were complaining of the disruption to radio reception that noisy legacy marine spark transmitters were causing. But shipping interests vigorously fought a blanket prohibition on damped waves, due to the capital expenditure that would be required to replace spark equipment that was still being used on older ships. The Convention prohibited licensing of new land spark transmitters after 1929.<ref name="Howeth3">{{cite book
| last1= Howeth
| first1= L. S.
| title= The History of Communications - Electronics in the U.S. Navy
| publisher= U.S. Navy
| date= 1963
| pages= [https://archive.org/details/historyofcommuni00howe/page/509 509]
| url= https://archive.org/details/historyofcommuni00howe
| isbn= 978-1365493225
}}</ref> Damped wave radio emission, called Class B, was banned after 1934 except for emergency use on ships.<ref name="FCC"/><ref name="Howeth3"/> This loophole allowed shipowners to avoid replacing spark transmitters, which were kept as emergency backup transmitters on ships through World War II.