Thanks, folks, this has been very helpful. In particular, Steve's "wire lengths to avoid" calculator will save me a bunch of time. I've purchased a kite and a bunch more wire, and we'll see how this goes.
On Tue, Mar 15, 2016 at 2:54 PM Ron D'Eau Claire <[email protected]> wrote: > The antenna efficiency drops very quickly when the radiator is made shorter > than 1/4 wavelength or 66' on 80 meters. When end fed the efficiency of a > short radiator is even lower depending upon the "ground" return system. The > RF power is divided between the radiator impedance and the "ground" > impedance, with the most power going to the higher impedance. With a short > radiator such as a 24 foot wire, the radiator may show something in the > order of 10 ohms while a typical "ground" will be in the range of 300 ohms > or more, so less than 5% of the RF power actually goes to the radiator. > Short (<1/4 wave) "counterpoises" may actually show impedances up to 600 > ohms or more, halving again the RF power going to the antenna. > > Note that many Hams have used such systems - a short whip on their back > dragging a single wire on the ground behind hem for pedestrian mobile - > with > considerable success. That just demonstrates how little radiated power is > required under some conditions to make good contacts. So what you > contemplate will certainly work to some extent. > > I have found that the best way to load an electrically short radiator is to > do so at the center. You can think of it as a short radiator and an equal > length counterpoise both up in the clear. Use parallel spaced feeders to > avoid the inherent losses in low-impedance coaxial line. Your tuner will > need to be able to efficiently match quite low impedances in many > situations. The Elecraft tuners use L-networks which are quite efficient > under those conditions, as long as they can find a matching combination of > L > and C. > > Whether it's a stack of full size yagi's on a 90-foot tower or a short wire > thrown into a tree, the compromises are always the same. It's a matter of > doing what you can within the constraints of space, cost and time. The > suggestions offered by Wayne in the Owner's Manuals are what he has found > will work with the ATU with a minimum of effort. Because of space > constraints inside the KX1 its ATU matching ranges are more limited than > the > KX3 or other Elecraft rigs. > > 73, Ron AC7AC > > -----Original Message----- > From: Elecraft [mailto:[email protected]] On Behalf Of > Stephen Shearer > Sent: Tuesday, March 15, 2016 2:11 PM > To: [email protected] > Subject: Re: [Elecraft] Portable 60-80m wire antennas > > I have used a G5RV (+/- 51') with ladder line using teflon 24ga silver > plated wire. > also see http://udel.edu/~mm/ham/randomWire/ ... I am working on a 9:1 > and > looking at the web site, a 70' wire should work fine for 80m... > > 73 steve WB3LGC > > > On 15-Mar-16 12:59 PM, Bruce Nourish wrote: > > Hi folks, > > > > For 40m, 30m, and 20m, the KX1 docs recommend a ~24' length of > > sorta-vertical #24 wire with shorter counterpoises as a good field > antenna. > > I've set that up for my KX1 and KX3, and (unsurprisingly) it works > > well on both. > > > > For 80m, the KX1 docs recommend a resonant antenna, and I'm > > considering my options. Most of what's written out there about low > > band antennas seems to be about durable (and heavy) mobile or home > > installations. Does anyone have any experience they'd like to share with > backpackable lower band antennas? > > > > Options and questions I'm considering include: > > > > * Build a coil big enough to load up my 24' vertical on 80m, with a > > tap for 60m. Will that be a long enough radiator? > > > > * Figure out the kite-vertical thing, fly a wire close enough to l/4 > > that the KX1 can tune it. How bulky would that be? > > > > * Will #24 wire be a decent radiator for the lower bands, or should I > > eat the (not-inconsiderable) weight of a bigger gauge? > > > > * Does anyone have any tips on constructing backpackable (minimum > > weight) coils? What's the smallest wire and lightest insulator? > > > > * I'm planning a vertical, as this would seem to require strictly less > > wire and coils than any dipole or inverted vee, but am I missing some > > other offsetting advantage? > > > > Cheers, > > Bruce > > > ______________________________________________________________ > 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 > Message delivered to [email protected] > ______________________________________________________________ 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 Message delivered to [email protected]
