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WL7M's questions re offset dish



Joe,
In answer to your posting:
The dish you see on my site is an offset dish (1.2m) by Channel Master. They
may make the Primestar units. I would guess that the Primestar is an offset
in any event. Most all of the DBS dishes were offset for the very reason you
mentioned. (Snow)
I did use the original struts on the dish. You will note that I marked the
focal point on the struts when the old 4Ghz horn was still on. When you get
ready to remove the old feed, take some good measurements from the top and
bottom of the dish to a point in the middle of the old feed so you know
precisely where the focal point is. Remember, this is not a prime focus dish
which is very easy to deal with. Not only is the location of the feed offset
from the middle, but there is an angle at which the new feed must look at
the dish, in my case 22.5 degrees. I mounted my dish upside down for two
reasons. #1 I wanted the face of the Patch feed pointing down so it did not
accumulate snow. #2 I used the original mount for the dish which could not
point at the horizon. Reversing the mount on the dish did the trick. It can
now be calibrated at 0 elevation and the working elevation is taken care of
by the 5500 rotor.
The only notes off caution I have about the 1.2m dish on the 5500 is that
the dish is heavy and MUST be counter-balanced and you should set your
parking positions on Nova, or whatever software you use, to tilt the dish so
it does not face the wind. The wind loading is significant on a dish of this
size and I do not think the 5500 would survive sustained high winds. For me,
so far so good. I have had 45 MPH gusts.  Another thing: If I had it to do
over again, I would have my mounting adapter made of aluminum not stainless
steel. SS weighs to much and is over-kill. When I made my mount I had to
much mounting pipe and the dish stood up above the rotor which turned out to
be BAD, in that I created a great lever which put way to much load on the
elevation rotor. I cut off 13" and snuggled the dish right down on the
rotors so that I reduced the loading and the amount of counter weight
needed. By the way, the picture shows the dish counter weight suspended
from the CW lever. DO NOT DO THIS. I soon learned that I had made a great
Grandfather Clock with a wonderful 10# pendulum. I now have the weight hose
clamped to the lever and now when the rotor says stop, I don't slap the
rotor teeth for a few seconds until the weight osculation runs down.
In closing I will tell you that perhaps I over illuminate the dish with the
patch, but I would not change a thing. I can hear the transponder come up
with it's noise floor measurable. That makes a qso a piece of cake. It
almost sounds like 20meters.
Good luck on your project.
Gunther Meisse
W8GSM
P.S. Have you thought about heating your dish? We do it in commercial
installations. It would keep it usable in bad weather, and reduce what could
be a nasty load on the rotors. Remember you can not park the dish horizontal
to avoid wind load, and not find yourself with a great snow catcher. PPS:
Drill a small hole in the low point of the dish for water to run out. 2-3
gallons of water screws up your center of balance and the 5500 will not be
able to lift it up. Don't do as I did and right the dish while standing in
front of it. I felt like the coach of a winning football team. Man did I get
wet!

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