Broadband Local Signal to noise margin

  Alf58 19:49 17 Jun 2007

This post is for the attention of folks who have an understanding of Broadband router stats. My local signal to noise ration has gone up from 14.5 db yesterday to 16.5 today. I have not disconnected the router since the last measurement. Shouldn't the noise reduce gradually over time? Or does the increase in noise indicate my line is faulty (though not faulty enough for BT to repair it)? There have been thunderstorms in my area and my local exchange is green and not faulty.

  Fingees 19:52 17 Jun 2007

The higher the ratio the better, yours has improved

  Alf58 19:59 17 Jun 2007

I had understood the noise margin should be at a level of 6db because if I have a high signal to noise margin (ie 16.5db) my broadband connection speed will be slower because of the noise interference. I was hoping my local signal to noise ratio would gradually improve but this does not seem to be the case.

  Dipso 22:22 17 Jun 2007

When on the fixed 1 or 2 Meg products, the higher the noise margin the better. On ADSL Max (up to 8 Meg) the default is 6.

If you experience any noise events or instability on Max the BT systems increase your noise margin by increments of 3db until your line seems stable, so from 3 to 6 then 6 to 9 etc., this however, has the effect of reducing your connection speed.

After maintaining a connection for around 14 days the BT system will take the line to be stable enough and reduce the noise margin by 3db, this then allows the connection speed to increase. A further reduction of 3db will occur every 14 days thereafter until back at the default 6.

As your noise margin is 14 to 16 the target noise margin will likely be 15, any slight variation either side of this is quite normal.

  Alf58 22:53 17 Jun 2007

Thank you for the information, Dipso.

  harps1h 08:21 18 Jun 2007


  Alf58 17:50 20 Jun 2007

My local signal to noise margin went down to 12 last night but its back to 16.5 as we I write this 5.45 Wed afternoon. My local line attenuation remains a constant 37.5! This seems very poor as I am plugged directly into the test socket. I have had an uninterupted connection since Saturday night.

  Dipso 20:58 20 Jun 2007

The 12 you saw was probably the drop you see due to crosstalk (noise) during the evening. As I said earlier it will take 14 days for a definite reduction. How much uptime do you have on your router?

The attenuation figure doesn't normally change.

  Alf58 21:10 20 Jun 2007

Uptime? There is no such category in the router stats. The router has been connected without interruption since late Saturday when there was an "outage" caused I presume by the exchange.

  Dipso 21:35 20 Jun 2007

I just mean the length of time the router has been up and running.

If you had an outage then the 14 days will start again from Saturday night. The SNR will only drop when the BT systems acknowledge the line has been stable for this period of time.

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