Somehow my previous thread (I just registered this morning) seems to have gotten lost so I am reposting:

I recently traded in my 1997 Ford Escort for a 2009 Focus. I have done a search of the forum and also Google and have found no definitive answer. I am questioning what the roof top antenna is used for. I thought it was for satellite only, so took the flexible portion off but it ruined my AM reception. As you can see, I haven't kept up with auto technology since I purchased my last Ford (I like to keep my Fords for awhile!). Will you please explain to this dummie what the antennas are used for. I figured the one in the windshield was for FM and AM but obviously I am wrong?

I do have XM satellite in the car but installed a portable receiver and a magnetic antenna on the trunk. Please forgive the lack of knowledge

 

I believe the 'radio' antenna is used for both AM and FM. This is standard technology that has been used on cars for decades. FM stations don't seem to need the antenna as much, especially if you are close to the station, but AM needs it.

My current antenna is broken (the mount threaded section broke off), and the FM works fine, but no AM.

Don't think this member may be still looking (posted in 2009), but thought I'd put the answer here in case others are looking with similar questions.