so ive been running a diamond x50 on my roof for a couple years now and its been fine for 2m but i want to add a dedicated 70cm yagi up there, probably a 9 or 11 element, pointing more or less toward the repeater cluster about 22 miles out. the problem is the coax run from the shack to the roof is maybe 55 feet of RG8X that i already have buried in the wall and i really dont want to tear it all out.

i know RG8X is fine for 2m but 70cm is a different animal and i cant remember what the loss numbers actually are at 440. anyone done this and thought it was acceptable or is it gonna be bad enough that i should just bite the bullet and pull LMR400 through there. the yagi would be doing most of the work obviously but still.

RG8X at 55 feet on 70cm is going to run you somewhere around 3.5 to maybe 4dB of loss depending on connectors. that's not nothing but if you're going from a yagi to a vertical it's probably still a net gain. the question is whether your feedline loss is eating into the advantage the directional antenna is giving you, and at 22 miles to a repeater, the link is probably fine either way unless you're running low power.

LMR400 would cut that loss roughly in half, closer to 1.8dB for that run. honestly if the wall is already done i'd just try the RG8X first. worst case you figure out its not enough and then you deal with the cable run later. people make that swap a bigger deal than it is sometimes.

yeah i had almost the exact same situation when i put up a 7el yagi for 432. ran LMR240UF because i could fish it easier and the loss wasnt terrible, maybe middle ground between your two options. but 55 feet of RG8X i dunno, i'd probably just try it. 22 miles to a repeater you're not exactly doing EME here haha