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iDirect 3000 Series Remote SCPC Errors

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Ex Member
Ex Member


Sep 27th, 2012 at 8:07am  
Hi,

I have 13 remote sites using iDirect 3000 series modems on T10 C-Band. 12 Sites are working well but 1 site is having a lot of SCPC Errors as much as +50,000.

Site details:

Antenna       3.0mtr
BUC             5W NJRC
LNB             Norsat 3220F PLL
Cable           RG 11 dual
Modem         iDirect 3100
Version   8.0.2.5

After checking the logs the site has only had 2 -3 SCPC errors down to 0

22/9
10:34    -    11:30
11:37    -    13:11

24/9
11:30    -   12:00
13:51    -   14:03

Times are GMT site is Victoria Falls Zimbabwe.

The antenna was moved from the roof of a 4 storey building when we noticed the SCPC errors down to ground level hoping to move away from suspected interference. We have changed the cables, LNB and even fitted a BPF. Still no change. Could the modem be faulty and cause SCPC errors?
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Eric Johnston
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Reply #1 - Sep 27th, 2012 at 11:51am  
I am assuming by SCPC errors you are referring to receive errors at the site.

Is there a security guard with a hand held radio or cell phone nearby ?
Vehicle parked with engine running - ignition interference ?
What was the weather like at the times ?
Weekdays versus weekends ?
Does the AC mains power supply have brief outages ?
Does someone with a radio or cell phone or electric vacuum cleaner go near the modem at times ?
Is the modem unusually hot due to restricted ventilation or sun shining through window ?

Zimbabwe is very well covered by the centre of the T10 beam pattern.  Is the C/N normally very good ?   Does the normal clear sky receive C/N at the site make sense relative to the all other sites in the network ?

Are the errors associated with the site transmitting a burst ?  If so, is the BUC overdriven ?  If overdriven, splatter will occur over wide frequency range and the BUC is more likely to cause interference into the LNB.   Is the BUC cable outer sheath properly connected?.   If not, the BUC DC power will return via the LNB cable and DC current jumps, when the BUC transmits, will be superimposed on the LNB supply voltage.

If the site has uplink power control activated, the modem output power to the BUC will increase at times.  Can it go too high ?  You should set, in the hub, the maximum output level from the remote modem that will not cause the BUC to saturate (-1dB gain compression test).

Is the modem receive tuning and the receive acquisition range the same as at the other sites?.
Look at the config files for all sites.  Can you find anything at all that is different for this site ?
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Ex Member
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Reply #2 - Sep 27th, 2012 at 1:08pm  
Hi Eric,

I am assuming by SCPC errors you are referring to receive errors at the site.  Confirmed RX SCPC Errors

Is there a security guard with a hand held radio or cell phone nearby ?  No
Vehicle parked with engine running - ignition interference ?  No
What was the weather like at the times ?  Clear Skies
Weekdays versus weekends ? SCPC Errors 24/7/365
Does the AC mains power supply have brief outages ? Backup UPS and Generator 
Does someone with a radio or cell phone or electric vacuum cleaner go near the modem at times ? Modem located in Server Room
Is the modem unusually hot due to restricted ventilation or sun shining through window ? Modem in Air conditioned Server Room mounted in Server Rack, no air restrictions.

Zimbabwe is very well covered by the centre of the T10 beam pattern.
Is the C/N normally very good ? C/N is relatively the same as compared with the other sites
Does the normal clear sky receive C/N at the site make sense relative to the all other sites in the network ? 

Are the errors associated with the site transmitting a burst ? No, SCPC errors are constant (in fact the site is not using the link due to it being unstable, Site is working on fibre link, VSAT is backup)
If so, is the BUC overdriven ? BUC is not overdriven, SCPC errors occur at different BUC Tx power levels MIN -21 through to  MAX -17.
If overdriven, splatter will occur over wide frequency range and the BUC is more likely to cause interference into the LNB.
Is the BUC cable outer sheath properly connected?. Cables Have been checked, replaced and swapped over   
If not, the BUC DC power will return via the LNB cable and DC current jumps, when the BUC transmits, will be superimposed on the LNB supply voltage.

If the site has uplink power control activated, the modem output power to the BUC will increase at times. 
Can it go too high ?  You should set, in the hub, the maximum output level from the remote modem that will not cause the BUC to saturate (-1dB gain compression test). 1dB compression set the max BUC Power to - 17

Is the modem receive tuning and the receive acquisition range the same as at the other sites?. Confirmed same/similar to other sites
Look at the config files for all sites.  Can you find anything at all that is different for this site ? All Configs have been checked and nothing is different.
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Eric Johnston
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Reply #3 - Sep 27th, 2012 at 3:24pm  
I have found 12 pages of discussion about iDirect SCPC errors and similar problems here:
http://www.datastormusers.com/ubb/ultimatebb.php?/ubb/get_topic/f/23/t/000005/p/...

Do you see low S/N when the errors occur ? That seems a common problem.

Have you checked the polarisation adjustment angle ? What angle is it set to ?

It is possible that there is an intermittent carrier on the opposite polarisation and if your site has misaligned polarisation then you will experience low S/N while the other carrier is active.

Is the rmtstat command any use ?  Do you see any abnormal status for that site ?

Best regards, Eric.
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Ex Member
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Reply #4 - Oct 23rd, 2012 at 9:08am  
Hi,

Sorry for delay in getting back. Just to update you, we have managed to move the uplink and downlink frequency with the SAT Operator and it seems the link is now working well with no SCPC errors. So at this stage I cannot tell if it was local interference (WiMAX) or possibly cross-pol interference on that frequency.

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« Last Edit: Oct 25th, 2012 at 7:47pm by Admin1 »  
 
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