Thanks for the info. When I next get to my parent's place I will be "dealing" with my Dad's very, er, "interesting" extension to his PC.

The master phone socket is in the same room as the PC but at diagonally opposite ends of the room.

At the moment Dad has strung a plug-in phone extension for 4m from master to Sky box where there is a microfilter. He then runs a very skinny modem wire up the wall and along the ceiling. About 2/3 of the way along the ceiling the modem wire runs out so he has double RJ11 female adapter and a further length of dodgy modem cable from there down the wall to the router.

They only use the router for the net (rather than for network data) so a wireless connection will be more than sufficient. I will be moving their router to the master socket with a filtered face plate. I will then put a wireless adapter in the PC which is 6m away in direct line of sight. Hopefull that should do the job!

I am expecting that it will sync at a higher speed, but presumably the night-time drop in SN margin will persist as this is more than likely caused by the 3000+ m of overhead wire to the exchange rather than the 8m of dodgy extension cable. Anyway, I will let you know how it pans out!

In 1946 my Dad was in the RAF doing national service installing and wiring up radar on Mosquito fighter bombers. Lucky for us all that the war was over by then!

What your dad should do is to run a short phone cable to a filtered master socket, then run a long ethernet cable from the ADSL router to the PC. Ethernet cables are far more immune to interference than phone cables.