On August 8, 2005 07:30 pm, Ron D'Eau Claire wrote: > Many Hams try to use lengths other than 1/2 wave for the radiator and 1/4 > wave for the feeders. When you do that, all bets are off. It's like any > "non-resonant" doublet or end-fed wire. They can work well, but you must > have a matching network that can handle some potentially extreme > impedances. Actually at any but the exact lengths for a proper Zepp, the > feeder will radiate as much as the antenna. That's why non-resonant > antennas fed with open wire line are usually center fed (so-called > doublets). Such center fed arrangements hold decent balance regardless of > frequency.
Even with a center fed multiband doublet, a balun would be presented with an extreme set of impedances. I would suspect that on some bands or frequencies the whole antenna system would be quite inefficient. But as QRPer's have proved it doesn't take much power to make contacts. A 100 watts into an antenna system that is only 5% efficient is still 5 watts ERP. Combine that with an antenna that is long in terms of wavelengths and the nulls and peaks of the lobes will be substantial. Perhaps I am way behind the times, but I still think that a link coupled balanced tuner is the proper way to feed a balanced antenna, whether center fed or end fed. Modern L or T antenna tuners with a balun on the output may be easier and cheaper to build, but just don't seem to be designed for the multiband balanced antennas. -- Darrell Bellerive Amateur Radio Stations VA7TO and VE7CLA Grand Forks, British Columbia, Canada _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
