In the original International Product Specification for Class B AIS Transponders, it was dictated that they should be “stand alone” systems that did not require any input from other devices. For this reason, you will not find any AIS Class B transponders that can take their position input from an external NMEA 0183 or NMEA 2000 GPS sensor.

I am afraid that you will need to use the supplied GPS antenna with your iAISTX, but if your boat has a GRP hull, then you might be able to install the GPS antenna inside the hull and not go to all the trouble of routing it externally. Just find a suitable location and use the GPS signal strength display on the iAISTX’s web interface to check that you are getting good reception, before finally bolting it down.