The amount of RF energy absorbed by a supporting or nearby tree is
controversial. There is no accepted defining work on the RF loss effects of
forest around a vertical, and some minor work was unable to adjust for
micro-local changes in ground conductivity around the trees.
Some interesting anecdotal-level experiments that suggest that there is no
great loss. W8JI once took a one foot by three foot section of green tree
trunk and measured its RF resistance in the long direction. It was in the
K-ohms, which would not support any significant current. Note that K-ohms is
what we consider a good block for common mode current on coax shield.
Intuitively once the sap is down, most water in a trunk is trapped in cells,
and that water is never salty.
Though wet wood is not a good thing to use for a HV insulator at the end of
a conductor with HV RF on it, neither is it conductive enough (in the tens
of ohms) to allow enough current to produce significant loss.
If one ran a wire up a tree tacked down to the bark or held to within an
inch of bark by some device, then dielectric loss would clearly be involved.
There is no reasearch money out there screaming for the answers to these
questions and most hams have day jobs. Careful definitive work to answer
these questions is suprisingly difficult and drawn out, with enormous
variations in weather, soil, etc to work out. One is easily talking about
tens of thousands of measurements taken in hundreds of locations with many
species of trees over several years, and some very careful definitions and
methods established up front with experienced researchers.
If the research was NOT done with the kind of peer review and oversight
attendant a PhD dissertation, it probably would not definitively serve the
amateur community. We have enough unvalidated opinions (however sincerely
held) and over-simplifications in the ether to suffice as jist for reflector
arguments.
As to whether the top 10-20% of a 160 meter vertical is bent, I defy anyone
to detect such a difference at the RX end. if nothing else, the percentage
of RF radiated from a given section of wire is proportional to the current
density in the section as a percentage of the summation of all current. How
much current flows at the end parts of a wire antenna?
Having great TX signals with amps and big TX antennas with dink RX is a
problem associated with too-high levels of testosterone.
If I were Lew, unless he's clearly maxed out on RX and done all he can do,
I'd set pat on those TX antennas and concentrate on RX antennas. On 160 it
is often reported that there are people hearing our CQ's and calling that we
are not hearing, that's WE'RE NOT HEARING.
The real secret to top band is being the guy who can always hear and work
the QRP ops.
Regards to all, and luck on top band this fall,
Guy, K2AV
On Tue, Nov 3, 2009 at 4:38 AM, DAVID CUTHBERT <telegrapher9@gmail.com>wrote:
> Lew,
>
> I'm thinking that the close spacing between each tree and each vertical is
> absorbing a significant amount of signal. How much I don't know.
>
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160 meters is a serious band, it should be treated with respect. - TF4M
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