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? ******

"Coaxial Line V.H.F. Receivers", Joseph Santangelo, W1NXY, QST, March
1948, volume XXXII, number 3.

Basically it was a superregen using a coaxial cavity to increase the Q.
Reported sizes were 7.5" x 2" for the outer conductor, 7.5" by 0.5"
for the inner. The author's version was silver plated, but he reported
that aluminum and copper had been used. He loaded it with a cap to get
the right frequency.

It didn't look too hard to build, but its going to have to grow for 6m.
You _ought_ to be able to do this with CATV hardline if you don't mind
lots of connectors at the bends or a really long, skinny radio. You
_may_ be able to get a decent Q just using some really efficient
flexible coax, coiled up. I'd even see if I could find some
semi-hardline that I could bend into a serpentine shape, were I playing
with this notion.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" was written for you.
See details at http://www.wescottdesign.com/actfes/actfes.html