Just to restate the obvious: Do not make the radials resonant on any of the operating frequencies. Doing so causes high current in the radials and you end up with a *very low *horizontally polarized radiator.
73, Tom (K7ZZ) On Fri, Jun 17, 2011 at 10:28 AM, Ron D'Eau Claire <r...@cobi.biz> wrote: > John, as a general rule I try to get at least 1/4 wavelength of radiator > up. > That's not always practical but it's worth striving for since below 1/4 > wavelength the feed point impedance and so the efficiency drops very > quickly. > > If you are working against a counterpoise, something close to 1/2 wave is > ideal since it raises the impedance is highest at the length. However, the > impedance can easily rise above that which the tuner can match. > > An easy way to adjust the length of the antenna is to loop the wire through > an insulator that is up as high as possible (at times I have used some > monofilament fishing line with a loop through which the loop of lightweight > antenna wire passed). Now, depending upon the amount of sag allowed, I can > adjust the length by simply letting out or pulling in the radiator wire. > The > RF sees the folded back-wire as simply a thicker single wire since the RF > field passes over wire, not through it. That adjustment is often enough to > move the feed point impedance to something the tuner can handle. > > A 1/4 wavelength counterpoise is ideal since it minimizes the RF voltage at > the rig. For that reason, it's good to avoid 1/2 wavelength counterpoise > since that puts a voltage maximum at the rig. > > A "random wire" antenna like this with one "counterpoise" wire is really > just an off center fed radiator. The counterpoise and radiator are one RF > circuit. The advantage is you only need one elevated point. The > disadvantage > is that the counterpoise also radiates but it only "warms the worms" Hi! > So, > whenever possible I try to get both wires up into the air with at least a > 90-degree angle between them (so the RF fields won't tend to cancel each > other) even though one wire might be a lot longer than the other. > > Ron AC7AC > > > > -----Original Message----- > From: elecraft-boun...@mailman.qth.net > [mailto:elecraft-boun...@mailman.qth.net] On Behalf Of John Shadle > Sent: Friday, June 17, 2011 7:20 AM > To: elecraft@mailman.qth.net > Subject: [Elecraft] [K2] wire antenna lengths for portable operations > > I'm headed up to KL7-land next week and am going to take the K2 with > me. I was thinking about using the KAT2 to tune a wire attached to the > BL2 (at the 1:1 setting). > > Probably going to cut some teflon-coated wire this evening and pack it > away in the bag. > > I'm seeking input on the best lengths of wire to cut for the active > part of the antenna as well as the counterpoise. > > If you have any other comments on this setup, I'd love to hear them, > too. In the past, I've used the K2 attached to my homebrew vertical > (SGC SG-239 at the base of a elevated ground plane vertical), so this > is my first adventure with "random wire" antennas. > > Thanks! > -john W4PAH > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:Elecraft@mailman.qth.net > > 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:Elecraft@mailman.qth.net > > 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:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
