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VSAT technology and installation >> iDirect Forum: hubs and terminals >> Remote keeps raising tx power
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Message started by DCampbell on Oct 19th, 2011 at 11:43am

Title: Remote keeps raising tx power
Post by DCampbell on Oct 19th, 2011 at 11:43am
I'm running a hub and I have 7 remotes on this one specific network.  All except 2 are running perfectly fine.  Two of them keep adjusting power until they transmit at 0 dbm.  I've changed it from my end through iMonitor and through telnet on their end.  I know the modem keeps adjusting power to get to the nominal C/N but 0 dbm tx power!?  Even at -9 dbm for tx power the down C/N reads 8.85 and my nominal setting is 9 but it keeps raising power.  Is there a possibility that the modem isn't reading its C/N measurment properly?

Title: Re: Remote keeps raising tx power
Post by Eric Johnston on Oct 19th, 2011 at 4:10pm
"Is there a possibility that the modem isn't reading its C/N measurment properly? "

Yes, if the initial level is already so high that the BUC is saturated (-1 dB gain compression point or above) and the signal is therefore badly distorted the error rate will be high and the modem may think this is a noisy, low level signal - so the hub tell the modem to increase the power even further making things worse.

Try starting at some much lower value.

Even better, set the modem to send CW and measure the CW level at the hub in 1 dB steps up from -35 dBm. Plot the line and see how the output from the BUC starts to level off.  The left side will be a straight sloping line. Extend this line upwards and see where a 1 dB vertical gap appears as the line curves over.  That is the -1 dB gain compression point and corresponds to the manufacturer's BUC rating, e.g. 2 or 5 watts.  Set the -1dB compression point as the maximum that the hub can tell that modem to send out.  Set the starting value about 10 dB to 6 dB lower.

If anyone with iDirect experience knows better please say here.

Best regards, Eric.

Title: Re: Remote keeps raising tx power
Post by DLC on Oct 20th, 2011 at 7:49am
Thanks for the quick response.  I tried both things you suggested.  Starting at a much lower power just dropped the nodes out of the net.  The second recommendation is barely understood due to my lack of experience.  I think you are saying to peak and pole, right?  I had the nodes reacquire and peek and pole but the same issues arise.  I apologize if I misunderstood your advice.

I do have some new symptoms to report if you don't mind commenting on them.  The symptom of raising the power continuously only occurs during the day.  Does anyone have experience with sun fades/outages or ionospheric scintillation?  The two troubled remotes are in very close proximity to two other remotes that do not have any issues.  The only difference between the troubled nodes and the "good to go" nodes are that the troubled nodes are both shooting to a different satellite.  Perhaps the sun is drowning out the signal to the point of having to transmit at higher rates?  Comments, suggestions?  

Title: Re: Remote keeps raising tx power
Post by TDMAMike on Oct 20th, 2011 at 12:00pm
DLC, when the NMS pushes up remote power (power offsets courtesy of the NMS's configured UCP) it is likely due to the remote being off peak...that, or its BUC is not sized (properly) for the operating location within the beam...and is therefore saturating.  Typically when the NMS sends power offsets (.5 or 2.0 dB)it is because your node is not able to meet the presecribed TDMA Nominal C/N setting configured for the inroute group UCP (ex: 9dB for QPSK .793 fpr iNFINTI, etc).  So, if your terminals are pushing power (courtesy of the NMS), it means they are off peak/pol or they are simply in BUC saturation.

Do you have other terminals operating in/around the same contour line as the terminals that are pushing power?  Do they have the same sized BUC?  

Recommend a good peak/pol and see what it yields.  If that has no bearing, then you clearly have an issue with the uplink chain. Either the BUC is not capable of what you are trying to close, or you have cabling that potentially bad.  

M

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