Resonant cavities have such good selectivity that are routinely used to
consolidate antennas for concurrent use with multiple transceivers on
same-band frequencies.

One can take a few interesting shortcuts to making them, both for ham
radio
( http://web.telia.com/~u85920178/use/cavity.htm )
and professional installation (e.g.
http://www.raeng.org.uk/news/publica...ue18/David.pdf
= http://tinyurl.com/cenqb - Not a joke, you can really use beer
barrels!).


Does anyone have experience in using positive feedback to turn, say, a
VHF fixed-frequency resonator into a regenerative IF filter for HF use?


Expected pros
- no images even with a modest front end low-pass filter
- single peak bandpass
- solid floor, possibly with ferocious immunity from strong nearby
signals
- may provide direct detection
- for isofrequency transceive operation, a PLL or huff-puff oscillator
could be converted back to receive frequency with good spectral purity
with little filtering

Expected cons:
- possible thermal frequency instability
- tricky to feed to and pick up from properly, compounded by having to
provide path for regeneration

Frequency would be rather unimportant, all tuning would happen in the
local oscillator.


Did anyone ever try that? In particular, I am curious about the
following:

1) Better a 1/4-wave resonator referred to ground or a ground-insulated
loop? (The latter may be easier to fith with multiple mutually
decoupled I/Os referred to ground).

2) Better single I/O or perhaps one each for signal path and regen amp?
(The former easier to fit on a standard 1/4 lambda resonator worked
against ground. Also, this could be done with a preexisting surplus
resonator.)

3a) Suggestions for ready made metal containers - such as coffee cans,
compressed gas canisters, large movie-type film spool cases, or
gold-flashed gas-inflated caramelized yak rumens?

3b) Is silver flashing a good idea, on either resonator or all over the
inside of a cavity

3c) Or, what ready made surplus cavity would you suggest?


73 es tnx de n1jpr/i2