I have to wade in here with some practical experience.
I've had up at about the same time a half-square fed at the top corner and a
dipole at almost the same height on 40M, and the half square lived up to its
promise of directivity and gain. It was a killer antenna for DX. The
dipole was the better domestic contest antenna, and was very good for DX,
but the long haul DX was always better on the half-square (in the direction
of the half square's lobe).
I had both for the reasons most of us have multiple antennas for contesting.
I replaced that half-square with a 402CD at 102' ASL, and don't miss it at
all. The dipole is now an OCF 80M at 85' ASL and works well.
I've used loops, both delta, rectangular, and trapezoidal ( to fit the
space) and they were always very good antennas on 80M, but the half square
and the Bobtail were better on 40M (long haul). I put up an inclined delta
loop on 80M with a open wire stub in the top corner for 40M fed at the
center bottom every Field day for several years for our QRP operation. It
was always quieter and worked far better than our expectations. One year I
put up a BobTail for FD, and of course the loop was the better antenna for
FD. These antennas were put up from my dock on the Intracoastal Waterway or
just adjacent to the dock, strung over the bay, and we enjoyed what I have
always called "Nature's Amplifier" .
My 2 cents,
Jon Hamlet, W4ZW
Casey Key Island, Florida
"A little piece of paradise in the Gulf of Mexico"
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