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Frequent intermittent connectivity loss

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johndball
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Frequent intermittent connectivity loss

New business customer with service, finally, connected on 25 June 2015.

Technician that came advised that the downstream signal strength was too high and installed a 3.5 decible splitter to drop the downstream rate. What started with downstream signals hovering around 9 dBmV is now between 0 and 4 dBmV.

Upstream signals, however, went from around 46 dBmV to 53 and 54 dBmV on channels 2 and 1, respectively.

 

Some other numbers:
SNR downstream 38-39 dBmV

Downstream modulation is QAM256 on all channels

Upstream modulation is QPSK and QAM64

 

Problems started and have persisted since installation last Thursday. Affecting both wired and wireless clients although wireless mobile devices (iPad and three iPhones) experience the worst service with webpages timing out.

 

Comcast signal - 30 June 2015 1332.PNG

Accepted Solution

Re: Frequent intermittent connectivity loss

Yes the upstream is out of spec; try removing the splitter if you can, and see if that changes anything. With DS power between 0-4, you have some headroom. Try to keep DS power below 9-10 if you can.
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Accepted Solution

Re: Frequent intermittent connectivity loss

Bypassed the splitter, still going through the lightning arrestor, and I am at 49/52 dBmV.

Downstream is 8/8/7/5/3/4/4/4.

 

Bypassed the lightning arrestor with no change at all. Removing the splitter brought it down. Should I continue to press for a service role as this will be an issue I deal with often (service-side issue [tap, amp, etc])?

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Trusted Forum Contributor

Re: Frequent intermittent connectivity loss

Yes the upstream is out of spec; try removing the splitter if you can, and see if that changes anything. With DS power between 0-4, you have some headroom. Try to keep DS power below 9-10 if you can.
johndball
Visitor

Re: Frequent intermittent connectivity loss

Bypassed the splitter, still going through the lightning arrestor, and I am at 49/52 dBmV.

Downstream is 8/8/7/5/3/4/4/4.

 

Bypassed the lightning arrestor with no change at all. Removing the splitter brought it down. Should I continue to press for a service role as this will be an issue I deal with often (service-side issue [tap, amp, etc])?

johndball
Visitor

Re: Frequent intermittent connectivity loss

More connection timeouts last night and this morning with the Comcast splitter removed from the mix.

 

Comcast signal - 01 July 2015 0519.PNGComcast - iOS 03.pngComcast - iOS 03.pngComcast - iOS 04.png

Forum Contributor

Re: Frequent intermittent connectivity loss

Hi!

 

A 3.5 decible splitter is not the appropriate way of reducing downstream power.  The tech should have inserted an attenuator like this one:

 

http://www.a1components.com/BVModules/ProductTemplates/Bvc5/Product.aspx?productid=5a1ca2ba-581b-484...

 

Unless something is connected to both legs of the splitter it won't do any attenuation at all.  If you have 1 leg of the splitter just hanging in free air that will be even worse as it can introduce interference into the line.

 

It sounds like you only have data, and no TV.  I think they raise power on the cable network because so many subscribers have multiple TV sets and need to use splitters.

 

It's going to sound like a pain but you need to call in for another service call.  Or maybe you can go to a local Comcast service center with the splitter and they will trade it for an attenuator.

Trusted Forum Contributor

Re: Frequent intermittent connectivity loss

tmittelstaedt,

a splitter or attenuator would raise his upstream levels. As he is already above the recommended 51dbmv upstream xmit power, I dont think that's what he would need here. I might question whether this is also the reason he is only bonding 2 US channels (most areas have moved to 3 these days).

I do agree that another service call would be warranted.
Forum Contributor

Re: Frequent intermittent connectivity loss

These are really 2 issues with this case even though attenuation and transmit power are interrelated.

 

The giveaway here is the claim that he's getting too much signal and needs attenuation (made by the first tech) and

yet his modem has jacked the output power way up.  Another clue is the 2 channel upstream that you pointed out.

I mainly was responding to the statement that the tech gave him a splitter as an attenuator.  A splitter isn't an attenuator.

 

My guesstimate is that he's got noise in the downlead.  If he's a business and has no television and is not in a

multi-tenant building then he should have a downlead straight from the street.  If he's in a multi-tenant building and

there's 6 other businesses in there than one thing that might cause this is if the downlead has a lot of taps off it

and then someone stuck in an amplifier.  For example suppose the downlead comes in from the street and daisy chains

through the building, and there's 2 taps off it to suites that go to Christmas trees inside those suites, then a cable tech has inserted a signal amp (because by then the signal is so bad) then the cable proceeds to feed 4 other customers.

 

In that case the amp is amplifying noise by the time he gets it so they put an attenuator on his lead, and now his modem has to shout at the top of it's lungs to get any signal back to the head end - but since it's doing that it's overdriving the

inline amp.

 

There's plenty of other scenarios I can think of but unfortunately he didn't post his geography so this is just speculation.

 

A knowledgeable tech needs to sort it out.  A tech that hands out a splitter as an attenuator isn't knowledgeable - unless he has all of the other splitter taps fitted with terminating resistors (which I very much doubt)  And if he's in a multitenant building and the tech has to get into other suites I can see how many techs might be thinking "OMG I have 5 other appts today I can't spend the time to fix this mess" and try to bandaid it.

 

If he IS in a multitenant building and all the other tenants are tv-only customers the installers may be thinking "everyone else works 'cept for him, it must be his gear" not realizing that the TVs can drop a few frames here and there due to noise losses and nobody will notice.

xtech1081
New Member

Re: Frequent intermittent connectivity loss

I'm seeing the same thing with what looks to be the same modem make and model (arris/motorola SB6141).

So I'm calling Comcast support tomorrow to start a ticket and watching to see if you have any luck.

Cheers, Steve H.

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