Noise margin on DG834G. Re 8Mb ADSL max

  John B 20:52 10 Apr 06

I've been regraded to ADSL max (f2s)but my connection is less than the maximum. I'm only 700M from the exchange and my speed is only 6Mb instead of the anticipated 8Mb.

Looking into this further I find that one of the factors affecting the speed is the SNR (or noise margin)

click here=

The suggested minimum is 6db (lower than this and you are likely to get a slower speed; higher seems to be better).

Checking my router I have a snr of 3db. My friend (lives very very close) has a snr of 15db and now has an 8Mb connection with f2s. Seeking info from click here I have found that my internal extension leads are not the problem. The BT line to my house is new (but not the drop cable that enters my property).

Could the problem lie in this cable (this is at least 10 year's old) and can I get BT to check this short length of external cable to see if this has anything to do with the low db?

Sorry for the lengthy post

Thanks in anticipation


  VoG II 21:20 10 Apr 06

This could be down to the contention ratio. Try at 3am and see what you get.

  John B 21:28 10 Apr 06

Thanks for the reply VoG. I'll try that. However it's the friend's snr that made me wonder about my connection. He's on the same bb package and lives in line-of-sight. Is it possible he would/could be affected by the contention ratio differently to me?



  Dipso 22:18 10 Apr 06

Quit complaining ;) I am also 700M from my exchange, I am sync'ing at 8128, my SNR is 9db and I am getting 2.5-3 Meg!

What is your sync speed? Does your friend have the same router? Do you have the latest firmware for yours, that could affect the SNR reading.

Were you told your estimated speed would be 6Meg by the BT guesstimator? That estimated me at 5Meg, I wish...

Seriously though, the speed you are getting is VERY good and I would be more than happy with that, the best anyone is likely to get is 7Meg so you're not far off. Has your friend shown you a speed test proving the 8 Meg? ;)

  John B 22:37 10 Apr 06

Not complaining.

Same router

Same firmware

Seen the test.


  John B 02:48 11 Apr 06

ADSL Link Downstream Upstream
Connection Speed 5856 kbps 448 kbps
Line Attenuation 26 db 8 db
Noise Margin 8 db 21 db

SNR better than before, does anyone know if this is low please?


  Dipso 09:29 11 Apr 06

The copy and paste from your router shows you are sync'ing at 5856 Down. That isn't the same as your data speed. So your friend is sync'ing at a higher rate than you but he may not necessarily be getting speeds of 8 Meg. I am seeing the same, see my speed test result below.

Try running a speed test click here at a quiet time (I'm concerned about you having to get up at 3am again though!)

From my router status this morning -

ADSL Link Downstream Upstream
Connection Speed 8128 kbps 448 kbps
Line Attenuation 25 db 6.5 db
Noise Margin 9 db 27 db

Results from broadband speed test recorded on Tuesday, 11 April 2006, 09:14 click here

Trying to find a link...but the higher your sync speed, the lower your SNR. If your line can't sustain a connection with a high sync because the SNR drops too low, you would be resync'ed at a lower speed and this would bring your SNR up, this will keep happening until your line is stable ie. the highest sysnc possible with the highest stable SNR.

I realise this doesn't explain why your friends stats appear better but line stats can be affected be a number of things even street lighting.

  John B 10:50 11 Apr 06

The SNR has been down to 1db today. Here is the reading at 10:40

ADSL Link Downstream Upstream
Connection Speed 6304 kbps 448 kbps
Line Attenuation 23 db 3.5 db
Noise Margin 1 db 20 db

I've read it should be MUCH higher. I still wonder if it's anything to do with the 'drop line' that comes into my house (since it's not the internal wiring)

Latest test results are click here

BT charge £64.63 for a call-out and £70.52 per hour to do any work.

Perhaps I'll get a mate with a slower connection!



  Graham ® 11:52 11 Apr 06

The trick here is to report a fault to BT as intermittently noisy, especially when it rains. You can do this on 151 or online
click here. You can track its progress, too.

This is important, because the Diagnostics Centre is likely to close the fault if the automatic test proves negative. If that happens, simply raise another fault - this throws up as a repeat fault and will be treated more seriously.

Do not mention Broadband, as BT cannot take a Broadband fault from you.

The line coming into your house is known as a dropwire. You can mention that!

  Confab 12:21 11 Apr 06

When were you upgraded? I thought that there was a 10 day period where BT would test the line to see what maximum reliable speed your line can support. During this period you may find you have fluctuations in your connection speed and line drops.

  Marsh Warden © ™ 13:12 11 Apr 06

If its any help, I was once informed by BT that it's not the distance from the exchange that counts, that's a common misconception, but the route the wiring takes from the exchange to your premises, which could be longer than the "as the crow flies" distance, especially if it's old wiring.

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