so ive been running a diamond x50a on the roof for a while now and its always been decent on 2m but 70cm has always felt a bit weak compared to what guys at the repeater are reporting back. the coax run from the antenna down to the shack is probably around 40 feet of LMR-240, nothing crazy, goes through the attic and down the wall. connectors are all PL-259 which i know isnt ideal for 70cm but i did my best to keep the solder joints clean.

been wondering if the cable loss at 440 is just eating me alive or if theres something else going on. i tried a mag mount whip in the car and honestly the signal reports werent that different which seems weird. maybe the x50a just isnt that great on 70cm to begin with? i always assumed collinears were kind of a jack of all trades situation but maybe im expecting too much out of it.

anyone run a dedicated 70cm antenna just for that band and notice a real difference or is this kind of splitting hairs territory

40 feet of LMR-240 at 440mhz is gonna cost you somewhere around 3-3.5dB which isnt nothing but its not catastrophic either. the PL-259s are probably adding another half dB or so if theyre not done perfectly. i'd actually look at the antenna itself first — the x50a is fine but its gain numbers on 70cm are honestly a bit optimistic on the box. i ran one for years and eventually put up a separate 5/8 wave collinear just for 70cm and yeah the difference was noticeable, maybe 2-3 S units on received signals from the local repeater.

if you really want to chase it down, LMR-400 or even LMR-600 on that run would drop your loss considerably. but honestly for a roof-mounted antenna you might just be fighting the physics of a dual band compromise design. a dedicated yagi for 70cm if you're doing anything directional would be a totally different world.

i had basically this same situation a while back and went down the rabbit hole on it. ended up putting a preamp at the antenna rather than at the radio and that helped receive a lot. wont do anything for transmit obviously but if the issue is hearing the repeater thats worth trying. mine is just a cheap SSB Electronics unit i got used, nothing fancy.

also -- and i know this sounds dumb -- have you checked that the antenna is actually resonant on 70cm? i borrowed an antenna analyzer from a club buddy and my x50a was way off on 70cm SWR from what i expected. dont know if it was a bad batch or what but its worth checking if you have access to a analyzer or even a basic SWR meter with a 70cm capable bridge.