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## [TowerTalk] Breaking up guy wires for nonresonance

 To: [TowerTalk] Breaking up guy wires for nonresonance k2av@contesting.com (Guy Olinger, K2AV) Thu, 7 Jun 2001 23:33:37 -0400
 ```Ken blends a number of things together in his post. Let's separate them out: Proportions are at issue. Most of the time I have seen a tribander and a two meter 10 element or some such up together, the two meter job has been five, six, ten feet above the tribander. This is like 50 or 100 feet separation on HF. The elements near the 2m driven element are something like ten, twelve inches apart. The interactions between the 2m elements have the time (space) to form before the tribander below comes into play. To keep it analogous or proportional with the HF problem, IF you put that 2m beam inline with the tribander boom, only five inches above it, you WOULD get notable interaction, because one of the elements of the tribander is JUST AS TIGHTLY COUPLED into the 2m beam as its other elements. In the case of an 8JK, both elements are driven and create PRIMARY areas of partial cancellation IN THE NEAR FIELD. None such happens with a yagi. The primary radiation from the driven element is like a dipole. Only hole is off the ends. In the case of an HF triband or monoband yagi (what most people on this reflector are talking about) at the top of a tower with guy wires to within a few feet of top, the guy wire is right smack in the dense part of the near field, CAN have significant current on it, CAN distort the pattern. Put it in the model. It doesn't radiate only when it serendipitously just happens to balance out by some happy aspect of the instant orientation of the yagi elements and the length and orientation of the guy wire. From there rotate the yagi a bit and you're back into interaction. Or don't rotate it and see how much is radiating off the other two guys. On HF that upper guy is just like a snake in your pant leg. Plenty close enough to cause trouble. Best not ignore it. 73 ----------------- Guy Olinger Apex, NC, USA ----- Original Message ----- From: To: ; Sent: Thursday, June 07, 2001 7:00 PM Subject: Re: [TowerTalk] Breaking up guy wires for nonresonance > In a message dated 6/7/01 12:49:46 PM Pacific Daylight Time, > k2av@contesting.com writes: > >> Further more beams have a vertical directive pattern that points > >> straight ahead. Therefore the pattern component pointing down at > guy wires is greatly attenuated and any reflected RF is attenuated > again back > >>toward the beam. The higher the gain of the beam the more isolated the > beam > is from surrounding objects to the side/back and below. It just doesn't > see > >> them. > >OK so far. > Actually, NOT ok. > > The typical image we form in our mind of a beams pattern is a FAR FIELD > pattern, that is to say when we are far enough away from the beam that > the sum of the radiations from the beam to the observer has > significantly converged toward a point source in appearance. > > The really destructive interactions are very much in the NEAR FIELD. The > intuitive pattern image does not apply. In order to figure out what is > going on, you have to consider such things as guy wires or any close > metal AS PART OF THE ANTENNA. Rather simple modeling applies well here, > just make sure that the model contains all the metal. None of the issues > that make it tricky are in force. Just a bunch of wires interacting with > each other. > > For each individual wire, the model will figure out the interaction with > EVERY OTHER wire and then add up the resultant vectors. Most of the > antenna modelers will either display or report the resultant currents on > each of the wires in the model. That's when you find out a bunch of > NON-INTUITIVE aspects about guy wires underneath a beam. > > There is an intuitive way to remember that near field stuff is > different. Ken's idea above incorrectly depended on all of the > interactions between driven element, reflectors and directors having > ALREADY been formed before the guy wire came into play. This obviously > is true in the far field. HOWEVER, energy from the yagi DE is going to > reach the guy wire in roughly the same or less time as it does the other > elements, and CERTAINLY before RE-radiation from the other elements has > reached the guy wire. The guy wire has PRIMARY radiation from the DE and > must be considered as part of the antenna. > > Far field considerations are a SUBSET (remnant) of the rules in the near > field. The published ARRL non-resonant lengths were invented without > benefit of computer based complete near field analysis, and have > perpetuated a myth ever since. > 73 > Guy Olinger > Apex, NC, USA > >> > Guy: You have some good points but as I suggested in my post -- take a 3 > element and a 11 element 2M beam connected to a MFJ SWR Anlyizer and hold it > next (really near field) to a variety of metal objects and you will see the > "extra isolation" the 11 element beam has on the SWR and therefore the free > space pattern. Put in a W8JK in Eznec and see how little affect other > parasitic elements have on it's pattern compared to regular yagis. Those 2 > elements are "so tightly coupled to each other'' they see far less of other > parasitic elements-even in it's major lobes. It literally doesn't see > anything above or below it. What I said was not only "intuitive" but based > on "actual live beam tests and in Eznec". I suggest you get yourself a > Palomar RF Current Meter and run some tests. I assume you have the MFJ. > "One test is Worth 1000 Opinions" (Old K7GCO Axiom) > > List Sponsor: Are you thinking about installing a tower this summer? Call us > for information on our fabulous Trylon Titan self-supporting towers - up to > 96-feet for less than \$2000! at 888-833-3104 > www.ChampionRadio.com > > ----- > FAQ on WWW: http://www.contesting.com/FAQ/towertalk > Submissions: towertalk@contesting.com > Administrative requests: towertalk-REQUEST@contesting.com > Problems: owner-towertalk@contesting.com > > List Sponsor: Are you thinking about installing a tower this summer? Call us for information on our fabulous Trylon Titan self-supporting towers - up to 96-feet for less than \$2000! at 888-833-3104 www.ChampionRadio.com ----- FAQ on WWW: http://www.contesting.com/FAQ/towertalk Submissions: towertalk@contesting.com Administrative requests: towertalk-REQUEST@contesting.com Problems: owner-towertalk@contesting.com ```
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