It is easy to achieve good sensitivity with a single-transistor superregenerative receiver. Such circuits used to be very common in simple walkie-talkies and RC models. Sometimes you can still find them there today. With such arrangements, sensitivities of 5 μV and better can be achieved without much effort. However, the problem is the too large bandwidth and accordingly poor selectivity of such circuits. Individual radio channels can not be separated from each other. Even in the low-occupied 29-MHz area must therefore be expected with interference from other frequencies.
Inspired by the remarks of Heinz Richter in his "Das große Fernsteuerbuch" (The Great Remote Control Book), I experimented with quench and super-regenerative circuits, where the functions quench-frequency-generation, regeneration and demodulation were distributed in different stages. Thus, a working on this principle circuit could be optimally adjusted. Selectivity and sensitivity could be significantly increased.
If the shown circuit is set to CB frequencies, stations operating on different channels could clearly be separated, as long as the channels were not too close to each other. Already at a distance of 20 kHz from the set frequency, with optimum justation of feedback and oscillation frequency amplitude a connected oscilloscope showed a reduction of almost 12dB. In contrast, several more closely-studied single-transistor super-regenerative receivers simultaneously picked up at least about 200 kHz wide areas without noticeable subsidence.
As with the simple super-regenerative receiver, which I first of all used in my homebrew walkie-talkies, I also designed a squelch circuit for this receiver later used there. As shown in the schematic, it was also possible to generate a DC voltage for the field strength display from the noise voltage. The blemish that the smallest pointer deflection thereby corresponds to maximum field strength can be compensated by a correspondingly reversed scale label. Another possibility is that the measuring unit is connected instead of ground with a corresponding to the maximum value supplied by the diode, adjustable DC voltage.
Although with integrated circuits today one can built superheterodyne receiver with significantly less effort and noticeably better properties, the construction of such a super-regenerative receiver is nevertheless an interesting experiment. In addition, it is unlikely that a receiver with comparable properties can be built, in which a single resonant circuit makes all selectivity.
The system-dependent control properties of a super-regenerative receiver are pleasant. Weaker stations are hardly received quieter, essentially increases - similar to otherwise only with FM - the noise component.