Power Levels

Should I be worried with these power levels?

Cable Modem Downstream
DS-1 DS-2 DS-3 DS-4
Frequency 298750000 306750000 314750000 322750000
Lock Status
(QAM Lock/FEC Sync/MPEG Lock) Y/Y/Y Y/Y/Y Y/Y/Y Y/Y/Y
Channel Id 101 102 103 104
Modulation 256QAM 256QAM 256QAM 256QAM
Symbol Rate
(Msym/sec) 6.952 6.952 6.952 6.952
Power Level
(dBmV) 15.45 15.12 14.40 14.86
RxMER
(dB) 38.61 38.61 38.61 38.98
Correctable
Codewords 38 24 25 32
Uncorrectable
Codewords 929 279 968 944

(dBmV) 15.45 15.12 14.40 14.86
RxMER

yea they are too high 10.00 is the max they should be

mine:
Power Level
(dBmV) 6.81 5.99 5.71 5.84

mine are slightly higher than they were a few mnths ago...but from what iv read they can increase slightly in the cold/winter time..

but yours are defo on the high side......the rest of your downstream stats look ok..

what is your upstream power level.??

upstream is 42.25. So I need to log a fault then. What would the effect of having such high power levels?

It's very much too high - get a call logged or pop to Maplin and buy some F-type attenuators. I bought a set of -3, 6 and -10dB for about 4 quid.

Personally I'd pop a 10 and 3dB on there as VM recommend -3dBmv to +7dBvm.

So at 13dBvm it'll be getting 4x the signal it would like, 16dBvm it's getting 8x the signal!

ok, thanks. I will take a trip to town next weekend then to pop into Maplin.

Ian

Remember to get the "Forward" Type attenuators or else it will mess up your upstream signal..

Have Maplin stopped selling these as can't find them on their website?

Ian

Looks like they have.

A quick google shows plenty of place selling similar, including 0-20dB variable ones.
Not sure if they are forward attenuators or not, but if they are makes them quite handy.

Ebay sell them..

http://shop.ebay.co.uk/?_from=R40&_trksid=p5197.m570...

In reply to a post by mrblobby:

upstream is 42.25. So I need to log a fault then. What would the effect of having such high power levels?

The effects of high downstream are (a) amplified noise - bad when your SNR/RxMER is <35 dB on 256QAM modulation; (b) Signal intrusion on the adjacent channel which corrupts data.

Upstream (if stable) was fine as I'm sure you know.

Edited by deleted (Wed 29-Dec-10 00:13:51)

Engineer booked for tuesday morning. The service has dropped every morning for past few days so might be related. Spoke to the 50Mb customer services and the agent I spoke to was very suprised at how high the levels were.

Ian

Engineer been and gone. Power levels now between 4 and 6. Apparently they are doing an upgrade of the street cabs and when upgraded they add 10 dBmV to the power on the new tap points. He moved me to a new tap point and looking good so far.

Ian

In reply to a post by mrblobby:

Engineer been and gone. Power levels now between 4 and 6. Apparently they are doing an upgrade of the street cabs and when upgraded they add 10 dBmV to the power on the new tap points. He moved me to a new tap point and looking good so far.

Ian

Where in the country are you please Ian? I see London and Southampton in your profile and would be interested in which bit of London if it was there.

Thanks.

In reply to a post by Ignitionnet:

In reply to a post by mrblobby:

Engineer been and gone. Power levels now between 4 and 6. Apparently they are doing an upgrade of the street cabs and when upgraded they add 10 dBmV to the power on the new tap points. He moved me to a new tap point and looking good so far.

Ian

Where in the country are you please Ian? I see London and Southampton in your profile and would be interested in which bit of London if it was there.

Thanks.

Live in Southampton but work in London. The broadband is at my home address. (Virgin area 021 I believe).

Ian

In reply to a post by djfunkdup:

yea they are too high 10.00 is the max they should be

Where do get that info from please?

Mine shows :-

Downstream Receive Power Level : 18.8 dBmV
Upstream transmit Power Level : 42.0 dBmV

On the Virgin Forums there is a sticky post here

Ian

Thanks.

"downstream in the range -15 to +15 dBmv"
"upstream is spec'd in the range 8 dBmv to 58 dBmv "

Unless I'm missing something?

Yes that is the spec but not all modems can handle high power levels properly.

DOWNSTREAM POWER (Optimal)

Rule of thumb: -3 dBmv to +6 dBmv

The above advice compares with the VM stated optimum values by region (according to implemented infrastructure standards) and modulation:

QAM64 (Knowsley networks) -7 dBmv to +3 dBmv

QAM64 (Langley/Bromley) -10 dBmv to 0 dBmv

QAM256 -3 dBmv to +7 dBmv



This is not cast in stone. A good modem (Cisco 2100 comes to mind) can handle nearer the DOCSIS spec if the level is steady and the experience good. If the experience is bad, then look for high downstream power, particularly above the 9 dBmv mark.

I would give the helpline a call (0800 - 0520431 is the dedicated 50Mb help line).

Ian