> I think the limit is about 18,000 feet. Then you might have trouble
>> carrying DSL over it ...
> Correct, but that's the approximate limit for the total length from
> the switch to the telephone. Beyond that, the signal is typically
> attenuated too much, mainly by cable resistance, and gets buried in > noise.
> As someone else has pointed out, you need decent cable, routed clear
> of sources of interference (such as power cables and cordless phones),
> otherwise interference will be a bigger problem than loss of signal.
If it gets too long, you might have trouble with ring trip. For that, add another battery to boost the loop current. Also, be sure to use twisted pair to preserve longitudinal balance.
If even that doesn't do it, I have heard of interfacing to magneto sets on distant parts of military reservations. I don't know much more about that than that the people who made it work reported to me at the time. They were a small group of mostly geezers who could interface anything to anything, so that is what they did.