The feed point on some of those bands would see a 150:1 swr (no kidding)! Your efficiency would be about 5%. Your tuner would still see a low swr and it will be an easy match because of the tremendous loss in that 100 pounds of coax. Sure you can work stations, with that height you could QSO with a light bulb, but you would be 100 times stronger using ladder line plus you wouldn't need 95 pounds of sand to hold up that lossy dummy load coax. I'm feeding a 200' doublet with ladder line then to a 4:1 current balun next to the K3. The K3's internal tuner finds a match on 160-6 meters and I have very little power loss on any band. Now if I could just find a fertilizer to make my tree grow another 50'!
Steve N4LQ n...@carolina.rr.com ----- Original Message ----- From: "Jim Brown" <j...@audiosystemsgroup.com> To: "Elecraft List" <elecraft@mailman.qth.net> Sent: Wednesday, July 22, 2009 1:03 AM Subject: [Elecraft] Big Coax on Dipoles > On Fri, 17 Jul 2009 09:19:03 +0100, Geoffrey Mackenzie-Kennedy wrote: > >>orgetting about RF performance for a moment, wouldn't the weight of RG-8/ >>RG-213 create a problem unless the antenna is supported at its feedpoint ? > > I have four fan dipoles suspended at 100-120 ft between tall trees > (redwoods), all fed with RG8 or RG11. There is no problem supporting the > big > coax. The keys to success are robust mechanical construction so that you > can > establish high lateral tension. If one of the objects you're suspending > from > is a tree, one end needs a weight and pulley to adjust to wind conditions. > I > use 6.5 gallon water jugs filled with dry sand (roughly 95 pounds), and > the > trees are typically 140-220 ft apart. I use 5/16-inch dual woven poly > rope, > #10 solid copper, and robust insulators. Do they sag? Sure -- at least 10 > ft > on the long dipoles. Does it matter? No. > > One of the side benefits of the big coax is that my 80/40 fans (at right > angles) work quite well on 30M, 17M, 12M, and 6M, thanks to the lower loss > with moderate degrees of mismatch. With relatively litte time on 6M, I've > made nearly two dozen QSOs of more than 2,500 miles with my K3 and one of > those dipoles. > > 73, > > Jim Brown K9YC > > > ______________________________________________________________ > 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
