A regeneration control is usually provided for adjusting the amount of feedback (the loop gain). In the regenerative circuit discussed here, the active device also functions as a detector this circuit is also known as a regenerative detector. In regenerative receivers using only one active device, the same tuned circuit is coupled to the antenna and also serves to select the radio frequency to be received, usually by means of variable capacitance. The tuned circuit allows positive feedback only at its resonant frequency. In a regenerative receiver the output of the tube or transistor is connected back to its own input through a tuned circuit (LC circuit). Because of the large amplification possible with regeneration, regenerative receivers often use only a single amplifying element (tube or transistor). This is called positive feedback or regeneration. The gain of any amplifying device, such as a vacuum tube, transistor, or op amp, can be increased by feeding some of the energy from its output back into its input in phase with the original input signal. ![]() Most regenerative receivers used this Armstrong circuit, in which the feedback was applied to the input (grid) of the tube with a "tickler coil" winding on the tuning inductor. Regenerative receiver Vacuum tube regenerative receiver schematic. It is still used in a few specialized low data rate applications, such as garage door openers, wireless networking devices, walkie-talkies and toys. One widespread use during WWII was IFF transceivers, where single tuned circuit completed the entire electronics system. : p.190 It was never widely used in general commercial receivers, but due to its small parts count it was used in specialized applications. : p.190 Regeneration (now called positive feedback) is still widely used in other areas of electronics, such as in oscillators, active filters, and bootstrapped amplifiers.Ī receiver circuit that used larger amounts of regeneration in a more complicated way to achieve even higher amplification, the superregenerative receiver, was also invented by Armstrong in 1922. 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 (via a "tickler" winding or a tapping on the coil) because it introduces some negative resistance.ĭue partly to its tendency to radiate interference when oscillating, : p.190 by the 1930s the regenerative receiver was largely superseded by other TRF receiver designs (for example "reflex" receivers) and especially by another Armstrong invention - superheterodyne receivers and is largely considered obsolete. It was widely used between 1915 and World War II. 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. ![]() One example is the Schmitt trigger (which is also known as a regenerative comparator), 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. Some of the output of the amplifying device is applied back to its input to add to the input signal, increasing the amplification. The tickler coil is visible inside the tuning coil and is turned by a shaft from the front panel this type of adjustable transformer was called a variocoupler.Ī regenerative circuit is an amplifier circuit that employs positive feedback (also known as regeneration or reaction). Rear view of the above radio, showing the simplicity of the regenerative design. The controls are (left) regeneration, (lower center) filament rheostat, (right) tuning capacitor. Homebuilt Armstrong one-tube regenerative shortwave radio with construction characteristic of the 1930s - 40s. For other uses, see Heat exchanger § Regenerative heat exchanger.
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