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11th February 2011 13:01

qrp-gaijin wrote...

Hi Alan,

I like this circuit because it is the only regen design I have seen which attempts to regulate regeneration level automatically. However this circuit only achieves partial regeneration control, not fully automatic control.

I've been thinking a lot (as certainly many others before me have, in the heyday of regenerative receivers) about if it is possible to design an analog (or failing that, digital) circuit that achieves fully automatic regneration control, namely, holding the regeneration level always at precisely the threshold of oscillation, but not oscillating, so that selectivity and gain are maximised. (The reason I want to try this is to test the maximum selectivity attainable by a regen, and to use such a non-oscillating regen with a BFO for highly-selective, possibly even single-signal, CW reception.)

I believe this would require a way to sense how *near* the regen is to the brink of oscillation (regardless of frequency), and generate a corresponding control voltage to pull the regeneration level down. Is there any way you can think of to achieve this?

I have considered ways to detect the onset of oscillation (e.g. using a BFO tracking the regen frequency to always inject a carrier of known amplitude close to the regen frequency, so the onset of oscillation would always cause a piercing audio tone to be generated, which could then be detected and used as an AGC voltage for the regeneration level), but it seems that such an AGC voltage generated based on the *onset* of oscillation is too late; the control voltage is *zero* before oscillation, and some high value *after* oscillation, so using this to regulate regeneration level would produce distortion as the regen is alternately allowed to briefly oscillate then is yanked back down again, over and over.

There are also mechanical ways of achieving "automatic" regeneration with ganged capacitors for tuning and regeneration level, but these assume a fixed relationship between frequency and required regeneration level, which is not necessarily valid if the regen parameters change due to factors like temperature-related capacitance changes, antenna loading, etc. So a sensing-based approach seems the "proper" way to achieve automatic regeneration control - but is it possible?

I suppose the gist of this post can be summarised as, "how can we detect how near the regen is to the oscillation threshold and generate a corresponding control voltage"?

I'd be interested in your thoughts on the subject.

27th December 2009 21:00

Alan Yates wrote...

Thanks for that, I've updated the links.

27th December 2009 17:54

guest a wrote...

hello, the link needs to be updated