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Advice on Noise Margin Please

Soxendom
Dabbler
Posts: 20
Registered: 21-08-2007

Advice on Noise Margin Please

I recently had to change my router to a Netgear dg834. I've noticed that when I've just rebooted the computer or the router the downstream noise margin is around 13 - 15db. As soon as I access the internet this shoots up to 2147483642db. The speeds I'm getting seem to be about normal, so is this figure anything to worry about. If so, does anyone have any suggestions as to how to cure it?
Thanks
17 REPLIES
James
Grafter
Posts: 21,036
Registered: 04-04-2007

Re: Advice on Noise Margin Please

Hi there,
I'm pretty sure that that is a known issue with the Netgear Routers, so I wouldn't be overly concerned by it.
Community Veteran
Posts: 14,469
Registered: 30-07-2007

Re: Advice on Noise Margin Please

This is a 'feature' of netgears. By feature I mean bug.... It's actually gone negative and indicated the router has not been able to determin the SNR for the line. In theory this should not cause a problem but normally indicated a very low SNR exists, which could result in loss of sync.
Make sure you have the latest firmware as SNR detection was flawed in earlier versions which could cause loss of sync even when SNR is actually much higher.
Community Veteran
Posts: 3,789
Registered: 08-06-2007

Re: Advice on Noise Margin Please

The 13-15db means that you potentially have a noisy line.
The huge figure is actually a negative SNR that the router is reporting.  To me this rings alarm bells.  Although the DG834 is known to report negative SNR values, it's usually when hovering around the 5-7db mark and you get a burst of noise on the line which drops the SNR.
First suggestion would be to isolate internal wiring by plugging the router into the test socket behind the master socket and seeing if the problem still occurs (and I would also be interested in seeing whether the sync rate actually changes for this too)
If the sync rate stays around the same mark, and the problem still occurs then it's probably the notorious bug in the firmware Smiley
Try that and report back!
B.
Soxendom
Dabbler
Posts: 20
Registered: 21-08-2007

Re: Advice on Noise Margin Please

I was unable to plug the modem directly into the test socket and still see the results as my computer is in a different room and I have to use an extension (that's why I wasn't particularly worried about the 13 - 15db. I did plug the extension into the test socket and tried again. The noise margin stayed steady. The line sync went up a bit but not by a great amount (2549 to 2848 kbs). I'll try updating the firmware to see if that helps.
Thanks
Community Veteran
Posts: 14,469
Registered: 30-07-2007

Re: Advice on Noise Margin Please

Note: make sure you also download the recovery software in case the firmware flash fails.
Soxendom
Dabbler
Posts: 20
Registered: 21-08-2007

Re: Advice on Noise Margin Please

I've just checked the netgear site and I'm a bit confused as to whether there is an update. It says V4.01.28 for UK (which is what I've got). The newest one says V3.01.30 (for outside NA). Do I use that one or am I up to date?
Community Veteran
Posts: 14,469
Registered: 30-07-2007

Re: Advice on Noise Margin Please

There are 4 versions of the netgear DG834/DG834G routers with the latest (v4) using diferent hardware and thus a different (V4) firmware. So just check which version you have then see what the latest firmware version for it is.
Note: the label underneath should tell you the version you have - if there is no v1/v2/v3 after the model number then you have the original v1.
Soxendom
Dabbler
Posts: 20
Registered: 21-08-2007

Re: Advice on Noise Margin Please

I have v3. The updates that I quoted were both from v3.
Community Veteran
Posts: 6,735
Thanks: 12
Registered: 02-02-2008

Re: Advice on Noise Margin Please

Just as a bit of an FYI if you are having SNR problems, the DG834 range are well known for hanging on to poor signals when many other brands have given up, so in general it's a good choice.  Smiley
VileReynard
Seasoned Pro
Posts: 10,863
Thanks: 252
Fixes: 10
Registered: 01-09-2007

Re: Advice on Noise Margin Please

BTW The Netgear reports the Noise Margin - this is different from Signal/Noise ratio (SNR).
You should only be on a 12dB margin if you have a line which is picking up quite a lot of noise.
The standard figure to aim for is 6dB - this could improve your speed by perhaps 1Mbps.
Only BT can change your Noise Margin.
Raise a ticket asking PlusNet to ask for this to be done.
Provide information about sync speed, download attenuation and try to make the speedtester work.
BT are very sluggish about this - expect at least a week!

scootie
Grafter
Posts: 4,799
Registered: 03-11-2007

Re: Advice on Noise Margin Please

Quote from: axisofevil
BTW The Netgear reports the Noise Margin - this is different from Signal/Noise ratio (SNR).
You should only be on a 12dB margin if you have a line which is picking up quite a lot of noise.
The standard figure to aim for is 6dB - this could improve your speed by perhaps 1Mbps.
Only BT can change your Noise Margin.
Raise a ticket asking PlusNet to ask for this to be done.
Provide information about sync speed, download attenuation and try to make the speedtester work.
BT are very sluggish about this - expect at least a week!

axisofevil there is away of setting your snr without the old sluggish bt having to do it.
James
Grafter
Posts: 21,036
Registered: 04-04-2007

Re: Advice on Noise Margin Please

Yeah, you can use something called the dmt tool.
scootie
Grafter
Posts: 4,799
Registered: 03-11-2007

Re: Advice on Noise Margin Please

yep i find the dmt tool very usefull as my line atten is 53db and b.t qoute my line as 2.5mb but with this tool i can easliy get 3.5mb and i presume if i had one of those netgears that r good at holding on to low snr i would be able to get a little bit more out of my line.
Soxendom
Dabbler
Posts: 20
Registered: 21-08-2007

Re: Advice on Noise Margin Please

Where would I find this dmt tool?