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Re: AIDC 3733 Picture of the Stub



What exactly is accomplished by doing this mod?  If it is after the amp,
will it really affect the noise figure very much?  If it just increases the
gain why would one want to do this?  There is plenty of RF coming out of the
unit already.  Am I missing something?

Thanks and 73,
Joe
ka0yos@amsat.org

----- Original Message -----
From: <BobsImsai8800@aol.com>
To: <hammond@surrealnet.net>
Cc: <amsat-bb@AMSAT.Org>
Sent: Saturday, April 07, 2001 1:12 PM
Subject: [amsat-bb] AIDC 3733 Picture of the Stub


Mark,

I posted a message on the BB on 4/3, here is an excerpt:


2. Notch in response at 2400 -- there is a 5-8 dB notch in response at 2400
MHZ or so on some of the converters. The little piece of rigid coax that is
on the output of the preamp section (before it goes to the second comb
filter) appears to be the culprit. It connects near the rear comb filter and
runs up above the circuit board to near the front comb filter. It appears to
be a 2.4 GHZ stub. I cut one at the connection to the preamp output, and the
gain is now flat across the range.

THE CUT IS MADE ON THE CENTER CONDUCTOR OF THAT COAX.

I have a picture of this part of the downconverter on an Ebay auction.  To
view it, go to ebay.com, search for auction number 1227956478.  It is the
upper right picture, click on it to make it larger.  The left side of the
stub (shorted end) can be seen sticking up at the bottom by the open front
end filter (left part of the picture) and the connection that needs to be
cut
is connected near the little green thing on the output side (right part of
the picture) of the preamp where it connects into the second filter.

I hope the picture and description helps.

Bob Seydler
K5GNA
k5gna@aol.com
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