[TowerTalk] Half Wave?

[Jim Brown]

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