Topband: Trees (not the N6TR kind)

[Tom W8JI]

> Pine trees taller than 100 feet could be an issue, since they could be 
> near resonance and lossy - a sad combination when within a wavelength or 
> so of vertically polarized antennas.  If your trees are 50 footers, they 
> would probably not be of concern on 160m, but could be on 80m.  For 
> horizontally polarized antennas, the trees aren't a problem.

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