Something is definitely wrong on that line. The SNRs are much lower than they should be and there is a wide variance of power levels with a high of 7.1 dBmV at 807 MHz and a rapid dropoff above 830 MHz to a low of -7.7 dBmV at 969 MHz. That's a range of almost 14 dBmV which is not normal or even close to normal. It's about the worst I've ever seen.
Unfortunately this could be caused by any number of things: faulty parts, faulty cables, etc, etc. Only a Cox tech can diagnose it. You'll need to call for another one, and another, and another until you get one who has the skill and time to resolve the issue. I wouldn't waste time or money on any type of filters or other add-ons until you can get those signals more in line with what they should be.
Thank you!!
So I actually just plugged in a new modem, have been using it for about 30 minutes, and the connection seems to be better--see below. Could it just be that the modem, which was purchased in 2018, needs to be replaced?
| Channel | Lock Status | Modulation | Channel ID | Freq. (MHz) | Pwr (dBmV) | SNR (dB) | Corrected | Uncorrected |
| 1 | Locked | QAM256 | 37 | 369.0 | 16.3 | 40.3 | 0 | 0 |
| 2 | Locked | QAM256 | 1 | 783.0 | 7.7 | 36.4 | 0 | 0 |
| 3 | Locked | QAM256 | 2 | 789.0 | 8.6 | 37.0 | 0 | 0 |
| 4 | Locked | QAM256 | 3 | 795.0 | 8.1 | 36.7 | 0 | 0 |
| 5 | Locked | QAM256 | 4 | 801.0 | 8.9 | 37.2 | 0 | 0 |
| 6 | Locked | QAM256 | 5 | 807.0 | 8.8 | 37.1 | 0 | 0 |
| 7 | Locked | QAM256 | 6 | 813.0 | 7.8 | 36.4 | 0 | 0 |
| 8 | Locked | QAM256 | 7 | 819.0 | 7.8 | 36.4 | 0 | 0 |
| 9 | Locked | QAM256 | 8 | 825.0 | 6.8 | 35.5 | 0 | 0 |
| 10 | Locked | QAM256 | 33 | 345.0 | 16.2 | 40.1 | 0 | 0 |
| 11 | Locked | QAM256 | 34 | 351.0 | 16.4 | 40.3 | 0 | 0 |
| 12 | Locked | QAM256 | 35 | 357.0 | 16.7 | 40.6 | 0 | 0 |
| 13 | Locked | QAM256 | 36 | 363.0 | 16.2 | 40.3 | 0 | 0 |
| 14 | Locked | QAM256 | 38 | 375.0 | 15.7 | 40.2 | 0 | 0 |
| 15 | Locked | QAM256 | 39 | 381.0 | 15.4 | 40.1 | 0 | 0 |
| 16 | Locked | QAM256 | 40 | 387.0 | 14.8 | 40.0 | 0 | 0 |
| 17 | Locked | QAM256 | 41 | 393.0 | 14.9 | 41.2 | 0 | 0 |
| 18 | Locked | QAM256 | 42 | 399.0 | 14.5 | 41.1 | 0 | 0 |
| 19 | Locked | QAM256 | 43 | 405.0 | 14.8 | 41.0 | 0 | 0 |
| 20 | Locked | QAM256 | 44 | 411.0 | 15.2 | 41.3 | 0 | 0 |
| 21 | Locked | QAM256 | 45 | 417.0 | 15.8 | 41.4 | 0 | 0 |
| 22 | Locked | QAM256 | 46 | 423.0 | 16.1 | 41.6 | 0 | 0 |
| 23 | Locked | QAM256 | 47 | 429.0 | 16.1 | 41.5 | 0 | 0 |
| 24 | Locked | QAM256 | 48 | 435.0 | 15.3 | 41.1 | 0 | 0 |
| Total | 0 | 0 |
Those signals are still odd. I think the reason you're seeing different numbers is because the modem locked on to a different frequency band. Now you have 400/800 MHz channels instead of 800/900 like you did in your first post. The signals on the 400 MHz channels are too high and there's still a dropoff of almost 10 dBmV between the lowest frequency channel and the highest. Something is affecting the frequency response of the line, and based on the signals I would guess that there is at least one unnecessary amplifier in there along with possibly a high-cut filter or else just a defective cable or other defective part that is negatively affecting higher frequencies.
Wow nice catch--the first Cox tech did install an amplifier.
But now my question is, if things seem to work well with this new modem, despite the less-than-ideal signals, do I need to worry? Could the underlying problem, whatever it is--unnecessary amplifier, defective cable, etc.--damage the modem, such I will eventually need to address it?
At a minimum, I will remove the amplifier and re-post the numbers. But to the extent it is in-house cabling issues, do you recommend I fix those, even if the new modem seems to work OK?
Thanks so much for your advice thus far.
Cable networks are inherently very fragile. You want everything as perfect as possible. So you want to remove any unnecessary add-ons and get everything you can control in the best possible shape. This isn't a unique problem to Cox. This is a problem for all cable internet networks. It's just a fragile technology.
16.8 dBmV is pretty high in terms of power but I don't think it's high enough to cause damage to the modem. But I would still remove the amp and test. Depending on the problem, removing the amp might cause problems with the 900 MHz channels. First get your indoor stuff as clean as possible then check signals and logs. If you still see issues, call for a tech. Also remember that less is more in the world of cable internet. Avoid any add-ons (amplifiers, attenuators, filters, etc.) unless absolutely necessary. The goal should be to fix it by taking things out, not by putting more things in. Sometimes an add-on is unavoidable but it's always best to try to avoid them.
