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HX 50 Polarization Problem

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HawkDriver
Ex Member


Dec 29th, 2011 at 11:02am  
Thank You in advance to any one who can help.

We are setting up the second of a two dish system. Both dishes are attempting to connect to the W6 satellite from a location of 63 East and 35 North (N.Afghanistan).

We have successfully locked one of the two satellites and were able to activate the modem using information I found in a previous post here on the forum. We have been unable to lock the second satellite and believe that our polarization is somehow wrong. My current signal is a 27, which leads me to believe that we are on the satellite but have the wrong polarization.

our settings as per the HX50 modem are as follows.

29.5 Degree Elev.
235 Degree Azimuth.
43.5 Degree Polarization.

Our first satellite came with the standard universal LNB and a Feed horn with 505 on the top as well as a 4 bolt plastic back plate that allowed us to rotate the dish. The second satellite, the one we are having trouble with. Has a Universal LNB, but the Feed horn does NOT have a 505 on it and the back plate is a metal type plate with no ability to rotate the dish itself. We have tried to rotate
the BUC in its holder to a (+) 43.5 degree polarization with no success, and we have tried to turn the BUC in its holder (-)43.5 degree polarization with no success. We even tried slowly turning it in its holder as it was attached to the modem and still no success.

I have reached the limits of my expertise and am looking for any suggestions. I do not have a meter to use to find the satellite so we are just using the signal from the modem. Any help would be greatly appreciated.

Thank You

[IMG]http://i36.photobucket.com/albums/e11/Dallas2881/IMG_0375.jpg[/IMG]

This shows our Irregular Feed Horn

[IMG]http://i36.photobucket.com/albums/e11/Dallas2881/IMG_0374.jpg[/IMG]

This shows our Universal LNB

[IMG]http://i36.photobucket.com/albums/e11/Dallas2881/IMG_0373.jpg[/IMG]

This shows our non standard back plate.
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Eric Johnston
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Reply #1 - Dec 29th, 2011 at 11:26am  
Your new dish has the feed arm fixed at the bottom centre, near the ground and to set polarisation you need to rotate the ORU/LNB assembly in its yoke.  Provided there is no 505 on the feed throat, this is perfectly OK.

Go to your good working system (505 type, with whole dish rotated) and look at the Universal LNB.  In what direction is the Universal LNB cable connector pointing, relative to the ground ?

Go to your new dish and set the Universal LNB cable connector pointing in the same direction relative to the ground.

Your 27 shows you are peaked up on some satellite.
I suspect that you are looking at a satellite at the wrong elevation angle.

...
On this picture above, note the following:
When the front face of the dish is vertical the beam elevation angle is the same as the dish offset angle, as stated in the manufacturers specification. I don't know the angle for this dish but it could be something like 22 deg. Other possibilities are 19 deg, 30 deg etc.
The dish is tilted backwayds by about 20 deg so the beam elevation angle could be 42 deg.  You want 29.5 deg beam elevation.

The satellites are in sloping line, so go down to the right and find the next satellite and so on.

Best regards, Eric.
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HawkDriver
Ex Member


Reply #2 - Dec 29th, 2011 at 12:38pm  
Eric,

Our LNB has the coaxial cable pointing in the same direction as the known working dish. I am looking in our documentation for the appropriate offset angle for this backplate, but as of yet have not found anything referencing an offset angle.

Question 1. the 43.5 Polarization would be set by rotating the  BUC assembly in its holder to the positive side of the assembly at the (+45) tick mark. The result would have the LNB pointing to the left of the dish as viewed from the back of the dish?

Question 2. Does it mater which way the Feed Horn is mounted for this system? Is there any way to tell which way the feed horn (This Type of Horn) should be mounted (Like the 505 on the other type)?

Question 3. Where should the Inclimometer be placed to derive the proper Dish angle on this type of BackPlate. Is the angle measured from at the same place as the Photo above?
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Eric Johnston
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Reply #3 - Dec 29th, 2011 at 1:22pm  
Question 1. the 43.5 Polarization would be set by rotating the  BUC assembly in its holder to the positive side of the assembly at the (+45) tick mark. The result would have the LNB pointing to the left of the dish as viewed from the back of the dish?  
The + and - signs, and even the numbers, on the scale are best ignored.  Think in terms of starting at one of the quadrant positions and then applying an adjustment amount, clockwise or anticlockwise. Count the amount along the scale.  The numbers may go forwards from 0 or backwards from 90 or whatever, so ignore the numbers.
Starting quadrant positions are Universal LNB cable up or down = vertical, Universal LNB cable sideways = horizontal.

Note the Hughes Universal LNB is not like a normal simple LNB module mounted on the end of a filter side arm.  In these cases, when the filter arm and LNB are up at the top that is Horizontal receive polarisation.
 
Question 2. Does it mater which way the Feed Horn is mounted for this system?
You have a simple, truly circular feed throat and horn.  It does not matter how this is turned round. It is the same all ways.

Is there any way to tell which way the feed horn (This Type of Horn) should be mounted?
No.
The 505 type is not circular symmetric and has three internal slots inside the fat lump. The fat lump must always be exactly towards the feed support strut. ( Once you have that right you can, in theory, connect any polarisation at the flange. Normally receive horizontal, but you can in fact set it at any 30 deg interval using a 12 hole flange. ). It is easier to always set horizontal polarisation with the feed arm at centre bottom, then turn the entire dish 90 deg if a vertical start position is wanted.  Then apply the adjustment amount.
...
Look at the sky.  Due south, at the top of the orbit needs no adjustment.  Satellites to the south west need you to turn it clockwise, satellites to the east turn it anticlockwise, as viewed from behind the dish and facing forwards towards the satellite in the sky.

Question 3. Where should the Inclinometer be placed to derive the proper Dish angle on this type of BackPlate. Is the angle measured from at the same place as the Photo above?
Measure the the slope of the backplate (approx 20 deg in the picture above) and then add the offset angle of the dish.  When the plate is vertical (measured angle = 0 deg) the beam elevation angle is equal the offset angle, typically 22 deg.
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HawkDriver
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Reply #4 - Dec 30th, 2011 at 7:48am  
Eric,

Thank You for your help so far. We have been able to eliminate several variables which is narrowing our troubleshooting and saving us time.

We went back through and found that the dish we are aligning has an offset angle of 17.3 degrees. When we take into account the 29 degree angle prescribed by the HX50 Modem, that gives us an angle at the satellite back plate of 12 degrees.

We have rotated our BUC in its holder to 43.5 degrees Clockwise as viewed from the rear of the dish. I will try and post some pictures later today,but we are still not locking the satellite. At this point I'm inclined to wait for a Sat Meter to help find the satellite.
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Eric Johnston
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Reply #5 - Dec 30th, 2011 at 1:50pm  
Quote:
We have rotated our BUC in its holder to 43.5 degrees Clockwise as viewed from the rear of the dish.

From what starting position ?
Sound good, but remember there are 4 possible polarisation quadrant starting positions.  Two starting positions are good, two are wrong.

Using the Hughes Universal LNB, the cable connector on the LNB is the direction of receive polarisation. If applying the adjustment amount causes the LNB or cable to hit metal, start 180 deg the other way.

Once you are peaked up (HX signal power reading maxed out at a value of 29) be prepared to flip the feed round by 90 deg to try both adjusted polarisation positions.

To find satellites adjust the elevation first. Then swing boldly sideways and peak on whatever you find. There may be negligible signal detected so look very carefully.  Once you find a satellite, mark the angles.  All the other satellites are in a diagonal line, up to the left and down to the right (in approx south east direction).

Best regards, Eric.
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