What factors affect the bandwidth of a transmitted CW signal?

The bandwidth of a Continuous Wave (CW) on-off keying signal is determined primarily by two factors: how fast the transmitter is keyed, and the shape of the keyed waveform. Faster keying speeds naturally require wider bandwidths to carry the rapid on-off transitions in the signal. Additionally, the shape factor—specifically the rise and fall time of the RF envelope when turning on and off—drastically impacts bandwidth. If the transition is too abrupt (square-wave like), it generates broadband noise known as "key clicks." Softening the edges narrows the transmitted bandwidth.