Eddy and others
I am a little unconvinced by some of the arguments that have been presented.
Consider a Yagi in free space with nice copper elements. It would work quite
well if one could find a way to connect the transmitter.
Now consider replacing one of those copper elements with one made out of wood.
Because wood is a poor conductor, very little current would be induced into it
from the driven element, and to all intents and purposes the Yagi would become
one having one less element. The pattern would (probably) be distorted because
of the missing element, but the efficiency of the array would be almost
By extension, keeping all the original elements in place, and introducing an
additional wooden element into the array (even if resonant), would have very
little effect because the current induced into that wooden element would be
negligible. This is a close parallel to having a tree near an antenna.
The question of whether it is good to have an antenna in the middle of a forest
is completely separate. If we put our nice Yagi into a big wooden box, it will
not work so well because there is now a lossy medium through which the wave
must pass. The thicker the walls of the box and the more conductive its
material the greater its effect will be.
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