The battery on my 06 R53 JCW with HK head unit finally died. I replaced it with a new battery.

Since then, I've noticed that my radio reception has decreased significantly. Areas where I used to have good reception are poor. And some poor areas are just dead now.

Any suggestions on where to start with diagnosing this?
Is there a way to test the antenna aerial diversity unit?

 

This may sound silly but I had a similar situation where the reception was poor and then the tuner went silent. Turns out the positive battery wire was not tightly connected to the battery post.

So far, so good.