Satellite Internet

Satellite Internet Forum.

Welcome, Guest.
Welcome to this satellite broadband discussion forum. Wherever you are and whatever your problem we are here to help each other. Connecting to the internet via satellite is not always easy but is critically important to those in remote places or with poor terrestrial infrastructure. Both service providers and customers are encouraged to contribute. Register at the bottom of the forum home page if you wish to contribute or ask question. May 2018: GDPR: Updates to Privacy and Cookies policies: As you may know, a new EU data protection law called GDPR will apply from Friday 25th May 2018. As part of satsig's commitment to protecting the privacy of site visitors and forum members, I have therefore updated the Privacy and Cookie policies. There are now links leading to these policies: Disclaimer, Terms of Use and Privacy, Forum User Agreement, Forum Rules and Cookies at the bottom of the home page and all forum pages. Read the Forum rules.
      Satellite internet forum          
Pages: 1

Circular to linear polarisation

(Read 5560 times)
Ex Member
Ex Member


May 31st, 2011 at 10:38pm  
Hello,

We have 11m C-band antenna and feed assembly which I am going to perform x-pol testing with AMC-7 for xmit and receive. I just informed that AMC-7 requires linear polarisation.

There is not any data sheet or installation manual available for antenna and feed assembly.

Looking at http://imageshack.us/photo/my-images/821/casi1p.jpg/
http://imageshack.us/photo/my-images/856/casi2.jpg/

can one determine that, Is the feed circular or linear pol.?

or if it is circular pol., then how to convert it to linear?
http://imageshack.us/photo/my-images/853/ant1l.jpg/
http://imageshack.us/photo/my-images/638/ant2c.jpg/

Please advice.

Thanks:
AEE





Back to top
« Last Edit: Jun 1st, 2011 at 9:07pm by N/A »  
 
IP Logged
 
Eric Johnston
Senior Member
***
Offline


Personal text from Profile,
Options, Top line

Posts: 2108
Reply #1 - Jun 1st, 2011 at 7:53am  
...  ...

The centre hub picture shows 2 receive waveguides with amplifiers attached, also 2 transmit waveguides with black tape covering the ends.

Look closely for any lables on the waveguides or amplifiers and indoors at the ends of the cables. Does it say RHCP/LHCP anywhere ?

I would point the dish at AMC-7 (linear C band satellite) and examine the spectrums at both receive waveguides.  Note your actual polarisation adjustment angle and consider this relative to the calculated polarisation adjustment angle for AMC-7.  Make sure the difference is not near 45 deg and adjust the polarisation if necessary.

If the signals are the same regardless of rotation of the feed system then you have a circular polarisation system.  

If the signals are different then you have a linear system.  Confirm this by turning the feed till you null out the cross-pol.  "Turning the feed" looks extremely difficult in the picture so my guess is that your system is circular and the feed rotation intended to remain fixed.  I can't tell which way is exactly up in the picture.  A photo ftom exactly behind, with the camera level would help.  If the system is linear there should be some means for readily turning the feed and adjusting the polarisation angle.

To see by inspection if the system is circular or linear you need to look behind the panel to find out what is there. That looks like being quite a big job. There may be an access panel round the front of the dish, sideways into the feed support tube.

Are you intending to use the antenna as receive only ? At one specific frequency ? Do you have LNAs or PLL LNBs with external 10 MHz reference ? If so, you might contemplate making your own external C band or L band combiner to get two circular polarisations back to linear. Not sure if it would work...

Best regards, Eric.
Back to top
« Last Edit: Jun 1st, 2011 at 3:47pm by Eric Johnston »  
 
IP Logged
 
Ex Member
Ex Member


Reply #2 - Jun 1st, 2011 at 10:22pm  
Hello Eric,

1. I have uploaded new pics.
2. I am intending to use Antenna both for Transmit and receive.
3. I have CA 140103 LNB, Norsat 3220 C-band PLL LNBs, Norsat 8520 C-band Digital DRO LNB(On dish). NJRC NJT5669F 5W C-Band BUC(on dish).
4. Found nothing on panel. Besides it's make & Model. "SA 8231 11m feed". I'll look behind panel using bucket truck.
5. Dish is pointed to AMC-7. and I have lock on CH. but not on CV.
6. "Turning the feed". I Can rotate feed from behind.
7. Will do some more testing and update Post.


Thanks much:
AEE
Back to top
« Last Edit: Jun 2nd, 2011 at 3:02am by N/A »  
 
IP Logged
 
Eric Johnston
Senior Member
***
Offline


Personal text from Profile,
Options, Top line

Posts: 2108
Reply #3 - Jun 1st, 2011 at 11:38pm  
...

Assuming it is linear polariation and the red line points directly upwards.

You are currently receiving horizontal polarisation, tilted 15 deg clockwise. e.g. From Nunavut perhaps ?
or
You are receiving vertical polarisation, tilted 75 deg anticlockwise. From where ?

Where are you ?

Best regards, Eric.
Back to top
 
 
IP Logged
 
Pages: 1