Morse code

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"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.

Morse code vs. voice transmissions

As a general rule, Morse code has a much higher signal-to-noise ratio than voice transmissions. The human ear can relatively easily distinguish between the dots, dashes, and silence that make up Morse code, even with a great deal of noise in the background; the range of sounds needed for producing intelligible speech is vastly greater than what is needed to produce intelligible code.

If Earhart and Noonan had been willing to buckle down and learn Morse code, they could have communicated with many more stations and at much greater distance than with voice communication. When they heard code on 7500 kcs via the loop antenna, they could have received instructions from the Itasca about how to transmit long enough for a bearing to be taken and they then could have learned the right bearing to fly to reach Howland Island.