Morse code

From HFUnderground

See CW.

Note that it is very commonplace for Morse code to be used for automatic station identification (amateur radio repeaters, land mobile radio systems - business band, public safety systems - simplex and repeater networks, etc.). In these instances, Morse code characters are transmitted over a traditional voice radio channel (FM, but sometimes AM, SSB, etc.) via use of a modulated tone. Often this is called "MCW" for "modulated CW".