At 17:57 2004-12-05, email@example.com wrote:
>Thanks for the Heads Up. Found it
In a cursory reading of K3LC's radial article, I found two data points that
seem counter-intuitive to me.
In general throughout Tables I - IX, for a fixed amount of wire (8000 feet,
say), the "peak gain" determined by EZNEC4 increases monotonically as the soil
quality is varied from "very poor" to "average" to "very good". This seems
reasonable to me, since the soil is effectively in parallel with the sparse
However, this does not appear to be true on 40 meters, where the "peak gain"
figures for 4000 and 8000 feet of wire are worse for the case of average soil
than they are for either very good or very poor soil. According to Tables I -
III, both "very poor" and "very good" soils provide higher peak gain (1.68 and
2.10 dBi, respectively) at 7.15 MHz than does average soil (1.4 dBi) when using
8000 feet of wire. A similar "dip" is reported for the case of 4000 feet of
wire (1.02 and 1.88 versus 0.9 dBi).
I wonder if these are typographical errors or anomalies in the modeling.
Other comments inspired by K3LC's article:
1. One thing that jumped out at me as I scanned Tables I - IX was that,
despite scaling the total wire lengths for the different bands, equivalent
progressions from minimum total wire length to maximum total wire length
resulted in less improvement at lower frequencies. On 40 meters, for instance,
the total variation in calculated peak gain for average soil was 2.89 dB (from
-1.49 dBi for 125 feet of wire to +1.40 dBi for 8000 feet of wire). On 80, the
corresponding total gain variation was 2.37 dB, and on 160, it was only 1.86
2. Two other data points I would like to have seen are the peak gain (in dBi)
for the same antenna model over "perfect" ground and over sea water, so I could
get a sense of how far down in gain EZNEC4 says the article's finite radial
fields are, compared to those two idealized situations.
3. The charts in the article make an excellent case for choosing well when
siting your future vertical, and for determining how "good" your soil is
*before* engaging in a major radial project. Consider 160 meters, for example.
With "very good" soil (Table IX), each doubling of total wire used in the
radial field results in only 0.1 dB improvement in peak gain. In "very poor"
soil (Table VIII), by contrast, each doubling of wire results in about a 2/3 dB
improvement -- more than 6 times as much! But in "very poor" soil, you're
starting from a far worse loss, so it's going to require a whole lot more wire
(and effort) to get comparable peak gain with "very poor" soil. Again
comparing Tables VIII and IX, and extrapolating additional 2/3-dB increments of
improvement for each doubling of radial wire in "very poor" soil, it's going to
take more than 128,000 feet of radial wire for a vertical over "very poor" soil
to have the same peak gain as one with only 500 feet of radial wire over "very
good" soil! Forget the wire cost -- the labor differential is more than 256
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Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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