I'm not looking to get into the "virtues" (or lack thereof) about 43 ft. verticals in this thread. Just looking for some answers concerning the proper loading of radials that are currently 33 feet long (for 40 mtrs) to make them play better on 75/80 mtrs. The vertical portion itself is mounted at 20 feet above ground and is base loaded for 75/80 mtrs. I have a homebrew relay and coil combo that I switch in and out to make the antenna naturally resonate on 75/80. I also use a remote automatic antenna tuner at the base of the antenna, for minimal mismatch losses along the coax when I am using 10-40 meters and the 75/80 coil switched out. The system works great. But currently, I only have one 75 meter radial on the system, but I have four 40 meter radials and four 20 meter radials, and four 10 meter radials. Since I do not use 40 meters often, I'd like to add some loading coils to the 33 foot 40 meter radials to make them play better on 75/80. I'm not worried about exact precision tuning using the radials, since any mismatches are tuned out by the remote tuner at the feed point. But I would like to know what the proper length of additional wire I need when constructing loading coils for the 40 meter radials to turn them in 75/80 meter radials. I assume that the proper placement would be out towards the ends of the radials, but correct me if I am in error. And I do realize there are several factors at play, such as the diameter of the turns in the coil and distance between turns, etc... Could someone please give me some examples or a formula to follow when calculating a ballpark figure of extra length of wire I need to wind the coils with, given a particular form diameter and length. Again, I don't need to be exact, just in the ballpark. Although the current radials I am using are specifically cut for each ham band, they are not "tuned" radials, even though this is an elevated antenna. I use my remote tuner to do the precision work. I know that non loaded set of 75/80 meter radials should be approximately 61-66 feet + 3-5%. But what about adding a loading coil to a 33 foot radial to make it electrically 66 feet long? I am on a 6,000 sq. ft. postage stamp lot which is why I am stuck with a single vertical antenna, and why I can't simple go for full length 75/80 meter radials. I only have one direction where I was able to use a full length 75/80 radial. With my vertical radiator base loaded coil kicked in, that one radial was able to bring the antenna very close to a natural resonance on 75. But I'd like to get any additional benefit I can on 75/80, by turning my 40 meter radials into loaded 75/80's. And yes, I know that they are not as efficient as unloaded full length radials. But on an elevated vertical, it should help a bit. It wouldn't be as much an issue on a ground mounted vertical, where you can simply make all the radials the same length (or a little longer) than the vertical element. I'm trying to gain any additional efficiency as I possibly can, even if it is small, because I am currently forced to run barefoot, albeit a 200 watt radio.