Topband: FW: Hi-Z Around Trees

[Michael Walker]

For my 80CW and 160 verticals, I have wires suspended through 90 ft tall
evergreens.  I have been doing that for years and I put them in place using
a drone (long before everyone was doing it).

I have radials underneath.  In fact, they are on a common feedpoint.

Based on my 160M or 80M WSPR / JT65 testing, I would be hard pressed to say
that much if any RF is being absorbed by the trees.

In my case, I work with what I have available.  For me, they just work.

Mike va3mw


On Mon, Nov 14, 2016 at 12:54 AM, Lee STRAHAN <k7tjr at msn.com> wrote:

>
>
>   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 at starpower.net<mailto:donovanf at starpower.net> [mailto:
> donovanf at starpower.net]
> Sent: Saturday, November 12, 2016 6:57 PM
> To: jim at audiosystemsgroup.com<mailto:jim at audiosystemsgroup.com>
> Cc: Lee K7TJR; k3lr at k3lr.com<mailto:k3lr at 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
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