Right you are, Larry.

The same company sells the "Smart Radioo VHF Antenna Splitter". So I would
have to add this to the equipment as well.....
"
Smart Radio VHF Antenna Splitter
The Smart Radio VHF Antenna Splitter allows you to safely share a single
antenna between an AIS receiver and a VHF radio that is used for both
receiving and transmitting. This active splitter will isolate the antenna
connection to the AIS receiver if a transmission from the VHF radio is
detected on the same antenna.

This is a great solution for situations where it is not possible to have a
dedicated VHF antenna for the AIS receiver. It is also a good solution for
sailing vessels that only have one VHF antenna mounted at the top of the
mast.

This splitter is very easy to install and use. One input connection is made
to the antenna cable. An output connection plugs directly into the BNC
antenna port on the AIS receiver. Another output connection plugs into a
cable to the VHF radio. The last connection is to a 12v DC power source
which powers the active VHF splitter. Simply turn the power on and use your
VHF radio and AIS receiver"