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Modem power levels and channels downstream/upstream

Frequent Visitor

Modem power levels and channels downstream/upstream

A few weeks ago we had an internet service interruption at my house.  The network appeared to be restored by mid-day and I thought all was good.  Let me first say that in my area, Comcast/Xfinity has been extremely reliable and has had pretty consistent speed, so outages like these are uncommon to my service.

 

About 3 days after the outage while I was away on business, my wife told me the internet was out at the house.  After some quick troubleshooting and conversations with tech support, I came to the conclusion that my SB1683 was malfunctioning and needed replacement.  I had a SB6141 in my spare parts so I had my wife temporarily installed it and got the network back up.  After returning home, I purchased an SB8200 DOCSIS 3.1 modem to replace the temp SB6141.  I also upgraded to the Gigabit plan.  My speed at the modem is about 930 down/40 up.

 

With all this swapping and replacing, I spent some time in the Modem status pages.  I noticed my downstream and upstream levels were a little off and I only had one upstream channel.  I traced the cable lines back to my demark and I only had a single 2-way splitter at my demarcation point.  I was able to replace it with a bullet connector because only thing connected to Comcast is the cable modem.

 

My current connection to the pole is: Cable from pole to grounding block on house.  Grounding block through wall to bullet connector (about 6 feet).  Bullet connection to 2nd floor wall jack (about 40 feet).  Wall jack to cable modem (6 feet).  So my total cable length from grounding block is about 52 feet.  The cable run from the demark is high quality quad shielded cable.

 

Removing the splitter allowed my upstream to get down around 54db (would like to see this around 40db) and gained me 2 more upstream channels so I now have 3 but I think it should be at least 4.  Removing the splitter also raised my downstream levels as well to about +7db, ideally, they should be closer to 0 db.


I think I need a tech to come out and balance the line, I have attached a pic of my current readings.  Any feedback or suggestion is appreciated.

 

Thanks

SB8200 Comcast modem status_Page_1.jpgSB8200 Comcast modem status_Page_2.jpg

Expert

Re: Modem power levels and channels downstream/upstream

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 and post the link to them here.



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Frequent Visitor

Re: Modem power levels and channels downstream/upstream

Huh, that's strange. As long as I'm signed in I can see them. I will see if I can link then as well.
Expert

Re: Modem power levels and channels downstream/upstream

Nah, it's not strange. It happens every day around here. The post authors themselves can see no but no one else can.



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Expert

Re: Modem power levels and channels downstream/upstream

Anywho, I can see them now. The upstream power is on the high side and may be intermittently fluctuating even higher to out of spec levels. 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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Frequent Visitor

Re: Modem power levels and channels downstream/upstream

Thanks for the response.  As I stated in the OP, 

 

"My current connection to the pole is: Cable from pole to grounding block on house.  Grounding block through wall to bullet connector (about 6 feet).  Bullet connection to 2nd floor wall jack (about 40 feet).  Wall jack to cable modem (6 feet).  So my total cable length from grounding block is about 52 feet.  The cable run from the demark is high quality quad shielded cable."

 

As you can see there are NO splitters in the line from the grounding block to the modem.  The wall jack may be "gold in color" and I can swap it for a different one if needed.  The bullet connect is silver and I believe was left over from a Comcast install some time ago.

 

I probably should have mentioned I'm a 30 year electronic / electrical / radar technician.  I deal with comm signals all the time, so the signal loss/gain in RF lines are familiar to me.  One thing I did notice is the better I make my connections the higher the downstream power levels go and the lower the upstream levels get.  When I started this process, my downstream levels were around 3db, now they are 7-8db.  My guess is since the entire house was once connected via a 6-port splitter at the demark when we used Comcast TV, the line was balanced to account for the 7-11db loss inserted by the splitter.  Now that the feed is essentially direct to the modem my levels are high.  I am more concerned about the 53-54db upstream level though and the missing 4th channel.

 

 

 

Expert

Re: Modem power levels and channels downstream/upstream

You may need a drop amp that has an active return. It may be best to have a tech properly balance your line. 

 

Bear in mind that if the premises facing techs cannot find or fix a problem at your home, it is they who are responsible for escalating it to their line / network / maintenance dept. techs. The problem may lie beyond your home in the local neighborhood infrastructure somewhere. Good luck !

 

P.S. also be advised that many local systems still have only 3 upstream channels configured / available.



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Diamond Problem Solver

Re: Modem power levels and channels downstream/upstream

Adding to EG, try to move your modem to before the first gold connector and see if your upstream levels change. That will tell you if the issue is inside or outside. Not all areas have 4 upstream channels, you may be in an area that has 3.

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Frequent Visitor

Re: Modem power levels and channels downstream/upstream

You read my mind, planned on trying that last evening but the other users in my house get really cranky when I take the network down...silly I know but they don't see it the way my techie mind does.  To me, it needs adjustment, to them...it's allowing them to surf.  I will try that as soon as I get a chance and report back here.

 

I also just bought some certified bullet connectors to replace the wall jack, just in case.

Frequent Visitor

Re: Modem power levels and channels downstream/upstream

Update - so I tried the modem at the entry point of demarcation. Downstream power went up about 2 db and upstream went down about 0.5db. That's pretty much what I would expect to see for calculating in the 45-50 foot run of RG6 I have installed to the normal location. So it looks like my cabling is good. I'm going to cleanup and replace the grounding block on the side of the house but pretty sure it's a line balance issue now.
Expert

Re: Modem power levels and channels downstream/upstream

0.5dB on the upstream is not nearly enough improvement. There is no wiggle room for the normal daily fluctuations and especially the seasonal ones where in the warm weather it always goes higher due to the increased line resistance associated with increased ambient temperatures.

 

Let a tech figure out what is needed.



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