PB,
For question one, the application is for a remote switch using an ultrasonic transmitter and receiver. The 40MHz transmitter signal is driven by a couple of CMOS inverters in parallel on one pin of the transmitter and another (inverted) pair on the other pin. A 9V battery powers the transmitter circuit. Only a few pulses (at 40KHz) will be sent at a time for a transmission. Will a pair of wires work or do I need to do something more?
For the other question, there can be perhaps 5 to 10 devices connected together. I'm just looking to make sure I don't get any false reset signals. I haven't selected the line drivers/receivers yet, but it will be normal digital logic to interface to a PIC. I would even consider using RS-232 line drivers/receivers if it would allow a single line instead of a differential pair.
The reason for these questions is that I don't know enough about the risks of noise interference on reliable operation.
DSG