Hi John
I really don't see how a wireless radio link can be better than two bits of copper wire carrying audio signals
Depends on the quality of the copper wire you have installed and what other interference there is in the house. Don't underestimate what you can do to drastically improve your home wiring. Sometimes making a few modifications to your home wiring can bring about massive benefits to the signal which reaches your modem.
I think we need to determine *what* is dropping out on your connection.
In your first post you say that your modem reconnects... do the lights on the modem flash steadily for a while, signifying a resync caused by a line condition, or do the lights stay solid and your PC reconnects to the 'dial up' connection?
If the lights do flash, meaning the actual ADSL connection is dropping out, then if you haven't done already, I'd suggest looking at the tips in
this guide for some tips you can follow. Specifically I'd recommend you look at the last tip which talks about removing the ring wire from your phone sockets. A lot of people have done this with quite drastic results!
This is especially valid in a big house, where there is possibly a lot of scope for the wire to act as a massive antennae and induce all sorts of nasty frequencies onto the phone line, interfering with your ADSL signal.
This is probably a long shot, but presumably you do have filters on all equipment connected to the phone line e.g. phone, sky box, etc?
As regards the router, I agree, a 3 storey house would struggle with a wireless link given the distance from the PC to the master socket. It would be ideal really if you could test your own setup with your own modem in the master socket downstairs, just to see if it made a difference, but if you haven't got a laptop that's often a pretty impossible task without a lot of major hassle!
However, it is often the case that a router will be more stable on a line that's even having problems with a modem, as a lot of routers seem to hold onto a line better than a modem does - better quality components / firmware perhaps? So, there's no harm trying the router instead of your modem upstairs and plugging into the PC via the LAN connection.
Perhaps, especially if the lights do flash when it drops out, you could post up a copy of your line stats from the modem, might give us a bit more of a clue
Hope this helps