so i finally got around to building my first dipole from scratch this weekend. been putting it off forever because i always just bought prebuilt stuff but figured its time to learn. i used the standard 468/f formula and cut the wire for 40m, ended up with two legs around 33 feet each give or take. wire is just 14 gauge stranded i had sitting in the garage, fed with about 50 feet of RG-8X into an MFJ-259B.

the swr at what should be resonance is sitting around 1.8:1 which isnt terrible i guess but i expected to get closer to 1:1 or at least under 1.5. the resonant point also seems to be about 150kHz lower than i calculated for. antenna is in kind of an inverted-V configuration, apex maybe 30 feet up on a push-up mast, legs going out at roughly 45 degrees tied off to some stakes. coax runs straight down from the feedpoint for maybe 10 feet before going horizontal.

is the high-ish swr because of the inverted-V angle pulling the feedpoint impedance down from 75 ohms? i read somewhere that steep angles can do that but wasnt sure if that really matters at 45 degrees. or is it more likely the coax acting as part of the antenna messing with the reading? i didnt put a choke or balun at the feedpoint because i dont have one made up yet. anyway any thoughts appreciated, trying to figure out if i need to trim or if its something else going on

yeah the missing balun is almost certainly your problem or at least a big part of it. without a choke balun at the feedpoint the coax shield becomes part of the radiating system and your analyzer is seeing a mix of the actual antenna impedance plus whatever common mode currents are doing. can throw your readings off enough to make a decent antenna look like a mess. honestly just wind yourself a quick ugly balun, like 8-10 turns of the coax in a coil about 6 inches diameter right at the feedpoint, even that'll make a noticeable difference before you go building something fancier.

the 150kHz low resonance is also pretty normal for an inverted-V vs a flat dipole. the formula 468/f is really for a flat dipole in free space and when you droop the legs you're effectively increasing the electrical length a bit. 45 degrees isnt super steep but it'll still shift things down some. try trimming maybe 6 inches off each leg and remeasure after you get that balun situation sorted. dont trim too much at once, easier to take wire off than put it back.

feedpoint impedance on an inverted-V at 45 degrees comes in somewhere around 50-60 ohms depending on height and ground conditions so actually youre probably not far off for a direct coax feed, the 1.8 might just be what it is without a matching network. i ran into the same thing with mine last spring and ended up just using it as-is because below 2:1 most rigs are happy enough. the balun thing the other guy mentioned is real though, i noticed my readings changed noticeably after i wound one.