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What are normal signal levels?

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What are normal signal levels?

Service interuptions multiple times a day.  SB8200 Modem. Only one 2-way splitter installed by the tech. 


Outage coincides with error log "Started Unicast Maintenance Ranging" followed by multiple "Commanded Power in Excess of 6 dB Below the Value Corresponding to the Top of the DRW" and "Dynamic Range Window violations"


After weeks of chats with tech support and the automated phone support that just wants to reboot my modem I finally got a live person who tells me you signal is within normal limits but can't tell me what those limits are.  Obviously my modem doesn't agree.


I believe these downsteam numbers are on the ragged edge of being too low. The modem panics and rescans, causing the outage.   I can't get any human tech support that knows enough to help me troubleshoot this.  All the other posts I"ve found show signal levels in the positive range for DS and I'm -10 dBm or worse.  If the system is asking for more upstream than the modem is willing to give, wouldn't that indicate a problem? 


Downstream Bonded Channels
Channel IDLock StatusModulationFrequencyPowerSNR/MERCorrectedUncorrectables
38LockedQAM256721750000 Hz-9.6 dBmV36.8 dB34762511
1LockedOther780000000 Hz-10.8 dBmV26.8 dB791041545982
11Not LockedQAM2560 Hz0.0 dBmV39.8 dB38563415
12LockedQAM256559750000 Hz-4.2 dBmV39.6 dB41473273
13LockedQAM256565750000 Hz-5.2 dBmV39.4 dB44113122
14LockedQAM256571750000 Hz-5.3 dBmV39.4 dB38923014
15LockedQAM256577750000 Hz-5.4 dBmV39.1 dB37903121
16LockedQAM256583750000 Hz-6.0 dBmV38.9 dB38373949
17LockedQAM256589750000 Hz-6.8 dBmV38.5 dB38253991
18LockedQAM256595750000 Hz-7.5 dBmV38.6 dB41483673
19LockedQAM256601750000 Hz-7.3 dBmV38.5 dB41783844
20LockedQAM256607750000 Hz-7.3 dBmV38.1 dB42194054
21LockedQAM256613750000 Hz-8.4 dBmV37.5 dB48284500
22LockedQAM256619750000 Hz-9.3 dBmV36.9 dB59404741
23LockedQAM256625750000 Hz-10.4 dBmV36.9 dB53144858
24LockedQAM256631750000 Hz-10.4 dBmV36.8 dB44734817
25LockedQAM256637750000 Hz-10.6 dBmV36.8 dB44474414
26LockedQAM256643750000 Hz-10.5 dBmV36.7 dB41074668
27LockedQAM256649750000 Hz-10.7 dBmV36.5 dB43044650
28LockedQAM256655750000 Hz-10.9 dBmV36.9 dB39514159
29LockedQAM256661750000 Hz-10.3 dBmV36.9 dB57686746
30LockedQAM256667750000 Hz-10.1 dBmV35.4 dB48975183
31LockedQAM256673750000 Hz-10.3 dBmV36.6 dB40194320
32LockedQAM256679750000 Hz-10.5 dBmV36.6 dB41684274
33LockedQAM256685750000 Hz-10.4 dBmV36.6 dB40013982
34LockedQAM256691750000 Hz-10.2 dBmV36.5 dB39543473
35LockedQAM256697750000 Hz-10.5 dBmV36.5 dB2359629249
36LockedQAM256703750000 Hz-10.4 dBmV36.2 dB117800200360
37LockedQAM256709750000 Hz-10.7 dBmV36.5 dB70485432
39LockedQAM256715750000 Hz-10.2 dBmV36.4 dB36823052
40LockedQAM256727750000 Hz-10.1 dBmV36.2 dB34443100
41LockedQAM256733750000 Hz-10.3 dBmV36.3 dB35952711

Upstream Bonded Channels
ChannelChannel IDLock StatusUS Channel TypeFrequencyWidthPower
13LockedSC-QAM Upstream23700000 Hz6400000 Hz41.0 dBmV
21LockedSC-QAM Upstream36500000 Hz6400000 Hz41.0 dBmV
32LockedSC-QAM Upstream30100000 Hz6400000 Hz41.0 dBmV
44LockedSC-QAM Upstream17300000 Hz6400000 Hz40.0 dBmV

Current System Time: Tue Aug 11 09:17:39 2020


Re: What are normal signal levels?

The downstream power is on the low / weak side and it may be intermittently fluctuating even lower to out of spec levels. That can cause random disconnects, spontaneous re-booting of the modem, speed, packet loss, latency problems, and the un-bonding of channels.

In a self troubleshooting effort to try to obtain better connectivity / more wiggle room, check to see if there are there any excess/unneeded coax cable splitters in the line leading to the modem that can be eliminated/re-configured. Any splitters that remain should be high quality and cable rated for 5-1002 MHz, bi-directional, and no gold colored garbage types like GE, RadioShack, RCA, Philips, Leviton, Magnavox, and Rocketfish from big box stores like Home Depot, Lowes, Target, Wal-Mart etc. Splitters should be swapped with known to be good / new ones to test

If there aren't any unneeded splitters that can be eliminated and if your coax wiring setup can't be reconfigured so that there is a single two way splitter connected directly off of the drop from the street/pole with one port feeding the modem and the other port feeding the rest of the house/equipment with additional splits as needed, and you've checked all the wiring and fittings for integrity and tightness and refresh them by taking them apart then check for and clean off any corrosion / oxidation on the center wire and put them back together again, then perhaps it's best to book a tech visit to investigate and correct.

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Re: What are normal signal levels?


Check your signal levels

To view your modem’s status page go to or


Specification      Min             Max

Downstream Power Level  
Cable Modems-10dBmV+10dBmV
Gateways and EMTAs-7dBmV+7dBmV
Downstream Signal to Noise Ratio35dB-
Upstream Power Level+35dBmV+50dBmV
Upstream Signal to Noise Ratio31dB-
Upstream Receive Power-2dBmV+2dBmV


Note: Not all modems will allow you to view the status page and some will have different URLs to access this info. If you are unable to access your modem’s status page, you can contact Comcast Customer Support and ask the support representative for these values.

I am not a Comcast Employee.
I am a Customer Expert volunteering my time to help other customers here in the Forums.
We ask that you post publicly so people with similar questions may benefit from the conversation.
Was your question answered? Mark the post as Best Answer!