SNR Margin on new line is very different to existing line,

[#1]

I have just had a 2nd ADSL line installed in my house. It didn't require a new line from the telephone poll as there were some spare wires in the existing cable. So I have 2 NTE5 sockets adjecent to each other, both connected to separate Draytek Vigor 2820n routers. You would imaging that they would report very similar figures but the older (existing line) is reporting a SNR Margin of 11 whilst the new line is 4. Likewise the download sync speed of the old line is 185600 whilst the new line is 1472000. Loop att. on the old line is 60  whilst the new line is 59.
Does the SNR margin change over the 10 day training period or does that just effect the sync rate?
Many thanks for any info.
Dave

[#2]

Hi Dave,
It's certainly possible for the SNR to change during the first ten days.
I'd suggest rebooting the router first thing in the morning for the first ten days and things should settle out.

[#3]

I'd imagine BT would set the SNR margin to the lowest possible value at the start of the 10 day training period.  This will give you the highest sync speeds. If the line is unstable at that margin they will increase the margin and your sync speed will drop.
I guess you have a 12dB target margin on your old line.  I am surprised with the low margin on your new line.  With such a high attenuation I'd expect them to start at 12dB, but it looks like it's at 6.

[#4]

The default noise margin, regardless of line length, is always 6dB.

[#5]

Thanks for the clarification, James.  I'd got the (wrong) impression that it can start at a higher level.

[#6]

Thanks for everyones input - I am learning....
Dave