[TowerTalk] modeling compare: 80M, 2EL vs 4SQ

[Erich]

Perhaps a better way to visualize it is that an antenna is a transformer 
between your radio and free space.  That transformer circuit includes 
both the antenna and the ground surrounding it.  Dirt is a relatively 
high dielectric constant, high loss material.  Near the antenna, current 
is fairly high.  Going back to Ohm's Law, P= I^2*R; this means that 
losses in the dirt go as the square of the current.  It makes sense then 
that reducing the losses near the antenna would greatly increase the 
efficiency of the the system.  Metal has low loss compared to dirt, so 
replacing some of that dirt with metal will cut some of the losses.

73, Erich
N6FD, DM15dp

On 3/17/2015 12:49 PM, Joe Subich, W4TV wrote:
>
> On 2015-03-17 2:26 PM, john at kk9a.com wrote:
>> If using elevated radials, I see no point in a buried ground system
>> unless they went well beyond the elevated radials.
>
> It really depends on the degree of screening provided by the elevated
> radials and the distance in wavelengths the elevated radials are above
> the ground.  If the screening is minimal (as is the case with two or
> four radials) and the distance from ground is small (< 1/8 wave), a
> dense ground screen can significantly reduce losses in "bad" soil.
>
> Old studies done for the US military show "losses in the dirt" increase
> at an accelerating rate as the "ground plane" moves below 1/4 wave.
> Even the vertical dipoles (center fed half wave) at WWV had substantial
> ground screens to reduce the losses close to the antennas.
>
> Unless I was prepared to install a radial system that extended .4
> wavelength beyond each element in an array, I would not use fewer than
> 6, preferably 8, elevated radials per element to minimize losses in the
> soil.
>
> 73,
>
>    ... Joe, W4TV
>
>
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