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| Satellite Internet forum › HughesNet and Hughes HX VSATs › Andrew dish assembly and polarisation setting |
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Andrew dish assembly and polarisation setting(Read 18522 times) |
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Feb 18th, 2007 at 9:38pm
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« Last Edit: Jul 30th, 2015 at 9:00pm by Admin1 »
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Eric Johnston
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Reply #1 - Feb 18th, 2007 at 11:08pm
Polarisation: The required adjustment is a feed/LNB/BUC rotation movement of (minus) -46.3 deg anticlockwise, while facing the satellite.
I don't know your correct nominal polarisation starting position, horizontal or vertical. Did they tell you nominal horizontal or nominal vertical (downlink receive)? The definition of the nominal vertical starting position is with the rectangular LNB input waveguide with its two broad faces on top and underneath. There are two alternative vertical polarisation start positions, with the LNB arm sticking out on the left or the right side.  If you still have the feed polarisation set to a start position, either horizontal or vertical, your signal will be -3 dB down and you may be suffering severe interference if there are signals on the opposite polarisation. The measurement level may increase whenever the dish points at any satellite. Once the correct satellite is detected the RX LED should change from yellow to green, and the measurement value increase further (above 12) in the iSite screen. Once you have found the satellite, I believe it is important that the lat and long coordinates are correct. Best regards, Eric. |
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« Last Edit: Jul 30th, 2015 at 9:01pm by Admin1 »
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Reply #2 - Feb 19th, 2007 at 11:45am
I am very thankful for your patience with me. Thank you for every word you wrote.
I will do what you say step by step , but can you kindly take look at these images of my dish . I am now at the correct satellite we found it using sat looker device, and from the link you gave me my coverage is at 49 dBW i am in libya . ****************** My dish is : 1.2 meter Part NO 8010842 Model no 1.2M-1 Made in USA ****************** I have internet now but the signal is very low . Is the dish cause that, Manufacturers defect ? here is some of my pic . first and second images for the LNB and BUC , when I were at AM1 at 40E they were Normal but now they are extended at AM22 53E The third and fourth Images for the dish is the position correct ? The last image for elevation, I am surprised for the angle; should that be 32?     
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« Last Edit: Feb 20th, 2007 at 3:31pm by Admin1 »
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Eric Johnston
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Reply #3 - Feb 19th, 2007 at 12:19pm
Your polarisation setting corresponds to nominal vertical polarisation, rotated by (minus) -46 deg anticlockwise while facing the satellite.
 This is correct. The elevation scale is reading 50 deg. It should be 32.7 deg. This is weird since you say you are now successfully accessing the internet. Does your iDirect have green RX led ? Please take a side view photo, with the camera in line with the two front sides of the dish and all of the mount, dish and LNB etc visible. Hold the camera level so the background is horizontal. email the picture to me eric@satsig.net if you wish and I will link it in. It is not clear in your picture where the feed support yoke is attached to the boom. Perhaps your feed is about 6 inches too far away from the dish ? This would explain everything: Out of focus axially and upwards of the focal point = Low gain + low gain + poor cross pol isolation. Upwards of focal point = wrong elevation reading. If it is like this, the bracket attaching the feed support arm to the bottom of the dish will be almost breaking the plastic as the arm is pulled upwards too far ?. Don't drop the arm if you need to change things. Get someone to hold it. Does it look like this:  Best regards Eric |
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« Last Edit: Feb 20th, 2007 at 1:25pm by Eric Johnston »
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Reply #4 - Feb 19th, 2007 at 1:41pm
I am writing to you from the same dish with the poor SNR.
There is internet access but it is very bad takes so long to respond to the page request . All modem leds lights green . There two or more weird things: 1) The BUC power now at max power (-14), initial power is (-16), Max Power (-14) 2) According to The iSite software in the (Look angel Calculator) : Elevation is 32.704213 and the Offest is 16.57 Elevation Actual is 16.134213 Azimuth True is 121.541268 Polarization is -46.332038 In the PDF document of remote installation the offset must be 17 Deg and in my case is 16.57 , Does that effect the signal ? What is the correct position of the LNB , if you can with picture ? in my case is it correct ?      
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« Last Edit: Feb 20th, 2007 at 3:41pm by Admin1 »
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Eric Johnston
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Reply #5 - Feb 19th, 2007 at 3:08pm
The attachment of the feed support yoke to the arm is completely wrong. It is attached at the end of the arm. It should be near the bend in the arm. See my RED line drawing.
Re-assemble like this:  Get someone to hold the arm while you reposition the two bolts into the pair of holes nearest to the bend in the arm. After you have moved the bolts the beam elevation angle will really be 50 deg so you need to readjust the elevation down to 32.7 deg. You will find the satellite when the scale reads 32.7. The scale will now read the correct angle. Best regards, Eric. |
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« Last Edit: Feb 20th, 2007 at 1:27pm by Eric Johnston »
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Reply #6 - Feb 19th, 2007 at 8:15pm
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Reply #7 - Feb 20th, 2007 at 11:32am
Words fail to express my thanks to you Mr.Eric Johnston .
I so happy the final result very good, I got 16 volts, and 11 SNR .... The big problem was in the wrong assembly of arm and position of the feed/LNB/BUC ...   Thanks a lot Mr.Eric Johnston . |
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« Last Edit: Feb 20th, 2007 at 3:18pm by Admin1 »
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Eric Johnston
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Reply #8 - Feb 20th, 2007 at 1:17pm
You are welcome
 This is the final image of the Andrew 1.2m antenna set for elevation angle of 32 deg. The nominal receive polarisation was vertical (starting with the LNB sticking out on the left side). The polarisation adjustment required was -46 deg, i.e. minus, anticlockwise rotation of the feed while facing towards the satellite. Do you want your imageshack images stored here permanently ? Best regards, Eric. |
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« Last Edit: Feb 20th, 2007 at 3:43pm by Admin1 »
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Reply #9 - Feb 20th, 2007 at 1:45pm
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Reply #10 - Mar 7th, 2007 at 6:28pm
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Email me: eric@satsig.net
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