Question on skew

[Mr Tony]

OK this didnt dawn on me until today when answering someone elses question

I know the farther away from the true south LNB you need to skew the LNB more but this is weird. Helping someone get Hispasat and he said his skew was -58. He was in Tampa. I checked what the skew was for it here in MN and its only -40

That makes no sence as Tampa is closer to 30W than MN is

So I picked a couple cities near the same longitude. Picked Minneapolis (93.5W) and Houston (95.4) and KC (94.6) and selected G10

skew for Houston... +39
skew for KC... +30.3
skew for Mpls...26.4

so now I'm confused as hell on why the farther south you go you need to skew the LNB more.

 

[Hermitman]

Simple geometry

Skew = -arctan(sin(your long - sat long) / tan(lat))

The further south you go, the latitude number gets smaller. Inserted into the formula, as the latitude number gets smaller, the tangent of the latitude get smaller. A smaller number divided into another number results in an answer with a larger number (more skew the further south you go).

Or maybe you want to visualize it. If you stand at the equator (facing south) and look straight up at a satellite at your same longitude, the vertical polarity will look straight up-and-down. If you are at 45 degrees latitude and look at a satellite at your same longitude, the vertical polarity will also look straight up-and-down. Now if you're back at the equator and look at a satellite that's straight off your right shoulder, the vertical polarity will now appear to be horizontal, like it's laying flat. But if you go to 45 degrees latitude and look at that same satellite, the vertical polarity will appear somewhere between vertical and horizontal (less that at the equator) because the angle you're now viewing the satellite is from a different perspective, a perspective that will never have a geo-stationary satellite located off your right shoulder (because the orbital arc is south of your location) and thus all angles at 45 degrees latitude will be less than angles further south.

Hope this helps. Good luck and have fun.

 

[Sadoun]

Hermitman, good explanation.

Skew depends not only on Longitude, but also Latitude.

 

[Mr Tony]

Simple geometry

Skew = -arctan(sin(your long - sat long) / tan(lat))

The further south you go, the latitude number gets smaller. Inserted into the formula, as the latitude number gets smaller, the tangent of the latitude get smaller. A smaller number divided into another number results in an answer with a larger number (more skew the further south you go).

OK. Thansk for the explanation. The rest I was confused as heck but I figured it had something to do with the farther north you went the less skew you need