Re: More to the point
I used to knock around with a bunch of TV repair guys in the 1980s and they used to talk about chopper power supplies which put all sorts of junk back down the mains and the electricity companies hated them but there was no legislation to prevent this at the time. I would imagine this was the source of the problem as the burst of interference would have happened at a frequency of 50 or 100Hz, often enough to prevent any re-synch of the broadband connection.
Biting the hand that feeds IT
