awalt
join:2005-08-01
Baltimore, MD |
awalt
Member
2024-Jul-3 6:52 am
Signals got worse?HI all, I am looking for your advice. A couple of days ago overnight, I instantly saw a big change in my modem signals. Downstream bonded went from 3-6 dBmV to what you see below; SNR went from 43-44 to below #s, sometimes as low as 30-32. Downstream OFDM channel went from 5-6.5 to -19, and even worse. (I did also have one of those notices on my account the night before, "Maintenance in your area at 1 am, there may be outages and disruptions..."), which is the main reason I checked things out the next morning.) I am on a 2G/200 plan, I used to get 2250/240 in a direct connection to the router via a switch. Now I get 1700/240. I have tried rebooting the modem, power cycling the modem, factory reset of modem, swapped out the modem for a same-brand (Netgear CM3000) I just happened to have for a friend's install, and I checked tightness of the connectors to the modem. I have no splitters, it's a straight shot from outside to the modem. I have a Comcast tech coming tomorrow, I am worried that they are going to say all is fine as the modem status on its web page is green (but I have seen yellow at times when some of the channels dropped below -10 dBmV). While in spec, to me the power/SNR is too low for 2G download speeds. Is that true? Or is the drop in download speed due to something else? How do you assess the current state of my signals/SNR for a 2G plan, and what should I say to the tech if they don't find anything? Thank you for your help!
Downstream Bonded Channels
Channel Lock Status Modulation Channel ID Frequency Power SNR Correctables Uncorrectables
1 Locked QAM256 4 469750000 Hz -2.0 dBmV 41.0 dB 0 0
2 Locked QAM256 1 451750000 Hz -1.9 dBmV 41.2 dB 0 0
3 Locked QAM256 2 457750000 Hz -1.8 dBmV 41.3 dB 0 0
4 Locked QAM256 3 463750000 Hz -2.0 dBmV 41.1 dB 0 0
5 Locked QAM256 5 475750000 Hz -1.7 dBmV 41.2 dB 0 0
6 Locked QAM256 6 481750000 Hz -2.2 dBmV 40.8 dB 0 0
7 Locked QAM256 7 487750000 Hz -2.3 dBmV 40.8 dB 0 0
8 Locked QAM256 8 493750000 Hz -2.3 dBmV 40.8 dB 0 0
9 Locked QAM256 9 499750000 Hz -2.6 dBmV 40.6 dB 0 0
10 Locked QAM256 10 505750000 Hz -2.6 dBmV 40.6 dB 0 0
11 Locked QAM256 11 511750000 Hz -2.9 dBmV 40.4 dB 0 0
12 Locked QAM256 12 517750000 Hz -3.0 dBmV 40.3 dB 0 0
13 Locked QAM256 13 523750000 Hz -3.2 dBmV 40.2 dB 0 0
14 Locked QAM256 14 529750000 Hz -4.2 dBmV 39.9 dB 0 0
15 Locked QAM256 15 535750000 Hz -4.3 dBmV 39.8 dB 0 0
16 Locked QAM256 16 541750000 Hz -4.6 dBmV 39.4 dB 0 0
17 Locked QAM256 17 547750000 Hz -4.9 dBmV 39.0 dB 0 0
18 Locked QAM256 18 553750000 Hz -4.9 dBmV 39.0 dB 0 0
19 Locked QAM256 19 559750000 Hz -5.2 dBmV 38.7 dB 0 0
20 Locked QAM256 20 565750000 Hz -5.4 dBmV 38.7 dB 0 0
21 Locked QAM256 21 571750000 Hz -5.6 dBmV 38.5 dB 0 0
22 Locked QAM256 22 577750000 Hz -6.0 dBmV 38.3 dB 0 0
23 Locked QAM256 23 583750000 Hz -6.1 dBmV 38.1 dB 0 0
24 Locked QAM256 24 589750000 Hz -6.4 dBmV 37.9 dB 0 0
25 Locked QAM256 25 595750000 Hz -6.6 dBmV 37.7 dB 0 0
26 Locked QAM256 26 601750000 Hz -6.8 dBmV 37.6 dB 0 0
27 Locked QAM256 27 607750000 Hz -6.9 dBmV 37.4 dB 0 0
28 Locked QAM256 28 613750000 Hz -7.0 dBmV 37.4 dB 0 0
29 Locked QAM256 29 619750000 Hz -7.0 dBmV 37.4 dB 0 0
30 Locked QAM256 30 625750000 Hz -6.7 dBmV 37.5 dB 0 0
31 Locked QAM256 31 631750000 Hz -6.6 dBmV 37.7 dB 0 0
32 Locked QAM256 32 637750000 Hz -6.5 dBmV 37.9 dB 0 0
Upstream Bonded Channels
Channel Lock Status US Channel Type Channel ID Symbol Rate Frequency Power
1 Locked ATDMA 2 5120 Ksym/sec 22800000 Hz 41.8 dBmV
2 Locked ATDMA 3 5120 Ksym/sec 29200000 Hz 42.3 dBmV
3 Locked ATDMA 4 5120 Ksym/sec 35600000 Hz 42.8 dBmV
4 Locked ATDMA 1 5120 Ksym/sec 16400000 Hz 41.5 dBmV
5 Not Locked Unknown 0 0 0 0.0 dBmV
6 Not Locked Unknown 0 0 0 0.0 dBmV
7 Not Locked Unknown 0 0 0 0.0 dBmV
8 Not Locked Unknown 0 0 0 0.0 dBmV
Downstream OFDM Channels
Channel Lock Status Profile ID Channel ID Frequency Power SNR / MER Active Subcarrier
Number Range Unerrored
Codewords Correctable
Codewords Uncorrectable
Codewords
1 Locked 0 ,1 ,2 ,3 193 957000000 Hz -19.32 dBmV 27.9 dB 148 ~ 3947 488069768 141352150 303210072
2 Not Locked 0 0 0 Hz 0 dBmV 0 dB 0 ~ 4095 0 0 0
Upstream OFDMA Channels
Channel Lock Status Modulation / Profile ID Channel ID Frequency Power
1 Locked 12 ,13 41 36200000 Hz 38.3 dBmV
2 Not Locked 0 0 0 Hz 0 dBmV
Extended Upstream Transmit Power
Current System Time:Wed Jul 03 05:39:53 2024
System Up Time:16:01:29
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3 recommendations |
something is wrong with the plant/lines most likely. Hard to see how that is going to be a you issue. Given the slant to the frequency SNR that is so smooth and "linear", hopefully it is something simple like a bad setting or they did some work and just didn't get to the balancing/tuning yet. |
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awalt
join:2005-08-01
Baltimore, MD |
awalt
Member
2024-Jul-3 8:34 am
Thanks for the thoughts! |
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| awalt |
awalt
Member
2024-Jul-3 8:43 am
@badtlc4, one other point that might point to your thought being correct - notice in my stats above, and it's 2 hours later - not a single error, even correctible! The line seems clean - just a massive drop in power and SNR. I suspect if the incoming coax or connectors were damaged, there would be errors...? |
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1 recommendation |
I'm not a coax expert but yes, I think you are correct. If there was line damage somewhere, I think there would be high error rates somewhere at some frequency. The linear nature of the power/SNR just screams poor tuning to me as higher frequencies naturally need a bit more power. |
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2 recommendations |
to awalt
said by awalt:HI all, I am looking for your advice. A couple of days ago overnight, I instantly saw a big change in my modem signals. Downstream bonded went from 3-6 dBmV to what you see below; SNR went from 43-44 to below #s, sometimes as low as 30-32. Downstream OFDM channel went from 5-6.5 to -19, and even worse. (I did also have one of those notices on my account the night before, "Maintenance in your area at 1 am, there may be outages and disruptions..."), which is the main reason I checked things out the next morning.)
I am on a 2G/200 plan, I used to get 2250/240 in a direct connection to the router via a switch. Now I get 1700/240. I have tried rebooting the modem, power cycling the modem, factory reset of modem, swapped out the modem for a same-brand (Netgear CM3000) I just happened to have for a friend's install, and I checked tightness of the connectors to the modem. I have no splitters, it's a straight shot from outside to the modem.
I have a Comcast tech coming tomorrow, I am worried that they are going to say all is fine as the modem status on its web page is green (but I have seen yellow at times when some of the channels dropped below -10 dBmV).
While in spec, to me the power/SNR is too low for 2G download speeds. Is that true? Or is the drop in download speed due to something else? How do you assess the current state of my signals/SNR for a 2G plan, and what should I say to the tech if they don't find anything?
Thank you for your help!
Downstream Bonded Channels
Channel Lock Status Modulation Channel ID Frequency Power SNR Correctables Uncorrectables
1 Locked QAM256 4 469750000 Hz -2.0 dBmV 41.0 dB 0 0
2 Locked QAM256 1 451750000 Hz -1.9 dBmV 41.2 dB 0 0
3 Locked QAM256 2 457750000 Hz -1.8 dBmV 41.3 dB 0 0
4 Locked QAM256 3 463750000 Hz -2.0 dBmV 41.1 dB 0 0
5 Locked QAM256 5 475750000 Hz -1.7 dBmV 41.2 dB 0 0
6 Locked QAM256 6 481750000 Hz -2.2 dBmV 40.8 dB 0 0
7 Locked QAM256 7 487750000 Hz -2.3 dBmV 40.8 dB 0 0
8 Locked QAM256 8 493750000 Hz -2.3 dBmV 40.8 dB 0 0
9 Locked QAM256 9 499750000 Hz -2.6 dBmV 40.6 dB 0 0
10 Locked QAM256 10 505750000 Hz -2.6 dBmV 40.6 dB 0 0
11 Locked QAM256 11 511750000 Hz -2.9 dBmV 40.4 dB 0 0
12 Locked QAM256 12 517750000 Hz -3.0 dBmV 40.3 dB 0 0
13 Locked QAM256 13 523750000 Hz -3.2 dBmV 40.2 dB 0 0
14 Locked QAM256 14 529750000 Hz -4.2 dBmV 39.9 dB 0 0
15 Locked QAM256 15 535750000 Hz -4.3 dBmV 39.8 dB 0 0
16 Locked QAM256 16 541750000 Hz -4.6 dBmV 39.4 dB 0 0
17 Locked QAM256 17 547750000 Hz -4.9 dBmV 39.0 dB 0 0
18 Locked QAM256 18 553750000 Hz -4.9 dBmV 39.0 dB 0 0
19 Locked QAM256 19 559750000 Hz -5.2 dBmV 38.7 dB 0 0
20 Locked QAM256 20 565750000 Hz -5.4 dBmV 38.7 dB 0 0
21 Locked QAM256 21 571750000 Hz -5.6 dBmV 38.5 dB 0 0
22 Locked QAM256 22 577750000 Hz -6.0 dBmV 38.3 dB 0 0
23 Locked QAM256 23 583750000 Hz -6.1 dBmV 38.1 dB 0 0
24 Locked QAM256 24 589750000 Hz -6.4 dBmV 37.9 dB 0 0
25 Locked QAM256 25 595750000 Hz -6.6 dBmV 37.7 dB 0 0
26 Locked QAM256 26 601750000 Hz -6.8 dBmV 37.6 dB 0 0
27 Locked QAM256 27 607750000 Hz -6.9 dBmV 37.4 dB 0 0
28 Locked QAM256 28 613750000 Hz -7.0 dBmV 37.4 dB 0 0
29 Locked QAM256 29 619750000 Hz -7.0 dBmV 37.4 dB 0 0
30 Locked QAM256 30 625750000 Hz -6.7 dBmV 37.5 dB 0 0
31 Locked QAM256 31 631750000 Hz -6.6 dBmV 37.7 dB 0 0
32 Locked QAM256 32 637750000 Hz -6.5 dBmV 37.9 dB 0 0
Upstream Bonded Channels
Channel Lock Status US Channel Type Channel ID Symbol Rate Frequency Power
1 Locked ATDMA 2 5120 Ksym/sec 22800000 Hz 41.8 dBmV
2 Locked ATDMA 3 5120 Ksym/sec 29200000 Hz 42.3 dBmV
3 Locked ATDMA 4 5120 Ksym/sec 35600000 Hz 42.8 dBmV
4 Locked ATDMA 1 5120 Ksym/sec 16400000 Hz 41.5 dBmV
5 Not Locked Unknown 0 0 0 0.0 dBmV
6 Not Locked Unknown 0 0 0 0.0 dBmV
7 Not Locked Unknown 0 0 0 0.0 dBmV
8 Not Locked Unknown 0 0 0 0.0 dBmV
Downstream OFDM Channels
Channel Lock Status Profile ID Channel ID Frequency Power SNR / MER Active Subcarrier
Number Range Unerrored
Codewords Correctable
Codewords Uncorrectable
Codewords
1 Locked 0 ,1 ,2 ,3 193 957000000 Hz -19.32 dBmV 27.9 dB 148 ~ 3947 488069768 141352150 303210072
2 Not Locked 0 0 0 Hz 0 dBmV 0 dB 0 ~ 4095 0 0 0
Upstream OFDMA Channels
Channel Lock Status Modulation / Profile ID Channel ID Frequency Power
1 Locked 12 ,13 41 36200000 Hz 38.3 dBmV
2 Not Locked 0 0 0 Hz 0 dBmV
Extended Upstream Transmit Power
Current System Time:Wed Jul 03 05:39:53 2024
System Up Time:16:01:29
interesting to see such a tilt. I am surprised it is even connecting at -19dBmV. My OFDM channel is sitting at -12dBmV at 674MHz something went bad with the AGC in one of the amps on my cascade as it will flux 6dBmV every few minutes. I am wondering if an amp is not properly balanced with AGC? |
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awalt
join:2005-08-01
Baltimore, MD |
awalt
Member
2024-Jul-3 10:58 am
@motorola870 on Monday it got as low as around -25 dBmV, and for awhile the OFDM channel was no long locked! It came back though. |
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| awalt |
to motorola870
@motorola870, what do you mean by "tilt"? |
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2 edits
1 recommendation |
said by awalt:@motorola870, what do you mean by "tilt"? tilt is where your power levels start to go up or down in a linear fashion. My downstream starts at -6dBmV at 477MHz and ends at 674MHz with it being -12dBmV making the tilt 6dBmV. Your tilt is about 18dBmV from lowest channel to the OFDM block. I don't think a amp is going bad considering Comcast has upgraded your area to Starline 1.2GHz gear with midsplit. Usually you want it to be close to 0dBmV as possible but I have heard -7 to 7dBmV is the usual target range. |
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awalt
join:2005-08-01
Baltimore, MD |
awalt
Member
2024-Jul-3 12:13 pm
Yes except the SNR seems too low for a 2G download speed. I think? |
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1 recommendation |
said by awalt:Yes except the SNR seems too low for a 2G download speed. I think? The OFDM profiles are based on SNR. With the SNR being 27dB at 957MHz I would think the profile has it receiving QSPK packets across the 192MHz wide channel. Your SC QAM channels are still within spec. I would setup a trouble call to get it fixed. |
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1 recommendation |
to badtlc4
I wish my signal was that clean. Right at a modem boot up I see errors. Look at the OFDM, seems like OP has lots of uncorrectables on it. Unless that is how mid split works. |
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2 recommendations |
to motorola870
You can actually get 256-QAM through at 27 dB  |
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1 recommendation |
said by fm:You can actually get 256-QAM through at 27 dB I was wondering. Because my OFDM channel is sitting at -13dBmV right now with 34dB SNR. Errors galore and it hasn't been up a full day and uncorrectables are at 71K. |
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awalt
join:2005-08-01
Baltimore, MD
5 recommendations |
awalt to fm
Member
2024-Jul-3 6:53 pm
to fm
Well thank you all for your help! I used your comments in a chat with Comcast via Reddit today. It was immensely helpful. This site is the greatest, I was very concerned about this getting fixed. So, I just got a call from "Comcast Advanced Technical Support", and they asked me to check and see if the problem has been resolved before the tech visit tomorrow. So I checked - @motorola870 you said power should be close to 0? How does this look now? 😁 Downstream Bonded Channels
Channel Lock Status Modulation Channel ID Frequency Power SNR Correctables Uncorrectables
1 Locked QAM256 20 565750000 Hz 0.1 dBmV 42.0 dB 0 0
2 Locked QAM256 13 523750000 Hz 0.5 dBmV 42.4 dB 0 0
3 Locked QAM256 14 529750000 Hz 0.0 dBmV 42.0 dB 0 0
4 Locked QAM256 15 535750000 Hz 0.0 dBmV 42.0 dB 0 0
5 Locked QAM256 16 541750000 Hz -0.1 dBmV 41.8 dB 0 0
6 Locked QAM256 17 547750000 Hz -0.2 dBmV 41.7 dB 0 0
7 Locked QAM256 18 553750000 Hz 0.1 dBmV 41.9 dB 0 0
8 Locked QAM256 19 559750000 Hz 0.0 dBmV 41.9 dB 0 0
9 Locked QAM256 21 571750000 Hz 0.1 dBmV 42.0 dB 0 0
10 Locked QAM256 22 577750000 Hz 0.0 dBmV 42.0 dB 0 0
11 Locked QAM256 23 583750000 Hz 0.0 dBmV 42.0 dB 0 0
12 Locked QAM256 24 589750000 Hz -0.1 dBmV 41.9 dB 0 0
13 Locked QAM256 25 595750000 Hz -0.1 dBmV 41.9 dB 0 0
14 Locked QAM256 26 601750000 Hz 0.0 dBmV 41.9 dB 0 0
15 Locked QAM256 27 607750000 Hz 0.0 dBmV 42.0 dB 0 0
16 Locked QAM256 28 613750000 Hz 0.3 dBmV 42.1 dB 0 0
17 Locked QAM256 29 619750000 Hz 0.4 dBmV 42.2 dB 0 0
18 Locked QAM256 30 625750000 Hz 0.8 dBmV 42.4 dB 0 0
19 Locked QAM256 31 631750000 Hz 0.9 dBmV 42.5 dB 0 0
20 Locked QAM256 32 637750000 Hz 1.1 dBmV 42.6 dB 0 0
21 Locked QAM256 33 643750000 Hz 1.3 dBmV 42.8 dB 0 0
22 Locked QAM256 34 649750000 Hz 1.2 dBmV 42.7 dB 0 0
23 Locked QAM256 35 655750000 Hz 1.5 dBmV 42.9 dB 0 0
24 Locked QAM256 36 661750000 Hz 1.6 dBmV 42.9 dB 0 0
25 Locked QAM256 37 667750000 Hz 1.6 dBmV 42.9 dB 0 0
26 Locked QAM256 38 673750000 Hz 1.5 dBmV 42.2 dB 0 0
27 Locked QAM256 39 679750000 Hz 1.1 dBmV 42.6 dB 0 0
28 Locked QAM256 40 685750000 Hz 1.3 dBmV 42.8 dB 0 0
29 Locked QAM256 41 691750000 Hz 0.9 dBmV 42.6 dB 0 0
30 Locked QAM256 42 697750000 Hz 0.7 dBmV 42.4 dB 0 0
31 Locked QAM256 43 703750000 Hz 0.7 dBmV 42.4 dB 0 0
32 Locked QAM256 44 709750000 Hz 0.3 dBmV 42.1 dB 0 0
Upstream Bonded Channels
Channel Lock Status US Channel Type Channel ID Symbol Rate Frequency Power
1 Locked ATDMA 2 5120 Ksym/sec 22800000 Hz 41.5 dBmV
2 Locked ATDMA 3 5120 Ksym/sec 29200000 Hz 42.0 dBmV
3 Locked ATDMA 4 5120 Ksym/sec 35600000 Hz 42.5 dBmV
4 Locked ATDMA 1 5120 Ksym/sec 16400000 Hz 41.3 dBmV
5 Not Locked Unknown 0 0 0 0.0 dBmV
6 Not Locked Unknown 0 0 0 0.0 dBmV
7 Not Locked Unknown 0 0 0 0.0 dBmV
8 Not Locked Unknown 0 0 0 0.0 dBmV
Downstream OFDM Channels
Channel Lock Status Profile ID Channel ID Frequency Power SNR / MER Active Subcarrier
Number Range Unerrored
Codewords Correctable
Codewords Uncorrectable
Codewords
1 Locked 0 ,1 ,2 ,3 193 957000000 Hz -1.82 dBmV 40.3 dB 148 ~ 3947 46088534 32949592 550156
2 Not Locked 0 0 0 Hz 0 dBmV 0 dB 0 ~ 4095 0 0 0
Upstream OFDMA Channels
Channel Lock Status Modulation / Profile ID Channel ID Frequency Power
1 Locked 11 ,13 41 36200000 Hz 38.0 dBmV
2 Not Locked 0 0 0 Hz 0 dBmV
And speeds are back where they should be when connected via Ethernet/switch (taken at a busy time of the day to boot), as you see at the top (2244, 233). Thank you again, @badtlc4, @motorola870, @strykerzr350, @fm - Kudos for you all just placed! |
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1 edit
1 recommendation |
to motorola870
There are some "it depends". CableLabs tested the failure points of some of the modulation orders a while back... 
If the noise becomes erratic (not flat)... Interleaving may or may not fix it.
It also depends on what the modem is displaying. There are several profiles. Each profile has its own set of counters, and keeps counting, even if not currently in use. It means that you may not be impacted by all of the collected uncorrectable codewords.
(The above failure point for 256-QAM doesn't apply to SC-QAM, which uses a different FEC)
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