Moto SB5100 signal drop

Your upstream could be a bit lower and SNR is OK, but could be a tad higher.

See if it persists and you may want to borrow a modem to see if your numbers change.

I think the real issue is the upstream strength. 55dB is marginal. If the Receive light is solid, but Send is blinking, the modem is trying to establish an uplink.

It's hard to fix upstream problems. Upstream uses frequencies below

54MHz (TV channel 2). It is more sensitive to poor ground connections which can let noise in. I would fully check all your connections, maybe even loosening and retightening them to make certain it is a clean contact.

I've heard of RF amps that can amplify BOTH directions, but they are pricey.

In article , Chuck Reti wrote: :I have a Motorola SB5100, about a year old. This past week I have been :frequently losing connection to my ISP (Comcast Detroit). :Cable feed is separate drop from pole, just before modem hits a splitter :one (-3.5dB) leg to modem, other (-3.5dB) to a TV in same room (yes, I :subscribe to video service, and there are no traps anywhere along the :feed). This splitter and cabling is a commonly used arrangement, exactly :same as cable company installations. :Last week the SB5100 was suddenly experiencing frequent loss of signal, :"send" lamp blinking and "online" lamp out. Pulled up the modem :diagnostic pages, showed Downstream signal at -3 dBmV, s/n 35dB; :Upstream 55dBmV. :I removed the splitter and show, predictably, Downstream 0 to +1 or +2 :dBmV, s/n 36-37dB, and with the splitter out, seem to be holding on to :the signal.

There is a problem with the upstream signal level. At 55 dBmV your modem is screaming just about as loud as it can in order to make itself heard, and if the upstream loss increases just a little bit you will lose the connection. What is the upstream power level with the splitter removed?

Oddly/interestingly enough, upstream reads 55 dBmV either way. The downstream numbers change favorably, 0 to +2 or +3; 37 db s/n with splitter out as opposed to -3 dBmV / 35 db s/n with splitter in. Am experiencing solid service, no drops with the cable direct into the modem. May try a directional coupler instead of a splitter, about 1 dB loss to the modem and 4 to 6 to the TV which would be fine. Don't have any idea how to convince Comcast that it's probably something on THEIR end. They'll just want to send out another guy with a wrench and a crimp tool. I'm still not suspicious of the modem itself, but may give Moto a call as well.

If you've got a next door neighbor with cable, maybe you could swap modems and see if things change.

In article , Chuck Reti wrote: :In article , : Robert Nichols wrote: : :> There is a problem with the upstream signal level. At 55 dBmV your :> modem is screaming just about as loud as it can in order to make itself :> heard, and if the upstream loss increases just a little bit you will :> lose the connection. What is the upstream power level with the splitter :> removed? : :Oddly/interestingly enough, upstream reads 55 dBmV either way.

That confirms that the head end is telling your modem, "Yell as loud as you can, I can barely hear you." The problem could be your modem not putting out as strong a signal as it thinks it is, or it could be trouble in the transmission path. The easiest thing to try is a replacement modem. Why not just rent a modem from Comcast for a month or two. If that fixes the problem you can buy a new modem and cancel the rental. If the problem persists, you can now tell Comcast, "It's your modem and your system, make it work."

BTW, when you phone in to tech support, they should be able to see what your upstream signal level and SNR are at the head end.

Chuck Wrote: "Oddly/interestingly enough, upstream reads 55 dBmV either way. The downstream numbers change favorably, 0 to +2 or +3; 37 db s/n with splitter out as opposed to -3 dBmV / 35 db s/n with splitter in. "

Looks like your modem is working properly. The cable techs are not. Sorry you have to live in an area with lousy service. If you can go to your local office (where the techs are dispatched), ask to speak to a technical supervisor. Go around 8:30 or so, adn bring along a printout of your signal.html page and explain the situation. HOPEFULLY, he will send out a tech who knows what he is doing and get things resolved. Of course, there's a high likelyhood that the tech sup. won't have a clue either, but maybe he can find someone who does.

BTW: the upstream tx power level not changing sometimes happens when you are attched to a Cisco CMTS (the headend equipment that converts data to radio frequencies). Cisco designed their CMTS to be a little more tolerant of level changes in favor of high carrier to noise ratios, at least as far as I can tell. Other manufacturers are much less tolerant of reciever levels. Often times I can see recive levels from a misbehaving modem to be -5dB, where on an Arris pizzabox or ADC 'Cuda (yes, that's the name. The guy who first designed the thing has a blue Plymouth Baracuda) will typically reset a modem if the receive level falls below -1dB.

Thanks all, for the replies and information.

Chuck R.

Comcast ran a separate line to my modem - avoiding all splitters but the one on the access box. That fixed the upstream # and it has worked great ever since. Only problem is that they cut the line short so it can't be tucked away very well.

The line to my modem is also a separate drop from the pole, running directly into the upstairs computer room. I'm taking one split off it to feed a tv in that room. I'm thinking the Motorola modem might be not as tolerant to my marginally low signal levels as it should be. My neighbor has a Thompson/RCA modem (Comcast self-install kit) and has -4.2 dBmV 33dB s/n up and 54 dBmV down and claims he has no service drops.

But does he get the same numbers if you plug it in at your house is the Q.