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Andrew dish assembly and polarisation setting

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Ex Member
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Feb 18th, 2007 at 9:38pm  
Quote:
I am now in am22 (53E) with new provider and i have big problem with SNR, the signal never reach level higher than 8, the aver signal 7.39 .

do you have any idea about what causing that ????

i will provide you with details info about BUC & LNB ...

Thanx for all advices .



**********************************************
Quote:
I don't know what SNR=8 means as I don't have iDirect.  


SNR is the signal strength, but 8 is very low it has to be 14 at least .

Quote:
Are you in a good part of the coverage beam ?
Is your terminal is working well ?


I am in good coverage place .
My iDirect 3100 Modem working very good .

Quote:
Is the bit error rate acceptable ?
Is the polarisation angle set correctly?
Dish pointing ?.


I need your help here to make sure everything is ok.

here is my numbers for Long and lat :

latitude=31.9249, Longitude=12.2538
Lat = 31 degrees, 55.5 minutes North
Long = 12 degrees, 15.2 minutes East
Dish elevation = 32.7, Azimuth=120.7, Polar=-46.3

I got them from this page :
https://www.satsig.net/maps/lat-long-finder.htm

My location is :

Latitude (Deg N) :
31 Degrees 55 Minutes 29.46 Seconds
------------------------------------------------
Longitude (Deg E)
12 Degrees 15 Minutes 13.60 Seconds

satellite is AM22 53E

Can you please give my picture of correct position of LNB & BUC .
The technical man got the sat using (sat looker) but the signal still weak ...
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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  
Thank you for the great assistance Mr. Eric Johnston .

I will do exactly like what you said, also I got new dish from the same type as seen above .

I can aver that the reason for the wrong angle is the wrong place for the feed support yoke .

I will do that tomorrow morning cause the weather now very bad here (so cold) .

Thanx alot
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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  
Mr.Eric Johnston Thanx alot for the modification ...

You can freely do what you need with images it's now belong to every one in this great forum,especialy you cause you the hero of solution ...

Thank you again for your great advice and step by step guide ..

I will never forget you ...
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Reply #10 - Mar 7th, 2007 at 6:28pm  
Hi  ALL.

i have a serious problem on my site i just lost two set of modem within a week.

what i noticed is that the modem Rx side does not give me good signal voltage,the best i could get is about 8volt which is very abnormal. i finally took my LNB to test in another site and it was working perfectly.i also tested the modem there and it was not working up to the right volt.i believe this must have been i am having a damage cable which i did not noticed in time that have result in me loosing my modems

i try entring the modem but its not accepting the general password and even when i try using the console cable, the area where i am suppose to apply USER NAME & PASSWORD is not accepting any carracter (letters).

please do any one have solution for me or what best to do.i believe i have to ship my modems (3) back to the factory (iDirect) but i dont know how to go about this.

please give me good informaton on how to fix my modem, who to contact, how much will  it cost me, how long will the repair take before sending them back to me and how to apply for this cos i can not afford to loose 3 modem just like that.i need your helps all.

thanks.

kayode (Nigeria)
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