Explanation of decibels in the context of ADSL

[Pwiggler]

after all that .... thanx eric 

[roseway]

[farmergiles]

Quite true. I mention it only because I had a hell of a time finding out what BT referenced their measurements to - I think it took 3 or 4 months before either I or Mr S on adslguide could find anyone in BT Wholesale (as was) who knew what the baseline was. It's a milliwatt (or it was) if anyone is interested 

If nothing else you should all remember that 3dB more attenuation (power) halves the signal strength and each additional 3dB halves it again - logarithmic you see. Start working out what 45dB and 60dB (old BT wholesale cutoff figures) actually are in power terms and you'll perhaps see how incredible it is that some people get a connection at all.

It is also possible to discriminate (detect and use) signals below the noise floor. ie you could have a 0dB connection which worked. Not with consumer router/modems though for the filters (electronic, not passive) would cost £100 on their own 

If a £100 filter  made a big difference to people like me on long lines,  many including me would buy one.   

[Ezzer]

Just to expand the subject a little more the following is a ratio for round db numbers

0 db  = ratio of 1   to 1
1 db  =            1.3 to 1
2 db  =            1.6 to 1
3 db  =             2   to 1
4 db  =            2.5 to 1
5 db  =            3.2 to 1
6 db  =             4   to 1
7 db  =             5   to 1
8 db  =            6.3 to 1
9 db  =             8   to 1
10 db =           10  to 1

In the teens multiply by 10, 20's by 100, 30's 1000 etc etc

so 2db   = 1.6 to 1
     32db = 1600 to 1
     52db =  a ratio of 160,000 to 1

[roseway]

I'll agree with that