I have also been curious about such an antenna, and with Field Day coming
up, your message prompted me to run a quick model on EZNEC. I set it up
as half of a vertical diamond configuration as you described, except I put
two quarter wave radials at each end (both the driven end and the far end),
all perpendicular to the plane of the half loop and positioned two feet
above ground.
The vertical pattern looks much like a vertical, with maybe one db extra
gain and an optimum takeoff angle of 19 degrees. The impedance at
resonance was roughly 65 ohms for the dimensions I chose, which are:
a. apex of loop at 55 feet above ground
b. ends of the half loop 110 feet apart, each 55 feet horizontally from a
point directly below the apex
c. each of the four radials 65 feet long (two each for each end)
d. all wires #14
A quarter-wave vertical might be simpler (minimal top-loading could achieve
resonance at the same 55 feet), especially if you needed to erect some sort
of pole or tower to support the apex of the loop. On the other hand, a
couple of trees, even closely spaced, could support the apex of the loop
nicely (I still have Field Day in mind) and give a slightly better gain and
feed impedance over the vertical.
I can picture myself tripping over the radials in the dark already.
Keep in mind the quicky nature of this rough analysis, and I'm certainly
not an expert on the topic anyway.
73,
Dave
At 03:51 AM 6/16/98 +0000, Brian K. Short wrote:
>
>The Antenna Compendium describes some experiments
>with the "Half-Loop" antenna which is a half of a full loop
>antenna fed against a ground screen.
>
>It would be fed at the ground, then go up to a support, and
>finally back down to the ground again, sorta like an inverted
>V dipole, but fed at one end against ground rather than at
>the center.
>
>I have had good luck with full-wave loops in the past, but
>height and size have prevented trying such on 80m or 160m.
>
>I am curious if anyone has experience with this type of antenna?
>
>73, Brian
>
>--
>Brian Short k7on@qsl.net http://www.qsl.net/k7on
>(602)839-3484 1994 E Laguna Dr Tempe, Az 85282
>--
> Dude's Law of Duality
>Of two possible events, only the undesired one will occur.
>--
>
>
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