Just sharing a link with some interesting BJT regen designs and discussion.sites.google.comBH1RBG RF Lab - Regen III: A Journey of BJT Regen Make up a Regen
BH1RBG mentions at the bottom of the page that loading the regenerative amplifier allows smoother regeneration control:
seanvn at the old TheRadioBoard forums also posted some similar circuits before. Some of his circuits can be seen here: https://discover.hubpages.com/technology/Regenerative-Receiver-Design-Blocks
From seanvn's web page above, he says:
So this is kind of a similar idea, to use extra damping to soften the regeneration control.
The difference between the BH1RBG idea and seanvn's idea is:
BH1RBG uses an untuned amplifier stage between the BJT regenerative stage and the following diode detector. The untuned amplifier stage provides damping of the LC tank that leads to smooth regeneration control.
seanvn uses a BJT detector (not a diode detector) directly after the BJT regenerative stage. The BJT detector provides damping of the LC tank that leads to smooth regeneration control. Furthermore, seanvn says: "The best place to do AM detection in a regenerative receiver is directly at the LC resonator. Using a buffer stage is likely to cause excess noise or instability."
I find BH1RBG's approach interesting because he was able to get improved detection with the untuned amplifier stage. I never really had any success with this approach myself, so I'm tempted to try out BH1RBG's circuit.
The GlobeSpan regenerative receiver at https://www.nutsvolts.com/magazine/article/the-globespan-world-band-receiver claims to offer up to 80 dB of untuned gain between the regenerative amplifier and the detector. I did some LTspice simulations of the amplifier chain and the gain was quite a bit less than 80 dB, especially at higher frequencies (and a comment on the GlobeSpan article makes the same observation). I tried, with dismal failure, to use a series of untuned BJT amplifiers to amplify the signal coming off of a regenerative loop antenna. I had big problems with hand capacitance that made the setup unusable. But still, I remain attracted by the idea of improving the regenerative receiver by the "simple" addition of an untuned amplifier before the detector.
Another note is that BH1RBG's final circuit seems aimed at AM BCB frequencies (0.5-1.6 MHz). The untuned amplifier (following the regenerative amplifier) will likely have less gain at higher frequencies, reducing the signal presented to the diode detector.
Very nice article. Thanks