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Very low noise margin?

wyvern22
Newbie
Posts: 7
Registered: 10-02-2013

Very low noise margin?

I've been looking through various forum posts and running various speed tests etc. and generally managing to horribly confuse myself, so I'm hoping some helpful person can get me pointed in the right direction!
I switched to Plusnet towards the end of January, and watched with bated breath to see what speeds I would end up with.  However, whilst not dissatisfied with 5-6 Mb download speeds, I noticed that the downstream Noise Margin was very low, 3dB dropping to 1 and even 0 dB.  I have tried swapping from the master to the test socket, which increased the download speed marginally, but made no difference to the noise margin.  I have also swapped from my 3Com router to the Technicolour one provided by Plusnet; again, no difference (except it seems to be reporting download speed as 9.935 - I suspect the period/decimal should actually be a comma?), the downstream SN Margin is 3,0
One interesting thing I did notice after changing to the plusnet router, was that my upstream attenuation had dropped from 25dB to 13dB, but my downstream attenuation didn't change  Huh
I have tried running the BT Speed test and its further diagnostics, which doesn't find any problems, although it does seem to suggest I'm 3 Mb below the IP profile (down speed 5.67 Mbps, range 4Mbps - 21Mbps, IP 8.77Mbps).  Likewise the Member Centre estimate is 10Mb, with the actual 6Mb.  The upload is also slower than I would have expected.
Anyway, if anyone has any suggestions as to why my noise margin is so low, and how/if I can increase it (if I need to), I would be very grateful.  Full router stats and the speedtest further diagnostics results attached.

13 REPLIES
Plusnet Help Team
Plusnet Help Team
Posts: 12,859
Thanks: 115
Fixes: 36
Registered: 27-04-2007

Re: Very low noise margin?

Hi there,
I'm not sure what exactly has caused this to happen, however I can see that the line has been dropping more since so a reset to bring it back to 6db might be a good idea.
Do you want me to give that a try?
Adam
If this post resolved your issue please click the 'This fixed my problem' button
 Adam Walker
 Plusnet Help Team
wyvern22
Newbie
Posts: 7
Registered: 10-02-2013

Re: Very low noise margin?

Quote from: _Adam_Walker_

I'm not sure what exactly has caused this to happen, however I can see that the line has been dropping more since so a reset to bring it back to 6db might be a good idea.

Dropping more since when?  I use the internet a lot and haven't noticed any interruptions, but there would have been several this morning and last night when I was fiddling around with hardware/cables etc.  However, if you think a reset to bring it up is a good idea, please do give it a try Smiley
Community Veteran
Posts: 4,783
Thanks: 106
Fixes: 20
Registered: 14-07-2009

Re: Very low noise margin?

I think you may be making the mistake of making changes to your set-up (e.g. using the Test Socket) but then not looking at the right parameters to see if anything significant has changed.  The things you need to pay attention to are your router sync rate and/or your IP profile.  Due to a flaw in Plusnet's system, your actual download speed could take days to adjust upwards.
If you go here http://www.kitz.co.uk/adsl/max_speed_calc.php and put in your attenutaion of 26dB then your sync rate should be around 17600kbps.  So you seem to have some excess noise on your line.  I would try the Test Socket again.        
wyvern22
Newbie
Posts: 7
Registered: 10-02-2013

Re: Very low noise margin?

This is what I mean by going in circles and confusing myself just as I think I've worked out what I'm doing... 
Is 'sync rate' effectively the upload/download rate?  I don't know if I'm correct in thinking that it is (in which case there was next to no change between master and test socket), or where to find this 'sync rate' if not, as no statistics that I've been able to find are actually labelled 'sync rate'.
Community Veteran
Posts: 4,783
Thanks: 106
Fixes: 20
Registered: 14-07-2009

Re: Very low noise margin?

The 'Sync rate' is labelled 'bandwidth' in the stats you quoted.  The BT IP profile is 88.2%  of the downstream sync rate and that is as fast as your line will go.
For some reason your actual measured download speeds (in the range 5-6 Mbps) fall way short of your IP Profile.  But in the short term ignore measuring the download speed, just be guided by the router (downstream) bandwidth.
wyvern22
Newbie
Posts: 7
Registered: 10-02-2013

Re: Very low noise margin?

Quote from: ReedRichards
  I would try the Test Socket again.       

Oops, missed that earlier; router is still connected to the test socket (i.e. the stats in my first post are whilst plugged into the test socket).
Community Veteran
Posts: 4,783
Thanks: 106
Fixes: 20
Registered: 14-07-2009

Re: Very low noise margin?

Then it looks like you have a bad line for broadband.  Is it okay for voice calls?  Do you hear noises or static?  If you dial 17070 then choose option 2 you can listen to the line to check that it is quiet.
The other thing to do whilst connected to the Test Socket is to ring your number and check that the only phone that rings is the one connected to the Test Socket (if you have one).
wyvern22
Newbie
Posts: 7
Registered: 10-02-2013

Re: Very low noise margin?

We've never had any obvious problem with the physical phone or the quality of calls on that line, although calling the quiet line as you suggested there seems to be a constant background electrical 'hum'.  In trying to rule out/minimise internal factors, would the proximity of the router power adapter to the test socket have a significant effect?  Currently it's plugged into a mains socket about 5 inches above the phone line's entry point to the house, and the router is then about 3 feet away from them both.
Also the phone is the only one that rings when calling it.
Community Veteran
Posts: 4,783
Thanks: 106
Fixes: 20
Registered: 14-07-2009

Re: Very low noise margin?

So you have a good line for voice calls and your extensions seem to be wired correctly so removing the faceplate cuts them off.  Yet your download sync rate is low for the reported attenuation and your noise margin is unaccountably low and wandering.  You could try a different filter or reconnect the router with the telephone temporarily absent to see if either makes a difference.  If not you're a bit stuck.  Your broadband speed isn't as high as it should be but since it has been the same for at least as long as you have been with Plusnet then I'm not sure if you can do anything about it.   
wyvern22
Newbie
Posts: 7
Registered: 10-02-2013

Re: Very low noise margin?

Thanks ReedRichards Smiley  I'll check out the different filter/no phone idea tomorrow and see how it goes.  It sucks to be so close to the exchange and yet unable to get better speeds and/or less noise Sad
Plusnet Alumni (retired) chrispurvey
Plusnet Alumni (retired)
Posts: 5,369
Fixes: 1
Registered: 13-07-2012

Re: Very low noise margin?

Hi there,
I've changed your line profile to match your sync speed so you should see an improvement.
I've also posted a graph of you connection which Adam was referring to, it's certainly more stable although you did mention that the disconnections may have been caused by you?
<img src="http://ccgi.psmith12.plus.com/visradius/generated/image13606600061642.png"/>
wyvern22
Newbie
Posts: 7
Registered: 10-02-2013

Re: Very low noise margin?

That's great, thanks Chris - download speed has increased to 8.26Mb Cheesy  And yes, I'd say the majority of those were me fiddling around with things.
Still going to try out swapping the filter etc. as ReedRichards suggested, just to see whether the noise margin will come up a bit higher.  Also need to move back into the master socket, so fingers crossed Smiley
Estragon
Rising Star
Posts: 811
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Registered: 07-02-2012

Re: Very low noise margin?

Note that Plusnet hold a copy of the IP Profile, which you can see in your Member Centre >> Connection settings. It is called Current line speed.
That is supposed to be updated within a few hours when the BT Original changes but the update can fail. So find that, and check it if this happens again. 
That may be what Chris corrected, but as I understand from some other posts by PN staff there is a third point, (within the BT Wholesale system), that can also get out of step. That's a bit trickier for them to spot.