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.
Post your signals.
Karl, MsRaye and others need those to help. They’ll get you squared away.
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.
do a straight copy and paste of the entire page including the US levels and correctables.
What's there is unreadable
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
Looks like severe ingress from broadcast TV ch 33... Something is corroded or loose
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?
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
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".
Thanks for the help. I will schedule a tech visit.