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Improving SNR

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Improving SNR

My Motorola MB8600 modem is reporting large numbers of uncorrected errors on channel 8 (Freq 579.0 MHz). The SNR is also low (28.4 d. There is sometimes a lesser problem on channel 9. Is there a way for me to improve the SNR on these channels or to switch to different channels? The screenshot is from shortly after rebooting the modem. My speed degrades over time, seemingly as these errors increase.

 

xfinity channels.png

Expert

Re: Improving SNR

That's on the UHF frequencies of TV broadcasts. If only one channel were affected, it shouldn't make any appreciable hit on your connectivity, but I also noticed that the downstream power levels are really high, which likely means a wiring issue somewhere. Looks like some basic troubleshooting is needed. Start here, and if you still need assistance, come back with all the information requested in this post


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Expert

Re: Improving SNR


@darkangelic wrote:

but I also noticed that the downstream power levels are really high,

 

Did you mean that they are really low ? Some of the SNR's are on the low side as well. 


 



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Re: Improving SNR

Thanks for your reply. It looks like my wiring may not be up to par. All of the connectors are crimp connectors, not compression connectors, and the cable itself, though unmarked, is .25" in diameter, so I'm thinking it is all RG59 and not RG6.  This applies even to the Comcast cable that is coming into the house (all done decades ago when the only concern was analog TV).

 

I'll try some experiments to see if directly connecting my modem to the Comcast cable where it comes into the house, bypassing the house wiring and all splitters, does better. That is still RG59, but it is buried, so maybe the earth above it will help shield it. In any case, it will make the total run shorter and it will take the house wiring out of the system.

 

Although I am also concerned that the RG59 conductor is thinner, so I wonder if I need some kind of RG59-RG6 adapter to make good contact with the female connector on my modem. I don't know what would be involved in getting Comcast to change the feed to the house to be RG6 (assuming that I am correct that the .25" OD cable isn't).

 

I am currently using the 1000Mbps service.

Expert

Re: Improving SNR


@EG wrote:

@darkangelic wrote:

but I also noticed that the downstream power levels are really high,

 

Did you mean that they are really low ? Some of the SNR's are on the low side as well. 


 


Yes, thank you, I meant high as in absolute values.


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Expert

Re: Improving SNR


@shacktoms wrote:

Thanks for your reply. It looks like my wiring may not be up to par. All of the connectors are crimp connectors, not compression connectors, and the cable itself, though unmarked, is .25" in diameter, so I'm thinking it is all RG59 and not RG6.  This applies even to the Comcast cable that is coming into the house (all done decades ago when the only concern was analog TV).

 

I'll try some experiments to see if directly connecting my modem to the Comcast cable where it comes into the house, bypassing the house wiring and all splitters, does better. That is still RG59, but it is buried, so maybe the earth above it will help shield it. In any case, it will make the total run shorter and it will take the house wiring out of the system.

 

Although I am also concerned that the RG59 conductor is thinner, so I wonder if I need some kind of RG59-RG6 adapter to make good contact with the female connector on my modem. I don't know what would be involved in getting Comcast to change the feed to the house to be RG6 (assuming that I am correct that the .25" OD cable isn't).

 

I am currently using the 1000Mbps service.


I agree, connecting your modem to the cable demarcation point where it enters the house should identify the wiring as the source of the problem. 

Did you get a professional install as part of the gigabit service? (Normally one is required to identify cabling issues like the one your described.) 


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Re: Improving SNR

There was a professional install in 2013 when I first signed up for the Extreme 105 service. The installer had a notebook computer with him that only showed about 60Mbps, but my computer speed tested at the full speed (or a little better), so we chalked it up to a slow notebook. I think the installer did look at signal quality and chatted with people back at his office to tweak some settings, but none of my cabling was replaced. The cables were ones that were installed (all by Comcast) to put a TV in my office a long time ago, but I don't have a TV in my office now.

 

Later, my service seemed to go up to 150Mbps "by itself". Recently, I went to the Xfinity page and clicked to upgrade to 1000Mbps, and was surprised to find that it upgraded immediately, seemingly without having to wait for a person to do anything. (It also knocked a few bucks off my monthly bill).

 

But there has been no installer since the 2013 install of the Extreme 105 service. I upgraded my modem a few months ago because I was hoping to solve slow-down issues, and then I noticed that the modem I had purchased was also suggested for the 1000Mbps service, so I went for it. The service is fast, especially after rebooting the modem, but sometimes I notice hiccups (occasional delays or pages that seem to load incompletely) and the speed degrades, until I reboot the modem.

 

Just now, I had noticed that my speed had degraded, so I took some screen shots before and after rebooting my modem.

 

Before...

xfinity 20180829a before reboot.png

 

After...

xfinity 20180829b after reboot.png

Frequent Visitor

Re: Improving SNR

I just had kinda same problem so they removed the amp from nid and now connection is rock solid. If you dont have amp maybe you need one.
Frequent Visitor

Re: Improving SNR

I tried the experiment, connecting the modem directly to the incoming cable, with no splitters or any joins to other inside cables. The numbers improved, except I am still getting low SNR on channel 8.

 

xfinity 20180902 after reboot.png

Frequent Visitor

Re: Improving SNR

I am really starting to think the fault is in my modem. I don't know what the settings mean, but there is a place to enter a frequency in Hz. I tried entering 585000000, hoping that would skip the troublesome channel. It did appear to do that, the list of frequencies seemed to start with 585.0 as the channel 1 frequency, increasing from there. However, I still got a low SNR and uncorrectable errors on channel 8, even though it was now using a completely different frequency. I quickly reset the modem to factory settings and reconnected, because I didn't want to operate out of spec, but it made me very suspicous that the problem was with my modem. Maybe I'll try a different one.

Official Employee

Re: Improving SNR

With your modem’s stats being so low without any splitters at all, I’d be leaning more towards it being a drop issue or a possible outside maintenance issue more than a modem issue

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Re: Improving SNR

I did try replacing the modem, with one from a different manufacturer, the Surfboard SB8200. The stats it lists have generally better power levels and SNR levels, but there is still a problem on channel 8. So I think you are correct that the problem isn't with my modem. Since my modem is directly connected to the Comcast cable right where it comes into the house, I think that puts the issue on the Comcast side, as you suggested. What is the best way for me to handle this?

 

xfinity 20180904 sb8200.png

Official Employee

Re: Improving SNR

Escalated to a colleague to assist getting a tech scheduled

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Official Employee

Re: Improving SNR

Hello, shacktoms. I apologize to hear of the issues you having with the signals and the uncorrectable. I would like to look further into this for you. Can you please send me a PM with your first and last name?

 

To send a private message, please click my name "ComcastMichael" then select "Send a Message" on the right side.


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Re: Improving SNR

I assume you contacted someone to fix things, for today, with no modem restart, the speed is great, the SNR is great on all channels (including channel 8) and running several speed tests (with different endpoints to find one that could really run at 1Gb/sec) there were no additional errors on any channel, and there were no uncorrectable errors anywhere. So, although all of the answers were helpful to me, I am accepting your answer as the solution.

 

Thank you for your help.