Topband: Vertical antenna near field efficiency

John Mitchell
Thu, 19 Apr 2001 14:35:46 -0400

Most of the time there seems to be a focus among us upon the angle of
radiation, the effects of the ground immediately under the radial structure,
and the resulting lack of low-angle radiation when few radials are used over
poorly-conducting soil.  A recent posting affirmed the importance of the
(very) low angle radiation gains to be realized over salt water, etc.  Other
sources I've read dispute the need for very low angle radiation on 160M,
citing increased D layer absorption, for one thing.  My sense is that angles
much below 15 degrees or so are probably less important than for the higher
bands, although they cannot be discounted completely.
What I think is working with salt water has more to do with efficiency than
lower angles of radiation.  Simply put, I believe lossy ground (all ground
is lossy to varying degrees) makes in-ground radial systems inherently less
effective than even a simple radial system over salt water.  This also
explains, I believe, why elevated radials work so well; a few elevated
radials placed high enough above the lossy ground equals many, many radials
on the lossy ground.  A ground-plane antenna (resonant elevated
counterpoise) an 1/8th wave above lossy ground seems to equal a maxed-out
in-ground system for many hams.  Certainly some of the strongest signals I
consistently hear are using well-elevated GP type antennas (N5IA, I believe,
qualifies as such, for one).
Maybe we need to re-think conventional wisdom on losses in the radial field.
It never made much sense to me to put miles of wire in the lossy ground,
when I could elevate that system and reduce near-field losses.  I'd like to
hear more experiences from hams who've used elevated systems at least 40
feet above ground and how that might have compared with more traditional
in-ground systems.

73, John  K4IQ

FAQ on WWW:     
Administrative requests: