[TowerTalk] Trees and Verticals

[Jim Brown]

On 12/28/2011 2:42 PM, Jim Lux wrote:
> At some point, though, if you have enough wires, the cage will be
> identical to the tube.
>
> I'd say off the cuff that when the spacing between wires is smaller than
> the distance to the tree (or broomstick) inside  the cylinder, you can
> start to ignore what's in the middle.

Jim -- one of the variables in this antenna is the current distribution 
within the live tree, which will depend on the distribution of moisture 
within the tree. The significance of this is the relationship between 
the effective electrical diameter of the tree and this wire cage (that 
is, the spacing between the wires and the "tree" as an electrical 
element).  The next question, of course, is what's that distribution and 
what's the effective diameter?

As a sanity check for those who don't know what to believe in this 
discussion, I would like to observe that Jim Lux is an EE working at JPL 
(that is, Jet Propulsion Lab, our space program), and both he and I are 
contributors to the ARRL Handbook. Notice also that Jim responded that 
Dave, AB7E, had correctly and very clearly articulated the fundamentals 
of this problem in his "three point" post.  It's also worth re-reading 
some of Jim's other posts in this thread, where he's citing some of the 
research that has been published on this topic.

73, Jim K9YC