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<blockquote data-quote="futumsch" data-source="post: 653685" data-attributes="member: 321089">Excuse me for bringing the science back into the subject, but I've been scratching my head over this since your post <a href="http://www.satellites.co.uk/satellite/dish-setup-single-sat-multi-sat-motorised-systems/153494-some-declination-angle-confusion.html" target="_blank">http://www.satellites.co.uk/satellite/dish-setup-single-sat-multi-sat-motorised-systems/153494-some-declination-angle-confusion.html</a> Huevos.Similar to what you said, at mid latitudes, you're not at the centre of the geo-orbit, and you're not on the same orbital 'plane' either. It's hard to visualise in 3D, but if your motor axis is parallel to the Earths axis, then you will be looking 'under' the arc. In a 2 dimensional point of view, with the geo-orbit drawn out as a circle, and a slightly smaller circle placed inside to one side, there is increasing difference in size further from that side where they touch, which would be your due south. But if you tilt the smaller circle upward in the middle, representing the motor axis tilted due south slightly', looking from above it becomes more elliptical and there is less error between the circles.I've got my 1metre set up with the 'traditional' elevation/declination values, and I get satellites from 0 south to 35 east no problem. I could see the modified polar angles becoming more important at larger (&gt;2.5m) dish sizes where the beamwidth becomes smaller. I'm no Scientist, but i do ike my engineering to be correct. When i first got a motorised dish, I was puzzled why there was no elevation control and then I learned about declination. I'm normally playing with Az-El mount 6.5m and 9.3m dishes for my day job, and motorized DBS dishes is a slightly different ball game. Hope you like my diagrams.</blockquote>

[QUOTE="futumsch, post: 653685, member: 321089"] Excuse me for bringing the science back into the subject, but I've been scratching my head over this since your post [URL="http://www.satellites.co.uk/satellite/dish-setup-single-sat-multi-sat-motorised-systems/153494-some-declination-angle-confusion.html"]http://www.satellites.co.uk/satellite/dish-setup-single-sat-multi-sat-motorised-systems/153494-some-declination-angle-confusion.html[/URL] Huevos. Similar to what you said, at mid latitudes, you're not at the centre of the geo-orbit, and you're not on the same orbital 'plane' either. It's hard to visualise in 3D, but if your motor axis is parallel to the Earths axis, then you will be looking 'under' the arc. In a 2 dimensional point of view, with the geo-orbit drawn out as a circle, and a slightly smaller circle placed inside to one side, there is increasing difference in size further from that side where they touch, which would be your due south. But if you tilt the smaller circle upward in the middle, representing the motor axis tilted due south slightly', looking from above it becomes more elliptical and there is less error between the circles. I've got my 1metre set up with the 'traditional' elevation/declination values, and I get satellites from 0 south to 35 east no problem. I could see the modified polar angles becoming more important at larger (>2.5m) dish sizes where the beamwidth becomes smaller. I'm no Scientist, but i do ike my engineering to be correct. When i first got a motorised dish, I was puzzled why there was no elevation control and then I learned about declination. I'm normally playing with Az-El mount 6.5m and 9.3m dishes for my day job, and motorized DBS dishes is a slightly different ball game. Hope you like my diagrams. [/QUOTE]

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