If my memory serves me well my sons old 97 T4 has only a conventional mast type antennae running up the windscreen pillar , I don't recall when I fitted a fold out screen multi media head unit ever needing to connect power to the antennae . Am is pretty hard to get these days although my latest one in my T5 which is an android system pulls in the Am pretty good in comparison to our older units from the past . The thing to look for is the antennae connector a single pole type on its own with no other wires if so then I doubt its powered . Most modern head units have a power wire to connect to an antennae IF IT is powered I would suggest to trace the aerial wire back to the base and see if there is a booster in line .