On Apr 14, 9:46*am, spamhog wrote:
As the sunspot cycle is inching forward, I've been considering adding
an upconverter to Charles Kitchin's 50MHz audio-squelched superregen
design, in order to make a sensitive and very quickly tuneable
15-30MHz receiver intended to take the pulse of propagation on the
higher HF bands. *The idea came from an unpretentious Russian design.
(No, it wasn't a fremodyne).

In a classic case of mission creep, I observed that a fixed IF lends
itself to a further step. I searched for prior art in inducing super-
regeneration in a resonant cavity.

If that could help narrowing the passband, it would be a nice trick
for upconversion.

I found few and laconic references at almost-otherwordly microwave
frequencies, Gunn diodes, folded spectra, etc etc.

If I could make a resonant cavity in no time I'd not ask for advice
before jumping in, but this would be my very first, and shooting for
40-60Mz IF it risks being somewhat monumental - short of pigtailing
the resonator, or doing a folded design, or some other "Grande
Complication" which might negate the very idea of using a cavity.

****** * Prior art pointers, anyone? * *******

TIA

Filippo N1JPR

___________________________________________

P.S.: Just to prempt repetitions of the obvious I'll repeat it myself:
Why don't you use a [ superhet ¦ xtal roofing filter ¦ downconversion
¦ cod liver oil ¦ snake oil ]. *Sorry I never heard of it, so it's
likely to be a bad idea. *Are you a Communist? *Never heard of a 40MHz
cavity. *A superregen won't demod [ CW ¦ SSB ¦ [QM¦P]SKxx ¦ delta-
sigma ¦ ancient Greek ] ! *Is this gonna be a portable receiver in
that you can put it in the back of a SUV - if someone helps you carry
the 6' long cavity, that is? *You will need a [ BFO ¦ product detector
¦ AMS ¦ DSP ¦ LPF ¦ postprocessing ¦ Photoshop ]. *IF passband will be
too broad, although I have no idea how broad since I never used a
cavity for that. *:-o

I think it's the APN141 that uses a gated regen with a cavity. You
might get some interesting ideas from it, if you can find any
documentation on it. It's a cute design that made me think "out of
the box" when I learned it many years ago.

You're talking about a low enough frequency that you'll probably
benefit from a calculation of the size of resonator you'll need to get
the same Q as you can get from an LC tank. I suspect that unless you
are willing to make a really big coaxial resonator, you'll be able to
do better with an LC tank, or equivalently a helical resonator. At
1GHz and above, a cavity or coaxial resonator usually makes a lot of
sense. At 1MHz, a cavity or coaxial resonator probably never makes
sense. At 50MHz---well, do some careful thinking about it before you
jump in. A coil a couple inches in diameter and two to four inches
long should get you to Qu well in excess of 1000, if you are careful
with the construction.

Cheers,
Tom