As a followup to the last post, this post deals with the FC90P dish.
I've been concerned about the dish angle scales on both the "U" version and "P" versions of these dishes, because
Sadoun seems to include the same bracket with all dishes despite the fact that the different dishes have different offset angles. In fact, my FC90P came with a parts box apparently intended for an FC80 dish (the instruction sheet actuall said FC80, and no parts other than the dish and lnbf arm looked like what I had), which has a different offset angle than the FC90. So I did an experiment to measure the dish elevation reading when the dish was vertical (ie apparent aim of zero, which should give an elevation reading equal to the dishes offset angle). Well the results seemed to indicate that when vertical, the elevation scale would read approximately 23.5, which is closer to the 22.75 spec for the FC80 than the 24.62 spec for the FC90. Either that or they have a generic scale in between the two. But this would be responsible for some error in setting the dish elevation. I suspect that there is even more error when using the "U" version mount, but I don't have that one to test.
I then decided to try to estimate the actual offset angle of the dish, and also try to verify the focal point. To do this, I needed to measure both the actual aim of the dish and the apparent aim of the dish. To do this, I decided to aim the dish at the sun. I was able to measure the actual elevation of the sun by watching the shadow of a yard stick aimed at the sun, and I had an inclinometer resting on the yard stick.
Determination of when the dish was aimed at the sun was more difficult, however I decided to use 5 little stick on mirrors, which would reflect the sun to the lnbf. I decided to use a fake lnbf so as not to hurt my real lnbf. See one of the stick on mirrors, ie the little diamond shape thing in the picture:
Also see that I've positioned them up,down,righ,left,center, and installed a fake wood lnbf:
When aimed at the sun, I got the following results:
As you notice, there is a slight problem, in that all the spots don't focus at the same point. I managed to find a better focal point, where 4 of the 5 spots focused at one point, but that was about an inch above the actual LNBF position, and would require bending the lnbf arm, which I didn't want to do at this point.
However, using this focal point, I measured the apparent aim of the dish with an inclinometer at the center of the dish, and obtained an approximate offset angle of 25 degrees, which is pretty close to the published spec of 24.62.
Anyway, I'm not sure what good all this will be, but I think it will help give some confidence to initial angles that the dish and motor are set to. However it does introduce some doubt with respect to just how good the surface of these dishes really are.
Some of the discrepancy may possibly be due to the fact that my little mirrors are about 1/8" thick, and so the reflected surface is 1/8" above the actual surface of the dish. I may try to see if I can repeat the test with something thinner, like aluminum foil or something. I also had not yet tightened down all the bolts on the dish mount, so it's possible that the dish might flex a bit after tightening the bolts.
But anyway, I thought the experiments were interesting.