"Larry W4CSC" wrote in message
...
"Meindert Sprang" wrote in
:

No.

NMEA is laid out to prevent ground loops in the datalines. This is
achieved by having every input isolated. The outputs need not to be
isolated. And if everyone adhered to that spec, there would not be any
problem. In your case, youll be fine since that situation is almost
exactly to the NMEA spec.

Meindert

But, alas, he's hooking one side of his NMEA dataline to GROUND! It's not
isolated at all at that point.

If the output had been differential, there would have been a path to ground
as well though the internal impedance of the driver an output filters. This
situation makes no difference since the other end at the autopilot is
completely isolated. So any induced HF on both the data line and the ground
line are in phase and therefore generate no differenctial voltage at the
isolated autopilot end.

Read a textbook on transmission lines if you don't believe me.

Meindert