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Originally Posted by wejones
Re the question of which is best, USALS or DiseqC 1.2 , I was curious just how accurately the rotation angle is calculated by the USALS receivers.
I decided to compare, for my location,
(1) the angle used by my Fortec Lifetime (ie in the USALS menu, it calculates the angle and displays it),
(2) the angle predicted by the http://www.gaaps.com.tw/ web page someone posted a while back.
(3) my own calculation of what I think it SHOULD be.
I first did a quick calculation based on the basic type of alignment, (ie rotation axis parallel to earth's axis... ie no 0.6 degree adjustment). I got 57.7 for G10r. I then looked at what the Lifetime receiver calculated. It was 57.1 . I then looked at what the GAAPS web page calculated, and it was 57.2 .
My problem is, that I can't figure out why there is a difference between what I did, and what the receiver is calculating. The only likely difference is if they were using the so called "Modified" declination angle, which I was NOT using. Calculation of the rotation angle is a bit more complicated using this assumption, so I didn't attempt it, however I really don't think this is the reason for the difference, because this small adjustment "should" have little effect on the USALS angle, but I may be wrong. ........ |
Well, I finally came back to this, and figured out the calculation using the modified declination angle. It turns out that this WAS the difference. When done this way, I got 57.16 in the above example, which corresponds to within roundoff error between the GAAPS web page and what my Lifetime receiver calculates.
Anyway, now that I know how they calculated it, I put the calculation on my little on-line TVRO calculator page, ie:
http://wejones.ftdata.com/bjdishcalc2.htm
it has also been included in the more complicated TVCALC program:
http://wejones.ftdata.com/tvcalc06.zip { EDIT: corrected error in this after post, current file time stamp= 10/29/06 11:56AM }
Anyway, I'm a bit surprised that the calculation in the Fortec program uses the modified declination angle, since it is a popular simplification to ignore this, as does the Sadoun instruction pages.