Morse code most common letter in English, the letter "E", has the shortest code: a single dot. Because the Morse code elements are specified by proportion rather than specific time durations, the code is usually transmitted at the highest rate that the receiver is capable of decoding. The Morse code transmission rate ("speed") is specified in "groups per minute", commonly referred to as "words per minute". Morse code is usually transmitted by on-off keying of an information carrying medium such as electric current, radio waves, visible light or sound waves. The current or wave is present during time period of the dot
Morse code identify the transmitter because the dot/dash sequence is written out next to the transmitter's symbol on aeronautical charts. Some modern navigation receivers automatically translate the code into displayed letters. International Morse code today is most popular among amateur radio operators, in the mode commonly referred to as "continuous wave" or "CW". (This name was chosen to distinguish it from the damped wave emissions from spark transmitters, not because the transmission is continuous.) Other keying methods are available in radio telegraphy, such as frequency shift keying. The original amateur radio operators used Morse code exclusively since voice-capable radio transmitters did not