so i finally decided to stop putting it off and just build a simple 40m dipole out of some 14awg stranded wire i had sitting in the garage. cut it to the formula, 468/f, came out to roughly 66 feet total, fed it with some RG-8X i had left over from another project. center insulator is just a piece of pvc pipe with the ends drilled out, which i thought was clever at the time.

got it up in an inverted-V config with the apex at maybe 25 feet using my push-up pole. SWR at resonance is sitting around 1.8:1 which honestly isnt terrible but i was expecting closer to 1.5 or even lower. the weird part is the resonant point ended up at like 7.050 when i was shooting for somewhere in the 7.150-7.200 range. so its resonating low and the SWR at resonance isnt great either. trimmed a bit off each leg and brought it up slightly but im kind of nervous to keep cutting and overshoot.

not sure if its the inverted-V drooping the ends down too close to the fence or maybe the coax isnt choked properly. i didnt put a choke on it, just ran the feedline straight down. running it to an FT-891 if that matters. any thoughts before i hack more wire off?

the resonant frequency shifting lower is almost certainly the inverted-V effect combined with end proximity to that fence. when you droop the legs down they electrically look longer than they actually are, so the antenna thinks its bigger than it is. the 468/f number is really for a flat-top dipole with the ends well clear of everything, inverted-V usually needs the legs trimmed a bit shorter than that formula gives you.

but honestly the bigger issue is probably the lack of a choke. without one the coax braid becomes part of your antenna system and that screws everything up - affects the feedpoint impedance, shifts resonance, all kinds of weirdness. wind like 8-10 turns of your feedline into a coil right at the feedpoint, or get some ferrite beads on there, and then remeasure before you cut anything else. you might find things look a lot better after that. i spent two weekends chasing a similar problem on my 80m dipole before someone told me the same thing.

yeah dont cut more wire until you sort the choke thing, that drove me nuts on my first build too. also 1.8:1 at resonance on a dipole usually means the feedpoint Z is a bit off from 50 ohms which makes sense for an inverted-V, the angle of the legs changes the impedance, closer to like 70-75 ohms at 90 degrees but lower angles bring it down. some people just stick a 1:1 balun on there and call it good enough, the tuner in the 891 can handle 1.8 no problem anyway