Cable modem & upstream power levels [Archive] - Glock Talk


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08-01-2010, 16:08
For the last two weeks, service keeps going down intermittently. Modem is a motorola sb5100. Evidently, motorola's will reboot if the upstream power levels hit 58dBmV or higher. I was unaware how to monitor this until today and have lost connection a hand full of times. Since I've been monitoring it, connection hasn't been lost and it's spiked up to 55. Of course the isp says it's the modem, but I'm not convinced that's the case.

Anyone else have any experience with this?

08-01-2010, 20:26
theoretically, you'd want a lower upstream power level, from what i understand +40 to +58 is about the norm.

the upstream power level is dictated by the cable company's gear telling your modem to increase or decrease power levels.

think of trying to talk across a room and the person on the other end saying they can't hear you and that you need to talk louder.

now, if you fill that room with a bunch of stuff, or noisy people, that could cause a problem, and that could be what you're running into, that your cable lines aren't clean somewhere, either inside your premises or outside to the cable drop, or somewhere in the cable between your drop and their closest aggregation point (a lot of times, this will be where the signal is converted to digital and sent upstream via fiberoptics).

you should check that your cable modem is sitting as close to the service entrance into your house and there are no unnecessary splitters or other boxes like signal boosters between it and the entry point. also, that none of the cables are corroded or damaged and the connectors are good, and secure along the path from the modem to the service entry point.

ideally, you'd want just a single 2-way splitter coming off the service drop, one side going to your cable modem, the other going to the rest of the lines of your house and any other required splitters.

what will probably be more telling would be the downstream signal to noise ratio, are you able to monitor that? if so, please report what kind of numbers you're seeing, especially when your connection drops.

the possibility does exist that your cablemodem is on the fritz, but spending a little time double checking the wiring is a good step the take before going out and spending any money.

the more stuff at your location we can rule out as being the cause of the problem, the harder it is for the cable company to pass the buck and blame your prem wiring or equipment as the issue and not do anything to fix it.

also, does it seem to drop when it's windy, or rainy, or after a good rain? or, even when the temperature changes, for that matter?

08-02-2010, 08:23
This is just a few minutes ago. Yesterday the ranged power level was 55 just after the connection dropped and came back up. Nope, the weather isn't a factor. It goes down at random times throughout the day.

Frequency 735000000 Hz Locked
Signal to Noise Ratio 36 dB
Power Level -1 dBmV Upstream Value
Channel ID 2 Frequency 30000000 Hz
Ranged Power Level 37 dBmV

This is from yesterday after dropping.

08-02-2010, 15:23
hm, nothing on that screen shot looks out of range that it should cause the connection to drop.

and, that's good the weather isn't related, that could have signified a problem with water getting in lines outside (a real pain to track down) or a marginal connection that's influenced by temperature changes (another pain).

can you post a screen shot of the logs page ?
that might provide some indication as to what's going on right before it drops

08-02-2010, 18:47
The biggest issues with Cable Modems is how many of your neighbors are also streaming stuff at the same time you want to go on line? The issue is that there is only one channel down to you and only one channel from you to the HUB. The time is divided between all of you on the same HUB. More users is less speed, less users is More speed. I am on ClearWire in Atlanta which is smoking cable and DSL. Been with it for 1 year as a Day one user. I hear from my neighbors using Cable Modems about their issues. Now the cable company has a new name for their Internet service, but it sucks just like their normal service does. I tell them to go to Clear! Cable and DSL from your phone company also sucks.

08-02-2010, 18:59
while cable service is shared to a certain point, so is dsl and wireless. at a point, every service is shared.

his neighbors use of service wouldn't explain the complete service dropouts he's experiencing. slowdowns, sure, but not complete drops.

08-02-2010, 21:25
Thanks guys, but this is on the back burner of importance for me now. I'm planning an emergency flight and trying to get loose ends tied up. To be continued on this matter.

08-02-2010, 21:55
no problem, good luck on your trip

when you get back and things return to normal, post up that logs page and we'll pick it up again

08-02-2010, 22:15
On an unrelated topic, I cannot find concrete info on carrying a box of 12 surefire cr123 batteries on Southwest Airlines. In reference to elc Equivalent Lithium Content).

08-02-2010, 22:43

"..Effective January 1, 2008, you may not pack spare lithium batteries in your checked baggage..."

"You may pack spare lithium batteries in your carry-on baggage.."

"For personal use, there is generally no restriction on the number of spare batteries allowed in carry-on baggage. This is the case for cell phone batteries, "hearing aid" button cells, and AA batteries/AAA batteries available in retail stores, as well as almost all standard laptop computer batteries...."

they also recommend keeping the batteries in their original packaging, but it sounds like they just don't want them rolling around in your carry-on freely.

and from this page,

"Most consumer lithium metal batteries such as AA, AAA, and CR-123A sizes, do not fall into the "Larger" category. Just follow the Basic rules."

I think the ELC discussion is in reference to the content of individual batteries, like those for professional video cameras and other gear.

but, this page

offers a formula to roughly estimate lithium content,

it's mAh/1000*V=watt hours

(they estimate 8g of lithium equals 100 watt hours)

so, if we assume your surefire cr123's are 1400mah's each,

1400/1000 * 3 = 4.2wh

4.2wh * 12 (batteries) = 50.4 watt hours = ~4.03g of lithium for all of them combined.

i would just leave them in the box, or their individual packaging and toss 'em in your carry on.

08-15-2010, 09:32

08-15-2010, 16:03
well, that is interesting.

it looks like the modem functions for a while, then can't establish contact with the upstream dhcp or tftp server to update it's ip address or modem profile and then it basically defaults to a dumb state (like a soft-reset) and tries to establish contact again.

i personally don't think your modem is the problem and that the root cause is a wiring issue, either inside or outside.

obviously, you don't control, nor are responsible for outside wiring issues, but, we do need to check the inside wiring to try and rule it out as the cause.

where the cable service comes into the house, i would place the cable modem and see how it performs (no splitters or anything between the cable drop and the modem).

if it works fine, then we can safely assume that between that point, and where ever it's located currently, lies a bad cable or connection (not hard to fix, generally).

however, if the service continues to be poor, as it is currently, then signs point to the problem being outside of our house/dwelling, and making it a cable company issue.

this 'experiment' will allow you do provide evidence to the cable company (assuming your inside wiring is good), that their wiring somewhere is the problem, if they need convincing to do something about it.

try plugging that cable modem directly into where the cable comes in and see how it does over the period of a couple hours (or however long it would take for the service to normally drop a couple of times)...

08-15-2010, 16:38
Lets see, the cable comes from the pedestal near the property line in the front yard and the house faces west. Cable goes to the front foundation vent at the corner all the way to the south side vent (vent is about midway on that side of the house). It then runs along the south side exterior of the house west to where the grounding strap is and coupled to another length of cable that runs back to the vent(east). The only change I've made is cutting off the cable end to pull through the floor and bring to another room. Used a new end, it was a compression fitting with appropriate tool. I suppose when I cut the jacket, there may have been an issue with my end fitting. If I connect the modem where it couples at the grounding strip, that still leaves quite a bit of cable between the ground and pedestal.

08-15-2010, 16:46
is the grounding strap a male/male type adapter?

if so, on the other side of the grounding strap, use the shortest cable pratical and plug the modem in there and see if it works.

i believe that would be considered where the connection transitions from being theirs, to yours.

everything from the grounding strap to the pole and further is theirs.

if we can eliminate everything in your location from the equation, we'll be better able to determine if the problem is actually yours or theirs (i'm going to guess it's theirs, but we need to take this step anyways to be sure).

08-15-2010, 17:30
Yes, its coupled with male/male in a metal bracket that has a screw that clamps down on one end of a solid copper wire and the other end clamps to the cable that is connected to a spike in the ground. Need to find an appropriate length of cable before I do this, so I can at least monitor the logs.

08-28-2010, 11:34
Got this resolved today, well sort of. Made a call about 1230 last night, had a tech here by 830 this morning. He did a few checks outside and immediately knew it was on their end. Evidently, equipment upgrades is causing the problem.

08-28-2010, 18:19
hey, that's great news, keep on 'em about it if you continue to run into issues with your service.