The only caveat I would add is DO NOT end your vertical in the tree. The tree will catch on fire even at the 100 watt level. The voltage potential at the end of a vertical can reach 10,000 volts or more. I have the experience... Instead, attach a U-Bolt with an insulator to extend the vertical another 20 feet or so above the tree. This worked for me. 73 N7RT
----- Original Message ----- From: "Guy Olinger K2AV" <[email protected]> To: "Lew Phelps K6LMP" <[email protected]>; "Elecraft Reflector" <[email protected]> Sent: Sunday, December 19, 2010 6:18 PM Subject: Re: [Elecraft] Semi OT: vertical wire antennas See interspersed. On Sun, Dec 19, 2010 at 7:21 PM, Lew Phelps K6LMP <[email protected]> wrote: > I'm currently running my K3-10 into a 40 meter horizontal loop antenna, > mounted on my roof about 35 feet above ground. It's impractical to use on > 80, and has a very high angle of radiation on 40 and 20 meters. > > So, I'm thinking of replacing it with a 43' wire vertical. Yes, I know it > needs a wide-range tuner, because it's non-resonant on any ham bands. I > already have that. And I know that it needs a 4:1 balun. I can make that. > > I have three questions for the group. > > 1. Is there any reason to expect that a wire vertical will perform > significantly differently than one made from aluminum tube (e.g. 2" OD at > base)? EZNEC modeling shows a slightly lower gain for a wire antenna, but > not significant. Is this borne out in real life? The DX will never know the difference. The succinct reason for aluminum is when the wire has to support itself. With aluminum it is possible to make a self-supporting 43' vertical. This is really important in situations where there are no other suitable means for support. It's a choice based on common sense mechanical issues that relate to your particular back yard. The only performance issue in your design is radials. That will be entirely responsible for wow, or why did I bother. > 2. The available grassy yard space where the antenna would be installed > would permit a maximum straight-line radial run of approximately 30 feet, > well under the desired length of 58 feet for operation on 80 meters. Would > it affect antenna performance if the radials were laid out in a series of > Z jogs rather than in straight lines? Radials are self-terminating. The higher the frequency, the less length actually carries any significant current. Ground radials are NOT resonant devices. Do them straight. Individual radials on/in the ground are severely attenuated by the ground around them, and will exhibit a per wire ground-absorbed resistance of upwards of a hundred ohms each for some kinds of dirt. The secret is to divide that resistance by a large number in parallel so that the COLLECTION of radials APPEARS to be a SMALL resistance to the antenna system. This concept is the huge gorilla in the room. Just about nothing else counts until you deal with this. Use bare wire and notch each one well down into the sod. Keep the angles even. BECAUSE you intend to use this on the higher bands, notch a minimum of 60 bare radials into the sod. The resistance is divided by sixty, and the density NEAR the center is MANDATORY for the higher bands. DO NOT SCRIMP on ground radials. What you do with the radials is about ninety-five percent of the multiband performance. Without this the power loss in the ground around the vertical on the high bands can be astonishing, so much so that lossy ground induction completely controls the impedance and turns a 100 watt transceiver into a QRP rig AND WORSE. This situation is responsible for the old saw that "A vertical radiates equally poorly in all directions." If you don't have the patience or time for this, don't do radials on/in the ground. Ground radials are a special case with brutal penalties for partial implementations. What those buried bare radials have going for them though, is once sufficient numbers are notched into the ground under the sod, and the grass has recovered and been mowed a couple of times, you have the best you can do, and they are completely invisible. > 3. The antenna would be suspended from a large sycamore tree. Will it make > any difference in performance if I run the vertical right up the side of > the trunk, as contrasted with suspending it from a limb at some distance > (e.g. 5 - 10 feet) from the trunk? How much loss tacking a wire to a tree trunk will give you is controversial. But there is no point in tempting all the physics in that unresolved question. It may vary by species of tree and time of year. Just don't go there unless you have to. Pulling a vertical wire up through a tree, ten feet or more from the trunk, has been a wonderful stealth vertical in developments. What that has going for it is that a radial center out ten or 15 feet from a trunk will allow the radials to be kept even and still pass around the tree. It is important on the high bands to have a dense uniform center coverage of the radials without any gaps. 73, Guy. > > Thanks, > > Lew K6LMP > > > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[email protected] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
