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fiveofakind
join:2013-04-25
Berlin, CT

fiveofakind

Member

[Connectivity] Bad Connectivity and Signal Power

Location: Berlin, CT

Problem: Hi everyone, we just recently had Comcast HSI installed (I think a week ago) and have been having some problems. The internet is very intermittent and seems to work ok sometimes, but suddenly pages won't load, or a streaming video will be very choppy.

Modem: Arris TM862G, with firmware TS070463A_011312_MODEL_862_GW_CT_SIP_PC20

(As a side note, we also have a Motorola SB6121 but during the install the tech said it kept power cycling and he couldn't add it to our account. Additionally since we have Comcast voice they said we needed an eMTA so they gave us the Arris above to rent.)

Home networking: A Linksys router is attached to the Arris in one of its lan slots. The Linksys has the custom firmware DD-WRT installed and is configured as a wireless access point following the instructions here: »www.dd-wrt.com/wiki/inde ··· ss_Point
However, we have tried disabling the Linksys router and simply using the wireless functionality of the Arris TM862G, but it didn't seem to increase connection reliability.

Anti-Virus software: Microsoft Security Essentials, not sure what version.

Here is a line test that I ran this morning:
»/pingt ··· 3027488#

For the wiring, I'm not 100% sure of the wiring outside of where the cable modem is, but someone told me it is as follows: the cable comes to the house to a 3-way splitter, then one of those 3 lines comes to the room where the cable modem is. This line is then goes into another 2-way splitter where one goes to the TV and one goes to the cable modem. From what I was reading, every time the cable goes into a splitter there is a power loss, so maybe the line is split too many times?

Here are the signal levels:


I noticed that in the Comcast FAQ it says the downstream power levels should be between +15 dBmV and -15 dBmV, but I've seen the power levels in our modem's status fluctuate anywhere between -10 dBmV to -20 dBmV, mostly around -15 dBmV or below. Additionally I've also seen the number of downstream channels alternate between 1 channel or 4 channels.

Here is the modem's event log:
quote:
Date Time Event ID Event Level Description
4/26/2013 8:04 84020200 5 Lost MDD Timeout;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.0;
4/26/2013 8:04 84000700 5 RCS Partial Service;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.0;
4/26/2013 8:04 84020200 5 Lost MDD Timeout;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.0;
4/26/2013 8:04 84000700 5 RCS Partial Service;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.0;
4/26/2013 8:04 84020200 5 Lost MDD Timeout;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.0;
4/26/2013 8:04 84000700 5 RCS Partial Service;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.0;
4/26/2013 8:04 84020200 5 Lost MDD Timeout;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.0;
4/26/2013 8:04 84000700 5 RCS Partial Service;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.0;
4/26/2013 8:05 84020200 5 Lost MDD Timeout;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.0;
4/26/2013 8:05 84000700 5 RCS Partial Service;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.0;
4/26/2013 8:05 84020200 5 Lost MDD Timeout;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.0;
4/26/2013 8:06 84000700 5 RCS Partial Service;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.0;
4/26/2013 8:06 84020200 5 Lost MDD Timeout;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.0;
4/26/2013 8:06 84000700 5 RCS Partial Service;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.0;
4/26/2013 8:07 84020200 5 Lost MDD Timeout;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.0;
4/26/2013 8:07 84000700 5 RCS Partial Service;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.0;
4/26/2013 8:07 84020200 5 Lost MDD Timeout;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.0;
4/26/2013 8:07 84000700 5 RCS Partial Service;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.0;
4/26/2013 8:08 84020200 5 Lost MDD Timeout;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.0;
4/26/2013 8:08 84000700 5 RCS Partial Service;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.0;
Thank you for any help.
ExoticFish
join:2008-08-31
Zebulon, NC

ExoticFish

Member

Basically you just need to call and have a tech come out to your house to fix your signal levels. There's no reason why the first tech should have left you looking that way !

You're right though. Every time you insert a splitter you make your signal weaker.
djoye
join:2009-08-15
Murfreesboro, TN

djoye to fiveofakind

Member

to fiveofakind
I wonder if the signal was too weak for the SB6121 to sync.

A 3-way splitter usually has two -7dB terminals and one -3.5dB terminal and I thought that 2-way splitters typically have two -3.5dB outputs but I can't remember. It looks like your modem/TV splitter may be connected to one of the -7dB outputs on the 3-way splitter. Disconnect one of the lines from the first splitter and see if you lose TV/internet, repeat this until you find the line that supports the modem/TV. When you find that line, if it's not already connected to the -3.5dB output on the 3-way splitter, move it there; that should gain you some signal.

You're going to suffer some loss since you're splitting twice. If you want to have the least amount of loss possible, invest in a splitter/amplifier like this to use as a splitter for your TV and modem. I use one of these to split a TV antenna signal and they work very well. May wanna do some research on that splitter to ensure it works with your cable modem before investing.

Although I'm not sure of the validity, I've read that -15dB and +15dB are the outer ranges for optimum operation of a cable modem and that operating within -5dB and +5dB is optimal.
fiveofakind
join:2013-04-25
Berlin, CT

1 edit

fiveofakind

Member

Thanks for the above help guys. This afternoon I went outside and checked the existing wiring setup. The line from the road goes into a 3 way splitter that looks like this:


except each of the 3 output terminals says -5.5 dB (none say -7 or -3.5) which from googling seems to be called a balanced splitter. Since I had a laptop and extension cord, I decided to test out the average downstream power levels using the modem at various points in the coaxial cable wiring:




If the estimate of 40 ft of wiring is correct, the signal loss according to this scales linearly, and the modem uses frequencies around 1000 Mhz (not sure?), then 40 ft of RG-59 cable would provide about a 8.6 dB drop just due to the wiring itself. This seems to agree with the amount of signal attenuation from immediately after the 3 way splitter, to just before the 2 way splitter after ~40 ft of wiring.

Based on this, I have a couple questions:

1) The 3 way splitter seems to be attenuating the signal more than 5.5 dB. Does this indicate the splitter is malfunctioning and should be replaced? Or is the listed attenuation not always accurate?
2) There is a large signal attenuation due to the cable from the output terminals of the 3 way splitter to the input of the 2 way splitter. Would it make sense to replace the 3 way splitter with a 4 way splitter, and then run RG-6 cable from the 4th terminal directly to the modem? In other words the following diagram:




If so, should the cable company provide these things or would I have to purchase/install them myself (something like this »www.monoprice.com/produc ··· format=2) ? I haven't called Comcast yet but I plan to soon.

Thanks again for all the help.

SeaSeaTee5
join:2010-05-06
Maryland

SeaSeaTee5

Member

Replacing a 3 way to a 2 way with a 4 way is only going to gain you 2 dB. The values on those splitters are pretty accurate. Your modem signals are probably running at around 600 MhZ btw.

Like mentioned above there are 2 different types of 3 ways. A balanced 3 way loses 5.5 dB per leg, while an unbalanced 3 way loses 3.5/7/7 per leg. If you absolutely need that 2nd 2 way, you should run the modem outlet off of the 3.5 leg of an unbalanced 3 way. Generally the modem should be off the a 2 way split at the side of your house, and all of your other equipment should be off another splitter.

If you're indeed currently running off the 7 leg, switching it to the 3.5 leg will get you back 3.5. That sill puts you at minimum spec at best. From your drawing above, it looks like you're losing too much signal through the splitter AND through the 40 ft section of cable. A 40 foot run of RG 6 should only lose 2 or 3 dB. RG59 maybe 3 or 4 dB.

My suggestion if possible would be to replace all cable with RG6 run to the side of the house. This would include a 2nd cable for your modem to eliminate that 2nd 2 way split. Your first split (at entry to the house) would be a 2 way with the modem off of 1 leg, and the other leg running to a balanced 3 way feeding each of your TVs. (your would need a small cable jumper between the splitters) That is pretty much industry standards. That would give you around 0 to -2dB hitting your modem, and around-6 to -8 hitting your TVs depending on the distances. This would also bring your upstream to spec as well.

Try at all costs to avoid using RG59 to your modem. There's a lot of RG59 out there with very poor shielding which could cause ingress issues with not only your service, but your neighbors as well.
fiveofakind
join:2013-04-25
Berlin, CT

fiveofakind

Member

Ok, I setup the splitters as per the above advice. A 2 way splitter takes the incoming road connection which splits it to the modem and to a balanced 3 way which handles the TVs. So it looks like this:


and I now have the following power levels:


which definitely seems a lot better than what I was getting before. What's weird is that there still seems to be packet loss problems going by the line test here: »/pingt ··· /3027992
Any suggestions on what this problem could be? Or is this something that a Comcast technician needs to look at/fix?

Thanks for all the help thus far.
fiveofakind

fiveofakind

Member

Hey guys, just wanted to give an update that I swapped out my Motorolla SB6121 for the Arris TG862 and everything is looking good now. I was able to register it to the account and connect to the internet. The latest line quality test doesn't show any packet loss: »/pingt ··· /3028097 and the signal levels look good:



Thanks again for all the help!