At 11:55 AM 8/27/01 +0200, i4jmy@iol.it wrote:
>In the case you slope those wires down near to the ground, it's no
>wonder the system efficiency drops because also the Rr becomes probably
>very comparable with the unavoidable ohmic losses you have (basically
>the ground resistance).
As I said, Mauri, my experience and modeling efforts agree with your
assessment. I think I need to define "short". Some folks seem to think a
short vertical is a couple feet less than a quarter wave. I consider an
short vertical to be less than 1/8 wavelength. Both my modeling exorcises
and my practical "portable" vertical antennas are almost always between
0.093 and 0.065 wavelength in the vertical portion.
>Keeping in mind that with short verticals the current is almost
>constant below the loading device, it's useless to have a longer
>antenna portion below the loading coil if the total current is
>consistently decreased by coil losses.
I have seen this to be true with very short antennas such as used in
mobile-in-motion applications. However, at lengths approaching 1/8 wave,
both modeling and experience have shown center inductor loading to have a
clear advantage over top load and a small advantage over base load.
Thanks & 73,
Larry - W7IUV
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