I have built countless regenerative radio circuits throughout the years and some have worked well – some haven’t. I was inspired by the circuit design of the TEN TEC regenerative radio kit. I used some of the same ideas, but changed the design to better match my design criteria. In this design, I had eight important design objectives:
Simplicity – this type of radio should not be complicated and I have seen designs on the web that may perform well, but seem unnecessarily complicated.
Tuning/fine tuning – I use a cheap poly variable for main tuning and a junk box rectifier as varactor for fine tuning.
No special inductor required – I have tried all sorts of junk box inductors and they all work great. With this design, no tapped coils or tickler windings are required. This design could easily be made into a multi-band radio
Extremely smooth and stable Regeneration control – I adjust a DC bias point condition instead of RF Feedback to control regeneration and the performance is excellent. There is no hysteresis or abrupt transition from regeneration to oscillation.
Ample Audio Gain with no motorboating or instability – I stayed away from the LM386(which could be used) and chose a TPA301 amplifier IC – which give excellent results.
Antenna Isolation – This is achieved with a simple grounded gate input stage which shares the LC tank with the oscillator.
Excellent sensitivity – This design is the best performing Regen I have ever built
No critical adjustments and easily repeatable results – I have built this circuit now three times with different inductors, for different bands and with different JFET device types on bread-boards, etc. The results have all been the same and I have only had to make minor tweaks to optimize performance for different JFET types and significantly higher or lower frequency bands. The radio currently tunes 7-11MHz.
The basic paradigm of this design is to break up the traditional oscillating detector into a separated regenerative amplifier and detector circuit.
The detector is a “plate detector”, where RF is fed back to the Amplifier via a partially RF decoupled source(normally bypassed all the way for RF when used as a detector).
Version 2: (07/30/2015)
Link to PCB for version 2:(expresspcb format)
Version 1 (shown in video):
picture of prototype: