Finally got around to doing systematic testing between my Larsen NMO2/70B (NMO mount, center roof) vs Diamond NR770HNMO (same antenna, mag mount, same location). Used my FTM-400XDR at 50 watts, measured with both S-meter reports and RF analyzer.

Key findings: NMO mount showed 0.7 dB better performance consistently across 2m band. The magnet mount is grounded through capacitive coupling between the magnet and metal, which is adequate for VHF/UHF frequencies. However, the direct metallic connection of NMO mount provides superior RF ground, especially noticeable during weak signal work.

A high mounting position is better for performance, along with having as much metal mass under the antenna as possible - roof center and center of trunk lid are considered best locations. The convenience factor of mag mounts is undeniable though.

Interesting results. I've always wondered about the actual performance difference. Did you test SWR as well? Also, how much difference in received signal strength did you see on your local repeaters?

Thanks for doing real testing instead of just theory! I'm setting up my first mobile rig and was leaning toward mag mount for convenience. A good antenna outside the vehicle will make the biggest impact on your radio system performance - cutting corners or buying cheap Chinese junk will just frustrate you. Sounds like NMO is worth the installation effort.

Good data points. For emergency communications, that 0.7 dB could mean the difference between reliable contact and missed traffic. We always recommend permanent mounts for ARES/RACES vehicles for exactly this reason.