EMRFD Message Archive 6622

Message Date From Subject
6622 2011-09-10 06:35:13 qrp.gaijin Single-transistor nulling Q multiplier - how?

At the following URL is a single-FET Colpitts circuit that claims to be able to act as both a peaking and a nulling Q multiplier:


I've built a few regenerative receivers so I more or less understand what is going on in the peak mode, but I don't see how the above circuit with just one transistor can work in null mode, which in other circuits I've seen requires a separate inverting active device. The peak terminal is at top of the Colpitts capacitive divider, and the null terminal is at the Colpitts capacitive tap, connected to the FET source. I'm not seeing what the significant difference is between the peak and null terminals.

Any explanation as to how (or if) this single-FET Q multiplier can provide null capability?