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Re: patch help



If you have a signal source and a watt meter there are two advjustments you 
can do.

First is circularity  What you are looking for is a "W" shaped dip in SWR 
(or reflected power)  If the SWR goes down a little, say at 2390 MHz and at 
2410 MHz (lets say 1.05:1 to 1.2:1 at 2401 and back to 1.05:1) then your 
circularity is adjusted properly.  Don't get the dip too small or too large. 
  Ideally the "W" shaped dip should just be measurable as a slight increase 
in SWR at 2401 with smaller swr's +/- 5 to 10 MHz.  This screw is the one 
that is present on the W0LMD patch

The other adjustment (the one I told you to add) is the "Center frequency" 
adjustment.  Adjust this for best SWR at 2401.  Recheck the "W" dip 
described above.  Go back and forth between these adjustments a couple of 
times.

If you are going to mount the feed in the exact phase center of the dish, 
you can tune the unit off the dish.  When you hit the exact center, the SWR 
will be exactly the same as on the bench.  This is a good secondary check of 
phase center placement.

If you are going to offset mount the feed (like next to a C-band feed, or 
like in Clair Cessna's QST article) then adjust the patch off the dish first 
and then readjust the SWR screw when the feed is in place in it's off center 
location.  The "W" dip should not move much, but you should probably recheck 
it just to make sure.

Fred W0FMS





>From: "James Murray" <w4lwt@knology.net>
>To: "Amsat" <amsat-bb@AMSAT.Org>
>Subject: [amsat-bb] patch help
>Date: Wed, 30 Jul 2003 07:40:35 -0400
>
>Have built a patch designed by W0LMD using modifications by W0FMS. It 
>works.
>Looking for suggestions about tunning it. have only limited test gear.
>Signal source, watt meter, and S-meter. any help appreciated.
>
>Jim
>http://www.knology.net/~w4lwt
>
>----
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