Editing Regenerative circuit (section)

=== Advantages and disadvantages ===
Regenerative receivers require fewer components than other types of receiver circuit, such as the [[Tuned radio frequency receiver|TRF]] and [[superheterodyne]].  The circuit's advantage was that it got much more amplification (gain) out of the expensive [[vacuum tube]]s, thus reducing the number of tubes required and therefore the cost of a receiver.  Early vacuum tubes had low gain and tended to oscillate at [[Radio frequency|radio frequencies]] (RF). TRF receivers often required 5 or 6 tubes; each stage requiring tuning and neutralization, making the receiver cumbersome, power hungry, and hard to adjust.  A regenerative receiver, by contrast, could often provide adequate reception with the use of only one tube.  In the 1930s the regenerative receiver was replaced by the superheterodyne circuit in commercial receivers due to the superheterodyne's superior performance and the falling cost of tubes.  Since the advent of the [[transistor]] in 1946, the low cost of active devices has removed most of the advantage of the circuit.  However, in recent years the regenerative circuit has seen a modest comeback in receivers for low cost [[digital radio]] applications such as [[garage door opener]]s, [[keyless entry|keyless locks]], [[RFID]] readers and some [[cell phone]] receivers.

A disadvantage of this receiver, especially in designs that couple the detector tuned circuit to the antenna, is that the regeneration (feedback) level must be adjusted when the receiver is tuned to a different frequency. The antenna impedance varies with frequency, changing the loading of the input tuned circuit by the antenna, requiring the regeneration to be adjusted. In addition, the Q of the detector tuned circuit components vary with frequency, requiring adjustment of the regeneration control.<ref name="TM11-665" />{{rp|p.189}}

A disadvantage of the single active device regenerative detector in autodyne operation is that the local oscillation causes the operating point to move significantly away from the ideal operating point, resulting in the detection gain being reduced.<ref name="decola">R. De Cola, "Increased Sensitivity With the Regenerative Detector", ''[[QST]]'', vol. XVIII, no. 12, p. 24, Dec. 1934</ref>

Another drawback is that when the circuit is adjusted to oscillate it can radiate a signal from its antenna, so it can cause [[Radio-frequency interference|interference]] to other nearby receivers. Adding an RF amplifier stage between the antenna and the regenerative detector can reduce unwanted radiation, but would add expense and complexity.

Other shortcomings of regenerative receivers are the sensitive and unstable tuning. These problems have the same cause: a regenerative receiver's gain is greatest when it operates on the verge of oscillation, and in that condition, the circuit behaves [[chaos theory|chaotically]].<ref>Domine M.W. Leenaerts and Wim M.G. van Bokhoven, “Amplification via chaos in regenerative detectors,” ''Proceedings of SPIE'' *, vol. 2612**, pages 136-145 (December 1995).
(* SPIE = Society of Photo-optical Instrumentation Engineers; renamed: International Society for Optical Engineering) 
(** Jaafar M.H. Elmirghani, ed., ''Chaotic Circuits for Communication'' -- a collection of papers presented at the SPIE conference of 23–24 October 1995 in Philadelphia, Pennsylvania.)</ref><ref>Domine M.W. Leenaerts, “Chaotic behavior in superregenerative detectors,” ''IEEE Transactions on Circuits and Systems Part 1: Fundamental Theory and Applications'', vol. 43, no. 3, pages 169-176 (March 1996).</ref><ref>In 1922, during his development of the superregenerative receiver, [[Edwin Howard Armstrong|Edwin Armstrong]] noted signs of chaotic behavior in his circuits.  See:  Edwin H. Armstrong (1922) [https://books.google.com/books?id=xUISAAAAIAAJ&pg=PA244 "Some recent developments of regenerative circuits,"] ''Proceedings of the Institute of Radio Engineers'', '''10''' (8) :  244-260.  From p. 252: " ... a free oscillation starts every time the resistance of the circuit becomes negative. ... The free oscillations produced in the system when no signaling emf. is impressed, must be initiated by some irregularity of operation of the vacuum tubes, ... ."</ref> Simple regenerative receivers electrically couple the antenna to the detector tuned circuit, resulting in the electrical characteristics of the antenna influencing the resonant frequency of the detector tuned circuit. Any movement of the antenna or large objects near the antenna can change the tuning of the detector.