Cable Modem Signal Levels / Performance / Discussion
I was originally just going to post this as a reply in the South Koreans 10Gbps thread, but rather than completely derail a thread, maybe this will start some new interesting conversations.
I have a typical SBG6580 gateway/modem (Eastlink standard issue, no BYOM) in bridging mode. My main issue is my signal levels seem to be rather off. The modem is connected via a 50' RG-6U run into a 2-way -3.5dB splitter which is connected to the main drop by a 3' RG-6 cable.
In this setup I'd expect decent signal levels, however right now I have a good downstream signal (+3-4 dBmV / 36-37 SNR) but the modem has to scream at 49.2 - 50.5 dBmV upstream. I connected the modem directly to the wall outlet, and this yielded a mild improvement in upstream signal (46 dBmV) but pushed my downstream signal to borderline spec in terms of signal and SNR.
Because of my arrangement and signal levels, I can't connect my cable box in my room - it also goes at the end of the 50' RG-6 run but putting a splitter causes too much signal loss. Right now my options are either move the modem and run CAT5E to the modem or run a second RG-6 cable from the second 3-way splitter to supply the cable box. I don't care for either of these options as they both present the problem of running another cable between rooms, and the former puts the modem in a spot harder for me to reach, and they still leave the signal rather shitty.
I should point out that when I had service hooked up, it was noted that unlike most units in my building, my apartment only had a single coaxial drop to the utility room from the master bedroom. The second feed is supposed to come from the living room, however I found the loose end of it hidden inside a wall between the living room and master bedroom. As it is, everything is connected to the single main drop:
One theory that crossed my mind is if there is some sort of configuration/settings that would be throwing my signals off because there's only one drop connected downstairs instead of two, but the technician didn't say anything at the time, though I think he was just glad I found that cable at all at that point.
Thoughts? I am in an older building wired with older RG-59, but I would expect to see some degradation in the downstream signal as well if there was a physical issue with wiring between my apartment and the utility room. If nothing else, I'd like to have an idea /what/ is causing the problem before I call Eastlink so I can bypass some of the tedious L1 tech support troubleshooting.
EDIT: I just noticed, when I first accessed the diagnostics on reboot a few days ago, only one downstream channel had any correctable/uncorrectable errors; likely from pulling the coax. That's obviously jumped since then as you can tell from the screenshot above.
You're the first person I've seen on here who seems to have more than a basic understanding of cable/HFC network infrastructure and I lack it myself so I'm just going to throw this out here and see if you or anyone else can give me input on a couple things before before I go calling Eastlink.Josh wrote:Upstream on cable is always going to be dramatically slower than downstream.
I usually sit around 50 meg down on my D3 modem but usually I'm out and about so much within our fiber network that I get ~1g symmetric.
snip
I have a typical SBG6580 gateway/modem (Eastlink standard issue, no BYOM) in bridging mode. My main issue is my signal levels seem to be rather off. The modem is connected via a 50' RG-6U run into a 2-way -3.5dB splitter which is connected to the main drop by a 3' RG-6 cable.
In this setup I'd expect decent signal levels, however right now I have a good downstream signal (+3-4 dBmV / 36-37 SNR) but the modem has to scream at 49.2 - 50.5 dBmV upstream. I connected the modem directly to the wall outlet, and this yielded a mild improvement in upstream signal (46 dBmV) but pushed my downstream signal to borderline spec in terms of signal and SNR.
Because of my arrangement and signal levels, I can't connect my cable box in my room - it also goes at the end of the 50' RG-6 run but putting a splitter causes too much signal loss. Right now my options are either move the modem and run CAT5E to the modem or run a second RG-6 cable from the second 3-way splitter to supply the cable box. I don't care for either of these options as they both present the problem of running another cable between rooms, and the former puts the modem in a spot harder for me to reach, and they still leave the signal rather shitty.
I should point out that when I had service hooked up, it was noted that unlike most units in my building, my apartment only had a single coaxial drop to the utility room from the master bedroom. The second feed is supposed to come from the living room, however I found the loose end of it hidden inside a wall between the living room and master bedroom. As it is, everything is connected to the single main drop:
One theory that crossed my mind is if there is some sort of configuration/settings that would be throwing my signals off because there's only one drop connected downstairs instead of two, but the technician didn't say anything at the time, though I think he was just glad I found that cable at all at that point.
Thoughts? I am in an older building wired with older RG-59, but I would expect to see some degradation in the downstream signal as well if there was a physical issue with wiring between my apartment and the utility room. If nothing else, I'd like to have an idea /what/ is causing the problem before I call Eastlink so I can bypass some of the tedious L1 tech support troubleshooting.
EDIT: I just noticed, when I first accessed the diagnostics on reboot a few days ago, only one downstream channel had any correctable/uncorrectable errors; likely from pulling the coax. That's obviously jumped since then as you can tell from the screenshot above.
Comments
I'd be interested to see more info on the signal levels. If I recall correctly, downstream is supposed to be within 10 and -10 dBmV, but most cable companies prefer to keep it around 5 to -5 dBmV. I don't know about the upstream.
For comparison, I'm currently showing 6 dBmV on my downstream signal and 39 dBmV on upstream.
I may fuck around with this a bit more when I have a chance, but since it disables both internet and TV while I'm doing so, I'm kind of limited on when I can experiment.
If I recall, in the past when I've had cable with this same modem readings were around -3dB downstream and 42-45dB upstream.
While Googling I came across this FAQ for the SBG6580: I also found this FAQ on DSLReports with more or less the same information.
Cable is usually a work or doesn't work medium. A lower tx power isn't going to have any affect over a higher tx power from a signal strength perspective.
I'd be curious to know how this worked out for you.