Antonio Vernucci wrote:
I would like to build an old-style receiver using a BC-453 stuck at 500-kHz as
IF chain. A possibility would be to put a pentode in front of the BC-453 mixing
the incoming RF signal with the signal generated by a variable local oscillator
(VFO). To improve selectivity, one could adopt a regenerative arrangement
whereby part of the pentode plate signal is fed back into the grid (by inductive
coupling), and the cathode resistor is then adjusted just before the tube starts
oscillating. In other words, a kind of Q-multiplying converter (I think this is
called "Q-dyne" receiver). What I am not fully sure about is if the increased
selectivity I so obtain turns into a higher rejection of the image frequency, or
just into a narrowing of the received bandwidth (which is already narrowed down
by the tight BC-453 85-kHz IF transformers). My feeling is that said
regenerative scheme would offer no advantage in terms of image rejection, but I
would value very much your opinion on that subject.

For CW reception, the Q-multiplier can give you tighter selectivity without
needed crystal or mechanical filters in the signal path. It's a pain in the
neck to operate, though.

Build yourrself a conventional super-regen receiver, then add a q-multiplier
stage after you have the rest of it working.
--scott


--
"C'est un Nagra. C'est suisse, et tres, tres precis."