Editing Regenerative circuit (section)

==Superregenerative receiver==
[[File:Edwin Armstrong and superregenerative receiver.jpg|thumb|upright=1.2|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.]]

The superregenerative receiver uses a second lower-frequency oscillation ([[Squegging|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.<ref>[https://archive.org/stream/Electronic_Circuits_and_Tubes_Cruft_Laboratory_at_Harvard_University_1947#page/n765 Cruft Electronics Staff, 1947, p. 744]</ref>  Ultrasonic quench rates between 30 and 100&nbsp;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).

===Advantages and applications===
Superregenerative detectors work well for AM and can also be used for wide-band signals such as FM, where they perform "slope detection". Regenerative detectors work well for narrow-band signals, especially for CW and SSB which need a heterodyne oscillator or BFO. A superregenerative detector does not have a usable heterodyne oscillator – even though the superregen always self-oscillates, so CW (Morse code) and SSB (single side band) signals can't be received properly.

Superregeneration is most valuable above 27&nbsp;MHz, and for signals where broad tuning is desirable.  The superregen uses many fewer components for nearly the same sensitivity as more complex designs. It is easily possible to build superregen receivers which operate at microwatt power levels, in the 30 to 6,000&nbsp;MHz range. It removes the need for the operator to manually adjust regeneration level to just below the point of oscillation - the circuit automatically is taken out of oscillation periodically, but with the disadvantage that small amounts of interference may be a problem for others. These are ideal for remote-sensing applications or where long battery life is important. For many years, superregenerative circuits have been used for commercial products such as garage-door openers, radar detectors, microwatt RF data links, and very low cost walkie-talkies.

Because the superregenerative detectors tend to receive the strongest signal and ignore other signals in the nearby spectrum, the superregen works best with bands that are relatively free of interfering signals. Due to [[Nyquist theorem|Nyquist's theorem]], its quenching frequency must be at least twice the signal bandwidth. But quenching with overtones acts further as a [[heterodyne]] receiver mixing additional unneeded signals from those bands into the working frequency. Thus the overall bandwidth of superregenerator cannot be less than 4 times that of the quench frequency, assuming the quenching oscillator produces an ideal sine wave.