What if my NMEA 0183 Listener does not have an isolated input or uses ground for the negative data connection?
Isolation is provided between the NMEA Talker ground and the Listeners RS232 ground.
The OPTO-4 uses the same ground as the RS232 connection for the connection to the NMEA Listener. Connecting an NMEA Listener that is not isolated or uses ground for the return line will negate the isolation, making the OPTO-4 into a normal serial cable. To maintain the isolation that protects the devices from damage, the NMEA listener MUST have an isolated input.