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W3A repointing Europe

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Jun 22nd, 2008 at 2:59pm  
I am not able to repoint Prodelin 1.2 m 1134 antenna to W3A. It was previosuly pointed at W3A, I marked azimuth and then change the feed asymbly. (part no 0400-1422). But now I have only max 8 volts on iSITE. I have replaced feed, LNB, iDirect Modem but i am not finding a carrier lock. I can see carriers on spectrum analyzer particularly at 1198.2 MHz a 1 MHz carrier. I have a 11.3 LO LNB. My location isear Ankara.  elevation angle of 19.4 (after subtracting antenna offset.) I have measured f/D to be 0.85.

I have tried all methods to repoint such as fixing  an elevation and doing an azmuth sweep. I have also tried Hor (+30) and Ver (-60 deg) polarization but no luck.

Please help.
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« Last Edit: Jun 22nd, 2008 at 4:41pm by Admin1 »  
 
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Reply #1 - Jun 22nd, 2008 at 4:43pm  
I am not able to repoint Prodelin 1.2 m 1134 antenna to W3a. It was previosuly pointed at W3a, I marked azimuth and then change the feed asymbly. (part no 0400-1422). But now I have only max 8 volts on iSITE. I have replaced feed, LNB, iDirect Modem but i am not finding a carrier lock. I can see carriers on spectrum analyzer particularly at 1198.2 MHz a 1 MHz carrier. I have a 11.3 LO lnb. My location isear Ankara.  elevation angle of 19.4 (after subtracting antenna offset.) I have measured f/D to be 0.85.

I have tried all methods to repoint such as fixing  an elevation and doing an azmuth sweep. I have also tried Hor (+30) and Ver (-60 deg) polarization but no luck.
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Reply #2 - Jun 22nd, 2008 at 5:11pm  
For dish pointing angles try this link: dish pointing Iraq.   Turkey-Ankara is just off the upper top left corner.  Put your mouse on Turkey, right click and drag to the middle.

Pointing for W3A from Ankara:  
Elevation 36.6      Azimuth 211.6 magnetic     Polarisation +27.5

The antenna manual is here:
http://www.gdsatcom.com/Prodelin/Technical_Docs/assembly_manuals/4096-393.pdf

The offset angle is 17.3 deg so if the front of the dish face is vertical the beam elevation angle is 17.3 deg.  Put a strip of wood up the front and measure its angle with an inclinometer.  Tilt further backwards as required.  36.6 - 17.3 = 19.3  so you have the correct calculation.

You don't say what is the nominal polarisation for your downlink signal.   Ask the hub.   Nominal horizontal means the broad faces of the LNB waveguide must be on either side.  Nominal vertical means the broad faces of the LNB waveguide must be on top and underneath.  The nominal position is the starting position.

You need to set the nominal polarisation and then apply a +31 deg clockwise rotation polarisation adjustment of the feed assembly, while facing towards the satellite.

A +30 deg clockwise or -60 deg anticlockwise adjustment (while facing the satellite) will be correct, so you have done the correct alternatives.

Ask the hub what is the downlink satellite frequency for your wanted carrier.  Subtract the LNB LO frequency and the result is the L band tuning frequency you are to put into the modem, and also what you will see on the analyser.   An 11.3 GHz LNB is suitable only for downlink carriers in the upper part of Ku band.  A 9.75, 10 or 10.6 GHz LNB would suit lower satellite frequencies.

If you can see a spike at 1198.2+11300 = 12498.2 then this is may be the horizontal polarisation beacon at 12500.5  This is what I see below in 100 MHz span and both Vertical and Horizontal.  Freq error about 2 MHz.
...

Best regards, Eric.
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Reply #3 - Jun 27th, 2008 at 9:16am  
Thanks  for your reply. I had to leave the site that day so the problem is still not resolved.

I tried a CW with Eutelsat but they say they did not see it and I am not on the correct satellite. This was with Hor pol. Later  I found out that the xpdr was actually Ver.

There was one thing odd that ISite showed Rx AGC volts as high as -11 dBm which are normally -25 dBm or above. I think the idirect modem has an AGC range of 0 to -60 dBm so can it saturate LNB/Rxvr.

Thanks.
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