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Noise Margin Conundrum

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Noise Margin Conundrum

I'm connected via a 1Mb connection - having recently upgraded from 512Kb, after the limits were changed (I'm a fair way from the exchange, with my line attenutation hovering between 58-59db).

However, my connection is good, never dropping and download speeds are respectable (usually around 930-960kbps).

[Prior to upgrading I did experience a deterioration in performance, but BT visited and eventually things seemed to pick up - although they never actually suggested there was a problem they proactively fixed.]

I'm interested in understanding the noise margin, as reported by my router (Netgear DG834G). I've only been able to monitor this since upgrading to the newest firmware (1.05.00).

This seems to vary widely - routinely between 11db and 21db within a space of hours - on occasion dropping to around 8db. Initially I though the figure was degrading over time - and rebooting the router appeared to restore a high value. However, of late I am less convinced of this with no clear pattern either based around time of day, or router uptime presenting itself.

I'm connected directly to a BT installed filtered master socket. The only other connections elsewhere in the house are a single DECT phone and 2 Sky satellite boxes. However - disconnecting this equipment seems to make no difference.

I stress I am not having a particular problem at this point in time - I just want to avoid one that may be around the corner. What makes me nervous is that being on a newly developed site, BT and the builders are forever opening up the access hatches on the street and tinkering (and letting the rain in)!!

Should I be expecting a little more "stability" around the noise margin figure?

Thanks in advance,

Tim
9 REPLIES
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Noise Margin Conundrum

Hi there

Got exactly the same problem with the same Hardware and also recently upgraded to 1mb.

My Noise Margin ranges from 11db-20db from what I have seen. I have only noticed this by looking occasionally. So am not sure if it dips below this level to cause disconnections. How are you monitoring your levels ?

I am not 100% sure that this is the problem and am in the process of getting a replacement DG834G due to the fact I have other problems which include:- random lockups (requiring the power cable to be pulled to get access back), also losing the wirless connection when using the Laptop and of course the disconnections.

Would be nice to see comments from people who are using a DG834G with Plusnet succesfully.

Cheers
Community Veteran
Posts: 14,469
Registered: 30-07-2007

Noise Margin Conundrum

I have the same unit and have an SNR range of 10 -> 15dB and line atten of 60dB.

Routers are not always as accurate as you think when measuring the line so it is to be expected that it will vary. Firmware v1.05.00 is also the first one to give this info on this router which may suggest they had problems with it on previous firmware versions - i.e. if the hardware can test the line, why was the feature not available in the first firmware version.
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Noise Margin Conundrum

Cheesy just upgraded today to 1mb (my line passed initially 58db and my westell 2400 router showed attenuation 62db with a noise margin of 25db for download for 512k in 2003) now my router shows attenuation 63db and noise margin of 17.5 db and have a rock solid connection, using a non filtered adsl faceplate nte5 by the way, thought i might of needed one with such a high attenuation. filtered adsl faceplates have helped from posts on different forums, i think the noise margin is most important for 1 mb conns, imho

Found out that i am on now plusnet.ptn-ag1.net 195.166.128.123
for my first hop doing tests on my router

Hope you get it sorted and have better reliable conns
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Noise Margin Conundrum

I use a Netgear DG834 router and have had no problems at all. Starts every time, never goes down at noise level is on average 21db and line attun is 57db. No problems using with Plusnet and use 1 x pc and two Mac's on shared home network. (Wires)

Find it interesting to note that people seem able to get a 1mb connection with similar figuers to mine but Plusnet/BT insist i can't have more than 512k due to line noise. How did you guys convince Plusnet/BT because I've all but given up with regrading and am now thinking of moving to local cabe ISP who can provide 1.5mb adsl ( how ironic is that ! )

Andrew Beevers
wisty
Aspiring Pro
Posts: 431
Thanks: 53
Fixes: 3
Registered: 30-07-2007

Noise Margin Conundrum

I'm using a DG834G to connect to Plusnet at 1Mb - just upgraded. I'm about 3.5km from the exchange. Noise Margin 21dB , Attenuation 39dB. I was experiencing the occasional lockup- even after upgrading to V1.05.00. However doing a hard factory reset, and reconfiguring the router seems to have solved that problem. Performance is just great. Always on Broadband!
I can't be absolutely certain because one of the causes of trouble was clearly power spikes - a decent lightning storm in the area would cause lockups - almost all the 3.5km is overhead! But so far so good. Try V1.05.00, but do a factory reset and reconfigure after the upgrade.
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Noise Margin Conundrum

Quote
My Noise Margin ranges from 11db-20db from what I have seen. I have only noticed this by looking occasionally. So am not sure if it dips below this level to cause disconnections. How are you monitoring your levels ?


No magic I'm afraid - laboriously going to the relevant screen in the router status on a regular basis.

Tim
keithcalder
Grafter
Posts: 182
Registered: 03-08-2007

Noise Margin Conundrum

I have a Netgear router also, noticed my noise margins going down as well although a reboot of the router or disconnecting did not improve things at all. Never had any lockups, nor random disconnections ( that I've noticed ). Have seen them as low as 7db downstream but I think the router may not giving a true reading. Oh forgot to mention, I'm using the 1.5.0 firmware as well.
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Noise Margin Conundrum

I'm using the DG834G, latest firmware on plusnet 0.5mb and it's very stable. My downstream noise margin varies from 17-22dB. Once it hit 10dB and oddly a reboot brought this back up again. Some of my DG834G stats here
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Noise Margin Conundrum

So, to summarise what I have drawn from this thread:

It seems that the considerable variation in Noise Margin I experience are not something I need to be concerned about - lots of people have similar, and it doesn't seem to be a "forewarning" of anything more serious.

Another case of "if it ain't broke......"

Tim