SB5100 Question

I've been corresponding with Motorola and talking to Comcast about a problem that I've posted here before. I can get a solid internet connection if there is no splitter between the wall jack and the modem. Power Level reads -1dB and sometimes

-2dB. With a splitter added so that I can feed the TV tuner, the power level reads -5dB. While TV reception is fine, I cannot get and maintain an internet connection. Have tried several splitters, changed cables and whatever without success. The software level is 2.3.1.3 FWIW Motorola says that the modem should work with the level between -15 and 15. Why should I not suspect the modem itself? Guess I don't understand how the modem works. There seems to be very little that I can do muself - everything has to be done by the ISP.

For transmit (or output power), modems above > 55 dBmV may experience randomdisconnects. What about your wiring - do you have at least RG6 or RG11 ?

Thanks, makes sense to me. Generally the upstream power is 55dBmV whether it's working or not. The log usually says that there was a T3 timeout. Right now it's working OK - and I'm watching TV and writing this. It probably will quit in a little while. FWIW - maybe it is significant - I never had this problem until I replaced the RCA modem I was renting with this modem. There has been some cable work in our neighborhood recently. Comcast is coming out tomorrow - hopefully they can bring the levels up (and it won't cost me anything.)

Thanks. Makes sense to me. The upstream value is at 55dBmV whether the splitter is in or not, but I guess that doesn't indicate what's getting out. I don't fully understand DOCSIS. Right now the damn thing is working and I am watching TV and writing this. It will probably quit soon. Maybe it's significant - I never had this problem with the RCA modem I was renting - but there has been some cable work in the neighborhood recently, installing boxes and grounding the connections. Comcast is coming out tomorrow - hopefully they can boost up the levels for me.

If they can't get adequate signal with the splitter, then they need to run you another line from the pole for the modem. That is how mine is set up.

The 55dBmv upstream is not good. This is the top end of the modem's upstream power capability and indicates that there is a line problem somewhere. In essense, the modem is "shouting as loud as it can" to be heard. I've discussed the DOCSIS standards with Comcast techs, not that either of us really knows, but DOCSIS has a 55dBmv upstream limit and the techs here have local practice that if the upstream power is above

45dBmv they look for line and grounding problems if the customer is experiencing disconnects and "they really like to see under 40dBmv". Line grounding at customer drops and wind/thermal effects on Comcast lines are problem sources in my subdivision (lines are pole-mounted, winds to 90mph gusts, 75 mph steady, frequent lightning and conductive soil).

In any event, the constant 55dBmv you see is likely a modem limit so the splitter in/out will not change the value if the problem is elsewhere. The "elsewhere" needs to be diagnosed before the effect of the splitter, if any, can be evaluated. There is probably no ability for the upstream power to be increased, and you wouldn't want that anyway.

IMO, YMMV

Well, with luck the problem is solved. The Comcast tech, who seemed knowledgeable, said "too many splitters" - and this is more so with the system upgrades they've made for higher speed and the forthcoming phone service. Anyway, he ran a cable from a single splitter at the box out back, and directly to the modem. The upstream power level dropped to 51dBmV (it was lower without the splitter, but there had to be one. Thanks to all who responded - it was very helpful. Jim

that is the way mine is setup

I'm curious - what was the upstream power without the splitter?

Q

I don't want to hijack this thread but I have a question about splitters. I too am running a 5100 and am having issues but I don't think it is my home.

I currently have my cable drop running to a 3-way splitter. The 3.5 tap goes straight to my modem. One 7.5 tap goes to my main tv setup which includes a 2-way splitting to 2 vcr units. My other 7.5 tap runs to a 3-way in my attic that in-turn branches to 3 bedrooms.

Is it better if my main line runs to a 2-way splitter with one going to modem and other line branching as required?

My modem signal levels are:

Downstream Value

Signal to Noise Ratio 35 dB

Power Level -8 dB

Upstream Value

Power Level 38 dBmV

Well, if it works, I wouldn't worry about it.

Do you have digital cable on the TV's in the three upstairs bedrooms? Does pay-for-view or Comcast On-Demand work from those sets? That's my guess at where you'll first be able to see a problem.

Otherwise if you're not having problems, it's not worth the effort to change anything for only possibly marginally better results. The risks include bending a center wire while re-coupling the coax, or twisting the connector, and disturbing it's connection with the braided outer wires. The pay-off would be, what?

Your numbers look fine. If you aren't having a problem, there's no need to worry.

Hi -

I'm no expert in this; however, I'd suggest that you have too many splitters, and a loss of signal strength occurs in the individual lines from the splitters.

Early on, I bought an amplifier for the incoming cable (TV) and routed the output from that to a five way-splitter for the TVs in our home.

With a two-way splitter prior to the amplifier, Comcast can route one to my modem and the other to the amplifier. The amplifier can generate sufficient gain for the TVs, and I only have to argue with Comcast about the signal strength inbound and my modem's capability to push a signal back. The line loss to the idiot boxes (TVs) in our home becomes a moot issue.

George (The Old Fud)

Well I am not trouble free however......... :-)

I do have a few channels on my TVs that I get bleedover from some local stations. I understand that and accept it knowing how many sets I have connected. FWIW, all the wiring was done by me. I purchased my own roll of RG-6, connectors, etc and did it all myself. The one thing I want to change is getting rid of crimp on connectors and going to compression ones. I just need to find a supplier either locally or order online. Eventually I will wire in a power amplifier to power the whole house except for modem of course and have an individual line to each set location.

When I first bought this house less than two years ago a new drop was run to my home. They were just out this past week and again replaced it as it was verified as bad again. They were called for a tv signal problem but internet was fine. I thought that might clear up my internet issue but it didn't

I am having trouble with my internet connection but it is kinda peculiar. I am on Comcast Gold tier(6000/768). My download speeds are very good. Routinely at 5500+ down with over 6000 quite often however my upload speeds seem to suffer extremely bad at random intervals. I have checked my speeds using various machines, with/without router, and with various OSs even testing using a Knoppix Live Boot CD. I have swapped modems (3 different ones) with no fix. Had a tech show up only to say not much he could do. I know more than him. lol Many times it's as if a switch is thrown and my upload speeds go back up to normal. I test using several SpeakEasy test sites but most of my upload test are done using WS-FTP LE and uploading a file to my Personal Web Space on Comcast. I verify speeds using the upload dialog in WS-FTP and also monitor using the small utility NetPerSec from PCMag. It appears that there is no issue at my home and I am guessing the problem is something with Comcast whether it is with my lines locally or something with the config file that is pushed to my modem from Comcast.

I am in the process of finding other local users to see if they suffer from the same issue to either verify it is something locally to me or others as well.

So my main reason for asking my original question was to see if it might help by what I had suggested. In reading some other posts on DSLReports it seems I might be better off running my modem off a 2-way and then using another 2-way to go between the upstairs and downstairs sets. Although my modem signal strength appears fine, any little bit might help.

Yes. It is always best to have a cable modem on its own, dedicated splitter prior to any TV distribution. Isolation between cable modem and TV outlets is improved, and you are also free to do whatever you want/need to with your TV distribution without worrying about how it will affect your modem. Just make sure that the splitters are

5-1000MHz, have RFI/EMI immunity of 110dB ot greater, and have blocking capacitors on all ports.

With 5 outlets in addition to a cable modem, I would have it setup as follows:

/--[Cable Modem] CATV /

------(2/way splitter) IN \\ \\--[Amplifier]--(8-way splitter)--Outlets (Be sure to terminate unused ports on the splitter)

The amplifier would need to be a 15dB gain amp, and have a bandwidth of

50-1000MHz w/passive return (5-42MHz).

CIAO!

Ed N.

That's essentially what you already have. Your 3-way splitter is just two 2-way splitters with one of the outputs of the first splitter connected to the input of the second splitter. That's why you get one

3.5 dB tap (the other output of the first splitter) and two 7.5 dB taps (the two outputs of the second splitter).

-Larry Jones

When you're as far ahead of the class as I am, it doesn't take much time.

-- Calvin

That value is still way too high. They need to find out why the value isn't below 44dBmV.

Do your speed tests at 0-dark:30; 4:00am is good since you can guarantee that no one else is sharing the line. I've been using

for testing. It is less busy and more consistent than speakeasy. Do your FTP tests show full upload speed?

Access your modem web interface and report the text for both upstream and downstream. You might review the cable modem FAQ at

about DOCSIS modem performance standards. FWIW (and not all agree with me), upstream power less than 40dBmv is very good. Anything above 48-50dBmv upstream is marginal. 55dBmv is max power for a DOCSIS modem and on Comcast you should not see this level, according to the local techs. Comcast users seldom have downstream power or signal to noise issues.

Q

The problem with FTP is that you also have to deal with two disk accesses (one at each end) which can also affect your CPU usage. A better test of the actual bandwidth would be to do as little as possible with the data.

FWIW, I just went thru a similar siege of problems. I thought it started when I installed an SB5100 to replace the RCA I was renting. I was getting frequent short drops, and finally it got pretty solid. Turned out that the system upgrades required better signal strengths. As I reported in another thread here I had a splitter to feed both the modem and the TV tuner on my video card. The upstream reading was

55dBmV. Someone here said that was too high, and sure enough it was. The Comcast tech said I had too many splitters (there were at least three in the chain.) He ran a new line in so that there was only one splitter and now the reading is 51-52 and it works just fine. Another responder says that that is too high, but I will not complain for now. In addition, this problem was not suggested by either the Comcast online support nor the Motorola support. It was this group that gave me the lead!!!