so i finally got around to building a proper dipole instead of just using the end fed wire ive had strung up forever. cut it for 40m using the standard 468/f formula, legs came out to about 33.2 feet each, center insulator is just a piece of PVC i drilled and threaded with some stainless hardware, fed with RG-8X down to the shack.

problem is the SWR at the calculated resonant freq is like 2.1:1 which i guess isnt terrible but i expected closer to 1.5 or so, and it gets worse the further up the band i go which i know is normal but the whole curve seems shifted up in frequency by like 30-40 kHz from where i expected it. trimmed a little off each leg thinking i was long, but that just made it worse. antenna is at about 25 feet at the center, slopes down on both ends to about 10 feet, not a flat-top. im wondering if the inverted-v configuration is throwing off my numbers since most of the calculators assume a flat dipole

also the feedpoint impedance — is 2.1:1 just what you get with an inverted-v because the impedance drops below 50 ohms? i read somewhere the legs being angled down lowers the feedpoint Z but i cant find a consistent answer on how much

yeah the inverted-v thing is definitely part of it. when you drop those legs down you're compressing the angle between them and the feedpoint impedance falls, sometimes into the 30-35 ohm range depending on how steep your angle is. so even a perfectly resonant antenna is gonna show higher SWR into 50 ohm coax just because of the mismatch. 75 ohm coax actually works pretty well for inverted-v centers for exactly that reason, brings the SWR down noticeably.

the frequency shift — if the resonant point moved up after you trimmed it you definitely went too short, but the original shift upward from calculated is common with inverted-v too. the formula assumes horizontal and free space basically, real world with ground reflections and the angle of the legs means you usually need to add a little length, not cut. i'd add 6 inches or so back to each leg and see where you land. also 25 feet center height on 40m is pretty low, ground losses are probably eating into things a bit but thats a separate conversation

what angle are your legs at roughly? like if center is 25ft and the ends are 10ft that means each leg drops 15 feet over 33 feet which is kind of a shallow slope actually, so impedance might not be as low as a steep V. the 2.1 SWR honestly most tuners will handle no problem, i wouldn't chase perfection too hard. my inverted v on 40 sits around 1.8 at the sweet spot and everything works fine