Radio Receiver Design - Regenerative

Regenerative

The regenerative receiver also had its heyday at the time where adding an active element (vacuum tube) was considered costly. In order to increase the gain of the receiver, positive feedback was used in its single RF amplifier stage; this also increased the selectivity of the receiver well beyond what would be expected from a single tuned circuit. The amount of feedback was quite critical in determining the resulting gain and had to be carefully adjusted by the radio operator. Increasing the feedback beyond a point caused the stage to oscillate at the frequency it was tuned to.

Self-oscillation reduced the qualitity of its reception of an AM (voice) radio signal but did ironically make it useful as a CW (morse code) receiver inasmuch as the beat signal between the oscillation and the radio signal would produce an audio "beeping" sound. The oscillation of the regenerative receiver could also be an annoying source of local interference. An improved design known as the super-regenerative receiver improved the performance by allowing an oscillation to build up which was then "quenched," with that cycle repeating at a rapid (ultrasonic) rate. From the accompanying schematic for a practical regenerative receiver, one can appreciate its simplicity in relation to a multi-stage TRF receiver, while able to achieve the same level of amplification through the use of positive feedback.