The BMW 525i was manufactured in several generations and designs. Hence, each generation will have a slightly different location for the radio antenna. Sometimes you may need to access the radio antenna to fix or replace it, fix a loose connection or fix the antenna amplifier.
On an E28 525i, look at the rear right-hand side of the car. The radio mast descends into the trunk of the car when not being used and looks like a nub on the right-hand fender.
On an E34 525i, the antenna is built into the rear window. According to an E34 electronics service manual, the antenna looks very much like the defroster loops below it, though it has two visible attachment and solder points near the upper-left corner of the window, one for AM and one for FM.
Like the E34 525i, the antenna on the E39 is located in the rear window.
The radio antenna is located on the roof of E60 and E61 525i models. It looks like a semi-triangular stub, centered just forward of the rear window. It is also called a "shark fin" antenna.
