so ive been running a basic mag mount dual band whip on the truck for about two years now and it works fine for hitting the local repeaters but ive been thinking about upgrading to something a bit more serious. was looking at the Comet CA-2x4SR or maybe the Tram 1185 with a proper NMO through-hole mount on the roof. mainly use it for linking into the local IRLP node and occasionally some simplex chat when im out on long drives.

my question is whether the gain difference between a 3dB whip and say a 6dBi collinear actually makes a noticeable real-world difference on 2 meters or is it mostly just marginal. i know on paper it looks good but the takeoff angle thing on high gain collinears always makes me second guess it. especially around here where the terrain isnt exactly flat. anyone actually done this swap and noticed a meaningful difference or am i overthinking it

honestly the NMO mount alone is worth doing regardless of what antenna you put on it. mag mounts are convenient but the ground plane is never quite right on most vehicles and you lose a surprising amount of signal to a mediocre connection at the base. i drilled my F150 roof about three years ago, was nervous as hell doing it, but the difference in receive was noticeable right away even with the same antenna.

on your actual question though — yeah the high gain collinear takeoff angle thing is real and it does matter in hilly terrain. i tried a 5/8 over 5/8 design on a trip through the Ozarks and there were spots where my old unity gain rubber duck on the HT actually hit the repeater better because i had a bit of elevation on me. for flat midwest driving though a good 6dBi collinear absolutely slaps. the Comet is solid, ive had one for years, well built and the PL-259 connector doesnt corrode nearly as fast as some of the cheaper ones i've tried.

the tram 1185 is what i have and its fine, nothing special but nothing wrong with it either. if you want to geek out on this stuff look up the radiation pattern data before buying, some manufacturers publish it some dont. the elevated takeoff angle issue with stacked collinears is real but in practice unless youre doing a lot of mountainous driving or trying to hit a hilltop repeater from a valley it usually doesnt bite you.

one thing i'd add — do the NMO mount properly with a good lip seal or grommet and use self-amalgamating tape over the coax entry point inside. ive seen guys do a clean install and then get water intrusion two winters later because they skipped that step.