Downstream signal strength has dropped significantly over the last 30 days

jrmayfield Posts: 12 Participant
edited September 2023 in Internet 2023 Archive

Modem: Motorola MB8600 (firmware 8600-18.2.12)

Location: Lexington, KY

Connection: Wired

Hi. I'll prefix this post by saying this doesn't seem to be a problem, yet, but since I telecommute full-time, I'm trying to be proactive to avoid problems in the near future.

I have a cron job that logs into my modem's admin page and grabs the signal strength info every 60 seconds and stores the data into a RRD database. This lets me plot things like signal behavior over time. Over the last 30 days, the downstream signal strength has steadily decreased.

There are no splitters between the modem and the point where the RG6 enters the house (see below).

If we look at the signal behavior over the last 360 days, we see that back in August 2022, all channels except for one were more or less equal-strength. Starting in September 2022, something happened and the strengths began to diverge and they -really- started to diverge in December 2022. (The jump in July 2022 was from me removing the only splitter from the path)

So if the trend over the last 30 days continues, I expect some of the channels to fall below the -15dB threshold sometime in the next 5-6 weeks.

For what it's worth, here are the current values as reported by the modem:

Is this behavior suggestive of cable damage somewhere? As I wrote earlier, I work remotely so I'd like to get ahead of the problem before it becomes a problem. Is suspect, though, that Spectrum phone support won't do anything until there's an actual outage.


  • Randy_S
    Randy_S Posts: 514 Spectrum Employee

    Good morning @jrmayfield

    Thank you for all of the details and there could be a myriad of reasons to see what you are seeing. With your login credentials I found your account. I checked your signals from here and they are all within range and the modem is responding to my pings very well.

    And yes, we do not send out techs until the signals are out of range or of course any kind of line or hardware problems/failures. That said, our system does set up automated notifications offering proactive maintenance once your modem frequencies trip that trigger by going out of range over a period of time. Given your ability to track this information, you may see them go out of range before that happens. If you do, contact us immediately and we can check and set up a tech appointment.

    The only other possibility is to schedule a trip through our billing team at 1-855-707-7328. That is the team that can post tech trips outside of trouble calls. There would be a trip charge though. It is up to the discretion of the tech but unless there is a verifiable failure within our scope of service, there would probably be a charge

    I see the modem has also been online for 15 days. Does the downstream improve at all (even for a short time) when you reboot the modem?

    I think it is cool you have those tools available.


  • jrmayfield
    jrmayfield Posts: 12 Participant

    Hi. Thanks for the response. That's about what I'd figured. Out of curiosity, what is the threshold that triggers a notification from Spectrum's automated monitoring processes? I vaguely remember that -15dB was the lower bound of what's "marginal" but it's been a while.

    I'd rebooted the modem in mid-April and signals dropped about 2dB and again about 2 weeks ago and they dropped another 1dB so I'd been hesitant to reboot again. I rebooted about 10 minutes ago and it looks like it gained 1dB back. We'll see how things go in the coming weeks.

    BTW, do you have any explanation for why there's such a wide spread from channel to channel lately? Is a 10dB spread from strongest to weakest channel expected?

  • RAIST5150
    RAIST5150 Posts: 918 Contributor

    Part of the slope is due to a phase shift in the resistance of the line.

    Coax is sensitive to multiple environmental factors... temperature is a big one (higher temps, higher resistance), but humidity can have an impact as well if the moisture works its way inside the cable or connectors--so things like exposure to sunlight and standing water can cause weird seemingly random behavior sometimes.

    Couple that with the frequency spread between each channel in play (higher frequencies are "weaker"), it can all add up to weird shifts throughout the year.

    May be worth a rudimentary inspection of your cables and connectors. If the shielding quality/color is obviously degraded, may be worth considering replacement if it is practical. Same goes for dull/oxidized/corroded connectors. A commonn "maintemance" practice for tech visits is to clip the ends and install new connectors to remove bits of losses that can creep up on you from that very thing.

    Also good to make sure the cables are not run too close to things that may inject interference or otherwise compromise the quality of signal in the cables (motors, unshielded electronics, flourescents, heaters/AC units). Nothing crimping the cable, no turns sharper than about what you would get wrapping around a 2 liter bottle, avoiding exposure to direct sunlight/hot spots/rainfall/standing water.

    And as always, making sure all connections are clean, dry, and snug--not "torqued up", but definitely at least a smidge more than finger tight.

  • jrmayfield
    jrmayfield Posts: 12 Participant


    It has been a little more than 2 weeks since I posted the above charts. Downstream signal strengthfor the weakest channels has deteriorated another 3dB:

    As someone who works remotely full-time, I'm concerned that this is going to start causing connectivity problems within the next month or so...

  • William_M
    William_M Posts: 942 ✅ Verified Employee Moderator

    I do understand your concern with the downward trend of the signal strength, however at this time it is all still in the appropriate range and has actually brought most channels closer to 0 which is ideal. If a few channels do start to go out of range it will most likely cause minor speed issues at first, and as you are being diligent with your monitoring I'm certain it would be noticed soon enough to provide ample time to arrange repair from a technician before more disruptive problems arise.

  • jrmayfield
    jrmayfield Posts: 12 Participant

    This is a follow-up to the post I made some weeks ago as I'd been watching my signal levels steadily decrease over a number of weeks...

    The decrease in signal strength continued, though at a lower rate, until July 13. On that day, there was a brief outage (~30s). Afterwards, levels jumped 5dB across the board and began steadily increasing until yesterday when there was another brief outage (~5 minutes). After things recovered, the signal levels were grouped much tighter together -- instead of a 15dB spread from strongest to weakest, there's maybe a 4dB spread.

    So seems like Spectrum did some work upstream of my house that resolved the issue.

    (For the chart, ignore the outages on Jul 2 and Jul 20. The first one was a 24h power outage due to storms; the second was a problem with the logging script)

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