If your asking about the TV antenna....no need to replace the antenna.
A 30 year old set of rabbit ears will receive the digital signal just fine but, the TV will need to be new enough to have a digital tuner in it.
2005 300DA, Garmin 740s w/Vision Charts and GMR18HD RADAR
Engines
5.0MPI w/BIIs, Kohler 5E Generator.
Congrats on the new 300DA... I have the same year and model. Would be great to talk and see what mods have been done to yours if any.
Regarding the TV... i changed out my factory TV for a 12v model this past season. There are several posts on here about it and all the parts (dont have the links handy here at work). As others have said, the current antenna will work just fine. You'll need either a digital to analog tuner/converter box (fairly cheap at radio shack / best buy etc) or to replace the TV with one that has a digital tuner in it.