"Larry W4CSC" wrote in message
...
How do we hook them up WITHOUT using the multiplexer you are selling?

Well, just replace the word "multiplexer" by "talker" :-)

How do you isolate the balanced output from ground in the bottom
diagram, without providing a galvanic path to the other instruments?

You don't. And it wouldn't be necessary if EVERY listener had a galvanically
isolated input. That's the trouble with instruments with a single-ended
input: they are not isolated from ground. The galvanic isolation has to come
from the input, which is supposed to be on every instrument, according to
the NMEA spec. But unfortunately....

Of course the crap instrument on the right provides its own ground
path for everything hooked to A+, anyway, along with a great path for
the SSB RF to tear into no matter what shielding you use.

Is there a path in your multiplexer from A+ to GND to develop this
signal? Is B- just grounded in your multiplexer so this will work?

Yes. A and B are two outputs from one RS-422 driver. So they're both
gavanically coupled with the ground. B/- is not just a ground, it is an
output that carries the opposite signal of A/+, just like any RS-422 output.