Looking for advice on antenna choice for mobile operation in mountainous terrain. Currently running a Diamond NR770HB dual-band 5/8λ over 1/4λ on my truck, but I'm getting mixed results working repeaters in the Sierra Nevada region. The pattern seems too low for the steep terrain angles to many repeaters.

I've read that 1/4λ antennas perform better at higher take-off angles. Would switching to a Larsen NMO-27 or similar 1/4λ dual-band antenna improve my coverage to mountain-top repeaters? My mount is center roof with good ground plane. Any real-world experience with this trade-off would be appreciated.

You're correct about the radiation pattern differences. 5/8λ antennas concentrate energy toward the horizon, while 1/4λ antennas have more high-angle radiation. In mountainous terrain, the 1/4λ will likely perform better for repeater access despite the 3dB gain penalty.

I made this exact switch on my Jeep for Colorado operations. The NMO-27 works noticeably better on steep-angle repeater paths compared to my old 5/8λ. You'll lose some range on flat-terrain simplex, but repeater coverage improved significantly.

Consider antenna modeling with EZNEC or similar before switching. You could also try adjusting your current antenna's mounting position - sometimes moving it forward or backward on the roof changes the pattern enough to help with difficult repeater paths.