yeah, mine doesn't have that little box, just the little plug on the back of it, then it has a little adaptor to make it into the "standard" arial adaptor but has a little adaptor thing... in the end it looks like it does the same thing as yours, although yours seems to have an additional earth wire or something...

I also note that my antenna in the roof has a black wire coming from it which improves reception when hooked up (mine was busted when I got the car)...