ContinuousWave

Continuous wave refers to a signal that, in principle, is a constant-amplitude sinusoid, or carrier, that may be turned on and off to convey information. In radio engineering, the term is often associated with the Morse code mode known as CW, where the carrier is switched on and off with a key. When the operator presses the key, a stable carrier tone is transmitted; when released, transmission stops. The information is encoded in the timing and duration of the on and off periods, known as dits and dahs. Historically, CW enabled long-distance communication with relatively simple hardware and good signal-to-noise performance, making it a staple of early and amateur radio. In practice, turning a carrier on and off introduces spectral components around the carrier frequency, but CW remains valued for its narrow effective bandwidth and robustness under weak-signal conditions.

Beyond radio, continuous wave can describe an unmodulated carrier in a broader sense of electrical engineering, though most practical systems apply some form of modulation. In optical contexts, continuous-wave denotes light that is emitted steadily in time, as opposed to pulsed sources. Continuous-wave optical sources such as CW lasers and LEDs are used in spectroscopy, metrology, fiber-optic communications, and interferometry, where a steady illumination or signal is advantageous.

Summary: continuous wave encompasses both the idea of an unmodulated or on-off-carrier in radio, especially for Morse code, and the concept of steady-state light emission in optics. Its defining feature is time-invariant carrier presence, apart from intentional on-off switching or modulation used to carry information.