"TheOldFellow" wrote in message
...
My broadband router drops out (DSL light goes out) every time I run
either my planer or my radial-arm saw. Nothing else seems to do it,
even the 3KW router with a big bit. These machines both have induction
motors, which I guess have a big start-up current.

I doubt if the start up current has any effect on the router, mine survives
visible brown outs without any problems.
It may be RFI, its cheap and easy to put a ferrite on the mains lead to try
to reduce RFI. Maplin sell them for a couple of quid.
If that doesn't work then you may well have to invest quite a lot of effort
in filters.