In reply to a post by Zarjaz:

Inside the black box looks messy, but seems OK. Cobwebs are not service affecting. The termination blocks are gel filled, so the damp isn't getting in there.

To put a conclusion to this thread....

As you surmised, it looked a lot better after a hoover and brush out!
Clean BT Box!
But it made no difference.... The only annoying thing is that only two of the pairs in all that lot are actually connected now, the 8(?)-pair fatter white cable is totally superfluous, used to carry ISDN-30/Kilostream services but is probably acting as a nice vertical antenna alongside the other cables.

It was, as suggested, REIN and at first I decided to live with it. However, it became obvious that it was steadily getting worse both in duration (anything from 5 mins to 3 hours) and the db drops which were hitting 12dB at times. So after chatting to Zen Support, they thought the BT REIN team should be called in - especially as I had established that several other properties were having the same problems. Armed with a small Roberts pocket portable radio, the interference was clearly and loudly audible on MW when wandering along under the overhead power lines for about 200 yards in any direction. Couldn't establish which house it was though with any certainty.

The ones I tried often didn't want to know but managed to get RouterStats into a few that showed a match with my drops. Makes a change to be knocking on other people's doors rather than the other way round after 40+ years as a Radio Amateur!

I then created a written log of every occurrence for BT going back to June 1st when I started monitoring. Towards the end of July it was now happening every day and several times a day as well so getting a bit fed up and now determined to find the cause.

Also had a second line here temporarily enabled for ADSL from Zen - which was helpful since it coped with the interference much better, drops were usually about half that of the current line.

Having done all that - it stopped!

The then last occurrence was at 04:20 on Saturday morning, 28th July, the earliest time of day I had seen it happen. A few days later, still with no interference, suggested someone had possibly gone on Holiday. Asked around and found a likely candidate a few doors away. For two weeks absolutely nothing, then it started again within minutes of that household returning.

I managed to get access to hopefully have a look at the satellite box etc, but quickly found out that the last occurrence coincided exactly with checking emails prior to leaving! And, behold, their LCD monitor was playing up and kept switching itself off after a few hours.... Duh!

Needless to say this was the culprit with a nicely overheating PSU board in the elderly Viewsonic VX924 - the radio speaker nearly exploded when I switched it on!

Anyway, interference is now gone so I assume they have changed/repaired the monitor although no one let me know.

So now I can happily run a 2-3db Target SNR (on the new line now) and around 11,600kbps all day with the DSLAM apparently happy with this on my 40dB attenuation.

Thanks also go to Zen support for their willing and knowledgable help over quite a few long phone calls and also with the swap of services between the two lines.

Good sleuthing!

They probably decided to get it fixed because they were having the same problem but worse and didn't know why their broadband was so lousy. So self-interest in sorting it out, not altruism.

Send them a bill for diagnostic services rendered!