Pete, N4ZR wrote:
"Also, in his recent series in NCJ, W4RNL went extensively into this
using NEC-4, which can accurately model buried radials. I remember being
surprised by his results; while radials could help, and certain radial
configurations offered the most return for effort, in the final analysis
his modeling seemed to show that inherently good ground characteristics
offered more benefit than the most extensive radial system."
==========
I can verify W4RNL's findings.
When I first used a series-fed balloon-supported quarter wave vertical
with four on-ground 125-foot radials at my dry salt lake 160-meter
contest location (which has soil conductivity better than sea water), I
measured the input impedance of the antenna at resonance to be 38+j0 ohms
(as measured by an Autek analyzer). With a perfect ground system, a
quarter-wave vertical is supposed to 36+j0 ohms, therefore I assume that
the ground resistance in my case was only two ohms for an antenna
efficiency of ~95%. The antenna performs extremely well as evidenced by
contest results.
Over "average" ground with only four quarter-wave radials, the ground
resistance would be over 20 ohms (as estimated from Table 9-1 in ON4UN's
book), with an efficiency of only ~65%.
The moral of the story is: The poorer the ground, the more radials you
need.
73, de Earl, K6SE
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