There's a "AF" button on the nav screen when I switch
to the radio function... What does it do? The owner's
manual has no mention of it... It doesn't seem to affect
radio operation at all...

Thanks!

 

Here's what my Navigation System Owner's Manual says about the "AF."

AF (Alternative Frequency) function: A station providing good reception is automatically selected if current reception worsens. This function switches over to the broadcasting station providing good reception within the same RDS network and is convenient for following the appropriate stations."

I think what this means is that, if you are listening to a Jazz RDS station that goes out of range, the radio will automatically switch over to another Jazz RDS station that has a stronger signal if one is available.