RE: NEC-LIST: Resistance of Trees

Duncan:

I have made use of trees as antennas, as long ago as 1967 in Thailand. They work! I shunt fed a single isolated tree with what could be viewed as half of a delta match. I drove in nails at 6-inch intervals deep enough to penetrate the cambium layer. I then attached a lead from the center pin of a coas to each nail in turn and measured the input impedance at my frequency of interest (about 7 MHz as I recall). The shield of the coax was grounded about 3 ft from the tree. I found the "50-ohm nail", tuned up my Collins KWM-2, and passed my grocery list to an operator in Bangkok (about 300 km to the north). My conclusion was that trees work, but not as good as wire.

My friend, Dr. Kurt Ikrath, berated me for injuring the tree with the nails, and he came up with the inductive coupling loop that he called the HEMAC. Indeed, he claimed that the internal resistance of the tree was increased by my nails, but not by his coupling loop.

But I dont entirely understand your question about tree resistance. I have some data on the conductivity of tree sap, in S/m, that I measured in Thailand. I have also measured the DC resistance of trees in my front yard
between two nails into the tree. In the latter case, the resistance depends on the nail spacing.

If you can be more specific, maybe I can give you some numbers. Of course, that implies that I can find my old data!

Regards,

George

Original Message:
-----------------
From: Prof Duncan Baker dbaker_at_postino.up.ac.za
Date: Wed, 06 Jun 2001 15:34:31 +0200
To: nec-list_at_gweep.ca
Subject: NEC-LIST: Resistance of Trees

Good day all.

I have received a query concerning the electrical resistance of
trees. I know there have been some articles on using trees as
antennas, and may be able to track down at least one of them.
However, sticking a loop around a tree to feed it as an antenna is
somewhat different from knowing the electrical resistance.

Can anyone out there give me suitable reference?

Best regards,
Duncan.

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Prof. Duncan C. Baker (Pr. Eng., FIEEE, FSAIEE, Sci. Nat.)
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