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Contributor
Posts: 20
Registered: ‎07-20-2003
Accepted Solution

Modem Installation Question

Hoping a few of the resident expert techs can provide feedback here.  Presently, I have xfinity internet and TV service from Comcast and I own the SB6120 cable modem.  On Feb 19th, I'm upgrading to xfinity Triple Play, which will be adding digital voice.  (I currently have separate home phone service).  My present comcast set-up is as follows: The main Coax cable enters the rear of the home and immediately enters the input leg of a two-way splitter. Two coax cables exit the splitter - one goes directly to the SB6120 (which is about 40 ft away) and the other goes to TV service.  I know that the digital voice service requires an eMTA modem to function. So I have a few questions.

 

1. Will the rented eMTA modem replace my SB6120 or is it common to use two modems?

2. If you use both modems, will it degrade the internet signal?

3. I would like to make sure I provide a good clear workspace for the technician, so, typically, where is the eMTA modem installed in the house? 

 

Thanks for any feedback you can offer.

 

Calvin

Cable Expert
JayInAlg
Posts: 11,459
Registered: ‎03-02-2007

Re: Modem Installation Question

Your are wired properly by the first 2-way splitter's one leg going the the modem, so the signal should be strong enough for another 2-way to feed both the 6120 and the eMTA.

 

You have your choice, keep your 6120 for your HSI, but you will still be paying rent on the eMTA each month.  If the Comcast installer installs a new D3 eMTA like a Arris 702G or 722G, then you can also change to one device for both CDV and HSI.  If the installer brings a older eMTA like a 502 or 602, then keep the 6102 for the HSI.

 

You can post the signal level of your existing modem to show us you have enough signal for another split by going to this link http://192.168.100.1 and posting your RF downstream power, downstream signal to noise, and upstream RF power levels.

 

It is not unusual to run two devices, one for HSI and one for CDV, but usually is not necessry, especially if the eMTA is a D3 unit.

 

In many area's you can purchase a eMTA, and save the rental fee's.  They are only sold at select Best Buy's that have Comcast Connection Centers inside the store in the TV dept.   They do need a professional install by a Comcast Tech, so if you want to buy one before your CDV install date and have the tech use that instead, it might be a good idea.

Contributor
Posts: 20
Registered: ‎07-20-2003

Re: Modem Installation Question

Thanks for the information, JaylnAlg.  Here is the existing signal level display.

 

Calvin

 

Modem.JPG

Cable Expert
JayInAlg
Posts: 11,459
Registered: ‎03-02-2007

Re: Modem Installation Question

There is plenty of signal for another split to a modem and eMTA.

Contributor
Posts: 20
Registered: ‎07-20-2003

Re: Modem Installation Question

The install referenced in the original post of this thread was done today as scheduled.  The tech brought in a Arris TM602 eMTA modem, so I am using the Arris rental for the voice and my own SB6120 for the HSI. Obviously, he had to install a splitter to feed both modems.  He was able to backfeed the phones in the house by putting a phone jack splitter on the existing single port jack in the room where the two modems are located.  

 

Everything seems to be working fine. The only difference I've noticed is that my Upstream Power Level has increased from 47 dBmV (pre-install) to 50 dBmV (post-install), presumably from adding an extra splitter into the line to feed both modems.  In another forum, some of the seasoned experts said this is going to cause problems because the 50 dBmV is too high.  Your thoughts?

 

Here is a screenshot of my signals post-install.  Thanks for your feedback.

 

Capture1.JPG

 

Cable Expert
JayInAlg
Posts: 11,459
Registered: ‎03-02-2007

Re: Modem Installation Question

I know people running 50 up with no problems that are on long drops.

 

Just watch the upstream when it warms up, as there is more loss in the RF portion of the cable system, when it's hot out.  If the temp get's into the 80's to 90's you might see it climb to 52 or so up, and +3 for the downstream..

 

Downstream levels tend to climb some in the winter, and related upstream levels will go be a little lower as there is less loss in the cold, both directions. 

 

If you start seeing some issues when it's hot out, then the tech might need to do something about it.

 

Thanks much for the update.

 

 

New Visitor
Posts: 2
Registered: ‎10-29-2009

Re: Modem Installation Question

I currently have a customer owned Motorola SB5100 and Netgear router/switch for Comcast inet and will be going to their triple play and a higher speed connection requiring a docsis 3.0 modem. I also currently have Vonage voice with a customer owned Linksys eMTA router for the phone connect. Can I keep my current Linksys router for the new Comcast voice and just go buy a Motorola SB6121 for the docsis 3.0 capability? I dont care about battery backup for phone  so dont need a sbv series Motorola eMTA?

Thanks for any help

C-Dub

Cable Expert
JayInAlg
Posts: 11,459
Registered: ‎03-02-2007

Re: Modem Installation Question

Comcast CDV only works on their supporte eMTA's, they will not work with any other VOIP provider.  They are completely different pieces of equipment.  CDV uses the digital RF channels directly for access to Comcast's network, not the IP address from the internet.

 

It is not the same, Vonage uses the internet to route traffic, Comcast does not use the internet, but their own internal IP network.

 

You must either lease or purchase an approved eMTA for CDV, and most installations use Arris equipment.

 

If they supply you a straight eMTA, you can still use your existing router.