Topband: FW: Hi-Z Around Trees

[Lee STRAHAN]

  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

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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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