<communications> (CW) A term from early radio history, when the spark gap
method of transmission was replaced by vacuum-tube oscillators. A spark gap
initiates a ringing, damped sinusoidal wave in a tuned circuit consisting of an
inductor and capacitor. The energy in this circuit is constantly changing
between the capacitor's electrostatic field and the inductor's magnetic field.
The energy is then coupled, loosely (so as not to dampen the wave too quickly),
to the radiating antenna.
In contrast, a vacuum-tube oscillator constantly adds energy to the tuned
circuit, compensating for the amount coupled to the antenna, and the transmitted
energy or "wave," is therefore "continuous".
Many (especially radio amateurs) continue to understand "CW" to mean
transmission by means a signal of a single frequency which is either on or off
(e.g. Morse code), as opposed to a carrier which varies continuously in
amplitude, frequency or phase. Some would even call the former "unmodulated"
even though turning on and off is actually an extreme form of amplitude
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