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How to diagnose intermittent connection

Frequent Visitor

How to diagnose intermittent connection

We've had an intermittent connection for months. It typically is worst during the day, but fairly reliable in the morning and evening.

 

Modem is NetGear CM600, firmware v1.01.18

 

The drop to the house was replaced over the winter in an effort to resolve the issue, but it has not helped. Multiple chats with Comcast tech support and visits from Comcast service personnel have not resolved the issue. Any suggestions here on how to proceed would be appreciated.

 

I have posted the router event log, which shows errors typical during the day. I have also posted the current signal levels, but the internet connection has been good for several hours and so it's not clear if this is useful.

 

My images don't seem to show up for me.

20190715_Event_Log.jpgEvent log

 

20190715_Cable_connection.jpgCable connection

 

 

Expert

Re: How to diagnose intermittent connection

Can't see your pics. Since you are a new poster, they likely need to be approved by a Forum Admin. Or you may need to make a minimum number of posts.

You could try hosting them at one of those free third-party pic hosting sites like Imgur or Photobucket and post the link to them here.



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Frequent Visitor

Re: How to diagnose intermittent connection

Thank you for approving the images.

Expert

Re: How to diagnose intermittent connection

The downstream power is weak / low and it may be intermittently fluctuating even lower to out of spec levels. It is, as a matter of fact, already out of spec at the higher channel frequencies. Seems there is a serious / typical "cable tilt" problem. That can cause random disconnects, spontaneous re-booting of the modem, and speed and latency problems.

In a self troubleshooting effort to try to obtain better connectivity / more wiggle room, check to see if there are there any excess/unneeded coax cable splitters in the line leading to the modem that can be eliminated/re-configured. Any splitters that remain should be high quality and cable rated for 5-1002 MHz, bi-directional, and no gold colored garbage types like GE, RadioShack, RCA, Philips, Leviton, Magnavox, and Rocketfish from big box stores like Home Depot, Lowes, Target, Wal-Mart etc. Splitters should be swapped with known to be good / new ones to test

If there aren't any unneeded splitters that can be eliminated and if your coax wiring setup can't be reconfigured so that there is a single two way splitter connected directly off of the drop from the street/pole with one port feeding the modem and the other port feeding the rest of the house/equipment with additional splits as needed, and you've checked all the wiring and fittings for integrity and tightness and refresh them by taking them apart then check for and clean off any corrosion / oxidation on the center wire and put them back together again, then perhaps it's best to book a tech visit to investigate and correct.



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Re: How to diagnose intermittent connection

Thank you for your answer, this was very helpful. A response, a comment and a question.

 

Response

Short:

Modem is connected directly to Comcast drop, with no splits from the end of the drop at the house.

 

Long:

There is a Comcast-installed splitter in the cable post on the port that feeds two drops: one to my house and one to my neighbor's. The drop then connects to a 1:1 junction in the Comcast installed service panel on the side of the house and the house coax connects to the other end of this junction.

 

We only use Comcast for internet, with the rest of the house using OTA signal from a rooftop antenna for TV. All household coax outlets are connected to the OTA coax from the roof via an amplifier, excluding the coax outlet for the cable modem. The cable modem coax outlet is connected straight to the junction in the house-mounted service box, with an additional 1:1 junction located inside the house near the OTA amplifier.

 

Comment

We've had multiple Comcast service calls over the past couple of years in an effort to resolve our intermittent internet. The drop to the house has been replaced twice. A tech has moved our drop to its own port, and moved the neighbor onto the second port with a daisy-chained set of splitters.  This would help us, but cause problems for the other customers. Then the neighbor would lose signal and another tech would move him to his own port and put us on the daisy-chain. We've been told our area is over-capacity, although I don't know exactly what that means.

 

Typically, the service call will end when the tech is able to demonstrate that the signal at the house is within spec. Usually, we'll have reliable service for a couple of weeks after the visit until the drops re-occur.

 

Question

Our neighbor who currently shares the port and splitter in the cable post uses a drop amplifier and reports no recent drops of his internet (or Comcast TV service). I see a well-regarded active return 1-port CATV amplifier on Amazon (PCT) for $40. Any reason not to give this a shot?

Expert

Re: How to diagnose intermittent connection

You could give it a try and return it if it doesn't help, can't hurt to try. Bear in mind though that if there is noise ingress on the line, an amp would make it worse. Garbage in = even more garbage out. YMMV.



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Re: How to diagnose intermittent connection

As a followup, I ran a test this morning measuring the signal at the house drop, by connecting the modem to the junction at the cable box on the side of the house.

 

Comcast_signal_at_house_drop.jpgSignal at cable drop

The signal is the same as when measured at the normal position inside the house, so I don't think there is any issue with the house wiring.

 

I guess I'll have to hope that the amplifier can help.

Expert

Re: How to diagnose intermittent connection

It's not quite the same. The downstream power is better. But the SNR is out of spec on channel 24 and the power is still a bit on the weak side.



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Re: How to diagnose intermittent connection

Thanks again for responding so quickly to these posts. You're right about the drop in power. I was focused on the SNR values.

 

I measured the signal before the test and it looks like the power loss is about 5-6 dBmV due to the house wiring. I have no idea if that is typical.

 

I'll give another update once I've installed the amplifier at the end of the month.

 

20190720a_Cable_connection.jpgSignal test at normal modem location.