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sb6101

@mchsi.com

2 edits

[Signals] Question about Signal Levels

To preface this message, this isn't on a Comcast system but I wanted the knowledge from the Comcast staff on this issue.

Since last year's fiber cut and some changed to the node, I noticed that Upstream Power Levels in my neighborhood increase as temperatures decrease. The Upstream Power Levels show the change first, but then the Downstream Power Levels change by showing a decrease as temperatures decrease. The Upstream shows the issue more than the Downstream, but both show the pattern.

Please see the 3 attachments. In about 14 hours, the Upstream Power Level increased by 3dBmV while the Downstream Power Level decreased by 2dBmV when temperatures went from 25F to 10F. This pattern is observed on other cable modems in the neighborhood that are on different taps on different streets. As temperatures continue to decline, the signal continues to degrade (higher Upstream Power Level and lower Downstream Power Levels).

When the temperatures warm during the day, the Upstream Power Level goes back down and the Downstream Power Level goes back up. When the temperatures cool over the night and early morning, the process repeats itself.

When I first reported this issue last year before we fully seen the cold temperatures, my cable provider said that the signals were within specifications and they wasn't concerned about the fluctuation and abnormal behavior being displayed. When temperatures dropped below 0F, the Upstream Power Level went up to ~61dBmV, Downstream Power Level went beyond -10dBmV and Downstream SNR dropped. Intermittent connectivity occurred. My cable provider came out in the neighborhood and said they fixed the issue.

The issue has returned as colder weather has arrived. Now, like last year, my cable provider is saying that the signals are within specification and the fluctuation and abnormal behavior is a concern to them.

Am I correct to believe there is a plant issue here?


Edited to add topic group category.

Screen shots removed as requested by sb6101 See Profile. Hopefully, he will post his corrected info. sortofageek See Profile



sb6101

@mchsi.com

Re: Question about Signal Levels

Small correction:

"The issue has returned as colder weather has arrived. Now, like last year, my cable provider is saying that the signals are within specification and the fluctuation and abnormal behavior isn't a concern to them."



JeepMatt
C'mon the U
Premium
join:2001-12-28
Wilmington, DE
kudos:2
Reviews:
·Comcast

I have to admit, all of your screen shots and levels are within spec.

A 2-3dB change with winter temps isn't out of the norm. And even at its worst, 49 upstream on a 16QAM system isn't bad.

Have you been seeing negative impacts? I know you mentioned you did last year - but these levels don't suggest anything.
--
"ONE team - ONE city - ONE dream!!"



tshirt
Premium,MVM
join:2004-07-11
Snohomish, WA
kudos:4
Reviews:
·Comcast
reply to sb6101

I'm not a comcast employee,, (and I doubt one would make any sort of "official" statement as to a competitors plant operation) but the MINOR fluctuation you are showing now IS normal and within spec.
whatever happened last year certainly has been fixed and any similar problems they are aware of are likely also repair ASAP.



sb6101

@mchsi.com
reply to JeepMatt

The signals are currently within specification. No debate there. But we haven't gotten the full cold weather and the pattern appears to suggest the signals will continue to degrade as temperatures continue to get colder.

But I'd like to ask all of you if you see a signal degradation on both Upstream and Downstream as temperatures decrease? Normally, attenuation on the line is lowered in colder temperatures and causes a stronger signal - not the opposite. Therefore, it appears there is some oddity, isn't there?

Expand your moderator at work


tshirt
Premium,MVM
join:2004-07-11
Snohomish, WA
kudos:4
reply to sb6101

Re: Question about Signal Levels

but AGC amps adjust within the current temp ranges and in areas with extreme temp ranges the plant MAY require some seasonal adjustment either hands on, or by remote command.
No doubt , your provider does this already as needed.


GusHerb94

join:2011-11-04
Chicago, IL
kudos:1
reply to sb6101

Re: [Signals] Question about Signal Levels

My upstream power increases as it gets warmer out, and downstream power decreases. SNR hovers around the same numbers year round. The network around me apparently does the opposite of what yours does.



joedb

@qwest.net
reply to tshirt

Re: Question about Signal Levels

If the US is impacted more than the DS and it's on a lower frequency it could be a condition known as suck-out. Typically you'll see the US decrease and the DS increase in colder temps. I wouldn't consider a 3db fluctuation as minor since anything over that is a good indicator of a problem in the field. I'd bet some tools there's a problem there.



SeaSeaTee5

join:2010-05-06
Maryland
reply to sb6101

Re: [Signals] Question about Signal Levels

They may be using thermal pads and thermal drive units in your area. We don't use them here so I'm not familiar with EXACTLY how they work but as the name would imply, they are for adjusting the signal for temperature swings.


n_w95482
Premium
join:2005-08-03
Ukiah, CA
reply to sb6101

I'm assuming you're posting about a Mediacom system. If so, I have had some experience dealing with them (my dad uses them and I often get pulled into the loop when he has issues). If not, ignore everything below this .

I've found them to be substantially more lax on signal levels than Comcast, both with absolute low/high readings, and deviation per channel on DOCSIS 3.0 setups. Here's a thread I made last year when I replaced my dad's modem. There was some additional behind-the-scenes communication beyond what was posted there, but their fix there was to do some adjustments to swing the signal way in the other direction (8-10 dBmV).

At the time, it was fine, but I had a strong suspicion that the upstream signal would go out of spec during the summer and cause problems. I communicated that to Mediacom, who said they would deal with it then if that was the case. Sure enough, it did happen - upstream went up to 58+. They finally balanced the line to a happy medium a couple of months ago (minus the variance between downstream channels, that's still there).

If you do end up having issues, I recommend posting in the Mediacom forum, or registering here and sending a private message to MediacomChad See Profile (good idea to register in either case). He seems to follow company guidelines for signal stats, for better or worse; but when there is a problem, he is quick to get the ball rolling. I didn't see this thread until after the screenshots were removed, so I can only go by what others here have posted.



tshirt
Premium,MVM
join:2004-07-11
Snohomish, WA
kudos:4
Reviews:
·Comcast
reply to joedb

Re: Question about Signal Levels

said by joedb :

If the US is impacted more than the DS and it's on a lower frequency it could be a condition known as suck-out.

and if he's going into the subzero range, umm, "shrinkage" is going to be extreme.( a coupler that looks perfect or even too long in july or august may not be long enough below zero)
Which they likely tried to check every fitting they could from the node/amp to his house last year.
And they MAY need to do it again this year, if conditions are more extreme or an end was recrimped over the summer or if water got into the cable/conduit.
There isn't anything they are likely to do in advance of a problem, and weather driven intermittents are very hard to pinpoint