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Re: RE: Calibration of AZ-EL

Ed has a really good point about the sun shadow of the feed on your dish.  Particularly for prime-focus-fed dishes, this aligns the entire system at once (feed to dish and dish to az/el).
Your uplink antenna *shouldn't* be as critical, since the beamwidths involved are ?Likely? much larger.  Or you run milliwatts :-)
Local noon also works best because the sun's relative motion in the sky is a minimum (i.e., the first derivative of the sine wave is a minimum).
Of course, this is all quite a bit trickier if your rotator is made by the ArmStrong company (like mine).  It would be nice to get the sun to stay still for about 30min (hey, that could be a SciFi story!).  Also, I am doomed to continuous compass-and-inclinometer work.  I'm getting pretty good at eyeballing azimuth now :-)

> From: "Edward R. Cole" <al7eb@ptialaska.net>
> Date: 2002/12/11 Wed AM 02:56:38 EST
> To: <amsat-bb@AMSAT.Org>
> Subject: RE: [amsat-bb] Calibration of AZ-EL
> >Subject: [amsat-bb] Calibration of AZ-EL
> >How are most of you calibrating your Az/El? With a compass and level? I
> >have heard of putting a solar cell at the end of a 2 or 3 foot tube
> >mounted to the boom, then aligning for peak voltage when facing the sun.
> >Once this is done, the local time and position are entered into a
> >computer program. This sounds like a good method to me. Any others? Ben
> >K9BF
> A lot of solutions given so far.
> But the easiest is to point your dish at the sun so that the feed casts a
> shadow in the center of the dish.  It is now pointed very close to the
> sun's position. If you are using an offset feed dish then the shadow falls
> at the center of the lower dish edge when properly pointed.
> Now point the dish at the az and el given for the sun by your tracking
> program.  If it is not still pointing right at the sun, adjust the dish and
> rotator until it is.  I usually like to do this a few hours within local
> noon so the sun is fairly high in the sky.
> Now this assumes that your feed is properly positioned on your dish for
> proper focus and centering...if not then the RF radiation peak will be
> offset.  You can test that by observing for sun noise on 2.4 GHz.  You
> should see about 1/2 to 1 S-unit rise in the noise floor when pointing at
> the sun versus pointing away from the sun at cold sky.  Be sure that the
> sun is far above the horizon for this.  Near the horizon you will see the
> noise floor come up and mask the sun's noise.  On my dish that occurs below
> 10-degrees elevation.
> Pointing the UHF beam is pretty much lining it up with the dish.  You might
> be able to look at the antennas shadow on the ground if the sun is bright.
> This is much easier than using a compass or levels.  No fancy photo tracker
> needed.
> Ed - AL7EB
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