[TowerTalk] Trees and Verticals

[K1TTT]

I have been trying to stay out of this since you all seem confused enough
and don't really have enough good information to really solve the problem...
and this one just adds to the confusion.  Building the antenna as a tube,
with or without 'enough' wires, is not the answer.  And not because of
fields inside the tube, you have to remember that each tube has 2 ends and
at the ends of the tube there will be very different fields than inside...
so a broomstick or tree sticking through the end fields will see much higher
fields than inside the cylinder.  Break out your copies of Jackson or your
favorite EM Fields and Waves book for this one and start with end and fringe
fields then add lossy dielectrics, its an ugly problem no matter how you
state it.

David Robbins K1TTT
e-mail: mailto:k1ttt at arrl.net
web: http://wiki.k1ttt.net
AR-Cluster node: 145.69MHz or telnet://k1ttt.net


-----Original Message-----
From: Jim Lux [mailto:jimlux at earthlink.net] 
Sent: Wednesday, December 28, 2011 22:43
To: towertalk at contesting.com
Subject: Re: [TowerTalk] Trees and Verticals

On 12/28/11 1:14 PM, Dan Schaaf wrote:
> Let's go a step further,
> What happens if you put a dry wooden broomstick down the center of an 
> aluminum tube vertical.
> Then a wet Broomstick.
>

solid tube is different than a cage o' wires in terms of internal field.

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.



>
>>
>> On 12/28/2011 1:41 PM, Dan Schaaf wrote:
>>> What happens if you make the vertical as a cage of vertical wires 
>>> around the tree ? Joined at the top and joined and fed at the 
>>> bottom. The tree is in the center of the cage.
>>>
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