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Poor QPSKBER on W6, but good on NSS6

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Ex Member
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Jan 15th, 2007 at 2:36pm  
I am switching providers from satellite NSS6 to Eutelsat W6. When I was on NSS6 I got a good QPSKBER signal of .00002. But when I am on W6 I get a poor QPSKBER signal of .001 or less. I have a Linkstar modem, a 1.2m Channel Master dish with Cross-Pol OMT, 2W BUC, and  Ku Band LNB (10.95-11.70 GHz). I am located Basrah Iraq (Lat 30.33, Long 47.40), so I should be able to pickup W6. I am located on an Airport, but there are no obstacles or interference. I get RX sync and NCR sync on W6, but just not a good enough QPSKBER to get a TX sync. I cannot get a good QPSKBER on W6, even after many small minute adjustments to Azimuth, Elevation, and Polorization. Does anyone have any suggestions or reasons why I cannot get a good QPSKBER on W6. Thanks, Terry Caulder
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Eric Johnston
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Reply #1 - Jan 15th, 2007 at 5:27pm  
Two ideas:

1. Satellite polarisation angle
Polarisation angles, by calculation, for Eutelsat W6 do not match up exactly with the actual angle as optimised by adjustment, which is 3.5 deg further clockwise when facing the satellite.   Be prepared to degrade the signal by turning the polarisation well away from optimum.  Mark and measure the quality.  Do the same on the other side and find the same degraded quality and mark that point.  Then turn the feed to the centre between the two marks.

2.  Adjacent satellite interference
It is a possibility with Astra satellites at 19.2E and 23.3E, either side of W6 at 21.5E.  Perhaps there were no close satellites with powerful carriers on the same frequency when you looked at NSS6.   If your dish is wrong assembled (out of focus) or has dish distortion it will cause an extra wide main beam or high first sidelobe pattern.  Check the dish front edge is flat.  Put tight fishing line up/down and across.  They should exactly and just touch.   Some thin plastic dishes get their sides pulled forwards by the weight of the feed assembly.  Get if flat to 1mm, somehow.

It is possible that your dish has two missing side struts at the back which go from the az/el adjuster box to the sides of the dish and prevent the sides being pulled forwards.  If these side struts are there, you almost certainly have them installed wrong.

There are elongated holes in the ends of these arms where the bolts go through.  It is critical that the sides of the dish are held firmly before and as the back side bolts are being tightened.  You may need three people, two to grasp the dish sides and one to tighten the nuts. Check for perfection with two fishing lines !

Best regards, Eric.
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Ex Member
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Reply #2 - Jan 15th, 2007 at 6:44pm  
I have found my problem. I was told by the new provider that I am using the wrong dish for Eutelsat W6 and that is why my QPSKBER is low. I have a Andrew (Channel Master) 1.2m Class 1 dish and need a Andrew 1.2m Class 2 dish.

Andrew 1.2m ClassI http://www.andrew.com/search/BN_PA-100549-EN.aspx
Andrew 1.2m ClassII http://www.andrew.com/search/BN_PA-100550-EN.aspx

Does anyone know if I can convert a ClassI to a ClassII. It looks like the actual dish is the same, just the mounting brackets are different?

Does anyone have any info on where I can buy the ClassII dish or mounting brackets?

Thanks, Terry Caulder
terry@tcaulder.com
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Eric Johnston
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Reply #3 - Jan 15th, 2007 at 10:47pm  
The class II one has:

1. The two short rear side struts that I make such a fuss about.  These make a big difference to the main beam beamwidth and to the sidelobe pattern.   If the elevation angle is low they stop the sides being pulled forward.  If the elevation angle is high up they stop the sides being pushed back.  You need to use common sense when tightening and get the front face edges flat to within 1mm at the normal operating angle.

2. The front side struts are lower down so they don't obstruct the beam so much (so lower sidelobes further out) and the main arm is stiffer in torsion, preventing polarisation angle movement and interference changes as the months pass.

Best regards, Eric.
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