Why Hams Call It CW: The Continuous Wave Story THE CODE ITSELF | MORSE CODE WORKS Ask a radio amateur what CW means and they will say 'Morse code' - which is true in practice and wrong in physics. CW stands for continuous wave, and the phrase is a fossil from the moment radio grew up. The first transmitters were spark sets: each key-press fired a burst of rapidly dying waves that splattered noise across the spectrum. When generators and then valves produced a steady, continuous carrier instead, keying it produced a single pure tone - and suddenly many stations could share a band politely. Operators named the new thing by its waveform, and the name never left. Key points - In regulations, CW is an emission type; on the bands, it means Morse - A clean keyed tone is shaped to avoid clicks - rise and fall take milliseconds - The old spark sound survives in museums and in the phrase 'spark gap' - Your receiver's CW mode narrows its filter for exactly this tone Try it yourself Translate any text to Morse code and hear it with sound, free: morse code translator audio