SCPC RX ERRORS

I'm not certain what you mean by SCPC errors.  I assume you are referring to the main outlink carrier from the hub to all the remotes.

Do the errors occur randomly all of the time or do they occur occasionally in bursts around particular times. If you have steady random errors all of the time the cause exists all of the time and should be easier to find.  If the errors occur occasionally at particular times you have some kind on intermittent problem, like intermittent interference or a loose connection.

If you have a continuous problem.  Is the outlink carrier level correct ?  Is the (C+N)/N normal when viewed on a spectrum analyser ?  Is the carrier shape normal ?  Do all sites show low Eb/No all of the time ?.

If the carrier, and the gaps adjacent, look normal then leave the spectrum analyser in max hold mode and see if anything builds up. Watch for little spikes from TDMA bursts that may add up over a while to form an interfering carrier shape.  If the adjacent co-pol carrier is TDMA wait to see if one of the sites on that carrier has a bad spectrum.  If a BUC is overdriven then they will have spectrum spreading and one burst every so often on the adjacent TDMA carrier will spread out and hit yours.

If the carrier shape looks abnormal, with humps or partly filled up guard bands, measure the cross pol spectrum and consider any correlation between the cross-pol spectrum and any humps in the wanted carrier.  Plotting the two spectrums on thin paper and putting one over the other is suggested.  Is so, plan an outage of your outlink carrier and during this outage record and plot the noise floor underneath your wanted carrier slot.  You may detect a cross-pol interferer within your carrier bandwidth.  If you see a TDMA carrier on the cross pol there may be one site amongst many sites on this carrier slot that is badly polarisation aligned and when this site transmits a burst it puts errors into your outlink.

If you do see TDMA type interference tune the spec analyser to the interfering frequency, set the RBW equal to approx the interfering carrier bandwidth and then set zero span and a slow sweep and wait.  Max hold will help record anything. Expect patterns of bursts at the TDMA frame rate.

When did the problem start ?  Tell Intelsat and ask if any new carrier or remote site was being lined up at that time.

If it is an intermittent problem try the spectrum analyser in max hold mode.  Leave it on for many hours waiting to see if it records anything.  You may have to experiment over several days with different settings. If the interferer is brief (under 1 second) make sure you have the sweep rate fast enough.  A 30 second sweep rate may miss a short noise burst. Ultra short bursts like 1mS need 1kHz video bandwidth.

At the hub I recommend that you have a spectrum analyser on all of the time monitoring the outlink and return link spectrum.

Best regards, Eric.

I have about 60 remotes distributed all over East and Central Africa.

Nick

Hi Space,
When can we sit and we discuss a few stuff?
Would like to know how you sorted out your problem.
Send me a mail on nmuttai@gmail.com

Mwafrika

Just wanted to quickly point out that he said ALL of his nodes were reporting it....and not just one.  Which is why I went the direction of possible energy underneath his operational carriers from the crosspol, or something is amiss in the uplink IF/RF chain at the teleport e/s (HPA, UC, or assoc cabling). 

Mwafrika, I sent you a PM with my contact details.