continuous wave

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 modulation.

(1995-03-15)