so ive been wanting to build my own dipole for 40m for a while now and finally just went for it last weekend. used some 14 gauge stranded wire i had laying around from an old extension cord project, cut each leg to roughly 33.5 feet based on the 468/f formula. fed it with some RG-8X i had left over from a previous install.

my question is about the feedpoint connection — i just twisted the wire around the SO-239 center pin and the shield tabs and used some electrical tape over it. SWR came out around 1.8:1 at 7.150 which honestly i thought was pretty decent for a first try but im getting some RF in the shack, touching the mic gives me a little buzz. i figure its a common mode current thing but not totally sure. should i be running a choke balun right at the feedpoint? i read some stuff about winding coax around a PVC pipe form but wasnt sure how many turns or what diameter to use.

the antenna is kind of a sloper right now because one end is higher than the other by maybe 8 feet, not sure if that changes the math much. running about 100w into it on a IC-7300.

yeah the buzz is almost definitely common mode, the coax shield is carrying some of the return current and it ends up radiating back into the shack. a simple choke at the feedpoint will fix it, i usually just wind about 8-10 turns of the coax on a 4 inch diameter form, something like a PVC coupler or even a coffee can works. for 40m you dont need anything exotic. some guys swear by the ugly balun method, just coil the first few feet of coax right below the feedpoint into a bundle and zip tie it, works surprisingly well in practice even if its not as clean as a wound choke.

the solder job on the SO-239 matters more than people think too — twisted wire under tape is gonna cause you grief eventually especially if theres any moisture. worth taking the connector apart and soldering it properly if you havent already. the sloper part is fine, actually slopers can have a little directivity which isnt a bad thing at all.

1.8:1 on a first dipole is actually pretty solid tbh. ive built a few and my first one was like 2.4 before i figured out the wire wasnt actually the length i thought it was because i measured wrong lol. on the balun thing i used a mix 31 ferrite toroid from the local surplus place, wound maybe 10-12 turns of coax through it, and it killed the RF in the shack issue i was having on my end-fed. probably overkill for a dipole but it works great. the sloper shouldnt matter much for the resonant frequency, might shift it a tiny bit but nothing dramatic at those heights.