Topband: Trees And RF

Wed Nov 4 07:37:09 PST 2009

I have no idea. Tree-antenna articles are scarce for sure. I dont have the issue with me, maybe a bunch of termites did. 
Will be good if you give us details on it and  also show how fuzzy my memory is. :o)

David  
HK1KXA
EC5KXA

> Date: Wed, 4 Nov 2009 05:09:24 -0800
> From: phriendly1 at yahoo.com
> Subject: Re: Topband: Trees And RF
> To: topband at contesting.com; hk1kxa at hotmail.com
> 
> April issue? ;o)
> 
> 
> Julius Fazekas
> N2WN
> 
> Tennessee Contest Group
> http://www.k4ro.net/tcg/index.html
> http://groups.google.com/group/tcg1?hl=en
> 
> Tennessee QSO Party
> http://www.tnqp.org/
> 
> Elecraft K2/100 #4455
> Elecraft K3/100 #366
> Elecraft K3/100 #1875
> 
> 
> --- On Wed, 11/4/09, David J. Sourdis <hk1kxa at hotmail.com> wrote:
> 
> > From: David J. Sourdis <hk1kxa at hotmail.com>
> > Subject: Re: Topband: Trees And RF
> > To: topband at contesting.com
> > Date: Wednesday, November 4, 2009, 6:21 AM
> > 
> > I read an article in 73 Magazine about 17+ years ago by a
> > guy who loaded a tree, about 25' (7.62m) high. 3 to 4 meter
> > long and 15 cm (6") diameter shaft  and ovoid shaped
> > leafy top. With a screw driven a couple of inches he made
> > the connection point for his gamma rod. He shunt-fed the
> > tree, and reported mostly vertical polarization even when
> > measuring around the leafy top. I dont recall if he used
> > radials. The man said that he made a few contacts with 100W
> > on 15 or 20m.
> > 
> > I have a group of four palm trees in the backyard, not in a
> > 4-square configuration :o( , abt 18 m (60') high the tallest
> > and 60 cm (24") diameter at the base. With nice and natural
> > capacitive hat. A couple of months ago, I tried to drive one
> > self tapping screw while at the top of a 4m ladder, but the
> > shaft's skin is very hard and the force I had to exert was
> > making the excercise a dangerous stunt. I had to climb down.
> > Palmtree, 1 -  Me, nada. 
> > 
> > I forgot about it until now, maybe I should try a less
> > dangerous and shorter omega match!
> > 
> > 73
> > 
> > David  
> > HK1KXA
> > EC5KXA
> > 
> > 
> > 
> > 
> > > Date: Tue, 3 Nov 2009 23:48:06 -0500
> > > From: n3ox at n3ox.net
> > > To: topband at contesting.com
> > > Subject: Re: Topband: Trees And RF
> > > 
> > > "A quick google on tree antennas gave me this:
> > > http://w5jgv.com/tree_antenna/index.htm
> > which has links to some stuff"
> > > 
> > > I don't buy that that guy is actually loading a
> > tree.... that is, I doubt
> > > he's coupling significant power in and out vs. using
> > the leakage of his air
> > > toroid as a magloop.
> > > 
> > > As far as I can tell, you can actually model a tree
> > trunk, at least,  just
> > > fine in EZNEC.
> > > 
> > > Resistivity of the material in use can be chosen by
> > the user.  The
> > > segmentation guidelines
> > > allow you to build ~100 foot "wires" with diameters of
> > a foot or two no
> > > problem.
> > > 
> > > Resistivity  = 1/conductivity.  Let's assume
> > the conductivity of a tree is
> > > roughly the conductivity of
> > > "good" soil, often quoted as 0.03S/m.  The
> > reciprocal of that is about 33
> > > ohm meters (about 20 billion times worse than copper)
> > > 
> > > For a 90 foot "trunk" two feet in diameter with a
> > resistivity of 33 ohm*m
> > > installed over *perfect* ground, maximum gain is about
> > -27dBi.  The current
> > > distribution is obviously highly modified (tapers much
> > faster)
> > > 
> > > And I think trees aren't even that conductive based on
> > anything I've found.
> > > Maybe a factor of ten less.
> > > 
> > > A tree would have to clock in around saltwater
> > conductivity to start to
> > > become reasonable as an antenna.  This makes it
> > > unlikely to develop much current as a parasitic
> > element.  However, I'd like
> > > to look at details to make sure, because it's not
> > exactly an insulator
> > > either.
> > > 
> > > I understand that most of the time other issues are
> > going to trump tree loss
> > > even if it exists and is important, because it's
> > certainly *small*  But it's
> > > probably worth thinking about occasionally. 
> > Caging trees is a good idea.
> > > Is it necessary if you're trying to squeeze out the
> > last dB?
> > > As far as I can tell the answer is "maybe," so it
> > seems like a discussion
> > > worth having.
> > > 
> > > 73
> > > Dan
> > > _______________________________________________
> > > 160 meters is a serious band, it should be treated
> > with respect. - TF4M
> >     
> >         
> >           
> >   
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> > _______________________________________________
> > 160 meters is a serious band, it should be treated with
> > respect. - TF4M
> > 

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