So ive been running a Diamond X50A on my garage roof for about two years now and its been fine for local repeaters but i keep hearing guys on the 70cm side with noticeably better signals than me even when theyre running similar power. My setup is pretty basic, IC-2730 in the shack, about 35 feet of LMR-400 to the antenna, nothing crazy.

Started looking at yagis and now im down a rabbit hole. Part of me thinks a decent 5 or 6 element yagi on 440 would just demolish the collinear for the stuff i actually use it for, which is mostly two linked repeaters that are both roughly the same direction from my house, maybe 30 degrees apart in azimuth. But then id lose the omni coverage for simplex and the occasional direction that isnt covered.

Anyone gone from a collinear to a fixed yagi for a similar situation and regretted it or not. Also wondering if theres something wrong with my X50A because 35 feet of LMR-400 shouldnt be eating that much signal at 440 right, like maybe 2dB or so which isnt the end of the world.

your LMR-400 loss calc is pretty close, at 440 youre looking at somewhere around 1.5 to maybe 2dB per 100 feet so your 35 foot run is not the problem. id check the connectors first honestly. a poorly soldered PL-259 or a water-damaged barrel connector will kill you way worse than the cable itself. ive seen guys chase antenna upgrades for months when the actual issue was a connector that looked fine on the outside but was corroded inside.

on the yagi question, if those two repeaters really are within 30 degrees of each other a yagi makes a lot of sense. something like an M2 or even a homebrew 6 element would give you a serious advantage on 440. the downside is exactly what you said, you give up the omni. what i did was keep the collinear for monitoring and put the yagi on a separate feedline, then used an antenna switch. its a bit more hardware but you dont have to choose.

yeah the connector thing is real, i had an N to PL adapter that was just barely finger tight and i was convinced my radio was dying lol. anyway the X50A is a decent antenna but its not magic, the gain numbers on those dual bands are always kind of optimistic in my experience especially on the UHF side.

if both your repeaters are in basically the same direction i honestly would just put up a yagi and not overthink it. fixed yagis are so simple and there's basically nothing to go wrong with them. ive got a cheap homemade 4 element on 2m pointed at a hilltop repeater like 60 miles away and it works way better than anything omni ive ever tried for that path.