[amsat-bb] Center of the rotator

[Mark D. Johns]

For satellites, there's no perfect direction for the azimuth stop,
because most LEOs in near-polar orbits tend to pass along an arc to
the east or or an arc to the west, and only relatively rarely right
overhead.

For me, living in Minneapolis, I use a north stop because a lot of
things happen south of me. For example, passes of CAS-4A and CAS-4B
almost always go from west-southwest, through south, and on to the
southeast from my QTH. A south stop would require a flip or a complete
turn for every CAS-4x pass.

For you, down in Florida, a 180 degree stop may be of slight
advantage. You'd probably have to do a plot of several birds you plan
to use over a period of a couple weeks, and see how many of those
passes would require flipping.
--
Mark D. Johns, KØJM
AMSAT Ambassador & News Service Editor
Brooklyn Park, MN USA   EN35hd
-----------------------------------------------
"Heaven goes by favor; if it went by merit,
   you would stay out and your dog would go in."
    ---Mark Twain

On Fri, Mar 6, 2020 at 11:50 AM Thomas Schaefer via AMSAT-BB
<amsat-bb at amsat.org> wrote:
>
> Hello all. Please forgive the novice question but I am new to dealing with Az/El rotator systems for satellites (always been the Armstrong method).
>
> I am finishing up the planning for my rotators. On my bench, I have my Az rotator and my elevations rotator (separate units —both AlfaSpids). I am using a Green Heron RT21 AzEl controller.
>
> I have PSTRotator in between SatPC32 and the Green Heron since SatPC32 does not control the GH AzEl directly.
>
> When I was testing, I went though a pass and when the Azimuth direction was 0, the rotator spun all away around since 0 was the bottom. That is no doubt a configuration point but it brings me to my question.
>
> When I have used various rotor controllers for HF beams, 180 degrees is always the bottom which works for us in the northern Hemisphere. But with the current fleet of workable satellites, is there a direction that makes more sense to use at the “bottom” of the rotator? I can rotate the AlfaSpid more than 360 degrees allowing for the coax loop. Is that the generally preferred way for maximum flexibility if one’s rotor supports it? Put another way, if I pick 180 as the “bottom”, will I have as many passes that the rotator will have to turn all the way around to get from 179 degrees to 181 degrees as I would have to go from 359 degrees to 1 degree?
>
> I am also using the Az rotator for a 6m beam so the usual sweep of 180 to 180 in a continuous arc is desirable but I was curious if I should allow an extra 90 degrees (to 470) for flexibility. The Green Heron will take care of not going too far from where it is programmed even though the AlfaSpid does not have limit switches in the Az rotator (but does in the elevation rotator).
>
> I hope that makes sense.
>
> Thanks,
>
> Tom NY4I
> Tom Schaefer, NY4I
> Blog: www.ny4i.com
> Madeira Beach, FL (Grid: EL87ot)
>
>
>
>
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