On Sat, 14 Jun 2008 22:04:53 -0700, Richard (Rick) Karlquist wrote:
>These are essentially the same array, just different feed
>implementation. There is no fundamental difference.
Yes and no. Remember that one of the most important properties of
any antenna installation is how it interacts with the earth in the
far field (that is, what does the first reflection do), which is
strongly affected by its height.
A quarter-wave vertical typically has its feedpoint on the ground or
close to it, placing its current maxima close to the ground. The
CLOSEST a half wave dipole's feedpoint (current maxima) can be to
the ground is a quarter wave. This has MAJOR impact on the vertical
pattern. The Power Point pdf I cited earlier in this thread has NEC
models for a 40M dipole at various heights that I was able to
achieve here (by hanging it from one of my redwoods). None of these
was particularly thrilling at low angles, and raising the vertical
dipole simply improved its vertical pattern at higher angles.
And I DO have this antenna rigged with the top of it at about 100
ft, I HAVE compared it to horizontal dipoles at that height, and the
horizontal dipoles kick its butt by 10 dB every day of the week. :)
73,
Jim Brown K9YC
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