Polar Mount Tracking Angles

[Greg Mueller]

I was poking around today and ran across this handy chart. It gives the adjusted Elevation and Declination for your polar Prime Focus dish

 

[Anole]

thought that looked familiar

Yea, the Geo Orbit Org site is a real resource for such info!
I got quite an education reading what they have there.

 

[Greg Mueller]

I tried to use the supplied formula in a spreadsheet and couldn't get it to work
L=Latitude

ARCTAN((3964*SIN(L)/(22300+3964(1-COS(L)))))

 

[Greg Mueller]

I spent some time last night putting this data into a spreadsheet and it looks like there are some inconsistencies in it. I was trying to break it down to 1/10° increments. The inconsistencies are pretty small but could be a problem (or not). If anyone runs across another chart or formula could you please post it. I'd like to see it.

Thanks

PS
If anyone wants this Excel (type) spreadsheet let me know

 

[B.J.]

First of all, the equation mentioned above works, however if you use Excel, you have to convert the angles to radians for the trig functions to work, then when done, you have to re-convert them back to degrees. Also, there is a "*" missing after the 3964.

HOWEVER, that equation does NOT give the values in the chart posted above, but instead it gives the values in the previous chart at the geo-orbit web page.
Ie the above equation gives declination numbers based on a satellite to your south, and if you use those, you'll be off by about 0.6 degrees on sats near the east or west horizon, because the declination of those sats is less by that amount because they are further away.

The chart posted above, which is referred to as "modified" declination, gives the MUCH better calculation which is based on the declination of sats near the east or west horizon, and what you should do to make it accurate for sats to the south is to add about 0.6 degrees to your latitude setting (or subtract from your elevation). You'll notice, that this is what they've done in what they have incorrectly called the elevation angle. It's actually the latitude plus about 0.6 in most cases, and the actual elevation to be used is 90 minus this number.
They don't give that calculation because it is a bit more complicated.

I have a calculator that does an approximation of what's done in the "modified" chart, at :
BJDISCALC2

I've made some assumptions for simplicity, so it isn't exact, but it's pretty close.

You can do a "page source" to see the equations I used.

 

[Greg Mueller]

That's great!