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Cable Modem Signal Levels

althomas049althomas049 Posts: 3 ✭✭
edited October 5 in Connectivity Oct 05, 2020

I am trying to figure out if my signal levels are ok or not. According to the Arris site:

My levels look pretty good on the downstream side as far as power and SNR, but I'm not sure about the upstream. Arris recommends a minimum of 45 and mine are only 35-38. Should I be concerned?


  • RAIST5150RAIST5150 Posts: 835 ✭✭✭✭
    edited October 5 Oct 05, 2020

    While technically "in spec" for the standard, the SNR and upstream levels are a bit out if the norm they generally aim for.

    They like higher SNR for more headroom if a line gets noisy, and upstream tends to be in the 40's more than the 30's. When we see upstream dropping below 40, the signal may be getting a little overdriven.

    If you are having stability issues, it may be from the line getting "boosted" somehow. If gains are ramped up or a drop amp is in play, they tend to exacerbate noise issues. If you are having issues, may want to call it in so a tech can check the lines.

  • misterjmisterj Posts: 107 ✭✭✭✭
    Oct 05, 2020

    althomas049, what symptoms do you have if any? Your DS SNRs look low to me. Do you own the modem? If not, I would suggest you get another from the ISP. Enjoy, John.

  • althomas049althomas049 Posts: 3 ✭✭
    Oct 06, 2020

    I have been noticing some intermittent issues, but didn’t really dig into this until I was cleaning up the cabling entering the house we just moved into. I noticed it was using a powered amplifier and upon further investigation, noticed the cable going to the modem was plugged into an amplified port instead of the dedicated modem port. After correcting this, I wanted to confirm everything was working correctly and so I checked the signal levels. I tried both with and without the powered amplifier to see if going directly from the outside connection to the modem was better. The SNR was about the same but the downstream levels were slightly better (2-5dbmv vs 6-8dbmv) and the upstream were slightly better (35-38dbmv vs 32-35dbmv) when going through the amplifier (using the modem port). It is a brand new Arris modem supplied by Spectrum in June.

  • RAIST5150RAIST5150 Posts: 835 ✭✭✭✭
    edited October 6 Oct 06, 2020

    Ideally, those drop amps should NOT be needed. They risk ramping up the noise factor and incur some insertion loss--even if it is just 1db loss, keep in mind that every 3.5db drop is a 50% reduction.

    If you can remove the amp and reduce the length and/or number of splits/barrels you may recover a spot of usable signal--not just strength, but the Signal to Noise Ratio as well.

    If they cannot get the line to stabilize on "raw" cable, they may want to boost signal... but it would be better if it can be managed at the pedestal. Unfortunately, this may not happen for a couple reasons... plus it may cause it to get kicked to maintenance versus the tech just putting in a drop amp much faster. If they go this route again though, hopefully with it being a "new" adjustment they will take the time to tune it to better match your run.

  • althomas049althomas049 Posts: 3 ✭✭
    edited October 7 Oct 07, 2020

    I removed the drop amp from the picture and now have the modem wired directly to the incoming line. There are no splitters, as we don't have cable tv only internet. Here are the numbers for this setup. The power on both the downstream and upstream were affected, but the SNR is only minimally impacted. Is it worth putting in a service request to have a tech check the line?

  • RAIST5150RAIST5150 Posts: 835 ✭✭✭✭
    Oct 07, 2020

    Technically it "could" be serviceable.... just not ideal in how they like to see the numbers. You do not have a lot of headroom to guard against errors if noise gets dumped on the line somehow, and may be prone to higher error rates in warmer weather cycles and elevated humidity.

    If you are getting instability on a "straight" run like that (no splitters/barrels/etc.), should probably make a service call. It may be an issue off your premises (at the pedestal, pole, or further out), but they will need to evaluate your site first to rule that out before bringing maintenance in to look at things upstream from the home.

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