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SCPC loss of TX signal

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Ex Member
Ex Member

Mar 5th, 2010 at 8:21am  
Hi all,

Had an interesting event occur yesterday. All well so far today. I have 5 x 5350 and 2 x 5100 modems running in SCPC mode and connected to a Music box. The Music box in turn connected to a 16W BUC on a 2.4 m antenna. I shoot these 7 links out to the far side remotes that also have 2.4 m antennas and 3w BUCs at each site. It is on KU band on a hot bird. We normally run the links at around 14 -15db - THE 1dB compression point is 17dB on these links. I know running the links at around 15dB is fairly hot but the sat operators are fine with it as long as we stay under 17dB.

These links have been up for 15 months with very few issues at all - running very well indeed. We have only had one outage due to rain and that was when we had HEAVY rain at the HQ site and one of the remote sites. Other then that no rain outages in 15 months! Ku Band is fine if you engineer the link the right way.

So the issue that has now come up. Yesterday i was called in to look at the setup as the links appeared to be down. I had 5 Green Leds on all modems at the HQ side. A phone call to each remote side told the same story - Blinking amber RX and NET led. So i was receiving the TX from the far side at HQ but the far sides were not receiving my TX from HQ.

I connected laptop to modems and logged into iSite - i had each of the modem icons blinking from blue to an icon with a red cross through it - i've seen this before and know it means one side of the link is up and one side down. I connected my spectrum analyzerto the system and then  telnet'd to each modem and turned up the power to each remote site in case it was weather related as it was raining at the HQ site at the time ( but not heavy - only a drizzle). This did nothing. I could see the power levels going up and down as i adjusted power levels up and down to see if i could jog some life into the links. Of course i was unable to telnet to the far sides. I rebooted each of the modems and the music box. Still no joy. I could see the carriers go off as i rebooted each modem and then come back on as the modems came back on. Stumped at this point.

It was odd because i could see that the BUC was OK and the music box must have been OK as i could see the power levels as i rebooted each modem and as i adjusted the power levels to each carrier - but still no RX at the far side was received.

At this point i concluded it looked like i must have lost the 10 Mhz reference as the modems at the far end would not lock to the HQ TX signal but i could see the power levels going up and down as i adjusted them with telnet to each modem - i could see my 7 carriers from the HQ side and could see them go up and down as i adjusted power but the far sides were not receiving it.

At this point a college arrived and i showed them how the signal disappeared on the spec an when i rebooted the music box - and then as i re-powered up the music box the modems on the far sides started to lock to the HQ TX signal. I was then able to telnet to the far side and adjust power levels at the far side to balance up the links ( i do this every now and then because it is running SCPC mode on KU band and i have no UPC at the far sides - so i manually adjust the links to balance out the links at each end).

So long story short the network is back up , passing traffic and all is well - so far.

I'm a bit puzzled to why this happened - solar outages are not due to start until the 22nd of this month so its not that.

Do you think it was temp loss of 10 Mhz ref? or perhaps the music box is playing up/? I have narrowed it down to either music box or BUC giving issues, but would appreciate any input from those who know iDirect SCPC.

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Posts: 826
Reply #1 - Mar 5th, 2010 at 12:03pm  
I agree with your assessment.  Esp if the carriers were at or close to contract power.  I dont have a lot of experience with the music boxes.  I know what they do and and how they are configed but I have never used any of them.  Glad to hear you were able to resolve it.  If I had to guess I would think that the 10Mhz was the culprit, but at this point who knows.  Gotta love it when you arent entirely sure what fixed it (for your own sanity).
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Regards, &&&&M
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Ex Member
Ex Member

Reply #2 - Mar 5th, 2010 at 1:51pm  
Hi Mike,

Thanks for your reply. The 10 Mhz ref seems to make the most sense to me given what i was seeing. The 10Mhz ref is being generated at the BUC. But when i reboot the music box it comes back to life. SO is this music box or BUC ? Could be either. When i reboot the BUC i get no change, when i reboot the music box i get results.

However it could be that when the music box is rebooted and the BUC loses all signals from modems and music box that it gets jolted back into service. Makes sense if you think about it. However given i get results when i reboot the Music box it leads one to conclude that it is a Music box issue. Hmmm i'm 50/50 on this. I guess swapping out the BUC with the spare that sits next to the rack is one one to test but its an expensive little beastie and i'd hate to crack the wrapping and open the box for no reason.

Anyone got an opinion on this ? This event occurred once last week but all was working before i got to the site. It happened the night before this event i have described , which i solved by a music box reboot and then it happened again yesterday. Something is breaking down. Makes more sense for it to be a BUC given its been out in teh rain and sun for 15 months, but if so why does a music box reboot solve a BUC issue?


Hope its stopped snowing in Colorado. Ya'all could do with a break from the snow over there .
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