W5HVV asked whether anyone had modeled or published a 3/4-wavelength
inverted L antenna design. Dennis Monticelli, AE6C, published a QST
article in 1989 or 1990 on this subject (something like "A Dual-Band
Inverted L Antenna"). Check with TIS@arrl.org for details on the
specific issue and page numbers. The article focuses on a project in
which the antenna is a 3/8 wavelength long at the lowest frequency of
operation and 3/4 wavelength long at 2f.
I've tried the 3/4-wavelength approach. It works okay, but has too much
high-angle response for a DX antenna. I've found that 3/8 wavelength
works better, with the appropriate matching (reactance cancellation) at
the feed point. As for impedance, the 3/4-wavelength version has a
relatively high input impedance--around 100 ohms, as I recall. This
gives you an efficiency advantage if your ground system is particularly
lossy, since the radiation resistance is a larger fraction of the total
feed-point resistance.
You need to decide what's best for you. If you're a DX-oriented
operator, the 3/8-wavelength version is clearly better. For mainly
stateside stuff, with some occasional DXing, the 3/4-wavelength version
is fine.
--73, Rus, NJ2L
nj2l@mdsroc.com
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