[Elecraft] OT: Ground Loss (long)

[Don Wilhelm]

Near field soil conditions become less of a factor with the use of 
elevated radials.  Consider a "ground plane antenna" with the base 
mounted at the rooftop of a 1 or 2 story building - it is reasonably 
independent of near field ground conditions because it is an antenna 
within itself - much the same as a vertical dipole.  A vertical with 
buried radials is quite dependent on ground conductivity unless the 
number of radials is large.

The far field ground conditions still do play a part and what Jim has 
pointed out below is valid.

IMHO, the main advantage of a vertical is that it has a null at the top 
of the elevation plots which will reduce the response to high angle 
reception (nearby stations).  If you look at the elevation plot for a 
horizontal dipole along with a vertical, you will see that the dipole 
has almost as much gain at low angles as the vertical - so from a pure 
gain standpoint, the vertical offers no advantage.
BUT that is comparing a vertical with a high dipole (at least 1/2 
wavelength high).  For the lower frequency bands, the height of a dipole 
with those characteristics is not practical for most hams and the 
vertical wins "hands down" for DX - provided a good radial field or 
elevated radials are used.

73,
Don W3FPR

On 7/23/2015 11:10 AM, Jim Brown wrote:
> On Wed,7/22/2015 6:15 PM, Al Lorona wrote:
>> This suggests that ground loss is sort of an impedance-matching 
>> problem. Clearly, as your ground gets really bad your antenna can 
>> still work just fine, even better in some cases!
>
> Hi Al,
>
> Several observations. First, soil influences vertically polarized 
> antennas in two ways.
>
> First, loss in the soil near the antenna as the field from the antenna 
> causes current flow in the ground. The result is simple I squared R 
> loss, and that power does not get radiated.
>
> Second is the reflection from the earth in the far field where the 
> radiated field hits it. That reflection adds (algebraically) to the 
> direct signal to form the vertical pattern. The strength of the 
> combined direct signal plus reflected signal depends on the relative 
> phase angle between them, which in turn is a factor of distance, the 
> elevation angle, and the soil.
>
> The second point is that conductivity is not the only soil parameter.  
> There is also the dielectric constant. In EZNEC, if you open the 
> Ground Description tab and right click on either Cond or Diel Const, 
> you'll get a window showing a continuum of soil types from very good 
> to very poor. BOTH Cond and Diel Const vary with those soil types, and 
> both quantities affect how the antenna behaves.
>
> A year or two ago, I did an extensive study of the interaction of 
> vertically polarized antennas with soil of different types and at 
> different mounting heights. I presented it to the Pacificon Antenna 
> Forum using these slides. http://k9yc.com/VerticalHeight.pdf
>
> 73, Jim K9YC
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