The technique John describes to significantly reduce the ground losses in
his short 160M verticals is well known by antenna engineers. One of the
best references is IEEE Transactions on Antennas and Propagation,
November 1973, "An Array Technique for Reducing Ground Losses in the HF
Range." This article describes how inefficient vertical radiators can be
arrayed together to improve their net efficiency. The improved efficiency
results from reduced ground losses brought about by the array's lower
ground energy density simply because the total energy is spread over a
larger ground area.
This method is also commonly used to reduce the losses of Beverage
antennas operating in the HF range by arraying three or more closely
spaced Beverages. Three Beverages spaced side-by-side separated by a
distance approximately equal to their height above ground improves the
efficiency by approximately 3 dB compared to a single Beverage for typical
soil conditions.
73
Frank
W3LPL
donovanf@sgate.com
On Wed, 30 Apr 1997, John Kaufmann wrote:
>
> I do indeed drive all three verticals in phase on 160 and switch in base
> loading coils to resonate them on 160. Each vertical by itself has a very
> low feedpoint resistance. With a laboratory grade General Radio impedance
> bridge I have measured the feed resistance (with loading coils in place)
> to be about 7 ohms. Compared to theoretical modeling predictions for my
> antenna over perfect ground with no resistive losses, I infer a loss
> resistance
> (primarily ground and and some loading coil) of around 2-3 ohms. The radial
> system consists of over 100 ground mounted radials per vertical, with most of
> the radials in the range of 60-100 feet long. However, when all 3 verticals
> (spaced 35 feet) are driven in phase, the mutual coupling between the elements
> drives the radiation resistance at each vertical up to around 15-20 ohms
> (which
> is a calculated number and is hard to measure directly). This improves the
> efficiency by making the actual antenna gain less sensitive to loss
> resistance.
> >
> 73, John W1FV
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