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July 18th 03, 08:01 PM

(Michael Black) wrote in message ...
....

Take note that most superregens use the same active element as both
the RF oscillator and as the quench oscillator. Separating them,
has certain advantages in trying to get the best quench, and these
days it pretty much costs nothing to add the extra circuitry, unlike
in the 30s when the superregen was pretty hot.

....

First of all, many thanks, Michael, for quite a nice summary about
regen and superregen!

A distinction between regen and superregen is that in regen, the
feedback is kept (just) below the point of oscillation, and in a
superregen, it's above, but with quenching, so that the circuit
multiplies the energy in the tank when it's gated on by some factor
depending on the feedback and the time it's left on by the end of the
gating time. A jitter-free gating time and stable feedback should
result in a low output noise level.

I believe the quench frequency will limit how narrow the detector will
be, and if one uses a high Q tank (such as a crystal) with relatively
low feedback, that will limit the gain available. During the off
time, the tank energy must decay sufficiently to track the input
signal amplitude. Is there any value in having a short time just
after the "on" period when the tank is actively quenched?

An example of a commercial use of an externally-quenched superregen is
in a radar altimiter...I think it is/was something like APN-141. It
applied the gate just once per transmitted pulse, at a time which
locked to the return pulse, as I recall. I wish I could remember now
just how they tracked changes in the return time. I do recall that it
would scan over a range of delay times from very short to relatively
long, and could track from just a couple of meters up to at least a
few thousand meters. I also don't recall for sure, but suspect they
changed the gate duration depending on the delay time, since close-in
returns are much stronger than distant ones. Shorter gates mean less
gain. That's one way to control the gain of an externally-gated
superregen.

It should be possible to build a pretty accurate model of an
externally-gated superregen in SPICE...though to limit the time it
takes to run the simulation, it's probably useful to start with an
operating frequency not too far above the quench frequency, perhaps a
couple dozen times f(quench).

Cheers,
Tom

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