THE 100 MOST INFLUENTIAL INVENTORS OF ALL TIME

7 The 100 Most Influential Inventors of All Time 7

This youthful invention that opened the age of elec-
tronics had profound effects on Armstrong’s life. It led
him, after a stint as an instructor at Columbia University,
into the U.S. Army Signal Corps laboratories in World War I
in Paris, where he invented the superheterodyne circuit, a
highly selective means of receiving, converting, and greatly
amplifying very weak, high-frequency electromagnetic
waves, which today underlies 98 percent of all radio, radar,
and television reception over the airways. It brought him
into early association with the man destined to lead the
postwar Radio Corporation of America (RCA), David
Sarnoff, whose young secretary Armstrong later married.
Armstrong himself returned after the war to Columbia
University to become assistant to Michael Pupin, the
notable physicist and inventor and his revered teacher. In
this period he sold patent rights on his circuits to the
major corporations, including RCA, for large sums in cash
and stock. Suddenly, in the radio boom of the 1920s, he
found himself a millionaire. But he continued to teach at
Columbia, financing his own research, working along
with Pupin, whose professorship he inherited, on the
long-unsolved problem of eliminating static from radio.

Invention of FM Broadcasting

In 1933 Armstrong secured four patents on advanced circuits
that were to solve this last basic problem. They revealed
an entirely new radio system, from transmitter to receiver.
Instead of varying the amplitude, or power, of radio waves
to carry voice or music, as in all radio before then, the new
system varied, or modulated, the waves’ frequency (number
of waves per second) over a wide band of frequencies. This
created a carrier wave that natural static—an amplitude
phenomenon created by electrical storms—could not
break into. As a result, FM’s wide frequency range made