downstream OFDM SNR????

I just connected a new netgear CM1000V2 because my old zoom modem had to be rebooted about once a day to to lock-up (would lose connection completely). Netgear seems to have solved the loss of connectivity. I pay for 300mbps plan and comcast speed test shows my downstream is 200mbps +/-. House desktops and TVs all hardwired with home run connections to aggregating PCs<->Gig-E switch <-> router<->cblmodem. After a lot of reading-up on modem signal levels, I am questioning my downstream OFDM SNR - its 30-31 db. All other downstream channels are 35-39 SNR. Power levels look good (downstream running 0-4dbmv). Uncorrectables are very small.

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Accepted Solution

kvjkhjkhdfghjdf

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6 Messages

5 years ago

Well, tried comcast phone support with no result other than hearing the script, so did more debugging by reading lots of posts for CM1000 users seeing what their levels were before/after issues, developed a list of things to check, etc.

Rehung 70' coax run in basement to move 12"+ away from AC power lines, removed 'Y' splitter that splits TV/Modem to boost signal a bit and turned off all options on linksys router to strip/simplify everything. Performace went from 200mbps to 385mbps which is a little higher than advertised plan speed. Success.

Case closed for now. Thanks to all who helped and answered PMs regarding their case as it helped me move forward with debugging.

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kvjkhjkhdfghjdf

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6 Messages

5 years ago

Tried to insert image of modem status page with channels/levels etc, no go. So, below is a text paste.... See RED line near bottom.

Also, I tried plugging coax enetering home straight to modem to bypass splitter that splits TV/internet and there was no improvement to SNR or download speed.

Frequency start Value

This field below allows you to modify the frequency the cable modem start with its scan during initialization and registration. Enter the new start frequency and restart the cable modem for it to take effect.

Starting Frequency

Startup Procedure

Procedure	Status	Comment
Acquire Downstream Channel	579000000 Hz	Locked
Connectivity State	OK	Operational
Boot State	OK	Operational
Security	Enable	BPI+
IP Provisioning Mode	Honor MDD	IPv6 only

Downstream Bonded Channels

Channel	Lock Status	Modulation	Channel ID	Frequency	Power	SNR / MER	Unerrored Codewords	Correctable Codewords	Uncorrectable Codewords
1	Locked	QAM256	13	579000000 Hz	1.0 dBmV	38.1 dB	3253066445	0	0
2	Locked	QAM256	10	561000000 Hz	1.5 dBmV	38.1 dB	3252151242	0	0
3	Locked	QAM256	11	567000000 Hz	1.4 dBmV	38.1 dB	3252155575	0	0
4	Locked	QAM256	12	573000000 Hz	1.4 dBmV	38.1 dB	3252158984	0	0
5	Locked	QAM256	14	585000000 Hz	1.2 dBmV	38.0 dB	3252162445	0	0
6	Locked	QAM256	15	591000000 Hz	1.1 dBmV	38.0 dB	3252166076	0	0
7	Locked	QAM256	16	597000000 Hz	0.4 dBmV	37.7 dB	3252169819	0	0
8	Locked	QAM256	17	603000000 Hz	0.0 dBmV	37.6 dB	3252174714	0	0
9	Locked	QAM256	18	609000000 Hz	-0.3 dBmV	37.4 dB	3252182066	0	0
10	Locked	QAM256	19	633000000 Hz	1.2 dBmV	37.3 dB	3252184269	13	19
11	Locked	QAM256	20	615000000 Hz	-0.4 dBmV	37.2 dB	3252189855	0	0
12	Locked	QAM256	21	621000000 Hz	-0.1 dBmV	37.3 dB	3252192232	0	0
13	Locked	QAM256	22	627000000 Hz	1.1 dBmV	37.4 dB	3252196705	0	0
14	Locked	QAM256	23	639000000 Hz	1.9 dBmV	37.2 dB	3252178876	3	31
15	Locked	QAM256	24	645000000 Hz	1.3 dBmV	37.1 dB	3252179190	6	28
16	Locked	QAM256	26	651000000 Hz	1.2 dBmV	36.8 dB	3252174005	7	28
17	Locked	QAM256	27	657000000 Hz	0.4 dBmV	36.6 dB	3252191404	12	28
18	Locked	QAM256	28	663000000 Hz	-0.1 dBmV	36.4 dB	3252193947	8	31
19	Locked	QAM256	29	669000000 Hz	0.2 dBmV	36.3 dB	3252197864	10	30
20	Locked	QAM256	30	675000000 Hz	0.3 dBmV	35.8 dB	3252202244	12	28
21	Locked	QAM256	31	681000000 Hz	0.8 dBmV	36.1 dB	3252203872	11	30
22	Locked	QAM256	32	687000000 Hz	1.3 dBmV	36.0 dB	3252209285	10	28
23	Locked	QAM256	33	693000000 Hz	2.4 dBmV	36.0 dB	3252212822	14	26
24	Locked	QAM256	34	699000000 Hz	3.1 dBmV	36.1 dB	3252217002	7	26
25	Locked	QAM256	35	705000000 Hz	3.9 dBmV	36.4 dB	3252220387	0	0
26	Locked	QAM256	36	711000000 Hz	3.9 dBmV	36.2 dB	3252224000	0	0
27	Locked	QAM256	37	717000000 Hz	2.9 dBmV	36.1 dB	3252227924	0	0
28	Locked	QAM256	38	723000000 Hz	2.7 dBmV	36.0 dB	3252230639	0	0
29	Locked	QAM256	39	729000000 Hz	2.2 dBmV	35.8 dB	3252236420	0	0
30	Locked	QAM256	40	735000000 Hz	2.7 dBmV	35.9 dB	3252238115	0	0
31	Locked	QAM256	41	741000000 Hz	2.6 dBmV	35.7 dB	3252241795	0	0
32	Not Locked	Unknown	0	0 Hz	0.0 dBmV	0.0 dB	0	0	0

Upstream Bonded Channels

Channel	Lock Status	Modulation	Channel ID	Frequency	Power
1	Locked	ATDMA	81	36500000 Hz	45.5 dBmV
2	Locked	ATDMA	82	30100000 Hz	45.5 dBmV
3	Locked	ATDMA	83	23700000 Hz	44.0 dBmV
4	Not Locked	Unknown	0	0 Hz	0.0 dBmV
5	Not Locked	Unknown	0	0 Hz	0.0 dBmV
6	Not Locked	Unknown	0	0 Hz	0.0 dBmV
7	Not Locked	Unknown	0	0 Hz	0.0 dBmV
8	Not Locked	Unknown	0	0 Hz	0.0 dBmV

Downstream OFDM Channels

Channel	Lock Status	Modulation / Profile ID	Channel ID	Frequency	Power	SNR / MER	Active Subcarrier Number Range	Unerrored Codewords	Correctable Codewords	Uncorrectable Codewords
1	Locked	0, 1, 2, 3	25	780000000 Hz	2.8 dBmV	31.0 dB	1108 ~ 2987	346999323	318918359	3906
2	Not Locked	0	0	0 Hz	6.8 dBmV	0.0 dB	0 ~ 4095	0	0	0

Upstream OFDMA Channels

Channel	Lock Status	Modulation / Profile ID	Channel ID	Frequency	Power
1	Not Locked	Unknown	0	0 Hz	0 dBmV
2	Not Locked	Unknown	0	0 Hz	0 dBmV

Current System Time: Mon May 18 10:03:23 2020

System Up Time: 19:53:27

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kvjkhjkhdfghjdf

Frequent Visitor

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6 Messages

5 years ago

Do we have a list of those known modems?? Based on prior posts on this forum, seems other CM1000 modems report in the correct range. See prior post https://forums.xfinity.com/t5/Your-Home-Network/Connectivity-Issues-with-Netgear-CM1000/m-p/3333159 where they show 39db on the OFDM channel. I think I'm running low at 30db??

Also, in my event log, I only get nags about OFDM. Not sure what they tell us if anything:

Time	Priority	Description
2020-05-18, 12:52:26	Notice (6)	CM-STATUS message sent. Event Type Code: 24; Chan ID: 25; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: 2 3.;CM-MAC=bc:a5:11:89:fc:74;CMTS-MAC=00:01:5c:77:fa:5c;CM-QOS=1.1;CM-VER=3.1;
2020-05-18, 12:51:42	Notice (6)	CM-STATUS message sent. Event Type Code: 16; Chan ID: 25; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: 3.;CM-MAC=bc:a5:11:89:fc:74;CMTS-MAC=00:01:5c:77:fa:5c;CM-QOS=1.1;CM-VER=3.1;
2020-05-18, 12:50:29	Notice (6)	CM-STATUS message sent. Event Type Code: 24; Chan ID: 25; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: 2 3.;CM-MAC=bc:a5:11:89:fc:74;CMTS-MAC=00:01:5c:77:fa:5c;CM-QOS=1.1;CM-VER=3.1;
2020-05-18, 12:49:52	Notice (6)	CM-STATUS message sent. Event Type Code: 16; Chan ID: 25; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: 3.;CM-MAC=bc:a5:11:89:fc:74;CMTS-MAC=00:01:5c:77:fa:5c;CM-QOS=1.1;CM-VER=3.1;
2020-05-18, 12:48:28	Notice (6)	CM-STATUS message sent. Event Type Code: 24; Chan ID: 25; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: 2 3.;CM-MAC=bc:a5:11:89:fc:74;CMTS-MAC=00:01:5c:77:fa:5c;CM-QOS=1.1;CM-VER=3.1;
2020-05-18, 12:48:07	Notice (6)	CM-STATUS message sent. Event Type Code: 16; Chan ID: 25; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: 3.;CM-MAC=bc:a5:11:89:fc:74;CMTS-MAC=00:01:5c:77:fa:5c;CM-QOS=1.1;CM-VER=3.1;
2020-05-18, 12:45:47	Notice (6)	CM-STATUS message sent. Event Type Code: 24; Chan ID: 25; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: 2 3.;CM-MAC=bc:a5:11:89:fc:74;CMTS-MAC=00:01:5c:77:fa:5c;CM-QOS=1.1;CM-VER=3.1;
2020-05-18, 12:45:15	Notice (6)	CM-STATUS message sent. Event Type Code: 16; Chan ID: 25; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: 3.;CM-MAC=bc:a5:11:89:fc:74;CMTS-MAC=00:01:5c:77:fa:5c;CM-QOS=1.1;CM-VER=3.1;
2020-05-18, 12:42:11	Notice (6)	CM-STATUS message sent. Event Type Code: 24; Chan ID: 25; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: 2 3.;CM-MAC=bc:a5:11:89:fc:74;CMTS-MAC=00:01:5c:77:fa:5c;CM-QOS=1.1;CM-VER=3.1;
2020-05-18, 12:41:14	Notice (6)	CM-STATUS message sent. Event Type Code: 16; Chan ID: 25; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: 3.;CM-MAC=bc:a5:11:89:fc:74;CMTS-MAC=00:01:5c:77:fa:5c;CM-QOS=1.1;CM-VER=3.1;
2020-05-18, 12:40:56	Notice (6)	CM-STATUS message sent. Event Type Code: 24; Chan ID: 25; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: 2 3.;CM-MAC=bc:a5:11:89:fc:74;CMTS-MAC=00:01:5c:77:fa:5c;CM-QOS=1.1;CM-VER=3.1;
2020-05-18, 12:40:32	Notice (6)	CM-STATUS message sent. Event Type Code: 16; Chan ID: 25; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: 3.;CM-MAC=bc:a5:11:89:fc:74;CMTS-MAC=00:01:5c:77:fa:5c;CM-QOS=1.1;CM-VER=3.1;

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EG

Expert

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111.5K Messages

5 years ago

It is a known issue that some makes and models of modem's measuring mechanisms do not read the power level and the SNR of the OFDM channel accurately.

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TraderJim

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3 Messages

Interesting. Do you know if the Netgear CM1000 or CM1200 have that problem? How far off are they if they do? I am getting -24.2 dBmv power level and 25.5 dB SNR on my OFDM channel, with very large uncorrectable codeword counts, larger than the unerrored codeword count. Been complaining to Comcast for years, and they never are able to fix it.

4 years ago

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EG

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111.5K Messages

@TraderJim

Please create a new topic of your own here on this board detailing your issue. Thanks. Year old dead thread now being closed.

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? Please mark an Accepted Answer! tick

4 years ago

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kvjkhjkhdfghjdf

downstream OFDM SNR????

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kvjkhjkhdfghjdf

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EG

TraderJim

EG

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