...The whole idea behind a grounded vertical folded unipole is twofold, first the tower is shorter saving expensive steel, and it also has a low vertical takeoff angle that provides a longer direct wave (ground wave is different being long range VLF) thus larger primary and secondary contours aka listener area. That's because the 90 degree point aka current node is at the top of the tower instead of the bottom. The beauty of the beast is longer sky wave propagation for great DX on the longer wavelength bands of 160 and 75-80M. I can't speak on 40M because when the band goes long at night it's clobbered by Area 1 SW broadcasters beginning mid afternoon on the right coast, there goes 4M AM, bye bye. Yeah, there are still a few around, just enough to crowd us down to that tiny slice of CW only at the bottom of the band...
Take-off angle depends on the design of the folded unipole, it's height, etc.
The main goal for the folded unipole was to get a 50 ohm match for towers less than or equal to 0.223 X wavelength and some broad-banding.
For a square tower there would be 4 skirts at a different impedance matching point above ground and a different skirt spacing.
One could have eight skirt wires for a square tower and six skirt wires for a triangular tower but for sake of economy and simple impedance matching one skirt along each face has been found to be sufficient.
AC0OB - Phil
