Seasoned Contributor

Fluctuating Power Levels

I know that the power level reported by the modem status page can vary.  But what is an acceptable range and is there anything I need to/can do about it.


For instance, today before refreshing the page, I had a number of channels showing high 9.x dBmV and one at 10.1 dBmV.  After refreshing the page, all the values dropped to the 5 or 6 dBmV range.



Proven Sharer

Re: Fluctuating Power Levels

Recommended incoming signal levels for 256QAM DS channels are between -7.0 and +9.0 dBmV.  Some techs will say -15 to +15 but that is a lab measurement with no other signals (TV or phone) on the cable.  Additional conditions are that the signal level can vary no more than 3 dB between the weakest and strongest channel, AND the minimum SNR (Signal-to-Noise ratio) must be 35 dB or greater on every DS channel, with over 39 dB preferred. 

When the level variation exceeds 3 dB the modem will usually drop the connection and reset itself.   If the signal strength is above -5.0 dBmV but the SNR is lower than 35, it usually points to broadcast ingress interference.  That can come from local TV stations or 4G LTE cell phone sites or the phones themselves.  

When you restart the modem it wipes the old levels from its memory, scans for active DS data channels, and then measures the new levels of each DS channel for the 3 dB reference check.

The best maintenance you can do is to make sure that all connectors remain tight - use a 7/16" wrench, not your fingers.  Cables with molded plastic ends or crimped-on connectors or any labeled RG-59 are junk, replace with good RG6-QS with compression fittings.


Re: Fluctuating Power Levels

don't reset the modem and post the page with at least 4 hours of up time


Seasoned Contributor

Re: Fluctuating Power Levels

Here's one I baked earlier.

Here's last night:

ChannelLock StatusModulationChannel IDFrequencyPowerSNRCorrectedUncorrectables
1LockedQAM2569567000000 Hz10.6 dBmV42.0 dB76227
2LockedQAM25610573000000 Hz10.4 dBmV41.7 dB81142
3LockedQAM25611579000000 Hz10.3 dBmV41.6 dB96313
4LockedQAM25612585000000 Hz10.2 dBmV41.3 dB143281
5LockedQAM25613591000000 Hz10.3 dBmV41.0 dB81281
6LockedQAM25614597000000 Hz10.0 dBmV40.9 dB107223
7LockedQAM25618621000000 Hz10.2 dBmV40.5 dB76179
8LockedQAM25616609000000 Hz10.1 dBmV40.7 dB14989
9LockedQAM25617615000000 Hz10.2 dBmV40.6 dB90218
10LockedQAM25620633000000 Hz10.2 dBmV40.3 dB7095
11LockedQAM25631699000000 Hz10.0 dBmV39.9 dB4160
12LockedQAM25627675000000 Hz10.4 dBmV39.9 dB8858
13LockedQAM25628681000000 Hz10.6 dBmV40.2 dB4072
14LockedQAM25629687000000 Hz10.4 dBmV40.1 dB2859
15LockedQAM25626669000000 Hz10.4 dBmV40.2 dB8578
16LockedQAM25632705000000 Hz9.8 dBmV39.9 dB4477
ChannelLock StatusUS Channel TypeChannel IDSymbol RateFrequencyPower
1LockedATDMA195120 Ksym/sec30600000 Hz43.3 dBmV
2LockedTDMA172560 Ksym/sec18500000 Hz41.5 dBmV
3LockedATDMA185120 Ksym/sec23300000 Hz41.8 dBmV
4LockedATDMA205120 Ksym/sec37000000 Hz43.0 dBmV

And now:

ChannelLock StatusModulationChannel IDFrequencyPowerSNRCorrectedUncorrectables
1LockedQAM2569567000000 Hz8.2 dBmV42.3 dB76227
2LockedQAM25610573000000 Hz7.9 dBmV42.0 dB81142
3LockedQAM25611579000000 Hz7.9 dBmV41.8 dB96313
4LockedQAM25612585000000 Hz7.7 dBmV41.5 dB143281
5LockedQAM25613591000000 Hz7.7 dBmV41.2 dB81281
6LockedQAM25614597000000 Hz7.3 dBmV41.0 dB107223
7LockedQAM25618621000000 Hz7.5 dBmV40.6 dB76179
8LockedQAM25616609000000 Hz7.4 dBmV40.8 dB14989
9LockedQAM25617615000000 Hz7.5 dBmV40.7 dB90218
10LockedQAM25620633000000 Hz7.4 dBmV40.5 dB7095
11LockedQAM25631699000000 Hz7.1 dBmV40.1 dB4160
12LockedQAM25627675000000 Hz7.8 dBmV40.1 dB8858
13LockedQAM25628681000000 Hz7.9 dBmV40.3 dB4072
14LockedQAM25629687000000 Hz7.7 dBmV40.2 dB2859
15LockedQAM25626669000000 Hz7.9 dBmV40.4 dB8578
16LockedQAM25632705000000 Hz6.9 dBmV40.0 dB4477
ChannelLock StatusUS Channel TypeChannel IDSymbol RateFrequencyPower
1LockedATDMA195120 Ksym/sec30600000 Hz44.0 dBmV
2LockedTDMA172560 Ksym/sec18500000 Hz42.3 dBmV
3LockedATDMA185120 Ksym/sec23300000 Hz42.5 dBmV
4LockedATDMA205120 Ksym/sec37000000 Hz43.8 dBmV

As pointed out, I have seen the levels drop to the 5 -> 6 dBmV range.

The cable is a single drop from the pole, uninterrupted to the crawlspace, where there is a single barrel connector used for grounding and from that barrel it's a single cable to the modem.  All cables and crimps were supplied/performed by the (insert name here) cable tech guys and have been tweaked with a spanner to be more than finger tight.

This is an internet only service.  No phone or TV.




Re: Fluctuating Power Levels

A slow change is normal when outside temperature changes a lot.

A couple correctables/ uncorrectables are tolerable. But, you should only have a small to no percentage of uncorrectables as they are basicly lost packets that have to be requested by your CPU all the way back to the remote site you're connected to.  whereas correcteds are fixed between your modem and the CMTS at the head end... If after one try it fails again, that's an uncorrectable.


If you're not having any issues, twc/ spectrum aren't going to fix the  correctables, lol. much less uncorrectables (and they really impact everyone on that node as well as the servers at the head end especially a lot of customers having to interupt a normal fast data stream to resend lost ones.


 Even then their techs dont look at them and in some areas  some modems have that screen zero'd out