7.
18 MHz
Inverted-delta full-wave loop antenna

This is for the 18 MHz-dedicated delta-loop antenna which I use since the end of 2024.

The quasi equilateral-triangle full-wave loop-antenna shows an input impedance of around 100 ohms. While, by keeping the full-wave length, if we elongate the triangle, the input impedance gets decreasing.

Thus if we elongate the triangle so that it shows the input impedance close to 50 ohms, we can directly feed by the ordinary coaxial cable.

After many trials, I finally came to settle in the form shown in the photos below.


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The white cable-ties dangling from the antenna element is for the warning to wild birds coming to my place.
It looks they notice the thin ellement of 1-mm diamete at a close range. However, that seems not sufficient to dodge the elements in some cases.
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Approximate dimensinos are as follows.

Top horizontal line: about 4 m
Right and left lines: about 6.5 m each
Triangle plane is tilted to the perpedicular plane by about 30 degrees

Though it might be better to apply a float balun, direct connection of 5D2V cable to the feed point shows no particular problem to the shack.

The antenna has been working well in the same manner as other wire antennas.

Applying the parameters above to the antenna analizing software, MMANA, and tweaking somewhat, resulted in the following.

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