erratic speeds with CM 500 Cable Modem

[tomham]

Hi just purchased a CM 500 cable modem for my daughter.  Comcast had trouble "finding it" but did eventually.  But I noted very erratic up & down load speeds.: 168 Mbps to 1.2 download and 2.5 to near zero download; it goes all over the place. Comast put in a new "drop" form the street pedistal to her home entry; said the signal was strong.

Are there any "tweaks" to the modem or any other suggestions to get the speed to be high consistantly?  (her service is "up to 300 Mbps", so I'd be happy with any where near 150 or so.

Thanks for any assistance.

[tomham · Accepted solution]

I have found the problem (after hours tracing down the wiring).  The problem is / was with the splitter / amplifier.  It was difficult to find because I did not install it and the wiring was (shall I say) not direct or obvious.

My Thanks to Net Gear & the knowledgeable folks here.  Knowing that the modem was fine and the irratic connection helped isolate the problem.

Case closed & Thanks.

[plemans]

do you have a screen snip of the cable connections page and the logs? 

Those help us check the connection. 

If you have any splitters, amplifiers, or attenuators in the coax line, I'd remove them. Check the line for kinks, damage, bad/cheap/loose connectors. 

[tomham]

Thanks for the rapid reply.

The download signal for all 16 channels range from 4.3 dbmv to 5.0, so that looks pretty good I think.

The upload signal for all 4 channels range from 40.5 dbmv to 42.5, again that looks pretty good.

My speed ranges from 1.2 Mbps to 23.5 to (at times) with 168.3 rarely (download).  Upload ranges from 0 to 1.2 Mbps.  All with a service of "up to" 300 Mbps; so something is drastically wrong here.   🙂

I'm having a Comcast tech come out on Saturday to take a look at, but if I'm getting those signal levels it sounds like the issue is not with the modem, but let me know your thoughts.  I'll post what I find out.   Thanks again.

[plemans]

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@tomham wrote:

Thanks for the rapid reply.

The download signal for all 16 channels range from 4.3 dbmv to 5.0, so that looks pretty good I think.-------a screen snip would be better than "i think"

The upload signal for all 4 channels range from 40.5 dbmv to 42.5, again that looks pretty good.

My speed ranges from 1.2 Mbps to 23.5 to (at times) with 168.3 rarely (download).  Upload ranges from 0 to 1.2 Mbps.  All with a service of "up to" 300 Mbps; so something is drastically wrong here.   🙂----Thats where the logs and the cable connection page helps. 

I'm having a Comcast tech come out on Saturday to take a look at, but if I'm getting those signal levels it sounds like the issue is not with the modem, but let me know your thoughts.  I'll post what I find out.   Thanks again.

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[tomham]

Cable Connects file attached.

(more to come, since I can only attach one file at a time)

[tomham]

Event Log file attached.

[tomham]

Status file attached (MAC address blocked ou for security)

[plemans]

again If you have any splitters, amplifiers, or attenuators in the coax line, I'd remove them. Check the line for kinks, damage, bad/cheap/loose connectors. 

The cable connections page is a snip in time from when you opened the page. yes the levels look good but your logs are indicating your signal is fluctuating quite a bit as you're getting frequent dynamic range window violations and t3 errors. 

[tomham]

Thanks for the review of the data.  This gives me some background to provide the Comcast Tech tomorrow.

My experience is that they are trying to "get in & get out" ASAP and ready not trying to do a root cause analysis.  They should be able to "see" this flucuating in real time with their connect box I would think.  That would help in locating the issue.

I will try and locate any splitters and check house wiring for bad connections, though I'm not sure where they are located (up to the attic !)  :).

I will post the outcome once I get a handle on it.  Again, Thanks for your help.  

[tomham · Accepted solution]

I have found the problem (after hours tracing down the wiring).  The problem is / was with the splitter / amplifier.  It was difficult to find because I did not install it and the wiring was (shall I say) not direct or obvious.

My Thanks to Net Gear & the knowledgeable folks here.  Knowing that the modem was fine and the irratic connection helped isolate the problem.

Case closed & Thanks.

[plemans]

glad to hear you fixed it!

Its challenging when its something you didn't install or even when something small causes issues. I had moisture in a coax once that was causing erratic signals. Was a challenge to find