The
autodyne circuit was an improvement to radio signal amplification using the
De Forest Audion vacuum tube amplifier. By allowing the tube to oscillate at a frequency slightly different from the desired signal, the sensitivity over other receivers was greatly improved. The autodyne circuit was invented by
Edwin Howard Armstrong of
Columbia University, New York, NY. He inserted a tuned circuit in the output circuit of the Audion
vacuum tube amplifier. By adjusting the tuning of this tuned circuit, Armstrong was able to dramatically increase the gain of the Audion amplifier. Further increase in tuning resulted in the Audion amplifier reaching self-oscillation.