A working definition of heterodyning:
To generate new frequencies by mixing two or
in a nonlinear device such as a vacuum tube, transistor, or diode mixer.
Reginald Aubrey Fessenden (1866-1932) is usual credited with the
invention of the heterodyne principle (reference).
As an example, we revisit our discussion of DSB-AM where
we see how two frequencies are shifted by the nonlinear operation of
Example of a Nonlinear Characteristic - Diode (Rectifier)
Edwin Howard Armstrong's Superheterodyne Receiver
History of Radio
the way was paved for a bright engineer to devise useful
circuits to exploit the audion’s potential. That bright engineer was
Edwin Howard Armstrong
who invented the regenerative amplifier/detector
1912 at the tender age of 21.
a 1914 paper titled 'Operating Features of the Audion,' Armstrong
published the first
correct explanation for how the triode worked, and provided
experimental evidence to
support his claims. …He Armstrong
went on to develop circuits that continue to dominate communications
to this day. While a member of the U.S. Army Signal Corps during World
War I, Armstrong
became involved with the problem of detecting enemy planes from a
pursued the idea of trying to home in on the signals naturally
generated by their ignition
systems (spark transmitters again). Unfortunately, little useful
radiation was found below
about 1MHz, and it was exceedingly difficult with the tubes available
at that time to get
much amplification above that frequency. …
so Armstrong had
work cut out for him.
He solved the problem by employing a principle originally used by
Poulsen and later elucidated
decided to employ Fessenden’s heterodyne principle in a different way.
than using it to demodulate CW directly, he used the heterodyne method
to convert an
incoming high frequency RF signal into one at a lower frequency, where
high gain and
selectivity could be obtained with relative ease. This signal, known as
frequency (IF), was then demodulated after much filtering and
amplification at the IF had
been achieved. The receiver could easily possess enough sensitivity so
that the limiting
factor was actually atmospheric noise (which is quite large in the AM
Furthermore, a single tuning control was made possible, since the IF
amplifier works at a
This page was prepared and is maintained by R.
Comments to: firstname.lastname@example.org.
updated March 23, 2004