Topband: Trees (not the N6TR kind)

[Terry Conboy]

On 2012-12-31 8:46 AM, Tom W8JI wrote:
> Years ago, when some fellow proposed that trees would radiate because 
> they were fractals, I measured the RF resistivity of freshly-cut pine 
> trees. I firmly attached copper or aluminum plates to a thick one foot 
> long trunk section, and measured resistance. These were wet, 
> freshly-cut, sappy, pines. Pines are acidic and very wet inside, so 
> they should reasonably be at the top of tree conductivity.
>
> I can't recall the exact RF resistivity, but I'm pretty sure it was 
> either high hundreds or low thousands of ohms per foot for a one foot 
> diameter log. I do know the number was significant. Resonance, 
> significant absorption, or radiation would be impossible with that 
> much resistivity per foot.
>
> Given a choice, I probably wouldn't have a high voltage area in close 
> proximity or contact with a tree. I doubt a few trees would produce 
> noticeable loss, and they certainly could not be by any stretch of the 
> imagination "resonant" with such high resistivity per linear foot.
>
> 73 Tom
I recall comments at a hamfest talk several years ago from Roy, W7EL, 
that his two-element 40m vertical array appeared to have an unintended 
null in the direction of a stand of evergreen trees not too far away 
from his antenna system.  While this is two octaves above 160m, it at 
least indicates the possibility of absorption problems.  In all 
likelihood, different tree species at different times of year could 
introduce a lot of variability.

73, Terry N6RY