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Radio waves and sound.

Radio communication first came into use only as a wireless telegraph, forming the dots and dashes of the Morse code in appropriate bursts of radio waves.

It occurred to the Canadian-born American physicist Reginald Aubrey Fessenden (1866-1932) to send out a continuous signal with an amplitude (the height of the waves) varying in such a way as to follow the irregularities of sound waves. The radio wave was said to have amplitude modulation (AM) imposed on it.

At the receiving end, the modulation could be reconverted into sound waves, with the result that you could use a radio for speaking and hearing thanks to modulated radio waves the same way you could use a telephone for speaking and hearing thanks to modulated electric currents.

On December 24, 1906, the first such message was sent out from the Massachusetts coast, and wireless receivers picked up music.

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Author:Asimov, Isaac
Publication:Asimov's Chronology of Science & Discovery, Updated ed.
Article Type:Reference Source
Date:Jan 1, 1994
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