Topband: Tree conductivity

[Tom W8JI]

> Some time ago I attempted to make direct measurements of the HF 
> conductivity of trees, at least for the trunk and limbs.  I simply put a 
> two rings, with nails to penetrate through the bark, around the trunk 
> spaced a couple of feet apart.  Basically what I had was a resistor.  I 
> then measured the impedance of this "resistor" using a network analyzer.
>

I think there is some confusion caused by  conversations on this reflector 
about **resonance**,  and conversations about attenuation.

I think there are some people who believe the issue is resonance and think a 
tree has enough conductivity to exhibit resonance effects. I've never seen 
any documentation or experiment to support a tree exhibiting resonant 
effects (at least for HF and VHF).

There isn't much doubt dielectric losses would play a role.

Years ago, because of some "fractal tree antenna" nonsense discussion, I 
measured a fresh cut pine tree log and it had pretty high RF resistance over 
a foot of trunk length. The resistance was high enough that a single tree 
could not show resonance effects. I did a sweetgum later, when I had to 
remove a sweetgum. It was similar.

This is different than attenuation by having either a strong electric field 
near a single tree's foliage, or attenuation through thick foliage.

Another place where this comes into play is with seawater. Another goofy 
thing appeared where someone was claiming a vertical jet of seawater could 
be used to make a good stealth antenna. We all know seawater has a profound 
effect and enhancement on patterns and loss, yet the resistivity of sea 
water is so high it really makes no antenna at all when used as an antenna. 
As a matter of fact, saltwater makes a pretty good dummy load when current 
density is high. Current would be high if seawater were used as an antenna 
conductor.

What we have is an inability to understand the difference between very good 
conductors, poor conductors,  and or lossy dielectrics. We'd have a 
difficult time powering something through saltwater conductors, or having 
resonance effects with saltwater jets at low frequencies. At the same time, 
even crummy soil has a profound effect on EM fields and other things when 
cross sectional area is large enough.

There is a danger that people will not understand the big picture, and write 
more seawater antenna or tree antenna articles.

73 Tom