Tom makes a very good point, perhaps, but widely missed the point of my
comments.
I made absolutely no assertion that my 160 feed point impedance had anything
at all to do with the antenna efficiency. The careful observer will note
that I only compared 3 radial Z with 4 radial Z, noted no significant
change, and CHOSE to infer that performance changed in accordance with Z.
Whether that's good physics WRT radiation efficiency is quite another
debate.
Again, I can only report that it works really really well in the pilepus.
73 Art K6XT
---------------------------------------------------
To: <topband@contesting.com>
Date: Mon, 16 Mar 1998 22:15:17 +0000
From: Tom Rauch <10eesfams2mi@mail20.MCIONE.com>
Subject: TopBand: Feedpoint impedance vs efficiency
To: <topband@contesting.com>
> Date: Mon, 16 Mar 1998 09:03:53 -0800
> The feed impedance altered !microscopically! with the change from 3 to 4 -
> barely visible, no change to tuning settings - so I infer that the
> performance changed in a similar way.
Hi Art and others,
Actually feedpoint impedance is often a very unreliable (or often
completely misleading) indicator of efficiency.
Even if a noticeable base impedance change is NOT observed,
efficiency can still be changing. Without measuring FS in the far
field, we have no idea what portion of the energy is being lost.
It's quite possible and common to install a ground system that causes
a vertical to have a very low base impedance, and yet provides
very poor efficiency. Inductor loaded resonant radials are one
example.
73, Tom W8JI
w8ji.tom@MCIONE.com
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