Re: [amsat-bb] Poor man's AO-40 Portable Rotor

[Bob Bruninga <bruninga@xxxxxxxx>]

On Tue, 13 Jan 2004, Bill Acito W1PA wrote:

> Should I point the axis of the rotor at the North Star, or should I key off
> the max elevation of the pass (tilt the base of the rotor to max elevation)?
> My latitude is 42.3 deg., but Nova says I get a 54 deg. elevation.

The tilt of the pole should always point to the north star to counteract
the rotatiuon of the Earth..  Then angle
how you mount the antenna to the rotator's pole down by the 0 to -5
degs depending on your latitude (I think its about -5 for say a
latitude of 40 deg) to compensate for the locaiton of the GEO ARC.

Then angle it UP by the latitude that your tracking program shows the
subsatellite point latitude.  These days it is from 5 to 10 degrees during
a pass.  Notice that this is in the opposite direction.  Meaning the -5
and +5 cancel.  Thus you only have to adjust the angle of the antenna to
its rotating pole by 0 to 5 degrees during the pass.  If the beamwidth of
your dish is 5 degrees or more, then just bolt it half way in between.

If not, you may have to adjust the elevation +/- 2 degrees during a 8 hour
long pass...

I think I got that all right, I just looked at INstantrack and that is
what appears to be going on now...

> Or is it both? Rotor axis towards the North Star, but while pointed due
> south, rotate the cross bar up slightly to the 54 deg point? How will that
> look at the E-W horizons? The crossing points on the E-W horizon for my
> location are at 85 deg and 275 deg.

Yes, when AO-40 is close in and near perogee, then angles start changing
real fast. But the other 90% of the time the one rotator system is
perfect.  More or less.

DISCLAIMER:  Of course, if you want to invest $1000 or more, then you can
go with the AZ/EL approach..

de WB4APR, Bob

> > Yes, just tilt the rotator pipe to point to the North Star and you got
> > it.  This is the low budget way to follow AO-40 with one motor just like
> > any Satellite TV dish since AO-40's track across the sky is always within
> > about 10 deg of the geostationary satellite arc and only changes very
> > slowly... see
> >
> > http://www.ew.usna.edu/~bruninga/ao40ant.html
> >
> > de WB4APR@amsat.org, Bob
> >
> >
>

de WB4APR@amsat.org, Bob

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