Greetings Top-Banders, I have been away for a couple days, sorry for the late
comments.
The fact is, for me there is no definitive answer to the effect of trees on
the Hi-Z arrays. I have made tests measuring phase shifts and amplitude changes
with a variety of objects around these elements. My original thoughts after the
tests were that any tree or large foliage would have to a minimum of 5 feet
distance from the elements. There are not many trees where I live so this sort
of test is very difficult. One of the things I did was to measure the
capacitance of the elements as a source impedance to the amps. Changes in this
capacitance would make amplitude changes at the amplifiers. The only real
changes I measured after numerous tests were when I would approach the element
with the capacitance meter in operation. When a 6 foot person approached the
elements I could see changes in the element at about 3 feet separation. Nothing
at 5 feet. This was with a 24 foot aluminum element and a low capacity mounting
insulator. This capacitance test was more sensitive than my voltage and phase
measurements.
Mike NI7T installed a 4 square system in the forest behind his cabin. Many
pine and redwood trees were within 5 feet of the elements. We were never able
to discern any negative affects to his array. Front to back rejection was well
within nominal and front patterns seemed proper. The array remained sensitive
to weak signals. Larry K1UO had his array in a brush patch. As I recall I
suggested a 5 foot spacing which he did. If you have not seen the DX Larry
posts from Maine you are missing something. In other words it was apparently
adequate spacing.
So with the 24 foot elements ¾ inch diameter that have around a 75pf source
capacitance I would say you are pretty safe at 5 feet. Shorter elements with
significantly less source capacitance would surely need more spacing. A 12 foot
similar element drops clear down to 42pf source capacitance. I would hazard a
guess that arrays using short whip elements at around 25pf would be quite
sensitive to close trees or foliage.
Barring all this I am confident you would be absolutely safe in my
estimation at 10 feet distance of brush, tall foliage, and trees from the
elements.
Lee K7TJR
>>Hello Jim
My HI-Z 4 square has trees about 15 feet away from two of the elements (I can
make exact distance measurements if that would help you).
I do not "think" the trees interact in my setup - but I am not 100% sure. Even
my HI-Z 8 circle has trees pretty close to 3 elements (10 feet). Without
measuring changes (impedance) to these elements due to location, I am not sure
how else to know. However, given Frank's comments - I will be trimming some
trees today!
I am certain K7TJR is the expert on this has he has heard from users about
element location and performance for years.
I wish you the best.
73
Tim K3LR
________________________________
From: donovanf@starpower.net<mailto:donovanf@starpower.net>
[mailto:donovanf@starpower.net]
Sent: Saturday, November 12, 2016 6:57 PM
To: jim@audiosystemsgroup.com<mailto:jim@audiosystemsgroup.com>
Cc: Lee K7TJR; k3lr@k3lr.com<mailto:k3lr@k3lr.com>; Joel Harrison
Subject: Re: Hi-Z Around Trees
Hi Jim,
My comments about short verticals not performing well near trees
applies only to high impedance verticals. Low impedance are
little affected.
73
Frank
W3LPL
________________________________
_________________
Topband Reflector Archives - http://www.contesting.com/_topband
|