so ive been pulling my hair out over this for a couple weeks now. got a comet gp-3 up on the roof about 35 feet of RG-8X running down to my FT-7900 and my signals into the local repeater are just... okay. not great. other guys hit it way cleaner than me and i know at least two of them are running less power.

the run goes straight down the side of the house through a hole i drilled near the window, no sharp bends or anything, feedline looks fine visually. SWR on the rig meter reads under 1.5 which i guess isnt terrible but something feels off. im wondering if 35 feet of RG-8X is just eating too much at 146mhz or if maybe my ground plane situation on the roof mount isnt ideal. the antenna is on a j-pipe mount off the chimney, probably 18 inches away from the brick.

would upgrading to LMR-400 actually make a noticeable difference for a 35ft run or am i overthinking this and the problem is somewhere else

35 feet of RG-8X isnt killing you that badly at 2m, youre probably losing maybe 1.5 to 2dB over that run which isnt nothing but its not the whole story either. LMR-400 would get you back most of that sure but honestly id look at your connectors first. one bad PL-259 will rob you way more than the coax itself, especially if somebody soldered it in a hurry or the center pin isnt making great contact. i had a similar situation last year and it turned out the connector at the antenna end had moisture in it, looked totally fine from outside but the inside was corroded green.

also the chimney mount thing is worth thinking about. 18 inches from brick isnt ideal for a vertical, the chimney can mess with the pattern depending on which direction your repeater is. might be worth temporarily sticking the antenna somewhere more in the clear just to see if your signal improves before you spend money on coax.

yeah what he said about connectors is real, that bites everyone eventually. but also -- whats the repeater input, is it on the east side of town? because if the chimney is blocking you in that direction thats gonna hurt way more than coax loss. i had my gp-6 on a chimney mount for like two years wondering why one repeater was always scratchy and turns out the brick was just in the way. moved it to a mast on the peak and night and day difference.