"Dick Locke" wrote in message
...

To follow up, the right solution was to hook the "high" output from
the GPS "current loop" to the GPS input of the VHF, and not to hook up
anything else.

Auch! That means that the return for the signal goes through the common
power ground. You want to make sure in this case that the main ground from
the battery goes to the VHF and from there on to the GPS. Otherwise the
voltage drop due to high current might influence the datasignal.

Makes me wonder everytime why manufacturers want to save on a $0.20
optocoupler. The NMEA standard is very clear on the REQUIREMENT for galvanic
isolation....
Too bad...

Meindert