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Need Pictures of Proper Polarization

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Ex Member
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Jan 29th, 2007 at 11:41am  
My Pol is to be set at +6

I am shooting at AM1 at 40E from Kirkuk Iraq.

When my feed cone is straight up in the center, am I at zero or 90 degrees?

If someone could post or email me pictures of proper polarization techniques I would appreciate it.
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Eric Johnston
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Reply #1 - Jan 29th, 2007 at 2:32pm  
Ask your service provider what is the downlink nominal polarisation called.

If it is called horizontal, then the polarisation angle starting position is with the broad flat sides of the LNB waveguide on either side.  The half diplole pin inside the LNB waveguide will be horizontal.  It does not matter on which side it is.
...

The second step is then to adjust the polarisation +6 deg clockwise (for a positive adjustment), while facing towards the satellite.  The satellite is a little to the right of due south.

ref: http://www.satsig.net/maps/satellite-dish-pointing-iraq.htm

On the other hand if you are told that you are to receive nominal vertical polarisation, then start with the LNB waveguide with its broad faces on top and underneath.

wxw
Best regards, Eric.
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Ex Member
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Reply #2 - Jan 30th, 2007 at 12:39am  
Quote:
My Pol is to be set at +6 ...When my feed cone is straight up in the center, am I at zero or 90 degrees?

The +6 POL represents an angle that is rotated around a horizontal plane. Some providers call it SKEW.

Pointing your "feed cone" straight up is unrelated to POL. Movement through the diagonal plane from horizon to zenith is called ELEVATION. Straight out is pointing at the horizon (zero degrees of elevation), straight up is pointing at zenith (90 degrees of elevation)

The third angle is AZIMUTH. It's basically an adjusted compass heading that's related to how far left or right of due south (from Iraq) you swing the dish to get in line with the satellite.

Unfortunately, none of this answers your POL question - I was just trying to clear up some of the geometry involved with dish pointing. For that, it would really help to know the manufacturer and model number of the dish. That way advice can be tailored to your specific hardware.

//greg//
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Reply #3 - Jan 30th, 2007 at 7:12am  
OK....so what if my "downlink nominal polarisation" is vertical? DO I start with the LNB to the left/counter clockwise side then go up 6degrees for +6?
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Eric Johnston
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Reply #4 - Jan 30th, 2007 at 8:24am  
If your nominal polarisation is vertical the starting position for the polarisation setting is with the broad faces of the LNB waveguide on top and underneath, like so:
....
If you completely rotate the feed assembly all the way round (if that is possible) then there are two opposite positions when you achieve vertical polarisation.
See here two examples of vertical polarisation
...
Look at the tiny squares showing the LNB waveguide flanges and you will see the wide faces of the LNB waveguide on top and underneath - this is vertical polarisation.   An alternative vertical polarisation angle start position is with the LNB on the opposite side.  It does not matter whether the pin in the LNB waveguide is at the top or the bottom broad face.

Sometimes, if you have a large polarisation angle adjustment to make (like 75 deg) it is necessary to choose the best starting position, as from one of the start positions it may not be possible to reach the final required angle because the LNB or BUC hits the metal arm or support yoke.

In your case, step 2 is to make a polarisation setting adjustment of +6 degrees.  While facing towards the satellite rotate the entire feed 6 deg clockwise.  Lay an inclinometer sideways across the BUC or LNB or use the tiny (but crude) scale on the horn throat clamp. +/-1 deg accuracy is required.

This is what it might look like after +6 deg clockwise adjustment, while facing towards the satellite:
...

Now raise the antenna elevation to 48.6 deg using the elevation scale behind the dish, swing the dish boldly sideways in azimuth in the general direction of due south and you should find the AM1 satellite.

Good luck, Eric
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« Last Edit: Jan 30th, 2007 at 10:48am by Eric Johnston »  
 
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