In reply to a post by MrSaffron:

Yeap timing suggests AM radio floor rise is the issue, can occur with UK am stations, and anything else throwing noise out in the AM range.

I'm not aware of the European regulatory authorities imposing the same sort of limits the FCC places on AM stations in the US (which forces many of them to either close down, or reduce power, to prevent interference to other stations at night) - Shame really, as this would also help out ADSL .

I've monitored it using the laptop via wireless connection, the only cable connected was the 1.2m line cable from the router into the filter plugged directly into the master socket (and yes, I've tried changing both of those as well!), the results are identical, same pattern day in, day out makes no difference if it's a weekday or weekend. My neighbours line gives a flat 6db 24hrs a day

One thought that occured to me, apart from the actual line from the BT pole the only thing that I haven't changed is the BT socket, I've assumed that being plugged into the internal test socket this would rule it out?.

Edited by jeff1106uk (Sun 22-Mar-09 20:08:37)

In reply to a post by jeff1106uk:

I've assumed that being plugged into the internal test socket this would rule it out?

Indeed; the internal test socket will give the same results as an ADSL filtered face-plate (provided you have just the ADSL router, a micro-filter, and a single telephone with no extension cables plugged in).
This will give the best possible connection (and the best immunity from interference) from your line.
Anything which still shows up, short of actual line faults, will be outside of your control.

Yes, only things connected are the filter, line to the router and the base station of a cordless Dect phone system (3 phones). Phone system was changed about 3 months ago so I've assumed it's not that either, previous phone was a similar 3 phone system.

Check that unplugged base station power supply does not make a difference, Power bricks can be an issue especially if Switched Mode type devices.

I'll unplug it about 4pm and see what happens.

OK, phones unplugged completely (inc PSUs) around 15:45, SNR steady at 12db (as it has been since 7am)

Now 17:50 and dropping as per usual, down 2db since 17:20 so it looks unlikely to be the phones

Edited by jeff1106uk (Mon 23-Mar-09 17:52:09)

You still haven't said where you are.
If you're on the east coast, or south coast (basically anywhere from Land's End to Aberdeen), and are less than 30-40 miles from the coast, you may be suffering more from distant European AM radio stations which propagate further at night, due to atmospheric changes.
I won't go into the technical stuff, but the edge of one atmospheric layer (which reflects AM radio waves) shifts up by some distance at night (basically merging with another layer) meaning the waves bouncing off the layer, are carried further.
This is why local AM stations get swamped by distant ones, and why ADSL is junk at night.
If this is what's happening; especially as you have an overhead wire feed from a telephone pole (long horizontal wires make lovely AM radio aerials), there's little you can do (except move somewhere which is fed by underground cables).

Next to Beamish Museum in County Durham so about 15 miles from the North East Coast.

I'm on the East Coast, literally, and suffer very little variation due to radio station noise effect on my ADSL. In fact I usually see about 0.5db change between night and day. I did used to get German Radio Stations on my poorly shielded speakers which have now been upgraded.