so ive been running a Larsen NMO2/70B on my F-150 for about a year now, had it on a fender mount the whole time because i was nervous about drilling the roof. finally bit the bullet last month and moved it to the roof center and honestly i cant believe i waited this long. the difference on 70cm especially is pretty noticeable, i was getting into a couple repeaters that were kind of marginal before and now they're rock solid.

anyway the actual question i have is whether anyone has done a comparison with a collinear on the same mount vs a 5/8 wave. i picked up a Tram 1185 from a swap meet and i'm wondering if its worth swapping out the Larsen or if the gain difference is just theoretical at mobile speeds. my main use is just commuting and some APRS so its not like im trying to win a contest or anything, just curious if people have actually noticed real world differences between them.

roof center is almost always going to give you the best ground plane on a vehicle, fender mounts work but you're giving up a lot especially on UHF where the geometry actually matters. good move drilling it.

on the collinear vs 5/8 question, honestly at mobile speeds and for what you're doing i'd say the pattern difference matters more than the gain numbers. a collinear like that Tram squashes the pattern down more, which sounds great on paper but if you're in hilly terrain or going through areas with a lot of vertical angle variation you can actually end up with worse performance than a simple 5/8. for flat highway commuting the collinear probably wins. for APRS specifically some guys swear by lower gain antennas because the packets are short and you want a more forgiving pattern. i'd just try both and see, an NMO swap takes five minutes.

yeah i had almost the exact same setup on an older silverado, went from a lip mount to a through-the-roof NMO and it was like night and day on 440. the lip mounts are convienent but you're basically compromising the whole antenna for the sake of not drilling a hole.

cant really comment on the Tram specifically but ive heard mixed things about their quality control, the one i borrowed from a club buddy had a loose connector that was causing all kinds of intermittent weirdness. might want to check the SO-239 connection before you do too much testing or you'll be chasing a gremlin that isnt really an antenna pattern problem at all.