[TowerTalk] How much do trees really affect verticals

[Jim Lux]

On 8/25/14, 10:49 AM, RLVZ--- via TowerTalk wrote:
> Hi Guys,
>
> FWIW, I will share an actual experience where a Ground  Plane Vertical
> located in dense trees worked very poorly.  One of my  favorite Field Day
> antennas over the years has been a simple Hustler 5BTV  vertical elevated 10-20'
> above ground level, and operated with 2 tuned  radials per band.  I've made
> thousands of FD Qso's on 40-10 meters with  this arrangement and often get
> real nice pileups going.   However, a few years back, my son-in-law asked me
> to do FD from his QTH in  Central Illinois, which was surrounded by hundreds
> of trees.  It was like  operating from within a dense forest.  The GP
> Vertical performed very  poorly and operating was a miserable experience as I
> found it very  difficult to makes Qso's, in fact it was more difficult to make
> Qso's than  many of my QRP experiences.  That said, my daughters cooking made
> up  for it!
>
> My personal conclusion is that I love Verticals and won't be  without one
> or more regardless how many Yagi's I have in the air.  But now  I'm a firm
> believer that they need to be located "in the clear".  (just  as many antenna
> books advise)
>
> 73, Dick- K9OM
>
>
> Pin
> Hi, Guys:
>
> My understanding  is that you'd have to put a vertical radiator very close
> to
> a tree for  sap/no-sap to have any impact on the antenna's performance --
> perhaps within a foot of the trunk. Having said that, I know of several
> hams
> who did very well with "disguised, stealth" vertical wires run right  up
> alongside the trunks of substantial pine trees. These gents worked lots  of
> DX with such setups. Of course, YMMV!
>
> 73 and HNY,
>
> Dean,  N6BV
> Senior Assistant Technical Editor, ARRL
> Editor, The ARRL Antenna  Book
> -----Original Message-----
> From: Hallas, Joel W1ZR  [mailto:W1zr at arrl.org]
> Sent: Tuesday, January 02, 2007 12:24 PM
> To:  Larry Banks
> Cc: Straw, Dean, N6BV
> Subject: RE: Dear Doctor: Antennas and  Trees
>
>
> -----------------------------------
> Larry,
>
> I  haven’t seen definitive words on the topic, however I believe trees have
>
> more of an effect for HF signals on vertically polarized signals then on
> horizontally polarized ones. Floyd Koontz, in his Horiz Ewe article in Dec
> 06 QST asserts that sap flow makes a difference and that if the sap drains
> in winter there is less of an effect on signals. This makes some sense,
> although I’m not sure why trees with wide branches wouldn’t have similar
> effect on a horiz component.
>
> I am copying ARRL Antenna Book editor  Dean Straw, N6BV, in case he has any
> thoughts,
>
>


those of you with a bent for modeling can model the trees by making a 
"wire" that is the height of the tree with the right conductivity and 
epsilon.

Most of the tables give an epsilon of 2-3 for wood, but that's for dry 
wood, not a green tree.  Sure, most of the heartwood is dry and only the 
cambium is noticeably sap filled, but that makes it like a big 
conductive tube.   You might use something like 4 or 5 for epsilon and 
see if it makes a difference.

Finding a handy reference in the journal "Tree Physiology" (GIMF)

http://treephys.oxfordjournals.org/content/26/9/1105.full.pdf  is the 
theory (no actual data)
http://treephys.oxfordjournals.org/content/26/9/1113.full.pdf  has 
buried deep inside a resistivity of 85.3 ohm-cm

Then there's this paper which attempts to use electrical methods to 
measure water stress in trees
http://www.agri.gov.il/download/files/ArieNadlerEtAl2008_1.pdf

They give epsilon of 2-6 for stems, and conductivity of somwhere between 
15 mS/m for olive trees up to 70-80 for banana and mango

These measurements are all at DC or low AC frequencies and probably not 
as relevant for RF, but they'd be a starting point.

NEC doesn't really allow for dielectric constant of wires (at least NEC 
2 doesn't.. you could fake it in NEC4 by making an insulated wire), so 
looking just at the resistivity/conductivity.   the LD card, type 5, 
specifies the conductivity of the wire in Siemens/meter, so you could 
just plug in the 0.050 and see what happens.