Many HF antennas don't need anything but coax attached, some need an impedance transformation and the vast majority can benefit from a common mode choke on the feedline. Take the OCFD, its usually tapped around the 200 ohm spot. Needs a transformer and will greatly benefit from a common mode choke. The common mode RF and radiation off the coax of an OCFD is so bad that one mfr puts a choke balun in a strategic spot and advertises their antenna now has a tuned vertical radiator on a few specific bands. Without that choke the whole feedline is a radiator. A 133ft 80-10m OCFD has been my main HF antenna for a couple of years now and I like it a lot but with a choke balun on the coax.
On any HF wire antenna I've had here, placing a good common mode choke, or choke balun with 30dB+ isolation has reduced my noise floor a lot on the lower HF bands. I run several radios with spectrum displays and its obvious, no choke, higher noise floor and birdies, cheap choke, a little improvement, really good choke, big cleanup of my noise floor and I can hear weak signals with chokes in line that I can't without the chokes.
I and many people have RFI riding on the coax and getting in somewhere on the path between the radio and antenna where its picked up by the antenna and received. Two of my operating positions have computers, routers and other noise makers nearby where the coax runs parallel with computer power leads, CAT5, USB, etc. Not only does a choke balun at the antenna improve my reception, another one at the radio end reduced it a little more.
The first time I noticed this many years ago was with a G5RV type antenna with a poorly made 1:1 choke balun at the ladder line/coax junction that arced over. I replaced it with a much better choke and noticed my noise floor went down. I put a similar lousy one back and the noise floor went back up a little. I turned off all my computer junk in the shack that was near the coax and the noise went back down. I temporarily routed the coax to a different area away from the computers and related cables and low noise floor with computers on. I think I proved noise was riding up my coax to my antenna and that a very effective choke was snuffing it out.
Since then I've seen similar results on other setups and tested a dozen different brands of choke baluns both on air and on the test bench and found one brand stands out above all others and I put those on most everything or make home made copies of them. I also found most tubular shaped choke baluns are simply a string of ferrite beads over some coax. At best I've measured about 18 to 20dB of isolation on those and that peaks near the middle of the bands and is worse on 80m. The choke types with turns wrapped around a toroid ring can reach 30dB or a little more isolation but still favor one end of the HF band or the other. The best have multiple large beads or cores with separate windings around each one and even different mix ferrites to cover different parts of the HF band. These can reach 40dB or more isolation and cost a lot more to make but they really clean up problems and lower your noise floor to the limits.
We can agree most HF antennas don't require a choke on the feedline but I can say most will benefit from one.
Still a choke ain't a balun, although the end result can be the same. Sort of the difference between chopping off a finger with an axe instead of going to a surgeon.
As for an OCFD, I ran one for quite some time. Didn't get 'bit' even once (no balun/unun).
PRCGUY, you weren't being singled out with the ferrite core thingy, everybody is included in that. It seems every time someone talks about making or putting up an antenna a balun is always included. In most cases I think it's waste of time and money.
