On Jan 17, 2012, at 10:52 AM, Paul Christensen wrote:
> With top loading for verticals, or end-loading for dipoles, super high
> efficiency can be maintained. I would start by reading Sevick's work as a
> general analysis of shortened antennas, and also study how and why a
> radiator's feedpoint Z, I, and E changes with radiator length.
Paul,
THERE I agree with you because the high current portion (e.g. center portion of
a dipole, or the "effective" quarter wave portion of a vertical) is used as a
radiator. End loading works well because the high current section of a half
wave is still the radiator), but just using the ends of a dipole (e.g. center
loading,etc.) is not nearly as effective.
Shortening a half wave dipole, without end loading, significantly reduces it's
efficiency.
A 70' dipole used on 80m without end loading is much less efficient of a
radiator than the same antenna with end loading. And the simplest way to end
load such an antenna is to add about 30' of wire on each end ;-)
Ken WA8JXM
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