Gig1 power levels
Hi there, I would like to know if my power levels should get looked at by a tech, a few years ago I had to move my hub upstairs I used webro hd triple screened cable and ppc compression fittings, it was extended by about 3m to the isolator then about 2m to the hub, it has always had an attenuator on it for over 20 years but that is just plain silver and has no markings on it, the cabinet is over a 100m at the top of my road.
Can the isolator make a difference as that was fitted over 20 years ago?
Thank you for the help.
3.0 Downstream channels
Channel Frequency (Hz) Signal Power (dBmV) Signal-to-Noise Ratio (dB) Modulation Channel ID
1 179000000 3.1 42 QAM 256 6
2 139000000 5.2 42 QAM 256 1
3 147000000 5.1 42 QAM 256 2
4 155000000 4.6 42 QAM 256 3
5 163000000 3.9 42 QAM 256 4
6 171000000 3.4 42 QAM 256 5
7 187000000 3.1 42 QAM 256 7
8 195000000 3 42 QAM 256 8
9 203000000 2.7 42 QAM 256 9
10 211000000 2.6 42 QAM 256 10
11 219000000 2.1 41 QAM 256 11
12 227000000 1.8 41 QAM 256 12
13 235000000 1.5 41 QAM 256 13
14 243000000 1.1 41 QAM 256 14
15 251000000 0.6 41 QAM 256 15
16 259000000 0.3 41 QAM 256 16
17 267000000 0.3 40 QAM 256 17
18 275000000 0.3 41 QAM 256 18
19 283000000 0.1 41 QAM 256 19
20 291000000 0.3 40 QAM 256 20
21 299000000 0.8 40 QAM 256 21
22 307000000 0.9 40 QAM 256 22
23 315000000 -1.2 40 QAM 256 23
24 323000000 -1.3 40 QAM 256 24
25 331000000 -1.4 40 QAM 256 25
26 339000000 -1.3 40 QAM 256 26
27 347000000 -1.4 40 QAM 256 27
28 355000000 -1.6 40 QAM 256 28
29 363000000 -1.9 40 QAM 256 29
30 371000000 -2 40 QAM 256 30
31 379000000 -1.8 40 QAM 256 31
32 387000000 -1.9 40 QAM 256 32
3.0 Downstream channels
Channel Locked Status Received Modulation Error Ratio (dB) Pre Reed–Solomon Errors Post Reed–Solomon Errors
1 Locked 42 0 0
2 Locked 42 0 0
3 Locked 42 0 0
4 Locked 42 0 0
5 Locked 42 0 0
6 Locked 42 0 0
7 Locked 42 0 0
8 Locked 42 0 0
9 Locked 42 0 0
10 Locked 42 0 0
11 Locked 41 0 0
12 Locked 41 0 0
13 Locked 41 0 0
14 Locked 41 0 0
15 Locked 41 0 0
16 Locked 41 0 0
17 Locked 40 0 0
18 Locked 41 0 0
19 Locked 41 0 0
20 Locked 40 0 0
21 Locked 40 0 0
22 Locked 40 0 0
23 Locked 40 0 0
24 Locked 40 0 0
25 Locked 40 0 0
26 Locked 40 0 0
27 Locked 40 0 0
28 Locked 40 0 0
29 Locked 40 0 0
30 Locked 40 0 0
31 Locked 40 0 0
32 Locked 40 0 0
3.1 Downstream channels
Channel Channel Width (MHz) FFT Type Number of Active Subcarriers Modulation (Active Profile) First Active Subcarrier (Hz)
159 94 4K 1840 QAM 4096 1108
3.1 Downstream channels
Channel Locked Status RxMER Data (dB) PLC Power (dBmV) Corrected errors (Active Profile) Uncorrectable errors (Active Profile)
159 Locked 32 -12.8 14549571 29686482
ChatGPT said:
Yes — the DOCSIS 3.0 levels look very good, but the DOCSIS 3.1 channel is concerning, specifically the MER and error counts.
DOCSIS 3.0
Your downstream power ranges from +5.2 to -2.0 dBmV, which is excellent. The slight downward slope across frequency is normal.
Power: excellent
SNR/MER: 40–42 dB, excellent for QAM256
All channels: locked
Pre-RS errors: 0
Post-RS errors: 0
So there's nothing concerning here.
DOCSIS 3.1 — this is the interesting part
Your 3.1 channel reports:
PLC power: -12.8 dBmV → quite low
RxMER: 32 dB → low for a 4096-QAM active profile
Corrected errors: 14,549,571
Uncorrectable errors: 29,686,482 → the big red flag
The uncorrectable errors mean the modem is receiving data on that OFDM channel that it cannot successfully correct. If those numbers are accumulating rapidly, that can absolutely correlate with packet loss, latency spikes, or intermittent speed issues.
The unusual thing is that your DOCSIS 3.0 channels are essentially pristine while the 3.1 OFDM channel isn't. That points more toward an issue affecting the higher-frequency/OFDM portion of the downstream spectrum, rather than a general downstream signal-level problem.
One important caveat
The error counters are cumulative. 29.7 million sounds enormous, but the number by itself doesn't tell us how bad the problem currently is. We need to know whether it's increasing quickly.
I'd do this:
Note the current 3.1 corrected/uncorrectable counts.
Leave the Hub running for 30–60 minutes without rebooting it.
Check the counts again.
If the uncorrectable count has jumped substantially, that's much more significant.
Also send me your DOCSIS 3.0/3.1 upstream channels. That's the other half of the picture, and with Gig1 I can then assess the whole RF connection and tell you whether I'd call Virgin Media about it.