Yeah that's what I thought. I can't really see it being a trial either (even thought Openreach told me there was an upcoming trial!) as my exchange only has about 6k lines.

That's what I initially thought but wouldn't my attenuation have dropped if that was the case?

No, remote noise has no affect on attenuation. Removal of a noise source *may* see a change in snr upon a restart, and a reduction in errors, but even this isn't a given.

Attenuation at each frequency is constant to within a cB (centiBels - 0.1 dB) or less. You might see a change if the modem type is changed and even if replacing one with an exact same model. What MAY change is the attenuation reported in the higher, D3 and U2 bands when additional tones are brought into use as a lower noise level allows.

Your SNR figure will keep being targeted towards 6.0dB - so again you may not see any variation there.

As the others have said, plus a bit.

The attenuation relates to the loss of strength of the signal over distance, and is effectively fixed at each frequency in use.

It is the ratio of the signal strength to the noise that matters. As in Signal to Noise Ratio. As the noise goes up, that falls, ultimately to the point where the noise swamps the signal and the equipment can't pick it up. Think of talking to someone when an aircraft comes in to land a few hundred feet above you.

Incidentally, don't confuse this real SNR with SNRM/Noise Margin. Link. For instance, MHC is referring to SNRM.

Edited by RobertoS (Wed 14-Oct-15 11:29:12)

The DLM will keep you at the same SNRM (e.g.6.3 dB), but as others have mentioned you will get different SNRM/attenuation over each tone in the bitloading graph.

The bitloading changes over time in line with attenuation at each frequency, whilst the SNRM remains the same - i.e. you can have more/less bits per tone for the same target SNRM.

MDWS isn't playing nice for me at the moment, but I'd expect your bitloading from a few weeks ago to be "lower" than it is currently - likewise I'd expect a subtle change to HLOG and QLN.

Reasons for this could include a change in the weather (it's getting cooler now) and things like atmospheric propagation(allowing interference from further away to reach your location) - e.g. during certain months of the year it's easier to pick up faraway radio stations and these will potentially cause interference.