Posted by
Darrell Bellerive on
Aug 09, 2005; 3:49am
URL: http://elecraft.85.s1.nabble.com/Re-Elecrafts-T-1-tp381070p381077.html
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
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