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1 dish 2 LNB'S

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Ex Member

May 6th, 2007 at 8:20pm  
Hi All
My name is Dave. I have a Bell Express Vu 20" dish and receivers. The question I have. The 20" dish supports two LNBs.At the end of the dish's arm, a Y-adapter is found which holds both LNBs. I know that this is used to receive
BEV 91 LNB is in the center of the dish while the BEV 82 LNB is offset to the left.Rotating the dish (ie. modifying the skew angle) changes the position of the 82 LNB while maintaining position for BEV 91. A switchbox, typically an SW21 or SW44, is used to merge both satellite signals into receivers.
How do I adjust  the skew angle to use both LNB's. One LNB for 1 receiver  the other for the second receiver . I know I can get a splitter to do the job but I would like to use one dish 2 LNB'S

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Ex Member

Reply #1 - May 7th, 2007 at 2:23am  
Depends upon the offset of the LNB brackets. One method splits the difference between two satellites, pointing the dish midway, then offseting the LNBs just enough to catch both signals on the resultant reflections.

Not saying that this is the way that BV doesn things, but it's worth a try. Just pretend you're pointing at one satellite halfway between the two from which you intend reception. Use the satellite pointing angle calculator to find the correct AZ/EL/POL for that point in the sky, point your dish there.

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Reply #2 - May 10th, 2007 at 9:36am  
Rotating the dish (ie. modifying the skew angle) changes the position of the 82 LNB while maintaining position for BEV 91.

Given that the BEV91 feed is central, rotating the dish (modifying the skew angle), will not affect the pointing of the BEV91 beam but it will affect the polarisation(skew) angle of the BEV91 feed.
The position and polarisation of the 82 LNB beam will change as the dish is rotated.   The position of the beam will vary up and down.  Note that when the polarisation angle is approx correct the feed will also be in approx the right position.
With two feeds the line between the feeds is the polarisation angle or slope of the curved line of the orbit. As Greg says you might have the two feeds both set slightly off centre and aim the dish midway between the two satellites.  This makes sense if the signals from each satellite are similar level.  If one satellite has weak signals it would be better to to use the central feed for that satellite since outer feeds generally give lower performance; this is the case where extra feeds have been added to dishes designed for just one feed.
These figures may help:
... ...
Satellites due south of you have polarisations which are about nominal.  Satellites to the south east have polarisations which are tilted anticlockwise, facing the satellite.  The figure shows the possibilities of 5 feeds or 3 feeds on the dish.   The pattern of the feeds is a mirror image of the sky, so in the case of the three feeds, the central feed will be lower down and the two outer ones slightly higher.  The polarisation angle is approximately level.   For perfection, it is possible to adjust the polarisations of each feed individually and also the spacing to suit the orbit positions.

Best regards, Eric.
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