Jay, I don't know which Standard Horizon VHF radio you have, but if it is one of the Matrix series with the built-in AIS receiver, be aware that this is AIS-receive only. It is not
an AIS transponder. You need a transponder to transmit AIS, and for other vessels (and AIS-tracking websites) to receive your signals.
But, the receive-only AIS capability of the Matrix VHF radio is still extremely useful. And has been mentioned, the DSC features off the radio can also be very useful, and you need an MMSI # (and GPS connection) to use them. If you eventually get an AIS transponder you will use that same MMSI #.