Aligning with Polaris

[Vorg]

I tried to reply to a related thread, but it was too old.

I have been digging around about using polaris to align the rotor. I googled polar scopes and found they start at $35 which is a bit much for me for something only used once. So I've been thinking about making one .

My idea was to use a foot long tube with a pin hole (1/16" or 1/32"?) at the eye end and mount a ring centered in the other end. an dthen use StarCalc find where on the ring it is when using it. From what I have found, Polaris is .75 degrees from true north. Working it out on my cad program It seems at 2' the ring would only be 5/8" dia.. Is that correct?

When I set this up the first time a couple years ago, I read the pole needs to be within .5 degrees vertical, so I got a "Dasco Pro" angle finder. But the scale is so small it's not likely it's that close. So I'm thinking of making a plumb bob with a ~2' pendulum. I didn't realize how fine the scale needs to be. No wonder I had so much trouble using the stamped steel scale. That brings me to another problem I ran into.

The dish is supposed to be a 30" Wineguard. I got it on ebay with the rotor, a DMS SG2100. The dish says nothing on it about who made it, so I don't know if it's real or knock off. I think the dish was dropped in shipping and the rolled flange was bent. I put put the dish on the floor and rotated it and it seemed to touch all the way around. So the dish shape was not damaged, but after having a lot of problems aligning it, I emailed wineguard and got the measurements to the lnb made a cardboard triangle. I found the lnb was off center down. I added 2 support rods and tried to align it back up, but forgot to check side to side. Latter checked and it is off also. Given how close the poll and motor needs to be, I'm wondering how close the lnb needs to be.


Any thoughts?

 

[turbosat]

I just use a level for checking the pole, hold it on 4 sides to be sure, that's always been good enough to work. Far as aligning the motor/dish , there's several threads here of how to do that. I just use a compass to find the south, and eyeball the dish/motor on the pole to that direction. Fine tuning the east/west adjustment comes once I find a signal to start tuning by.

 

[Vorg]

I went the compass route before. I'd like to avoid all that swinging back and forth peaking. Get the motor done right and then just adjust the dish to the motor shaft.

btw, the lng is one of those Invacom circular/linear lnbs.

 

[Vorg]

I found the following in another post and it seems to be saying that aligning to the polar axis is wrong. And the last part, tipping the mast forward should be the same dropping the motor shaft angle.

What the consumer satellite industry uses to track satellites in the geosynchronous, Clarke Belt is called a modified polar mount. If you mount a dish on a polar mount set to exactly the latitude but with no declination angle, it will sweep out a plane parallel with the equatorial plane but not intersecting it. If you tilt the mast forward, it will intersect the equatorial plane in a straight line.

If you set a polar mount axis to exactly the elevation angle and introduce a declination angle equal to the declination angle of the southernmost satellite, the dish will sweep a cone that intersects the equatorial plane in a perfect circle that intercepts the Clarke Belt just to the due south, but it tracks "inside" of that belt, which is also a circle, over the rest of its travel.

If you set a polar mount axis to exactly the elevation angle, but then set the declination angle equal to the declination angle of the satellite lowest on the horizon, it will sweep a cone that intersects the equatorial plane in a perfect circle that intersects the Clark Belt at the lower ends of the arc only, but tracks slightly above the Clarke Belt between those horizons.

And finally if you then tilt the mast forward by a fraction of a degree, it will track an ellipse that intersects with the Clarke Belt arc at both the southern and horizon azimuths and misses the arc by less than one tenth of a degree elsewhere. That is the track of the so-called modified polar mount.