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JDookie
join:2005-04-29
New Orleans, LA

JDookie

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[LA] Lower DL signal but better UP signal??

Cox has been doing a lot of repairs in my neighborhood lately, and just recently I noticed a drop in Upstream dB, from 45-47dB down to what you see below, which is good right? Oddly enough though, my Downstream signals still suck. How can the Upstream get better without the Downstream changing?



Optimus2357
Premium Member
join:2010-11-21
West Warwick, RI

Optimus2357

Premium Member

Lots of ways, they are totally different frequencies. Actually usually the few times it does change together is a splitter. The general US SNR is set by the person furthest away from the signal's source. So if they fixed some issue, probably the areas US SNR went up which meant the CMTS worked out a lower Tx with your modem.

DocDrew
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DocDrew

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said by Optimus2357:

The general US SNR is set by the person furthest away from the signal's source. So if they fixed some issue, probably the areas US SNR went up which meant the CMTS worked out a lower Tx with your modem.

huh? That doesn't make any sense.

The upstream snr isn't generally set by the furthest customer and transmit levels don't depend on received snr.

Optimus2357
Premium Member
join:2010-11-21
West Warwick, RI

2 edits

Optimus2357

Premium Member

Really? Would you care to quote a source why that doesn't make sense? And what do you think the US SNR is set by? Please, by all means, state your experience.
JDookie
join:2005-04-29
New Orleans, LA

JDookie

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Well, I don't know if this will help your theory or not, but I have been told by various Cox techs that I am "at the end of the line" which is why my signals are always on the lower end of the scale. My downstream signals have always hovered around -1 to -4 at the lowest until about a six months ago, when they totally tanked. That being said, I have *never* seen Upstream power so low until now.

Optimus2357
Premium Member
join:2010-11-21
West Warwick, RI

Optimus2357 to JDookie

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to JDookie
Hmm, its almost like I know what I am talking about. Almost anyway.

»[ALL] Too low Upstream Power levels?

I believe that last response is from a engineer.

DocDrew
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3 edits

DocDrew to Optimus2357

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to Optimus2357
Read this:
»www.cisco.com/en/US/prod ··· 38f5.pdf

That's a paper by an engineer on upstream snr. I'll explain more later. I'm busy and posting by way of phone.

Edit. I'll add this to the reading list: »www.cablefax.com/tech/op ··· 990.html
»www.cascaderange.org/pre ··· sues.pdf
»www.sctedakotaterritory. ··· tion.pdf
DocDrew

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DocDrew to JDookie

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to JDookie
To the OP... Your modem isn't showing frequencies for each channel so it's a guess but it looks like the higher channels are dropping in level pretty quick. That's usually a sign of water intrusion or a low frequency rated splitter or other device. If the channels shown are actually higher in frequency, long or poorly maintained cable runs could also do it.

Downstream signal losses caused by corrosion due to water infiltraion or losses due to long cables or splitters with low frequency ratings won't affect the upstream signal much. Downstream and upstream signal levels can also be independently adjusted in multiple places within the cable distribution network and headend.
cmos100
join:2004-08-24
Lafayette, LA

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to Optimus2357
From my years of troubleshooting, quite often the the noise problems will come from the end of lines where there is low value taps and very little isolation, but at any point in the node ingress can get in and cause low SNR. Modems won't normally transmit higher if the SNR is low. All the 10k knows is, it wants 0 dbmv hitting the port and instructs the modem to change it ouput level until it is 0.

To the OP, you don't happen to have a upstream house amplifier?

Optimus2357
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join:2010-11-21
West Warwick, RI

Optimus2357

Premium Member

@ DrDrew/CMOS100 Here is the source I was thinking of when I made my comment.

»Question about modem Tx power level

"Unfortunately, the fact that your upstream signal is low means that the upstream SNR at your tap is also low. Remembering that the noise is amplified by the upstream amplifiers just as the desired signal is, the end result is that the users with the lowest upstream power tend to set the SNR for the entire upstream channel. "

Granted, its on Comcast's forum, but I thought it was a Cox employee. I mixed up Kip P with Kip K (who I see here on this forum alot) though so that might explain it. It sounded like a pretty technical answer though, but maybe thats more how Comcast does it but it seems its a matter of debate there too. Either way sorry for Hijacking the thread. I thought I was giving good info :-/ Thanks for the education.
JDookie
join:2005-04-29
New Orleans, LA

JDookie to cmos100

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to cmos100
said by cmos100:

To the OP, you don't happen to have a upstream house amplifier?

No amplifiers or splitters. I only subscribe to Internet and phone from Cox so the line comes from the street to a gray plastic box on the side of my house. Out of that box is my telephone line and a coax line that goes straight to my modem. The line does have two breaks in it though (barrel connectors). One is outside, and the other is in my attic. The one outside is brass and has the ground attached to it. The one in the attic is just the standard silver barrel connector.

Optimus2357
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join:2010-11-21
West Warwick, RI

Optimus2357

Premium Member

@ JDookie Oh I didn't mean to imply a wiring problem on your end, or even any end. Simply my theory of how Tx can lower without any change of Rx. Which was the OP right? Apologies if I offended
JDookie
join:2005-04-29
New Orleans, LA

JDookie

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said by Optimus2357:

@ JDookie Oh I didn't mean to imply a wiring problem on your end, or even any end. Simply my theory of how Tx can lower without any change of Rx. Which was the OP right? Apologies if I offended

I'm not offended, I was just answering cmos100's question.