Folks, I fail to see the advantage of constructing an end fed dipole with coax for half of the antenna - it requires a choke that has a parallel resonant frequency equal to the operating frequency, and the overall length is a half wavelength.
I believe it is much easier to construct a half wave radiating section and make up a parallel resonant circuit using discrete components - wind a wire around some kind of form (PVC, 35mm film container, etc) and tune it to resonance with a capacitor. The transition to 50 ohm coax can be either a link or a tap on the coil. YMMV. My preference for portable operation is a balanced dipole fed with 300 ohm ladder line. The radiator length is not critical - I use 44 feet (22 feet per side) for 40 thru 10m and carry clip-on extensions 22 feet long if I need to cover 80 meters. The feedline attached to the antenna is 25 feet long and I carry an additional 25 foot length of 300 ohm line if the 25 foot length is not sufficient to reach from the antenna to the transmitter. It can be strung as an inverted VEE when there is only one support (I use a 32 ft telescoping pole), or it can be a vertical - string it up alongside the fiberglass pole, or if two supports are available, it can be deployed as a horizontal dipole, or use it as a sloper - just get the wire in the air as high as possible using whatever works best. A switchable 1:1/4:1 balun at the transmitter end of the feedline completes the antenna - use whichever setting provides the best match to the auto-tuner, it will vary depending on the deployment method. There is no "magic" in antennas, the laws of physics cannot be defeated no matter what the antenna manufacturer's advertising hype may say. If you can mount the antenna in the clear and can feed power to it, it will radiate, and it need not be expensive - add up the cost of 44 feet of wire and 50 feet of 300 ohm feedline and compare the result to the price of a constructed (or kit) antenna. 73, Don W3FPR Jim Brown wrote: > On Tue, 3 Mar 2009 00:15:04 -0000, Geoffrey Mackenzie-Kennedy wrote: > > >> If a resonant trap is placed at the bottom end instead of a choke as an >> insulator, >> > > A coaxial choke wound on a ferrite core IS a parallel resonant circuit. > Properly done, the choke should be wound to place the resonant frequency > where the antenna will be operated! Study the references I cited in the > earlier post. > > As to your other suggestions -- yes, this method of feeding opens up many > interesting possibilities! > > 73, > > Jim 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 > ------------------------------------------------------------------------ > > > No virus found in this incoming message. > Checked by AVG - www.avg.com > Version: 8.0.237 / Virus Database: 270.11.5/1979 - Release Date: 03/01/09 > 17:46:00 > > ______________________________________________________________ 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
