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Wow! Kuhne preamp

Wow, what a difference a better preamp makes!  Keeping everything
else constant, I swapped out the Confier preamp for a Kuhne
MKU 232 A2 TM unit.  The test sheet that came with it shows a noise
figure of .65db, and a gain of 40db; significantly better than the
Confier.  With a squint angle exceeding 33 degrees, and shooting
through several trees, I can still copy the beacon and some faint SSB
QSOs.  They are about as strong as I remember the signals with the
very first setup, under much much better conditions.  It also seems
that I can decode telemetry better with signals that are close to the
noise level, than before.  Before, shooting through those trees would
net absolutely nothing.

I haven't tried transmitting yet, as I am concerned about the
proximity of the 70cm uplink antenna.  The Kuhne is rated to only 1mw
of RF on the front end, and there have been reports that this is easy
to blow.  The plan here is to modify the feed antenna to reject 70cm,
through some sort of stub.  I've had one suggestion to put a 3/4 wave
(at 70cm) open stub at the input to the preamp, but I also remember
seeing a helix design that had a built-in trap of sorts as part of the
matching section.  If anyone remembers where that website is, please
let me know.  I remember that it had a brass strip that was grounded
on one end, with the helix and feed tied to it in certain spots.

I still need to work on the weather proofing (the weather enclosure
only works when upright), and with a 3 turn helix, I now calculate
that I'm over-illuminating the antenna, so that can be improved.

If you want to see what I did, I put a few pictures at the bottom of:


Greg  KO6TH

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