Autodyne

This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. Find sources: "Autodyne" – news · newspapers · books · scholar · JSTOR (August 2011) (Learn how and when to remove this message)

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.^[1] The autodyne circuit was invented by Edwin Howard Armstrong of Columbia University, New York, NY.^{[citation needed]} He inserted a tuned circuit in the output circuit of the Audion vacuum tube amplifier.^{[citation needed]} 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.

This oscillating receiver circuit meant that the then latest technology continuous wave (CW) transmissions could be demodulated. Previously only spark, interrupted continuous wave (ICW, signals which were produced by a motor chopping or turning the signal on and off at an audio rate), or modulated continuous wave (MCW), could produce intelligible output from a receiver.

When the autodyne oscillator was advanced to self-oscillation, continuous wave Morse code dots and dashes would be clearly heard from the headphones as short or long periods of sound of a particular tone, instead of an all but impossible to decode series of thumps. Spark and chopped CW (ICW) were amplitude modulated signals which didn't require an oscillating detector. Such a regenerative circuit is capable of receiving weak signals, if carefully coupled to an antenna. Antenna coupling interacts with tuning, making optimum adjustments difficult.