Morse code

"Morse code is a type of character encoding that transmits telegraphic information using rhythm. Morse code uses a standardized sequence of short and long elements to represent the letters, numerals, punctuation and special characters of a given message. The short and long elements can be formed by sounds, marks, or pulses, in on off keying and are commonly known as 'dots' and 'dashes' or 'dits' and 'dahs'" (Wikipedia).

Morse code can be used in any medium that allows discriminating between dots and dashes (electrical lines, radio waves, pulses of light, tapping on resonant objects, etc.).

The discussion in the Ameliapedia is concerned with Morse code carried on continuous wave (CW) or modulated continuous wave (MCW) radio transmissions. Where the sources refer to CW or MCW without other qualification, they generally mean "Morse code transmitted on continuous wave" or "modified continuous wave."

When Earhart asked the Itasca to transmit the letter A (.-) repeatedly, what she would have heard was this:

.- .- .- .- .- .- .- .- .- .- .- .- .- .- .- .- .- .- .- .- .- .- .-

and so on, with periodic interruptions for Itasca to insert its call sign into the transmission.