Last year I put up a 40m Bottom Fed Delta Loop between two tall trees near my camp site. The results were Impressive. With a little effort, we worked all of the stations the we could hear on all HF bands with my FT-817 (at 5 watts).
(last years photo to be inserted here)
The top of the Delta Loop was at 90 feet AGL (some very tall trees) and was fed from the bottom with 450 ohm ladder line via a balun. We used the formula: "1005/Freq" to calculate the length of wire, which was folded in thirds to fine the corners.
In practice, the antenna resonated on a slightly higher frequency than I expected, but still within the 40m band. The LDG Z817 tuner on the FT-817 was able to match it on all HF bands. I may be wrong, but I think the impressive performance is due to the massive capture area of that much copper high in the air.
Because space and hight is available, I plan to double last years wire length, and put up an 80m Delta Loop. I am expecting good things, and will report the results.
There is a third tall tree that I might be able to use to convert the Vertical Delta Loop to Horizontal. It would be really fun to use an 80m Horizontal Loop at 90 feet AGL (I may need to splice in some more feed line).