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 <[email protected]> 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: [email protected]<mailto:[email protected]> [mailto: > [email protected]] > Sent: Saturday, November 12, 2016 6:57 PM > To: [email protected]<mailto:[email protected]> > Cc: Lee K7TJR; [email protected]<mailto:[email protected]>; 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 > _________________ Topband Reflector Archives - http://www.contesting.com/_topband
