1866-1932. Canadian physicist who worked in
the USA, first for Thomas Edison and then for
George Westinghouse. He patented the
modulation of radio waves (transmission of a
signal using a carrier wave), an essential
technique for voice transmission. At the time
of his death, he held 500 patents. Early
radio communications relied on telegraphy by
using bursts of single-frequency signals in
Morse code. In 1900 Fessenden devised a
method of making audio-frequency speech (or
music) signals modulate the amplitude of a
transmitted radio-frequency carrier wave -
the basis of AM radio broadcasting.