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:elecraft-boun...@mailman.qth.net] On Behalf Of Stephen Shearer Sent: Tuesday, March 15, 2016 2:11 PM To: elecraft@mailman.qth.net 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:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
