so ive been going back and forth on this for a few weeks now and figured id just ask. i have a decent 2m/70cm setup at home, currently running a diamond X50 on a j-pipe mount off the chimney and it gets me into the local repeaters just fine most of the time. but theres this one repeater about 35 miles out that i can hit but its kinda marginal — sometimes full quieting sometimes it sounds like im in a tunnel.

someone at the club told me to try a yagi and aim it at that repeater but like, i use 4-5 different repeaters in different directions so that doesnt make a ton of sense to me. another guy said just get a taller collinear with more gain. the X50 is rated at 6.5 over 4.5 dbd i think, something like that. is going to like a 5/8 over 5/8 actually gonna make a noticeable difference or is it marginal enough that im wasting money

also wondering if the issue is actually my feedline. im running about 40ft of RG8X right now which i know isnt ideal at 70cm but on 2m its probably fine right

the feedline is probably eating more than you think, especially if thats older RG8X. at 146 MHz youre looking at maybe 2-2.5dB loss over 40ft which isnt catastrophic but its real. at 440 its pretty ugly though, closer to 5-6dB and thats essentially cutting your power in half and then some.

as for the collinear vs yagi debate — for hitting multiple repeaters in different directions a collinear is the obvious answer. a yagi makes sense if you had ONE direction you cared about, like a distant linked system or simplex with a buddy. but the gain difference between a X50 and say a Diamond X300 or a Comet GP-9 isnt huge. maybe 3dB real world. thats noticeable but its not going to turn a marginal path into full quieting if the path is genuinely difficult. i'd honestly look at whether the repeater itself has a good antenna before assuming its your end.

had almost the exact same situation last year, marginal on one repeater that was like 40 miles out. swapped my RG8X for LMR400 on just a 30ft run and honestly it made a bigger difference than i expected. not like night and day but definitely cleaned things up. the repeater in question also turned out to have a crappy antenna on their end lol so there was only so much i could do anyway

one thing nobody mentioned — have you tried just repositioning what you have? chimney mounts can sometimes put the antenna right next to stuff that causes pattern distortion. i moved mine like 18 inches away from the brick on a standoff and it actually helped more than i thought it would for one specific direction.