Roy Lewallen wrote in message ...
With a typical ground plane antenna, the feedline can radiate
significantly, distorting the pattern. This effect could easily be
different for the different antennas. Modeling indicates that two baluns
are often needed to suppress the current on the outside of the feedline.
A model which includes the feedline might give some insights as to why
the antennas behave so differently.

Roy Lewallen, W7EL

It's quite possible. The 1/2 was the only one I actually added a
decoupling section to. It was a 1/4 wave length of coax below the
feed, and a grounded set of 1/4 wave radials at the base of that
section. About the same scheme as cushcraft uses on their ringo ranger
2 verticals. It did improve the antenna. I never added extra
decoupling to the 1/4 or 5/8 antennas. But I did try both 1/4 and 3/4
wave radials on the 5/8 antenna. Ended up prefering the 3/4
radials..The 1/2 wave was a very good antenna, but in my case, not
once did it ever beat the 5/8. Actually, thinking about it, and even
included many CB antenna setups going back years and years, I've never
seen a 5/8 GP that didn't handily beat a 1/4 GP by 2 S units to a
local ground wave station. Even using the 1/4 wave radials, which I'm
not crazy about for a 5/8 antenna. These were all using various
length feedlines I'm sure. MK