Upstream/downstream question

When I was on ADSL(1), my upstream noise margin was steady as a rock so there was no need to pay it any attention.

Since moving to ADSL2+ (albeit, I can only get around 5Mbps), the upstream noise margin is, naturally, lower as well and it also, understandably, varies a bit.

What I haven't quite worked out yet is why the upstream and downstream noise margins aren't affected by noise at the same time - to some extent, just the opposite.

These two graphs show that, when one is stable, the other is inclined to vary. It's nothing significant but I'm just wondering what the reason for them both not being affected at the same time is.. The only conclusion I can think of is that it may indicate where along the cable run the interference is...

Any thoughts?

John.

the upstream and downstream are in different frequency ranges, bit like LW and MW radio, so the interference may only be in one band and not the other.

duh! Yeah, of course!

Cheers,

John.