Our FM signal is tapped off an amplifer/splitter from the TV antenna, which is mounted immediately below the 4kW radar antenna and I've never gotten any ill effects on the TV or stereo from having it so close (it does a GREAT job, btw ,plus eliminates an antenna & the running of the associated antenna cable to the stereo) . I would be worried if the radar was transmitting directly into the FM antenna...I suppose then there could be issues. I'd be more concerned about the antenna being too close to the VHF antenna. That's when you would see a problem since the frequencies of the VHF & stereo are very close & the VHF is outputting a continuous 25 watts of power directly into the stereo receiver. A (recreational) radar's output is pulsed and is a way higher frequency than the FM band.