>I noticed you said you ran your vertical up the trunk of
>a tree. How did it work?? what was the input "z"
>like. Sounds to good to be true to me . :o)
It worked like every other vertical: poorly in comparison with a
horizontal antenna at the same height, except for local-area
I researched the topic of tree conductivity a few years ago, and
received much useful info from subscribers of the PROP-LIST (for
info, send an email to <email@example.com> with
just the word 'help' in the message body). One of them, I believe
George Hagn, had measured the conductance of living tree trunks, and
had even used them as vertical antennas -- _without_ running wires up
their trunks. No, I'm not joking.
He did this with very large, very tall trees in Southeast Asia --
Thailand, IIRC. Depending on where you live, YMMV.
He used two methods of matching 50-ohm coax to a tree trunk. The
simpler method was to drive large nails into the trunk, one nail at
ground level and another nail vertically above it by some distance.
The coax is connected directly to the nails. The load impedance that
you see increases with increasing distance between the nails. I
guess this is a form of shunt feeding, or beta-matching. I imagine
that you'd have to cancel the inductive part of the load impedance
with a series capacitor, as you do when you feed a metal tower.
The other method was nicer because it was non-invasive. He
constructed a very large toroidal coil of wire, like the winding on a
ferrite toroid, except with no ferrite (just air), and much larger.
I believe he constructed a skeletal coil form of lightweight wood or
bamboo. The axis of rotation of this toroid was vertical and
coincided with the axis of the tree trunk. In other words the toroid
formed a ring around the tree.
The toroidal wire winding was the primary of a step-down transformer.
The tree trunk was the secondary. I imagine that this transformer
would have a large leakage inductance that you'd have to tune out
with a series capacitor.
If you have NEC-4 you could simulate this system pretty well, so you
could get it to work and to present a 50-ohm resistive load to your
feedline relatively easily without much cut-and-try.
Although I have NEC-4 I have not simulated this system, so I can't
supply design data and I can't tell you how lossy the antenna would
be. I did simulate the 55-foot White Pine trees that support the
ends of my present station antenna, which is a wire doublet, mostly
horizontal but with 5 m hanging vertically at each end. I wanted to
know how how much power would be dissipated in the trees by currents
induced in them by the nearby wires, especially by the vertical
wires, which carry substantial currents when the antenna is excited
on the high HF bands. I forget the answer, but I recall that I
decided that just a few feet of horizontal separation of the vertical
wire from the tree trunk was enough to reduce the dissipation to a
If you can get a wire high enough in the tree, then the wire will
work better as an antenna than the tree by itself; and the antenna
will work better if you can get the wire horizontal and feed it at
its center. But if you have a healthy 150-ft. tree in your yard and
absolutely no way of reaching even its lowest branches, then you
might try exciting it as a top-loaded vertical for 160 meters. :-)
73 -Chuck, W1HIS