so ive been running a center-fed 40m dipole at about 30 feet for the past couple years, inverted-V configuration, apex tied off to a tree in the backyard. its worked okay but lately the noise floor has been driving me nuts, sitting around S5-S6 most evenings and i can tell its picking up a ton of local QRM from the neighborhood — neighbors LED lighting, some kind of switching supply someone runs, the usual suburban nightmare.

been thinking about trying a vertical instead, maybe something like a trap vertical or just a homebrew quarter wave with a decent radial field. the idea being i could mount it out back further from the house and maybe get a lower angle of radiation for DX which would be a bonus. but i keep reading conflicting stuff — some guys swear their vertical is noisier than a dipole, others say the opposite. im guessing a lot of it is site-specific but curious what people here have actually experienced going from one to the other on 40.

also not sure how many radials is actually enough. ive seen everything from 4 to 120 mentioned and obviously 120 isnt happening in my yard but whats a realistic number before you hit diminishing returns for a typical suburban lot.

the noise thing is really site dependent like you said but in my experience a vertical on 40 is almost always louder for local noise than a horizontal dipole at any reasonable height, at least in a typical suburban setup. the dipole has some rejection off the ends and if you orient it right you can null out some of the worst offenders. verticals are pretty much omnidirectional all the way down to the ground so they grab everything.

that said the low angle radiation on a vertical is real and does help for DX, so theres a tradeoff. if DX is your main goal maybe consider a phased pair of verticals someday but thats a whole project. for radials honestly 16-32 on the ground does most of the work, going from 4 to 16 is a bigger jump than going from 32 to 120. read the ON4UN low band book if you havent, he goes into the numbers pretty thoroughly. i run 24 radials under my 40m vertical and its working fine, compared to my old dipole the noise is worse but the signal reports into europe are consistently better which is what i wanted.

had almost the exact same situation a few years back. ended up putting up a vertical and yeah the noise went up but so did the DX contacts so i just deal with it lol. one thing that helped me a lot was adding a common mode choke right at the feedpoint — had a ton of garbage coming up the coax shield and it was making everything worse. made a ugly balun out of a few turns of coax through a couple stacked toroids and the noise dropped like 1.5 S-units. might be worth trying on your dipole too before you give up on it actually