

Re: FW: Elevation rotor question

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

Jim Walls - K6CCC
Ofc:  818-548-4804
AMSAT Member 32537 - WSWSS Member 395