Editing Continuous wave (section)

{{Short description|Electromagnetic wave that is not pulsed}}
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{{Modulation techniques}}
A '''continuous wave''' or '''continuous waveform''' ('''CW''') is an [[electromagnetic wave]] of constant [[amplitude]] and [[frequency]], typically a [[sine wave]], that for [[mathematical analysis]] is considered to be of infinite duration.<ref>{{cite web |url=https://encyclopedia2.thefreedictionary.com/continuous+wave |title=Continuous wave |work=The Free Dictionary |publisher=Farlex |archive-url=https://web.archive.org/web/20210922015111/https://encyclopedia2.thefreedictionary.com/continuous+wave |archive-date=2021-09-22 |access-date=2023-04-10 |url-status=live}}</ref> It may refer to e.g. a [[laser]] or [[particle accelerator]] having a continuous output, as opposed to a [[Pulsed laser|pulsed]] output.

By extension, the term ''continuous wave'' also refers to an early method of [[radio]] [[transmission (telecommunications)|transmission]] in which a sinusoidal [[carrier wave]] is switched on and off. This is more precisely called '''interrupted continuous wave''' ('''ICW''').<ref>{{cite web |url=https://encyclopedia2.thefreedictionary.com/interrupted+continuous+wave |title=Interrupted continuous wave |work=The Free Dictionary |publisher=Farlex |archive-url= https://web.archive.org/web/20230410073209/https://encyclopedia2.thefreedictionary.com/interrupted+continuous+wave |archive-date=2023-04-10 |access-date=2023-04-10 |url-status=live}}</ref> [[Information]] is carried in the varying duration of the [[on-off keying|on and off periods]] of the signal, for example by [[Morse code]] in early radio. In early [[wireless telegraphy]] radio transmission, CW waves were also known as "undamped waves", to distinguish this method from [[damped wave]] signals produced by earlier ''[[spark-gap transmitter|spark gap]]'' type transmitters.