Well the BT engineer visited this morning and confirmed everything we already know... I have massive fluctuations in my SN margin being caused by REIN. I have to say he was more than a little impressed with the investigation I had already done (thanks to all of you...
).
He checked the line from the cab to my house and the internal wiring and said that my line was actually very good (physically at least). With the attenuation and noise margin you get at initial sync the BT test software showed that my line was capable of up to 3mb
. Shortly after initial sync at 2mb the line drops and then re-syncs at 800k and the noise margin fluctuates from 22db down 9-12db and back up continuously as shown the previous graphs I have posted.
He fitted an NTE5 faceplate and re-connected all my extension wiring (disconnected by the last BT engineer) and everything is still the same.
The engineer is now going to escalate the problem so that a REIN specialist picks it up. He said there is a specialist in my area who is very good at finding the source so hopefully he will pay a visit in the near future.
I'll keep you all posted. Once again thanks for all your help so far.
Mark.