fpb600

I am getting minimal radio reception since I installed the Clarion 765MP in my ride (2001 Nissan Maxima). I remember getting exceptional reception when I had the factory Bose deck installed but now I rarely get a lock on any stations. The Maxima needed a special adapter for the antenna, I think the antenna is embedded on the rear window, and so i'm wondering if the cars antenna system was somehow powered. Now that i've installed an aftermarket deck maybe the antenna reception sucks because it is no longer powered? Any insights?
Much appreciated...

System:
Clarion 765MP
Focal seps (front)
Focal coax (rear)
Alpine 4ch (front/rears)
MTX 2160 (subs)
1pr Kicker 12"