Did a test on a 60 meter piece of CAT.6 cable with oscilloscope, comparing the signal on entry and exiting signal after a roundtrip thru my appartment (wich included going over or next to CRT TV's, heaters, power lines, etc.) @
10MHz square signal (my oscilloscope is way to old to go over that) and signal distortions were close to none... I'm gonna build a differential signal generator and receiver today too see if i can fix the noise and distorsions a bit more.
Currently with any luck i'd be able to squeeze in about 2 Mbit/s useful data into this system (wich is way over what i need for phase one), plus about another 1.5 Mbit for error corrections, serial device addressing and other overhead, i've not yet decided on protocol, but it will probably be similar to USB, although not at all compatible ;-) So if I manage to clean up signal a bit more, i should have near-10Mbit/s experience on a 50 meter bus. The cat6 cable is declared to carry 250 MHz, i hopefully will ever need only 1/10th of that clock speed :-)
Another idea i've had is to create "smart" signal repeaters along the line since latency isn't really an issue, at least not now. They'd read the bit-stream, analyze it, check if data+address bits "hash" agree with control bitstream and if yes, forward it further on the line... if no, signal repeat. But i'm gonna hold on this complication until i've got no other smarter solutions.
My head hurts :-p