ABSTRACT
The concept of a continuous wave (CW), also called a continuous waveform, has at least two connotations: as an electromagnetic wave it has constant amplitude and frequency, and as a mathematical entity it has infinite duration together with a preassigned amplitude and frequency. A radio signal consists of a radio-frequency sinusoid, known as the carrier wave, that has undergone modulation in amplitude (AM) or in frequency (FM), such that the modulating signal creates variations in the carrier amplitude in the former case, while it does so in the carrier frequency in the latter. A carrier wave used to be called a CW in the early days of radio transmission when this wave was switched ‘on’ and ‘off’, to carry information in varying duration between the ‘on’ and ‘off’ periods of a signal. This was the case in the Morse code transmission. The CW waves were also called undamped waves in early wireless telegraphy, in order to distinguish them from the damped waves.
