Hi all,
Some interesting comments on wood and plunging Q of LF coils. It also made
me think about "live wood" and that definitely does have sap. It strongly
suggests that a transmitting antenna should be well clear of trees. For a
vertical, the up-wire is where the current is maximum, and that situation is
similar to a one turn inductor as far as magnetic induction is concerned.
If the wood is also a lossy dielectric, then the top loading wires and
electric fields could also be contributing to losses with trees in the
antenna environment.
In terms of efforts made to maximise radiated power on LF, it would be
unbalanced to focus only on loading coil loss, even if that is more directly
under the control of those making the coil. It would be interesting to find
out for top loading that is tied off to a tree (with suitable insulation,
and in a situation where there are no other practical choices for suspending
the top loading) if there is an optimum spacing of the insulator from the
tree. It may be better to accept moderately lower capacitance for top
loading if the net losses are lower.
73, Bob ZL2CA
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