Time of day related fault

[#1]

I have an odd fault in which I lose broadband every night.  It started about 2 and a half weeks ago when the blackout would occur at about 6:13pm.  It now occurs a little after 6.30pm.  After that time I have no broadband all night except that some pings are returned.
I note that the fault is occuring at about the time it gets dark.  The start time has become later by about 20 minute in 2 weeks which is about the rate at which sunset is getting later.
Plusnet support has at last refered this to BT but BT will only come out during the day up until 6pm when all is working OK.    I have, of course, checked that nothing in my house is coming on at night and causing interference.
Does anyone have any suggestion?  I have little confidence that a day time visit by BT will be of much use.

[#2]

What do your line statistics look like? Attenuation and noise margin?
I have a relatively long line here, and with my old router I had similar problems to you. It was related to night time interference from medium wave broadcast stations which are stronger after dark ( when the D layer in the ionosphere vanishes). The eventual solution was a new router.
The original router was an old Netgear DG834G v2.
Replacement router is Netgear DGN2000.

[#3]

Dusk... streetlights maybe? Do they come on when you notice the signal drop?
If so I suspect it'll be a case of needing a filtered faceplate and most likely an RF3 filter too. We can raise it as a fault for you if you submit us a ticket - http://faults.plus.net
Hope that helps,

[#4]

Thanks for the suggestion about the router.  I will try to borrow one.
I am not sure, however, that I have the same problem.  The blackout is very sudden and at nearly the same time every day.
This has already been raised as a fault.  I am concerned that the current plusnet plan to send a BT engineer out during the day (when the system is working fine) will not be of much help.

[#5]

Well if it's dropping out at the same time each day you should be able to ask him to take a look at the radius logs (the logs of what times you connected and disconnected on the exchange equipment) and that should prove that it's a regular disconnection. It'd definitely be worth asking him if an RF filter would help too.

[#6]

Does your line come back automatically when it gets light again, or do you have to reset the ADSL line or reboot your router?
If you can, download Routerstats Lite (or the full Routerstats program if your router is catered for) and set it to monitor your noise margin. See if it drops, gradually or suddenly, as it gets dark.
My noise margin drops after it gets dark, by about 6dB. In my case I suspect street lighting is the problem, but I could be wrong. Getting the bell wire snipped on my phone line(s) helped quite a bit (the equivalent of getting a filtered faceplate). Before then I had regular disconnections (the ADSL line itself stayed up and so Plusnet/BT didn't notice any disconnection, but the PPP connection was lost). Generally my line came back up - at a lower speed - after I reset the line.
You're right that getting someone to look at the issue during daytime won't help. When I first noticed the problems on my line I raised a fault and the only time any checking was done (by the Plusnet faults team) was during office hours.
Ask Plusnet to tell you what your current line profile is (not your IP profile, which is different). If you can put that together with your router statistics (sync speed, attenuation, noise margin, error counts) it might tell an interesting story.
Graham

[#7]

Thanks for all the replies.  I am away from home at the moment enjoying a good Internet connection but will do some more investigating on returning home.
One interesting point, that I have just discovered is that someone living a few houses away is having exactly the same problem at the same times.  I may have felt a bit critcial that plusnet has not been getting to grips with this problem very rapidly.  However, my neighbours ISP (Taltalk) appears to be far slower.