On Apr 15, 8:08�am, "
wrote:
On Apr 14, 11:46 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

IIRC N1TEV's design used a sine wave waveform in the quench
oscillator. �As such the receiver is slope controlled, in which case
the bandwidth depends upon the rate of change of the admittance across
the tuned circuit as it goes into an oscillation condition, and not
the Q of the resonant circuit.

The standard reference is "Super-Regenerative Receivers", by J.R.
Whitehead, Cambridge University Press, 1950.

73 John �KC0G-

I meant to say "conductance" not "admittance"

Tim, Tom, Jimmie, John, thanks you all! This thing might work, There's
no way around the need to get my feet wet and build/find some cavity.

Filippo N1JPR

On Apr 16, 8:42*am, spamhog wrote:
Tim, Tom, Jimmie, John, thanks you all! This thing might work, There's
no way around the need to get my feet wet and build/find some cavity.

Filippo N1JPR

Further to my comment about how big a coaxial resonator must be to get
high Q: to get Qu of 1000 at 50MHz will require an air-dielectric
line almost 1.5 inches OD. A quarter wavelength is about 60 inches;
you can shorten that some by loading the open end with capacitance,
but expect it will be at least half that long. Compare that with a
coil of 8 turns of #10 AWG copper wire 1.25 inches ID, spaced 2 wire
diameters center-to-center (less than 2 inches total length) that will
also give you a Qu over 1000.

I think if I had an overwhelming urge to try a design using a cavity
(or coaxial cavity) resonator, I'd do it at about 1GHz, or maybe even
500MHz, where I can make a resonator with high Qu in a practical size,
and where I can't wind a coil that's big enough to get really high Q
and also have a high self resonant frequency. For example, at 1GHz, a
quarter wave air dielectric cavity will be about 3 inches long, and if
I make it from "3/4-inch" copper pipe (properly cleaned), I can get Qu
well over 2000; it will be very tough to make a coil that has a self-
resonance above 1GHz that has a Qu even close to 1000 (short of using
superconducting wire!).

There are very practical reasons that you don't see cavity resonators
at low frequencies: you can do better with smaller, cheaper parts.

Cheers,
Tom