In chasing down all the wiring I've found three antenna cables in the aft head wire access (to the right of the mirror). They are:
SSB DSC antenna
Fax 30(Furuno Weatherfax) antenna
The thing is, there are only two antennas on the mizzen. There isn't a combiner in the aft head wire access, so are two wires connected to one antenna?
The Fax 30 and the SSB were original equipment. I'm pretty sure the AIS (Nauticast B) was owner added.