Editing Continuous wave (section)

===Key clicks===
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{{redirect|Key click|the sound of a Hammond organ|Hammond organ#Tone generation}}
In order to transmit information, the continuous wave must be turned off and on with a [[telegraph key]] to produce the different length pulses, "dots" and "dashes", that spell out text messages in [[Morse code]], so a "continuous wave" radiotelegraphy signal consists of pulses of sine waves with a constant amplitude interspersed with gaps of no signal.

In on-off carrier keying, if the carrier wave is turned on or off abruptly,  [[Shannon–Hartley theorem|communications theory]] can show that the [[Bandwidth (signal processing)|bandwidth]] will be large; if the carrier turns on and off more gradually, the bandwidth will be smaller. The bandwidth of an on-off keyed signal is related to the data transmission rate as:
<math> B_n = B K </math>
where <math>B_n</math> is the necessary bandwidth in hertz,
<math>B </math> is the keying rate in signal changes per second ([[baud]] rate),
and <math> K </math> is a constant related to the expected radio propagation conditions; K=1 is difficult for a human ear to decode, K=3 or K=5 is used when fading or [[multipath propagation]] is expected.<ref>L. D. Wolfgang, C. L. Hutchinson (ed) ''The ARRL Handbook for Radio Amateurs, Sixty Eighth Edition'', ([[ARRL]], 1991) {{ISBN|0-87259-168-9}},  pages 9-8, 9-9</ref>

The spurious noise emitted by a [[transmitter]] which abruptly switches a carrier on and off is called ''key clicks''. The noise occurs in the part of the signal bandwidth further above and below the carrier than required for normal, less abrupt switching. The solution to the problem for CW is to make the transition between on and off to be more gradual, making the edges of pulses ''soft'', appearing more rounded, or to use other modulation methods (e.g. [[phase modulation]]). Certain types of power amplifiers used in transmission may aggravate the effect of key clicks.