Continuous wave
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Acontinuous waveorcontinuous waveform(CW) is anelectromagnetic waveof constant amplitude and frequency, typically a sine wave, that for mathematical analysis is considered to be of infinite duration. It may refer to e.g. a laser or particle accelerator having a continuous output, as opposed to a pulsed output.
By extension, the termcontinuous wavealso refers to an early method of radio transmission in which a sinusoidal carrier wave is switched on and off. This is more precisely calledinterrupted continuous wave(ICW). Information is carried in the varying duration of the 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 earlierspark gaptype transmitters.