Re: ATM Alt-alt telescope mount - and image rotation

[Bruce Schupler <schupler3@comcast.net>]

>From your description, it sounds to me like your alt-alt mount is what is
called "an XY mount with the fixed axis North/South" in the satellite
tracking community.  These used to be fairly common and provided excellent
coverage except for 2 keyholes located low in elevation in the North and
South.  The oddest thing about these mounts is the rotation of the antenna
(or telescope if you will) as the mount moves in azimuth.  If you are high
enough in elevation to be above the keyholes, the antenna will rotate around
its own central axis as the X and Y axes are driven to do a constant azimuth
scan (ie, if a point on the edge of the antenna is down when the antenna is
pointed South, it will be horizontal when pointed East, up when pointed
North, and horizontal on the other side when pointed West).

Bruce Schupler