page_title: Regenerative circuit
section_title: Superregenerative receiver
hierarchical_section_title: Regenerative circuit / Superregenerative receiver
caption_attribution_description: English: American radio researcher Edwin H. Armstrong and his new invention, the superregenerative receiver in 1922. This was probably taken at the June 28, 1922 meeting of the Radio Club of America in room 306, Havemeyer Hall, Columbia University, New York, at which Armstrong demonstrated the superregenerative receiver. The receiver used only 3 vacuum tubes (visible), but was as sensitive as existing receivers with 9 tubes. However it didn't prove as useful as the other receiver circuits he invented: the regenerative receiver and the superheterodyne receiver, which is used in virtually every radio and television today. The black metal bell (left) is the horn loudspeaker (modern cone loudspeakers hadn't been invented yet), and the wires on the frame (right) is the loop antenna for the radio. The caption of the photo read: "THE MAN WHO ORIGINATED THE ARMSTRONG CIRCUIT Hertz, Marconi, De Forest - and now Edwin H. Armstrong, head the list of scientists who have made radio, as we know it today, possible. Armstrong has the honor of making three definite contributions to radio. FIRST, he originated the regenerative feedback vacuum tube circuit. SECOND, he originated the super-heterodyne circuit, the most sensitive receiver ever produced. THIRD, he invented the superregenerative receiver, which has just taken the world by storm and which bears his name."
context_page_description: A regenerative circuit is an amplifier circuit that employs positive feedback. Some of the output of the amplifying device is applied back to its input so as to add to the input signal, increasing the amplification. One example is the Schmitt trigger, but the most common use of the term is in RF amplifiers, and especially regenerative receivers, to greatly increase the gain of a single amplifier stage.
  The regenerative receiver was invented in 1912 and patented in 1914 by American electrical engineer Edwin Armstrong when he was an undergraduate at Columbia University. It was widely used between 1915 and World War II. Advantages of regenerative receivers include increased sensitivity with modest hardware requirements, and increased selectivity because the Q of the tuned circuit will be increased when the amplifying vacuum tube or transistor has its feedback loop around the tuned circuit because it introduces some negative resistance.
context_section_description: The superregenerative receiver uses a second lower-frequency oscillation (within the same stage or by using a second oscillator stage) to provide single-device circuit gains of around one million. This second oscillation periodically interrupts or "quenches" the main RF oscillation.  Ultrasonic quench rates between 30 and 100 kHz are typical. After each quenching, RF oscillation grows exponentially, starting from the tiny energy picked up by the antenna plus circuit noise. The amplitude reached at the end of the quench cycle (linear mode) or the time taken to reach limiting amplitude (log mode) depends on the strength of the received signal from which exponential growth started.  A low-pass filter in the audio amplifier filters the quench and RF frequencies from the output, leaving the AM modulation. This provides a crude but very effective automatic gain control (AGC).
caption: Edwin Armstrong presenting the superregenerative receiver at the June 28, 1922 meeting of the Radio Club of America in Havemeyer Hall, Columbia University, New York.  His prototype 3 tube receiver was as sensitive as conventional receivers with 9 tubes.
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