On 1/17/2019 9:46 AM, Warren Wolff via TowerTalk wrote:
My understanding is that a yagi should be at least 1/2wave above ground to avoid warming the
clouds. So, considering that thought, how much does an antennasuffer if such antenna is
63 feet up instead of 67 feetfor 40 meters over VERY rocky "soil"?
I have two answers to your question, one of which is simple and the
other is not. The simple one first -- several years ago, I did a
modeling study using NEC studying the effect of height and soil quality
on horizontal and vertical antennas for the HF bands. NEC is only able
to consider flat earth. The results of that study are summarized in this
report. http://k9yc.com/AntennaPlanning.pdf ; The executive summary is
that higher is better.
The more complex answer is the interaction of antennas with terrain. For
that, a study of the ARRL Handbook and use of N6BV's HFTA (High
Frequency Terrain Analysis) software is in order. The executive summary
is that 1) being close to a drop-off can provide a LOT of gain in the
direction of the drop-off and that antennas don't need to be high; and
2) that terrain in any direction can strongly influence optimum height
for antennas for each band.
73, Jim K9YC
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