so i finally got around to building a proper 40m dipole instead of using that crappy random wire ive had strung up for the past two years. cut it to roughly 66 feet total using the 468/f formula, fed it with some RG-8X i had lying around and a SO-239 chassis connector i pulled off an old dummy load enclosure. center insulator is just a piece of pvc pipe with a couple holes drilled through and some cord to support the coax.

heres my issue though — when i measured with my antenna analyzer before i got it up in the air i was getting a pretty clean resonance right around 7.1 MHz, SWR was like 1.3:1 which i was happy with. but once i got it up (its an inverted V, apex at about 30 feet off a tree with the ends closer to 10 feet), the resonance shifted down to like 6.85 or so and now the SWR at 7.1 is more like 2.8:1. i know the inverted V config shortens the effective electrical length a bit but i thought it went the other way... like it gets shorter electrically not longer? or am i wrong about that. my buddy said just trim it but i want to understand whats actually happening before i start cutting.

also the coax is running along the ground for most of its length to the shack window which is maybe 80 feet of feedline. doesnt seem like that should matter but figured id mention it.

youre not wrong that inverted V tends to look a bit shorter electrically compared to a flat top, but proximity to ground when the ends are that low can actually add capacitive loading and push resonance down. 10 feet for the ends is pretty low and the ground coupling is probably doing exactly that. the coax on the ground shouldnt shift things that dramatically by itself but if you dont have a decent choke at the feedpoint youre also potentially getting some common mode current on the shield which will mess with your measurements and your SWR readings both.

i would try trimming maybe 6 inches per side and re-check. and seriously slap a 1:1 choke balun on there before you do anything else — can make a huge difference in getting consistent measurements. i use the W2DU style with ferrites on the coax, cheap and easy to wind yourself.

had almost the same thing happen with mine last fall. ended up being the ends were too close to some metal gutters and it pulled resonance way down. moved the ends out a few feet and it came right back up. might not be your issue but worth checking whats near the end insulators.