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# Re: FW: Elevation rotor question

• Subject: Re: [amsat-bb] FW: Elevation rotor question
• From: Jim Walls <k6ccc@xxxxxxxxxxxxx>
• Date: Mon, 23 May 2005 08:49:49 -0700
• User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.4) Gecko/20030624 Netscape/7.1 (ax)

```Jose M. Valdes R. YV5LIX wrote:

> I purchased an elevation rotor for my SAT antennas system, the unit is a
> Kenpro KR-500 and I have a question.
>
> I was under the impression that an elevation rotor for satellite/EME work
> should have a 90 degrees elevation movement, with 0 degrees over the horizon
> (horizontal position) and 90 degrees at the zenith, but this unit is some
> what different, it has 0 degrees at the center of the meter's scale with 90
> degrees at each side of the scale, also it reads DOWN at the left and UP at
> the right of the scale, and has a 180 degrees movement.
>
> Is there any special reason why in this unit horizontal (0 degrees) is at
> the center of the scale?

I don't recall that mine is that way...

> If I'm tracking a bird I will star at the horizon and will go up until
> maximum elevation to them start going down until it is gone, so that will
> give me, in the best case of a bird passing over my zenith, a 90 degrees
> elevation, so
>
> Why 180 degrees movement (horizon/zenith/horizon)?

There are two answers to that.  One is that on an overhead pass, you can
just keep elevating the rotor past vertical to continue tracking.  Since
you will almost never have a directly overhead pass, this is sort of a
non-issue.  The second reason is that it can eliminate the problem of
getting to the end of rotation on your azimuth rotor.  Let me explain
that one a little.  Assume for the moment that your azimuth rotor will
rotate from 0 - 360 degrees (as opposed to 180 - 180).  You have a pass
wherein AOS will be at 20 degrees, and then the satellite will pass
north and west of you and have an  LOS of 230 degrees.  The maximum
elevation for this pass will be 35 degrees.  If you start the pass with
your antennas pointed at the satellite and continue tracking it, you
will shortly get to 0 degrees azimuth and the end of rotation on your
rotors.  You will then have to rotate your antennas all the way around
to resume tracking.  During that time, you can't use the satellite -
VERY annoying.  On the other hand, if you start with the azimuth rotor
pointed at 200 degrees and the elevation at 180 degrees, the antenna
will actually be pointed right at the AOS, but with the antenna upside
down.  As the satellite rises above the horizon, you move it "down"
which will really be up since it's upside down to track the satellite.
You no longer have a blockage on your azimuth rotor.  This takes a
little thinking to keep it right if you are tracking manually, but most
of the computer tracking progams will do this automatically

--
73
-------------------------------------
Jim Walls - K6CCC
k6ccc@amsat.org
Ofc:  818-548-4804