> 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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