> March/April 2005 National Contest Journal has
> the last part of a two-part article by K3LC. He used
> Eznec Pro 4.0 with a double precision NEC-4
> calculating engine. Much much data, but here's
> a simplified conclusion:
...etc. de W4ZV
____________
The K3LC article has valuable comparison data, but we need to consider a
significant variable in his modeling process. I have found Al's work very
interesting and useful over the years, so this is just nit-picking...
The entire vertical + radial system is elevated for modeling at different
heights -- meaning that the 160M vertical with buried radials is approx. 135
feet tall, while the vertical with radials elevated 60 feet has the top at
195 feet. For a 0.5 dB improvement (over very good soil), the cost/benefit
ratio for a tower that is 44% taller may not be acceptable to many of us.
There are two other important parts of his data -- the first is curve of
gain vs. number of buried radials, which confirms other reports that you
need around 60 radials to get close to maximum gain, and more radials will
improve performance, but at a smaller rate of return.
The other interesting result is the spread between maximum and minimum gain.
With average soil, the total gain variation from the low point (4 elev.
radials at 10 ft. or about 24 buried radials) to the high point (120 buried
radials) is less than 0.5 dB. Whether this number is correct is a subject
for an extensive measurement study rather than more modeling, but it does
lend credence to claims of competitive performance with a relatively small
number of buried/on-ground radials or a few elevated radials at relatively
low height.
Thanks to K3LC for the data, and thanks to W4ZV for bringing the discussion
to the Topband reflector.
73, Gary
K9AY
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