Topband: Effect of Trees

[Mark Lunday, WD4ELG]

Mike

Although I am an antenna enthusiast and EE by training, I am not expert on
this topic...however, I have been doing some reading.  IEEE did some
research at VHF freqs
http://ieeexplore.ieee.org/Xplore/login.jsp?url=/iel5/74/17390/00801512.pdf?
arnumber=801512 

And there are other papers out there on foliage attenuation
http://www.radyn.com/Papers/gmc/Foliage_Attenuation.pdf

I also came across a government study which had some test results which
indicate that trees can be a factor.
 
http://stinet.dtic.mil/oai/oai?&verb=getRecord&metadataPrefix=html&identifie
r=AD0484239

Some notes on other discussion groups indicated that northerly climates
where sap in pine trees impacts signals in winter because the sap stays in
the tree due to the cold...and in warmer climes it will have less of an
effect because the sap tends to drain in the winter.  

My limited empirical evidence on this topic comes from attaching my Cushcaft
40/80 vert to a bradford pear tree, nestled among several oaks and pines,
after I first wrapped the vertical in black electrical tape from top to
bottom (it is VERY stealthy!).  4 radials for 80, 4 for 40.  Soil is moist
clay in the piedmont of North Carolina. Works great on 40 (lots of good DX).
But on 80, it's marginal for 80 meters with 100 watts, but I have had some
good success on 80 CW.  Not great, but I am up to 78 worked...and with no
towering trees for a dipole, this is the best I can do from this QTH.

Based upon my reading of authoritative texts like ON4UN's book and the
elmers/gurus on this discussion list...it is my opinion that radials (or
lack thereof) will have a much greater impact on a vertical antenna than the
trees which we are discussing.  Given that you have indicated a
less-than-optimum radial setup (and I feel your pain), that is most likely
the reason for the disappointing performance.


Mark Lunday
WD4ELG
wd4elg at arrl.net