Low Level of a single DS QAM Carrier

[twcidg]

I have a strange issue. The level of most of the DS carriers averages at +8 dbmv (+/- 2 dB). However, the carrier at 585 MHz is nearly 9 dB lower (-1 dbmv). The modem is connected to one port of a 2:1 splitter directly from the cable entrance (the other port feeds the rest of my home cable distribution). The issue has no impact on the performance of my system, but I thought it is very strange. I was wondering whether it is my SB6183 modem issue since I cannot imagine a 9dB drop off from its nearest carrier (at 597 MHz) on the cable system.

[scjr]

Post your signals.

Karl, MsRaye and others need those to help. They’ll get you squared away.

[twcidg]

DS signal levels (freq:level): 507:7.4, 513:7.5, 519:7.5, 525:7.6, 531:7.6, 537:7.7, 549:7.9,555:7.9,

585: -0.9, 597:7.4, 603:8.4, 615:8.9, 621:9.0, 627:9.1, 633:9.1, 645:9.2

The freq are in MHz and levels in dBmv. Channel ids are 1-6, 8-9,14, 16-17, 19-24 respectively (so as an example the 585 MHz is Channel 14). SNRs are between 42.5 and 44.4 dB except for Ch 14 which is 37.8 dB. 

[MsRaye]

do a straight copy and paste of the entire page including the US levels and correctables.

What's there is unreadable

[twcidg]

Channel Lock Status Modulation Channel ID Frequency Power SNR Corrected Uncorrectables
1 Locked QAM256 1 507000000 Hz 7.0 dBmV 42.4 dB 0 0
2 Locked QAM256 2 513000000 Hz 7.1 dBmV 44.0 dB 0 0
3 Locked QAM256 3 519000000 Hz 7.1 dBmV 43.9 dB 0 0
4 Locked QAM256 4 525000000 Hz 7.3 dBmV 44.0 dB 0 0
5 Locked QAM256 5 531000000 Hz 7.3 dBmV 43.9 dB 0 0
6 Locked QAM256 6 537000000 Hz 7.3 dBmV 44.0 dB 0 0
7 Locked QAM256 8 549000000 Hz 7.5 dBmV 44.0 dB 0 0
8 Locked QAM256 7 543000000 Hz 7.3 dBmV 43.9 dB 0 0
9 Locked QAM256 14 585000000 Hz -0.9 dBmV 37.3 dB 26 0
10 Locked QAM256 10 561000000 Hz 7.5 dBmV 43.8 dB 0 0
11 Locked QAM256 11 567000000 Hz 7.5 dBmV 43.8 dB 0 0
12 Locked QAM256 12 573000000 Hz 7.5 dBmV 43.7 dB 0 0
13 Locked QAM256 20 621000000 Hz 8.6 dBmV 44.3 dB 0 0
14 Locked QAM256 13 579000000 Hz 6.5 dBmV 42.8 dB 0 0
15 Locked QAM256 15 591000000 Hz 4.6 dBmV 41.1 dB 0 0
16 Locked QAM256 23 639000000 Hz 8.6 dBmV 44.1 dB 0 0

[MsRaye]

Looks like severe ingress from broadcast TV ch 33... Something is corroded or loose

[twcidg]

Please note that the two adjacent channels at 591 and 579 have also somewhat lower levels. Anyway, I assume that if it was interference, the measured level would not have been affected as much but the SNR and/or the error rate would have been degraded. Is it worth a service call?

[MsRaye]

What's your zip code? Lets see if there's a 33 on the air in your area.. I know there's one in Austin tx that's been an issue.

As for s/n, it's not an actual measurement but actually what the dsp rates it

 This could also be a nailed coax issue or chewed up outside. Looking at how your channels are so far out of order, It appears to be ingress

[agentx5]

This is either a trap or an active (LE or street amp) maintenance issue, possibly both.

Please schedule a Troublecall, we need to get out on-site to see what's going on at the tap in order to know how to fix.  But yes, a big dB differential between channels in such a short span of frequencies makes it really difficult for your modem to stay locked on.  The proper terminology for this is "uneven tilt on DOCSIS forward frequencies with a >9dB deviation".

[twcidg]

Thanks for the help. I will schedule a tech visit.