2 Feb 19

Known as class B emission by the International Telecommunications Union, Damped Wave has been prohibited since 1930 due to its wide bandwidth and additional electrical noise. The transmission wave started at max signal and tapered off to zero for each key. The Spark Gap Transmitter and Damped Wave were last used in 1920 and replaced by Vacuum Tube Transmitters…

Source… Wikipedia (Damped Wave) …… Wikipedia (Continuous Wave)