Your problem reminds me mine. Measuring antennas in a crowded FM broadcast band may be impossible.
You could try to find an "empty" channel and take the measurements there. If no channel is left for it, then you have to move off the FM band.
You can try scaling, try to use twice the FM band frequency: at 200 MHz there may be no interference.
My problem was even worse; I wanted to record solar radio noise. I can hear it but cannot make a record, due to interference
Good luck!