Continuous wave (CW), the first method of radio transmission, consists of an unmodulated carrier wave; unlike modulated modes, it has no information (in the communications sense) embedded within the signal; information is carried in the rhythm and spacing with which the signal is sent. It was called radiotelegraphy because like the telegraph, it worked by simple on/off means to transmit Morse code. However, instead of turning on electricity in a cross-country wire, it turned on and off a radio transmitter instead. This mode is still used by some amateur radio operators today. In common modern usage, CW and Morse code are almost synonymous, despite the real distinction between the two (Morse code may be sent using sound and light, for example). Most information concerning the use of CW by amateur radio operators is found at Morse code.

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