125M : Exposed VM coax cable in junction box

[jb66]

this is why there are splitters in cab

[Coffeeguy]

While we're on the subject, does anyone know why one of my downstream channels is a whole dB and a bit below the other 3 channels? I've checked with my neighbour and his Superhub reports the same phenomenon:

Cable Modem Downstream
Modulation 256QAM 256QAM 256QAM 256QAM
Symbol Rate
(Msym/sec) 6.952 6.952 6.952 6.952
Power Level
(dBmV) -0.34 0.29 0.18 0.03
RxMER
(dB) 34.93 33.72 34.77 35.25
Correctable
Codewords 7670 68030 6237 2205
Uncorrectable
Codewords 1009 295 316 303

[RB2004]

It's because different frequencies have different losses. Higher frequencies more than lower frequencies.

Also
I gather there is some kinda setup on the amp in the cabinet which dictates this also.

[Coffeeguy]

They were all level at 35 a couple of days ago for maybe an hour or two but the one channel has always been 1.5~ dB below the rest. Not that is causes any problems but interesting to know nonetheless

[jb66]

The amps pump out higher frequencies at a higher level than low as high frequencies loose more signal over a shorter distance compared to low signals. So if your close to the amp usually high frequencies are higher and if your far away high frequencies are lower than low frequencies. It's basically a balancing game

[Coffeeguy]

Thanks jb, that explains it as I live literally next door to the cab and I suppose this is why my SNR never goes above the figure reported. Is there anything I can do to improve or boost this. I see some reports of people who have a SNR of 43.

[qasdfdsaq]

No, that's VM's job.

[kwikbreaks]

Originally Posted by Coffeeguy

I see some reports of people who have a SNR of 43.

Yes you can get that...

Downstream Channels
Lock Status Channel ID Frequency Modulation Rx Power SNR Pre RS Errors Post RS Errors
Locked 80 467000000 Hz QAM256 4.9 dBmV 42.6 dB 10202 0
Locked 76 435000000 Hz QAM256 6.4 dBmV 43.3 dB 1950 0
Locked 77 443000000 Hz QAM256 6.2 dBmV 43.4 dB 2427 0
Locked 78 451000000 Hz QAM256 6.3 dBmV 43.2 dB 2769 0
Locked 79 459000000 Hz QAM256 5.6 dBmV 43.2 dB 3520 0

[RB2004]

You can but it depends on your local network.

The reason some is higher than other with same signal strength is because of noise on the line.

This can be caused by unterminated connections, loose connections, customers doing DIY modifications using improper stuff and / or methods, some equipment as jb66 said reporting lower snr than other equipment, damaged cables, tired lasers in the nodes etc.. Lots of factors.

Terminating unterminated connections, making sure that connections are tight but not over tightened... And if really must do modifications.. Using proper quality cable, connectors, splitters and methods etc might not drastically increase snr or even give a noticeable difference but it all does a little bit to help.

Yes it's VMs problem, and they are slowly refurbishing cabinets and I heard a while back sent all engineers on a particular day going round tightening connections. So they are trying to fix it.

But as fast as they are, some installers are still making installations with loose connections (loosely hand tight) and contractors doing cable repulls are leaving unterminated cables which in turn undermine vm efforts.

But while not our responsibility as customers, we do often pay a lot and want a performing network as much as vm do... So it doesn't cost anything for us to nip up loose connections in our own homes.. Just a little more than hand tight is fine.. Not so much it breaks your equipment as that would be stupid.

As tesco would say every little helps

[Coffeeguy]

Heh. Will VM be upgrading cabs during the speed upgrades?

[RB2004]

Nope that is separate, as far as I'm aware the cabinet refurbishment is an ongoing project that has been ongoing a while and still is.. They are going around tidying up the cabinets, repairing them, replacing tired amps and node lasers, some also seem to be getting repainted grey.

[Eeeps]

Originally Posted by Coffeeguy

While we're on the subject, does anyone know why one of my downstream channels is a whole dB and a bit below the other 3 channels? I've checked with my neighbour and his Superhub reports the same phenomenon:

Cable Modem Downstream
Modulation 256QAM 256QAM 256QAM 256QAM
Symbol Rate
(Msym/sec) 6.952 6.952 6.952 6.952
Power Level
(dBmV) -0.34 0.29 0.18 0.03
RxMER
(dB) 34.93 33.72 34.77 35.25
Correctable
Codewords 7670 68030 6237 2205
Uncorrectable
Codewords 1009 295 316 303

Those MER figures are a bit too low IMO. Note that the channel with 33.72 has counted over 68K of errors compared with your best of just 2K.
This suggests that it is very marginal for 256QAM.
Also having any uncorrectable errors (if the SH stats are true) can lead to T3 if the codewords relate to a CMTS range response.

[Sephiroth]

Originally Posted by jb66

Snr always appear lower on a vmng300

I hope you don't mind my coming in late.

The VMNG300 shows rising correctable codewords (but no uncorrectables). This is consistent with the lowish SNR reported by the modem. Eeps noticed this too. The uncorrectables you had at the time are highly likely to be what happens at boot time when the modem starts out in a non-graceful state. So I wouldn't read anything into those values. If the uncorrectables grow, then VM would have a case to answer.

As regards the one channel having a power level difference; unfortunately you stripped out the frequency data from your stats. if the first channel frequency is higher than all the others, it would explain the difference as JB66 has also explained. If the frequency is lower, then the cabinet amplifier is out of slope and needs adjusting.

HTH.
Throughout this thread you have been correctly advised by RB2004.

[StevenNT]

Originally Posted by RB2004

Nope that is separate, as far as I'm aware the cabinet refurbishment is an ongoing project that has been ongoing a while and still is.. They are going around tidying up the cabinets, repairing them, replacing tired amps and node lasers, some also seem to be getting repainted grey.

Good to hear that's an ongoing project. Quite a few cabinets are badly damaged where I live in North Camp, Farnborough so a refurb is badly needed here.

I've been asking VM to fix them and they like to drag their feet in eventually fixing them only for the installers to bust the lock open (with screwdriver and a mallet) and no I'm not joking as I've seen it happen in front of me twice so frankly given up getting getting it fixed again if that's the attitude of their installers

[Coffeeguy]

Haha engineers bruteforcing cabs! Should've video'd and put it on Youtube.

Seph, sorry thought it was meaningless but yes, the frequency increases chronologically

Frequency 299000000 307000000 315000000 323000000
Power Level
(dBmV) -1.05 -0.40 -0.53 -0.59
RxMER
(dB) 34.48 33.38 34.48 34.93
Correctable
Codewords 786305 4416722 518646 219480
Uncorrectable
Codewords 314 314 329 312

Touch wood there have been no T3 timeouts since fitting the terminator last Sunday. I even capped my neighbours coax who unsubbed and moved over to Infinity a while ago. Surprised his coax was live and worked with my modem! Thanks for everyone's input, very much appreciated