Xfinity plant
Xfinity globe
Community Forum

Increased DS power and lower SNR

Regular Contributor

Increased DS power and lower SNR

For the past two years I've been using a new Netgear CM600 cable modem and have always had good signal levels. Downstream with 24 bonded channels, power around 10-12dBmV and SNR between 38-40dB. Upstream with 4 bonded channels with 45dBmV power level. Past 3 months it showed zero Correctables and Uncorrectables.

 

Then two nights ago all the Comcast service was down (TV/Internet/Voice). I checked the Account app and it showed scheduled maintenance being done in the area. It doesn't say that any more, but now I've been getting inconsistent readings. 

First off, the 24 downstream channel frequencies are out of order, power levels are much higher, SNR had lowered, and I'm getting thousands of Correctables. Also, some of the downstream channels are showing a negative power level, which never happened before.

 

https://www.dropbox.com/sh/oqbwlmvfi317rrf/AABj4mw1kMMI_NQnxd-VsoSVa?dl=0

 

I'm on the Extreme 150 plan, and usually get 178Mbps. Now I've seen it fluctuate between 80 and 170.

Regular Contributor

Re: 2 days of maintenance issues

I've subscribed to your new posting.

 

Something obviously went amiss during Comcast maintenance in your south FL area ... very interesting.

 

We're still seeing a 90% decrease in Correctables (per my PM message from a few days ago) since Comcast Maintenance in our area in the PacNW and our account status shows that maintenance has been completed for several days now.

 

Regular Contributor

Re: 2 days of maintenance issues

I've also noticed that when checking the DXC cable boxes, the inbound channel SNR has decreased from 37-38dB to 32-33dB.

Expert

Re: 2 days of maintenance issues

Oh boy @FAUguy, those are some crazy looking levels you got there. You're probably going to need a tech to address that. I'll ask an employee to review your account/power levels and node health. They can see what's going on in your neighborhood and get a tech out there as needed.

 

I've asked a Comcast employee to help you. You should expect a reply in this thread. 

Regular Contributor

Re: 2 days of maintenance issues

I reset my modem at 5am, and just checked it at 5pm:

https://www.dropbox.com/s/30c0vfdkawlov28/Screenshot_20180318-165343_Dolphin.jpg?dl=0

 

As you can see, the levels remain all messed up, and tons of Correctables.

I'm not sure what was done between the plant in Pompano and my location, but the DS power went up by 4dBmV on most channels, but some are now negative power, the SNR decreased by 5dB, channel frequencies are now out of order, and getting Correctables and Uncorrectables.

Regular Contributor

Re: 2 days of maintenance issues

Over the past hour (5am) the download speeds have been pretty bad.

https://www.dropbox.com/s/7d9ucti1tyy5g21/Screenshot_20180319-054210_Speedtest.jpg?dl=0

Regular Contributor

Re: 2 days of maintenance issues

7am and download speed it back to normal.

 

But signal levels are still off.

This would be like 4 days now.

https://www.dropbox.com/s/szxh1tiffii4avh/Screenshot_20180319-070328_Dolphin.jpg?dl=0

Regular Contributor

Re: 2 days of maintenance issues

Wow. It's nice to see that no one from Comcast has looked at this.

It's pretty clear to me that whatever work was done last week increased my downstream power leves a good 7-8dBmV, but also decreased my SNR from 38dB to 33dB.

 

So tonight I did some testing.

These first levels is with my CM600 connected to the same 2-way CommScope splitter that Comcast installed a few year ago.

https://www.dropbox.com/s/7tggeqj0ewmm51c/2waysplit.jpg?dl=0

 

Then I connected the modem to the 4 way splitter that is what is feeding the DCX cable boxes. As you can see the DS power decreased some, but some channels are still showing a negative power reading.

https://www.dropbox.com/s/njaj5hylmawme85/4wayspliter.jpg?dl=0

 

Then for the final reading, I had the main line coming in connected to the 4 way splitter, and then that connected to the 2 way splitter with the Modem on it. 

This was the only way to get the power levels lowered, and with any showing a negative power level.

https://www.dropbox.com/s/tkre2bdd3efnk77/4wayand2waysplit.jpg?dl=0

 

But even when using both the 4 way and then 2 way splitter to fix the power levels, I'm still getting a ton of Correctables that I hadn't been getting before.

Regular Contributor

Re: 2 days of maintenance issues

This is the current levels with the 4 way splitter and then the 2 way splitter used.

https://www.dropbox.com/s/y1j524r6oj2q11y/Screenshot_20180319-220627_Dolphin.jpg?dl=0

Regular Contributor

Re: 2 days of maintenance issues

This is with the modem connected to the coax without any splitters.

https://www.dropbox.com/s/bb3r8vz4c3897w8/Screenshot_20180320-034346_Dolphin.jpg?dl=0

DS power is 20-21dBmV, which is just way to high.

It use to be 14-15dBmV, and then after the 2 way splitter it was lowered to 11-12dBmV.

So it's pretty clear something was done that increased the line power, but also decreased the SNR from 38-39dB to 32-33dB.

Regular Contributor

Re: 2 days of maintenance issues


@FAUguy wrote:

I've also noticed that when checking the DXC cable boxes, the inbound channel SNR has decreased from 37-38dB to 32-33dB.


Here is the posting I was curious about in my prior PM .... I think it is d04 on the TV menu .... I'm normally running 37-38 (occassionally 36) with "Good" .... Did you happen to notice if if was still "Good" when at 32-33?

Regular Contributor

Re: 2 days of maintenance issues


@eecon1 wrote:

@FAUguy wrote:

I've also noticed that when checking the DXC cable boxes, the inbound channel SNR has decreased from 37-38dB to 32-33dB.


Here is the posting I was curious about in my prior PM .... I think it is d04 on the TV menu .... I'm normally running 37-38 (occassionally 36) with "Good" .... Did you happen to notice if if was still "Good" when at 32-33?


The DCX menu d04 Inbound Status that was 33dB was still listed as "good".

But it is now 35-36dB depending on which cable chanel frequency is used.

Regular Contributor

Re: 2 days of maintenance issues

I also had a CommScope 6 way splitter that was left by the Tech two years ago, so I just tried it.

https://www.dropbox.com/s/dsamj474movt06h/6waysplit.jpg?dl=0

As you can see the DS power level is 10-11dBmV, which is in spec.

 

When I had the 4 way splitter + 2 way splitter installed earlier, this was the levels:

https://www.dropbox.com/s/tkre2bdd3efnk77/4wayand2waysplit.jpg?dl=0

It lowers the DS power about 2dBmV than the 6 way splitter.

Expert

Re: 2 days of maintenance issues

@FAUguy,

You're still in the queue, they didn't forget about you. They just had some staffing/workload issues over the weekend and are catching up as we speak. 

Regular Contributor

Re: 2 days of maintenance issues

After using the 6 way splitter last night for a while, I noticed that the TVs picture quality wasn't as good (looked soft). So I removed it and went back to using the 4 way splitter (that the DCX boxes are connected to) and then the 2 way splitter for the Netgear Modem and Arris (only used for phone).

 

It has been like this for 12 hours now (6am-6pm) and these are the current levels:

https://www.dropbox.com/s/3sm8b6iyt4u1705/Screenshot_20180320-181926_Dolphin.jpg?dl=0

 

Still getting high amount of Correctables that I never got before, and the SNR is down from 38-39 that I use to get.

Official Employee

Re: 2 days of maintenance issues

Hi FAUguy, I will gladly check signals on my side for you,  please send me a private message with your account information (your name, address and account number). 

 

Thank you

Regular Contributor

Re: 2 days of maintenance issues

@FAUguy .... You're in good hands now that Comcast Phill is on your case .... He helped me self-find a kinked coax just behind a wall plate 9 or 10 months ago and we've been rock steady ever since!

Regular Contributor

Re: 2 days of maintenance issues

So here's a brief overview of what's happened.

The coax power coming into my house at the tap use to be 15-17dBmV for the past few years, but a week ago there was scheduled maintenance in the area (cable was out at night) and afterwards my Netgear CM600 modem was getting too much power (15-17dBmV) causing it to not work right and showed millions of Corrrectables and Uncorrectables (which for the past two months I had zero).

I tested the modem (with all spltters removed) and it was showing 19-21dBmV of power, and then installed the Commscope 2 way splitter that I had been using and the power was 15-17dBmV.

So what I ended up doing was to first use the 4 way splitter (with the 3 cable boxes) and also connected it to the 2 way splitter wth the Netgear Modem and Arris eMTA connected.

This brought the power at the modem back into specs (8-10dBmV).

 

But the other problem was that after the scheduled maintenance my SNR that use to be 39-40dB was now 32db.

The SNR does not change with or without splitter, so again I know that happened outside of the house.

We had a few cold(er) nights in FL where the temps dropped below 50, which caused the SNR to drop to 28db, and the download speeds less than 10Mbps instead of 150-178Mbps.

 

Two days ago the Comcast Tech came out. He looked at the signal at the Tap and it showed 17-21dBmV of power.

He replaced the RG-6 Coax from the Tap and new MoCA PEO Filter in the outside box (this was also done 2 years ago), but also installed a -3db attenuator at the tap.

Then he came inside and removed the 4 way and 2 way splitter and installed a 9 way PPC EVO1-9-U/U amp/splitter. On the input line at the amp/spltter he installed a -6db attenuator (so that is a total of -9db with the -3db installed outside). Then connected the cables that feed the 3 DCX cable boxes, Netgear Modem, and Arris eMTA.

When it was all done, we cheked my levels, and everything was uncahnged!

The modem still showed between 8-10dBmV of power (which is what it was getting with just using the splitters) and SNR was still 32-33db and download speeds seemed to vary.

So he agreed with my first thought that something was changed on their end, which increase my downsteam power levels, while also lowering the SNR. So he put in a Trouble Ticket to have the local Node and area checked.

That night then temps were in the mid-50s, the SNR got to 30db, and download speeds were 50-80Mbps.

 

One thing I have noticed with this amp/splitter installed is that the picture quality on the TVs look different (using Motorola DXC3400/3200). It's not as sharp, a bit "softer", and colors and brightness is a tad "duller".

So I'm not sure if between having the -3db and -6db attenuators insatlled, then the amp/splitter which splits the signal into 9 ports and then has to insert power to compensate for the loss, is causing the picture quality to not look as good as it was with just the regular 4 way splitter.

 

So in the 2 horus that he was here, and the lines and splitters that were changed out, all that was acomplished is now knwing the issues doesn't lie isnide of the house, but somewhere outside in the local area.

Regular Contributor

Re: 2 days of maintenance issues

@FAUguy

 

Silly question, but did you swap out your CM600 modem for another modem just to make sure yours didn't get messed up by the service outage or when it came back on?

 

Kudos for all the detail and your restraint in this thread. I feel your pain.

 

Please keep us updated.

Regular Contributor

Re: 2 days of maintenance issues

I have a Arris TM822G eMTA that is currently only being used for Voice. But last week I did remove my Newgear and used the Arris as the data modem, but it still showed the low SNR, Correctables and Uncorrectables. So after I while I changed back to the Netgear. Since the warranty is 12 months, I'm about 8 months past it, and would have to buy a new one if I thought it was going bad. But the Arris is showing the same line issues. So I'm pretty sure the problem isn't with the two modems.

Regular Contributor

Re: 2 days of maintenance issues

Thanks for the update.

 

That's good to hear for (my) selfish reasons. I'm planning on replacing my TG1682G with a CM600 after I've had the former for a month to verify the lines and everything are ok. Your thread and another concurrent thread, also with a CM600, had me concerned. His problem also was not the CM600 but something with Comcast.

 

I hope they get you fixed up soon.

Regular Contributor

Re: 2 days of maintenance issues

 At this point if I were to replace my CM600, I'd go with a DOCSIS 3.1 model, such as the Netgear CM1000 or the MB8600 from Motorola (Zoom), not the Arris SB8200 (heard of too many problems with it).

Regular Contributor

Re: 2 days of maintenance issues


@FAUguy wrote:

 At this point if I were to replace my CM600, I'd go with a DOCSIS 3.1 model, such as the Netgear CM1000 or the MB8600 from Motorola (Zoom), not the Arris SB8200 (heard of too many problems with it).


Right. I'm going back and forth on that. I still haven't decided.

 

I'm only at the Performance tier (60Mbps after the speed bump a couple of weeks ago) with no plans to increase that at this point. I'm a little concerned about buying into first generation DOCSIS 3.1 modems with such a limited choice and relatively high cost. The CM600 would be plenty capable for now, is about half or just over half the cost of the 3.1 modems, and would pay for itself in about 9 months.

 

Decisions, decisions.

 

Regular Contributor

Re: 2 days of maintenance issues

I'm on the Extreme 150 plan (get 175/24). Even if Comcast does a "free" speed increase here, it would probably be somewhere between 200-300Mbps, which the CM600 can do up to 960 I believe. The newer CM700 can do 1.4Gb since it has 32 bonded DOCSIS 3.0 channels instead of 24.

But the CM700 has the same Puma chip, which causes the same issues that had been on Surf Board over the past few years.