[TowerTalk] Re: antennas and trees.

[Jim Lux]

----- Original Message -----
From: <john.brewer at us.schneider-electric.com>
To: <towertalk at contesting.com>
Sent: Friday, September 17, 2004 11:05 AM
Subject: [TowerTalk] Re: antennas and trees.
>
>
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
^^^^^^^^^
> It's actually  realistic, not fatalistic
>
> There's way too many variables to make sense of:
>
> Types of trees
> Size of trees
> Number of trees
> Geometry of trees
> Moisture of trees
> Time of year
> etc etc etc...
>
> ...to actually model something that would be useful (in your or my
lifetime, anyway).
>
> In this case one could doodle ones self to death on paper, with the
liklihood of
> not coming up with any useful analytical model,  or break out the
slingshot
> and wire, and get on the air.

True, if you only model for yourself.  If someone were to take on a serious
modeling effort, and cover the variations you've mentioned, AND if they
publish their results in a usable fashion, it would be a noble service to
amateur radio (and, possibly to field expeditions that still rely on HF
radio for comms, although satcom is getting quite reasonably priced for that
application).

The real value of modeling would be to identify those things that don't make
a difference, more than trying to figure out the last tenth of a dB.  For
instance, if you could say, with confidence, that keeping the wire X feet
from a tree makes it immaterial what kind of tree or what time of year, etc,
then that's a useful thing.  Or, that vertically antennas are affected more
or less than horizontal antennas.  I'd love to have some numbers that would
guide me at field day.. Should I hike a bit further, string an extra 200' of
coax to get the antenna really in the clear, or is that real convenient tree
right next to the car good enough?

I have to say that based on my initial quick and dirty models, it kind of
looks like trees are a non-issue for lower frequencies.  However, I'll bet
if you get up into the 20m and up range, it starts to make a bigger
difference, if only because the antenna is smaller, and for the same
radiated power, the fields are stronger close to the antenna.  The trees
also start to be a bigger fraction of a wavelength and things like branches
might have an effect.