CW

Continuous wave, or CW, is a radiofrequency signal transmitted at constant amplitude and frequency with no interruption or modulation. Unlike pulsed signals or amplitude-modulated broadcasts, a CW signal is exactly what its name suggests: a steady oscillation that continues indefinitely at a fixed carrier frequency. In practice, the transmitter is keyed on and off to create Morse code or other patterns, but during transmission, the wave itself remains uniform.

CW signals are generated by an oscillator locked to a stable frequency reference, then fed to a power amplifier and antenna. The simplicity of CW generation makes it reliable and efficient; there is no envelope shaping, no sideband suppression, and minimal bandwidth consumption. A CW transmitter requires far less power supply capacity than one producing amplitude or frequency-modulated signals of equivalent range. This economy made CW the standard for early radio telegraphy and it remains dominant in amateur radio, maritime distress systems, and certain navigation aids.

Variants and applications

CW appears across many bands and frequencies. Amateur radio operators use CW on shortwave and VHF for long-distance communication; the narrow bandwidth (typically 50 to 150 Hz for intelligible Morse reception) allows CW signals to penetrate where modulated signals fail. Radar systems emit CW pulses whose reflections reveal target range and velocity. Some medical and industrial heating equipment employs CW microwave or RF energy for consistent, controllable thermal output. Navigation beacons and radio direction-finding systems traditionally used CW transmission because the unmodulated carrier is easiest to detect and locate by simple means.

The term CW is also used colloquially in amateur radio to mean Morse code transmission itself, regardless of the technical modulation. This usage reflects history: CW and Morse became synonymous because unmodulated RF was the only practical way to transmit digital symbols over long distances before audio-frequency tone modulation was developed.

Problems with CW are few but important. The transmitted bandwidth is theoretically zero, but any modulation (key clicks, frequency drift, oscillator noise) spreads energy into adjacent channels. Poor keying technique generates sidebands that can interfere with nearby frequencies. CW offers no inherent advantage in noise performance compared to properly modulated systems, and human operators must have trained ears or automated decoding hardware to extract meaning from the dot-dash pattern. For these reasons, CW is increasingly restricted to amateur radio, legacy maritime safety systems, and specialist military and research applications.