Moxon in his excellent book, HF Antennas for all locations, talks extensively
about antennas over sloping ground. Sadly, years ago I attempted to visit with
him through the RSGB but he was too late in life for them to want to forward
the message. I do agree with his ideas, but have some unanswered questions.
1. He prefers to put the antenna down the slope (if there is enough slope left
to make up the Fresnel zone) rather than at the lip. It appears to me that
reading his discussion that for low radiated angles the negative Fresnel zone
near limit he discusses does not exist. At least for angles below maybe 30
degrees and who wants to go above there?
2. He uses two heights: the normally thought of height and the height at a
right angle from the slope. So if you placed the antenna out over the slope
you now have the height at a right angle from the slope plus the now much
longer traditional height. If you put the latter in HFTA you get the antenna
almost on the ground. What height do I use in HFTA.
3. I'm assuming that HFTA only uses radiation in free space out front as on a
slope. With the close spacing to ground a lot of the energy heading toward the
slope is going deep into the earth while the grazing energy down the slope
looses less.
4. A weird thought: An antenna over flat ground basically sees (for losses)
180 degrees plus the angle to ground for each reflection point while one at the
lip of a (say) 20 degree slope sees that much more sky (less ground loss).
Does that make a difference?
5. Even more weird: Is it possible to put a few tuned wires in the Fresnel
zone near the ground to help with ground loss?
Thanks, I know the sloping ground works. Just want to optimize.
N0UU
38.808739, -97.513172
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