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Got my free regrade!

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Got my free regrade!

Got my free regrade to 2Mbps today, nice Smiley

I've noticed though that my SNR has dropped down to 11dB (was 17.5dB). Why would it do this?
8 REPLIES
Community Veteran
Posts: 14,469
Registered: 30-07-2007

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This is normal.The higher speeds use a wider spectrum of frequencies to send more data through which means the overall level of noise increases thus your SNR (signal to noise) reduces. A decrease of 4->6db normally occurs when your speed goes from 512K -> 1Mb and between 4 and 10dB from 512k /1Mb -> 2Mbs. The amount of SNR reduction is also dependant on your line quality to stat with - i.e. a higher SNR on 512K/1Mb often means less of a decrease at the higher speeds.

ADSL: Understanding Line Loss and measurements explains all this in more detail.

FYI any SNR above 10dB is good, below 10dB and you are susceptable to line drops and below 7dB you tend to get frequent disconnections so 11dB should be fine.
Community Veteran
Posts: 6,983
Thanks: 8
Registered: 10-04-2007

Got my free regrade!

Also see my post here for a further explanation
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Got my free regrade!

Thanks Peter/John, i understand it better now Smiley

BTW Have limits for 4Mb/8Mb been set yet? Last time i checked BT don't know what limits are acceptable.

I'm getting ATEN 40dB and SNR is 11.5dB (just gone up 0.5dB Smiley ) - so d'[ya think my line could support the higher speeds?
Community Veteran
Posts: 6,983
Thanks: 8
Registered: 10-04-2007

Got my free regrade!

To be honest I dont think you will get much more from your line. Sad
You are only 3dB away from the 2meg limit.
But as you say the limits are not set yet so thats just my reckoning.
Community Veteran
Posts: 14,469
Registered: 30-07-2007

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As the higher speed trial is still going, BT are unlikely to release any figures until it has finished - Maybe Sept/Oct/Nov time.

Your SNR is the problem, line attenuation is OKish but I suspect higher speeds may cause your SNR to go below 10dB and thus cause unstable connections.

MaxDSL (the high speed connections) will auto-sync at 0.5Mbs steps so my gues is you may get 2.5Mbs or 3Mbs but 4Mbs may be out of reach and I think 8Mbs will need a much better SNR to start with.
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There must be some pretty dodgy cabling in my home town then, i live less than 2Km away from my exchange Sad
Community Veteran
Posts: 6,983
Thanks: 8
Registered: 10-04-2007

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The cable doesn't alway follow the shortest rout though.
It could go all over the place before getting to the exchange.
Community Veteran
Posts: 14,469
Registered: 30-07-2007

Got my free regrade!

But the telephone line probably takes a much longer route to the exchange than you think. Location or distance from the exchange in no guarantee of line length and quality.

I new of 2 houses, side by side where one could get 2Mbs ADSL and the other only 512K due to line attenuation. It turned out the 512K house took a different and much longer route back to the exchange than the 2Mbs house which resulted in a lower quality line and thus the lower supported speed. BT were able to run another cable from the pole to the slower house and connect it to the shorter line back to the exchange and they then got a 2Mbs connection.