Offset dish, what angle is it actually looking at - Technical

sat12345 · 05-03-2007, 16:19

Just wondered out of interest if somebody could tell me either rough angle size on horizon size as to where the actual sat are compared to where the dish looks straight if that makes sense?

rai uno · 05-03-2007, 16:24

Not really!

The offset angle is a design feature of each and every Dish (ie It varies). Generally about 22 to 25 Degrees.

That is why, bearing in mind most worthwhile Sats are within a few degrees of 25 deg Elevation in the UK, the Dish itself seems more or less Vertical ie Zero degrees.

In case I've misunderstood your question, here is an explanation which should cover it:

http://www.satsig.net/22-deg-offset-dish.htm

sat12345 · 05-03-2007, 16:31

Not sure lol, basically If I was behind the dish (at 1w) and could see 22,000miles i.e. the sat in space where compared to the dish would it be in the sky?

rai uno · 05-03-2007, 16:34

As I say, upwards at a few Degrees either side of about 25 deg. You know what it is for Thor as you have just set the Dish up on it!

Peak Elevation occurs for your South Satellite. As you go East or West, the Elevation drops away until you can't see any more Satellites as they are over the Horizon.

Just watch watch happens as you pan your Dish from Thor to Turksat.

sat12345 · 05-03-2007, 16:34

Think I've found my answer it says:

''If you put your eye behind the lower rim of the dish and look forwards just over the top of the feed horn you will be looking approximately directly towards the satellite.''

rai uno · 05-03-2007, 16:36

That's true - It's simple optics.

Angle of reflection = Angle of incidence (All that stuff!)

sat12345 · 05-03-2007, 16:38

Quote:

Originally Posted by rai uno

That's true - It's simple optics.

Angle of reflection = Angle of incidence (All that stuff!)

Cheers again rai much appreciated.

JamesE · 05-03-2007, 20:54

This is how it works:
http://img211.imageshack.us/img211/4435/graphqm6.jpg

Sam Radford. · 06-03-2007, 14:00

I like the movie at the bottom of this page:
http://www.satcure.co.uk/audio.htm

05-03-2007, 16:19	#1
sat12345 Forum Member Join Date: Nov 2006 Services: 40e - 61w Posts: 919	Offset dish, what angle is it actually looking at Just wondered out of interest if somebody could tell me either rough angle size on horizon size as to where the actual sat are compared to where the dish looks straight if that makes sense?

05-03-2007, 16:24	#2
rai uno Inactive Member Join Date: Apr 2006 Location: Tremp (Catalunya) Services: Variety of Motorised and Fixed Non-Sky Satellite Systems Posts: 20,830	Not really! The offset angle is a design feature of each and every Dish (ie It varies). Generally about 22 to 25 Degrees. That is why, bearing in mind most worthwhile Sats are within a few degrees of 25 deg Elevation in the UK, the Dish itself seems more or less Vertical ie Zero degrees. In case I've misunderstood your question, here is an explanation which should cover it: http://www.satsig.net/22-deg-offset-dish.htm Last edited by rai uno : 05-03-2007 at 16:28.

05-03-2007, 16:34	#4
rai uno Inactive Member Join Date: Apr 2006 Location: Tremp (Catalunya) Services: Variety of Motorised and Fixed Non-Sky Satellite Systems Posts: 20,830	As I say, upwards at a few Degrees either side of about 25 deg. You know what it is for Thor as you have just set the Dish up on it! Peak Elevation occurs for your South Satellite. As you go East or West, the Elevation drops away until you can't see any more Satellites as they are over the Horizon. Just watch watch happens as you pan your Dish from Thor to Turksat. Last edited by rai uno : 05-03-2007 at 16:35.

05-03-2007, 16:31	#3
sat12345 Forum Member Join Date: Nov 2006 Services: 40e - 61w Posts: 919	Not sure lol, basically If I was behind the dish (at 1w) and could see 22,000miles i.e. the sat in space where compared to the dish would it be in the sky?

05-03-2007, 16:36	#6
rai uno Inactive Member Join Date: Apr 2006 Location: Tremp (Catalunya) Services: Variety of Motorised and Fixed Non-Sky Satellite Systems Posts: 20,830	That's true - It's simple optics. Angle of reflection = Angle of incidence (All that stuff!)

05-03-2007, 20:54	#8
JamesE Forum Member Join Date: Dec 2002 Location: Hibaldstow, N. Lincolnshire Services: BTbroadband,DTT,fta & ftv satellite,Digitalb. Posts: 5,303	This is how it works: http://img211.imageshack.us/img211/4435/graphqm6.jpg

06-03-2007, 14:00	#9
Sam Radford. Forum Member Join Date: Jan 2003 Location: N Yorks Services: Apple Mac, wheelchair & pacemaker. Thanked 354,768 times Posts: 13,713	I like the movie at the bottom of this page: http://www.satcure.co.uk/audio.htm