Some things to know about the OCFED are that the height of the feed point determines the BALUN needed. The most common BALUN would be a 4:1 current BALUN. The 4:1 works best if the height of the feed point is 35 to 45 feet, or even 50 feet. If you go any higher, the BALUN may need to be adjusted.
The second thing to know, is that ground radials below the antenna, will help tremendously, or i would say they are essential for a well working OCFD.
The ground radials can be place in the ground, just cut a V in the dirt, and place the radial into it and cover it up. The radials should be grounded to your station ground point. In my case, that is several ground steaks around my tower, and a short connection to the well pipe that is very close to the tower leg.
You MUST also connect your home ground to the station ground , if you don't, you will create a dangerous situation for lightening strikes that will hot one ground point, then run through your home toward the next ground point, blowing out everything in between.
Lastly, the 4:1 BALUN I originally made did not work so well. I was not an expert at making BALUNS, but I followed directions very well. After a lot of testing and not getting what I considered good performance, I called BALUN DESIGNS by getting their number off of their website. I spoke to Bob, and Bob explained a few things to me, and suggested that i try on of his 4:1 BALUNS that was made specifically for an OCFD. It was rated for 5KW, and had a duel core. Mine was not anything like that. That BALUN Designs BALUN was the first step in getting an OCFD that worked pretty well. The next improvements came later. one was the height of the feed point went higher, and the next was the ground radials My OCFD is now amazing, and tunes from 10 to 40m, only skipping 30M. It has flat SWR across 12m, and gives me nice working spots on each band that do not need a tuner. I do use a tuner to widen some of the bigger bands, like 40m. I also can tune to a small section of 75M. Low low you can go, is alls about the total length of wire you are working with. I work with roughly 45'x90' , but if you have more room, you can double those lengths, and do much better. My property is not that big.