greybeard I will post my bitloading so you can see how bad my adsl power cutback is, yours seems mild in comparison. Also note how weak my D1 is. Which considering your line is longer is odd. I also found a line on the btcare forums, that guy has almost no power cutback at all, barely a dent in his D1.
here is the link.
Also I now posted how my bits and snr looked in dec 2012. Even back then the power cutback was removing approx 15mbit of attainable sync. Some people seem to be barely losing 5mbit from the cutback. Also if you remember my earlier comment ref crosstalk, you can see my D3 is least affected by it.
http://community.bt.com/t5/BT-Infinity/Compare-Graph-stats-please/m-p/1044242/highlight/true#M113165
Hmm, puzzling. As far as the ADSL power cutback is concerned, I think it depends mainly on the length of the line on the E-side of the cabinet. The further the cabinet is from the exchange, the weaker the ADSL DS signals are by the time they get there, so the more the VDSL power has to be cut back to avoid swamping them with crosstalk. My cab is only about 800m from the exchange; I suspect yours is further away whereas the guy whose stats you linked has a cab that is very close to the exchange.
However, as you say, that has nothing to do with the D2 band, or the D1 above the ADSL frequencies. You certainly seem to have had a loss of SNR in both bands, resulting in reduced bitloading. Whereas SNR and bitloading have actually improved at the top of the D3 band. I still do not think this can be caused by crosstalk from other VDSL lines, or you would be seeing the opposite effect - the biggest loss at the top of D3, reducing at lower frequencies. Also your graphs are quite smooth, without much of the jagged, notched, profile I see on mine from some tones being worse affected by noise than others. So if your problem is interference, it must be some sort of "white noise" source spread across the frequency spectrum - no idea what that could be.
Another explanation might be that a power cutback has been applied to the D2 & upper D1 bands, but I have no idea why that should be either.
yep I am far from the exchange, or rather my line routing is long as its very indirect. So when people say distance from exchange has zilch affect on vdsl, it does actually have an affect as the power cutback is worse on longer E sides.
I wont argue with you much on the crosstalk because I cant say for sure what it is, I can only guess, my gut feeling is it is crosstalk, the cause is between the PCP and FTTC cabinet an engineer diagnosed it the other week, the cause is affecting many pairs between the 2 cabinets, but as far as I know no rectification work has been done yet. My install engineer insists its crosstalk. Because it happened when there was installations.
Your theory is crosstalk has more impact where the signal is weaker?
My theory is/was the disturber lines are not using D3 perhaps they too long or something so thats why that is barely affected.
I also have considered the dslam been faulty eg. incorrect power masking been applied cutting back too much, of course if it is that I think it would never get fixed as these cabinets once installed cant be accessed by regional engineers.
I also had some weird behaviour before as well. I had for a while my sync speed jumping between 73 attainable and nearly 90mbit 86-88 range, it was mostly at 83 tho, but would randomly jump up for short periods of time. At the same time this was occuring I did have a fault affecting my stability at night which I reported to BT and a engineer came out, the engineer said he found nothing wrong and closed the fault. But something was changed as the night time instability stopped and the sync speed jumping up to nearly 90mbit also stopped.
