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QPSK BER VALUE

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Feb 15th, 2007 at 7:35am  
Hi all, I have a good signal on my Linkstar Modem but the QPSKBER value that is meant to be in the region of 0.0001xxx was 0.01xxx. I replaced the LNB and the Feedhorn but still no improvement. Suggestions anybody?

Daniel Abugo.
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« Last Edit: Feb 15th, 2007 at 9:17am by Admin1 »  
 
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Eric Johnston
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Reply #1 - Feb 15th, 2007 at 9:16am  
Try improving the dish pointing.  For example, alter the elevation angle by turning the nut 1/2 a turn.  Then make more BER measurements.   If an improvement, then continue another 1/2 turn in the same direction.

Check the polarisation angle adjustment.  Using your lat/long and the satellite orbit position calculate the dish pointing and polarisation angles and then set the polarisation exactly.

Best regards, Eric.
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« Last Edit: Feb 15th, 2007 at 3:32pm by Admin1 »  
 
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Reply #2 - Mar 15th, 2007 at 9:00am  
Hi Eric,

Thanks for the reply, but the dish pointing was done with a good value of 74 dbm on the pointing meter. other sites with pointing values of less than 72 dbm have given better QPSKBER values. the modem was taken to another site where the meter reading less than 74dbm, and the QPSKBER value was ok.what seems to be the issue. This brings to fore the question how is the QPSKBER value related to the signal strenght.
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Reply #3 - Mar 18th, 2007 at 4:02pm  
the BER value while functioning, it shows just the single carrier RX quality.

- But the Satellite meter (or anything like pointing meter) must show you any transponder on the concrete satellite on what you should connect at the same time the terminal and check the values with the QPSKBER. Here you will see how to improve it on the time of adjustment of the pol..

Regards,

Discovery Global Team
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Reply #4 - Apr 16th, 2007 at 8:20am  
Hi;

If your sure of your pointing, and you clarified that the modem is reading good QPSKBER values in other site, then its most probably a cable/connector issue.

Check your cable and make it the shortest you can, and I would recommend to cut off the cable ends and terminate the connectors again.

Regards
Support Engineer
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« Last Edit: Apr 16th, 2007 at 11:56am by Admin1 »  
 
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Reply #5 - May 23rd, 2007 at 1:14pm  
what about footprint? your dish eirp is covered "well" by the sat. signal?? The crosspol angle needs a little mm rotation to shift towards 0.0000x
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Reply #6 - Jan 30th, 2009 at 7:01pm  
I currently had same problem. My QPSK BER value was 0.00005 during installation months ago and 2 weeks ago it turn to be 0.002xx. I have use shorter cable, realign ODU, change LNB and RCST but problem still the same. I'm using NWIEE dish. From NOC side, they said my transmit signal was good but receive signal was bad (0.0024). Currenly using Linkstar DVBS2a.

Any help, please?
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Reply #7 - Jan 30th, 2009 at 10:25pm  
A guess.   Maybe until two weeks ago there was no carrier on the opposite polarisation transponder, so you received no cross-pol interference, even if your polarisation was wrong. Maybe a carrier was put up on the opposite polarisation and from that time you were affected.

Check your polarisation angle - the rotation of the feed/LNB/BUC assembly in its yoke.  Mark the existing angle exactly so you can get back to it.  Then try microscopic adjustments, like 1mm, and stop and carefully measure the QPSK BER at each adjustment.  If it makes no difference then this guess is wrong.  Put the polarisation back exactly where it started.  If adjusting does make an improvement then call the hub and get them to help you do a proper CW x-pol carrier test.  They will measure your x-pol level and talk you into the narrow null.

Best regards, Eric.
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Reply #8 - Jan 31st, 2009 at 3:10am  
I have done the rotation of the feed/LNB/BUC but still the original position giving me the best BER (0.0024). So I rotate it back to the original position.  

Just wondering. How to know whether NOC transmitting enough power to the remote VSAT to receive? by checking at RCST?

If the transmit power from NOC to side is low, that might cause my ODU can't get better BER as my transmit is good as detected at NOC side. Is it might cause by problem at NOC GCU?

Any idea on those matters? I won't publish this to our NOC. Its just for my knowledge.
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« Last Edit: Feb 4th, 2009 at 6:11pm by N/A »  
 
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