Power levels and SNR value for 100mb connection cable modem.

[mkol]

Hi

I just recently upgraded to 100mb from Virgin media and was wondering about my power levels and SNR value on the cable modem.

Please see the image and let me know are they ok or too low or too high?

thanks

[xendrome]

Look fine to me, IIRC, 45 is about right in the middle of where you want to be, so your numbers look fine.

[mkol]

what about the down stream power level they are 0. ?

[Jub]

I think that's quite close to "as good as you'll get". You have better numbers than me and I get 103 Mbit out of mine.

The fact that it's overcrowded and unusable at times other than 1am-9am is another matter...

[mkol]

Hi now the down stream power level are fluctuating between -3 and 0. Is it normal?

[Jub]

I think that's within what they classify as "normal". Can I ask... does your connection work and perform well?

[mkol]

It does work well but I have two 6db forward path attenuators connected on my cable modem and I am thinking about dropping down to 10db attenuator as I have one.

[Jub]

Temporarily remove the attenuators, call up Virgin and report your power levels and ask them to send an engineer to fix it on their end. Saves you the entire issue...

[neufuse Veteran]

your signals are perfect, having fluctuations are normal, signal levels change with tempature normally and node conditions...

never use attenuators, they hurt signal more then help... if your signal is too high an attenuator wont help, because it attenuates usually forward carries (singals to you) but the Reverse carrier will get deminished..

if there are attenuators on your line, remove then have the cable company come out and balance your node correctly, attenuators are just cable techs not doing their jobs right

[+BudMan MVC]

If I recall correctly normal downstream power for cable can be between -12 and 12db, so sure 0 or -3 would be fine. Some specs even say -15 to 15 I believe.

But if your running your own attenuators in front of your modem, I would also agree with the suggestion to remove them and call your provider to adjust the levels if they are off. You should not ave to run your own attenuators that is for sure. Now if they put them in then leave them.

[mkol]

Hello Guys

Thanks for the feedback. I had before 50mb and 6db attenuators was put in by their engineer long time back to balance the power level. But since I have gone to 100mb the power levels are shown as the image I was bit concerned.

As I had 10db attenuator, I thought I should plug it and see how that works. Upon calling virginmedia the team said the power levels are fine, the Down stream one can range from -10 to 10+

And if I was fussy about it I can have an engineer visit ME but that will cost me ?99 and I said no THANKYOU!!

[neufuse Veteran]

Hello Guys

Thanks for the feedback. I had before 50mb and 6db attenuators was put in by their engineer long time back to balance the power level. But since I have gone to 100mb the power levels are shown as the image I was bit concerned.

As I had 10db attenuator, I thought I should plug it and see how that works. Upon calling virginmedia the team said the power levels are fine, the Down stream one can range from -10 to 10+

And if I was fussy about it I can have an engineer visit ME but that will cost me ?99 and I said no THANKYOU!!

-15db to +15db for downstream is "in spec" -10 to +10 is good, 0 is perfect

upstream over 55dbmV is problematic this is how loud the modem has to scream back to the node for the node to hear it and understand it... under 50 is good... 35-50 is great

SNR is your biggest issue, you could have 0dbmv and have a SNR that is 10 then your connection will suck... the higher the SNR the better... 35+ is a good SNR number

[SnoopZ]

-15db to +15db for downstream is "in spec" -10 to +10 is good, 0 is perfect

upstream over 55dbmV is problematic this is how loud the modem has to scream back to the node for the node to hear it and understand it... under 50 is good... 35-50 is great

SNR is your biggest issue, you could have 0dbmv and have a SNR that is 10 then your connection will suck... the higher the SNR the better... 35+ is a good SNR number

Those downstream power levels are out of spec for the ops Virgin Media UK ISP cable connection.

Downstream optimal:- -3 to +7 dBvm

Upstream optimal:- 31 dBvm to 54 dBvm Stable

SNR:- 35+ is in spec.

http://community.vir...011/td-p/846181

Your levels are pretty good Mkol.

[mkol]

thank you people.:)

[neufuse Veteran]

Those downstream power levels are out of spec for the ops Virgin Media UK ISP cable connection.

Downstream optimal:- -3 to +7 dBvm

Upstream optimal:- 31 dBvm to 54 dBvm Stable

SNR:- 35+ is in spec.

http://community.vir...011/td-p/846181

Your levels are pretty good Mkol.

I'm going by cable labs specifications, which is the industry standard specs, by the people who design all the specifications for stuff like HFC networks, cablecards, DOCSIS, etc

[SnoopZ]

I'm going by cable labs specifications, which is the industry standard specs, by the people who design all the specifications for stuff like HFC networks, cablecards, DOCSIS, etc

Yes i thought you were, which DOCSIS the OP is on and QAM makes a difference also, he is on DOCSIS 3 and QAM 256 whatever than means as i am no expert. :)

[neufuse Veteran]

Yes i thought you were, which DOCSIS the OP is on and QAM makes a difference also, he is on DOCSIS 3 and QAM 256 whatever than means as i am no expert. :)

DOCSIS levels and QAM channels dont have an impact on signal levels...

DOCSIS1, 1.1, 2 and 3 are just specifications

now upstream channles can change based on signal strength... you can get from QPSK to QAM16 to QAM64, etc, but not being on QAM-64 for an upsteram channel doesn't mean you have a bad connection, your CMTS could just be configured for QPSK or QAM16 due to where they placed the upstream channel in the spectrum

QAM256 just means its Quadrature amplitude modulation with a 256 point constellation... meaning that each pulse of information can have 256 possible values... kind of like binary has 2 values, a QAM256 channel could be anything from 0 to 255 per "character" sent the higher the QAM the higher you can potentially send the data rate to... since you get this with basically a wave form, the higher the QAM the more likely the interferance from RF noise

[JJ_]

The upstream is OK but keep an eye on it, ideally it should be under 55. Your levels will fluctuate depending on what the weather is outside, that's the nature of coax cables. I upgraded to 100 Mbit from 50 Mbit yesterday. My 4 downstream channels SNR values have been out of spec for a year. Sometimes all 4 channels drop as low as 29 & uncorrectables sky rocket. I've had several engineers out who say the SNR can't be improved as I'm 10 meters away from the cab. Here are my levels (sorry about formatting, coped & pasted)

Cable Modem Downstream

DS-1 DS-2 DS-3 DS-4

Frequency 315000000 291000000 299000000 307000000

Lock Status (QAM Lock/FEC Sync/MPEG Lock) Y/Y/Y Y/Y/Y Y/Y/Y Y/Y/Y

Channel Id 208 205 206 207

Modulation 256QAM 256QAM 256QAM 256QAM

Power Level (dBmV) 1.20 1.25 1.33 1.25

RxMER (dB) 33.72 33.72 31.92 33.16

Correctable Codewords 113620 135825 3216806 289090

Uncorrectable Codewords 311 307 972 285

Cable Modem Upstream

US-1 US-2 US-3 US-4

Channel Type 2.0 N/A N/A N/A

Channel ID 3 N/A N/A N/A

Frequency (Hz) 35800000 N/A N/A N/A

Modulation 16QAM N/A N/A N/A

Symbol Rate (KSym/sec) 5120 N/A N/A N/A

Power Level (dBmV) 45.00 N/A N/A N/A

[neufuse Veteran]

The upstream is OK but keep an eye on it, ideally it should be under 55. Your levels will fluctuate depending on what the weather is outside, that's the nature of coax cables. I upgraded to 100 Mbit from 50 Mbit yesterday. My 4 downstream channels SNR values have been out of spec for a year. Sometimes all 4 channels drop as low as 29 & uncorrectables sky rocket. I've had several engineers out who say the SNR can't be improved as I'm 10 meters away from the cab. Here are my levels (sorry about formatting, coped & pasted)

Cable Modem Downstream

DS-1 DS-2 DS-3 DS-4

Frequency 315000000 291000000 299000000 307000000

Lock Status (QAM Lock/FEC Sync/MPEG Lock) Y/Y/Y Y/Y/Y Y/Y/Y Y/Y/Y

Channel Id 208 205 206 207

Modulation 256QAM 256QAM 256QAM 256QAM

Power Level (dBmV) 1.20 1.25 1.33 1.25

RxMER (dB) 33.72 33.72 31.92 33.16

Correctable Codewords 113620 135825 3216806 289090

Uncorrectable Codewords 311 307 972 285

Cable Modem Upstream

US-1 US-2 US-3 US-4

Channel Type 2.0 N/A N/A N/A

Channel ID 3 N/A N/A N/A

Frequency (Hz) 35800000 N/A N/A N/A

Modulation 16QAM N/A N/A N/A

Symbol Rate (KSym/sec) 5120 N/A N/A N/A

Power Level (dBmV) 45.00 N/A N/A N/A

your Signals are perfect going by what you posted there... if your SNR drops suddenly that is not you usually, as you have a high SNR right now... that is usually the HFC network node going bonkers OR someone else on your outside line feeding noise back into the network... ingress causes major SNR issues... there could be someone on your node that is feeding unknowingly bad RF into the HFC network... when you do this the SNR is going to go out of wack... this could be as easily done as a bad ground on someones TV or an old VCR that sends the signal down the wrong line (someone connected the cable in to the cable out, and it is a noise generating device) I know comcast around here proactively looks for ingress and will disconnect the people that cause it until they fix the issue... some cable companies dont want to spend the money and wait till a whole node is complaining then drag their feet out and say its not us its you blah blah do nothing let the problem continue...

[SnoopZ]

JJ_ on Virgin Media if the SNR falls below 34.5 dB which is on the low side, you start getting uncorrectable errors as their network is so sensative, those errors would probably vanish if a little higher, your other power levels are perfect though.

Luckily since an engineer visit my SNR is steady at 35 dB and i now have no errors in my log.

[JJ_]

your Signals are perfect going by what you posted there... if your SNR drops suddenly that is not you usually, as you have a high SNR right now... that is usually the HFC network node going bonkers OR someone else on your outside line feeding noise back into the network... ingress causes major SNR issues... there could be someone on your node that is feeding unknowingly bad RF into the HFC network... when you do this the SNR is going to go out of wack... this could be as easily done as a bad ground on someones TV or an old VCR that sends the signal down the wrong line (someone connected the cable in to the cable out, and it is a noise generating device) I know comcast around here proactively looks for ingress and will disconnect the people that cause it until they fix the issue... some cable companies dont want to spend the money and wait till a whole node is complaining then drag their feet out and say its not us its you blah blah do nothing let the problem continue...

I've been checking up on their forums recently and it seems like Virgin Media in some areas actively seek out people feeding back noise and are kicking them off the network until they remove what modifications they've made. Most of the time it's due to incorrect coax cables being used or badly fitted f connectors.

JJ_ on Virgin Media if the SNR falls below 34.5 dB which is on the low side, you start getting uncorrectable errors as their network is so sensative, those errors would probably vanish if a little higher, your other power levels are perfect though.

Luckily since an engineer visit my SNR is steady at 35 dB and i now have no errors in my log.

The power levels sway one side during summer then the other during winter months. I haven't noticed SNR fluctuate during a change in weather but my correctable codewords stop rising at 34.5 which is a rare figure for my modem to attain. Virgin Media consider anything below 35 out of spec. At 29 I get considerable packet loss. Anywhere between 30-33 and my uncorrectable codewords are in their millions - thats with my modem being online for a few days.