Topband: Radials, EZNEC and far field

[Jim Brown]

On 12/20/2022 4:25 AM, n4is at comcast.net wrote:
> The assumption that "next to the water" is the same as "in the water" , is a
> not right.  It is not the same !

In this discussion, it's important to realize  that the earth, salt 
water, and radials, serve two functions. Soil in all its forms is a big 
resistor. Radials serve to carry return current for the antenna IN PLACE 
OF LOSSY EARTH (caps added for emphasis). Think of that loss as a 
resistor in series with the antenna, forming a voltage divider with the 
radiation resistance, where loss is the voltage divider ratil. They also 
serve to SHIELD (screen) the field produced by the antenna from the 
lossy earth. Salt water, being an excellent conductor, serves as a very 
low loss return for antenna current, and needs no such screen. All of 
this matters ONLY very close to the antenna, and it only applies to 
vertically polarized antennas.

The second contribution of the earth (including salt water) is in the 
far field, where it produces the reflection from the antenna that forms 
the vertical pattern. The strength of that contribution is directly 
related to the earth's conductivity, which is why salt water is so much 
better than soil. A vertical with its base very close to the water 
produces a very strong and very narrow low angle lobe; if the antenna is 
raised, very strong and very narrow lobes are produced.

The contributions of radials and a counterpoise to ground loss is 
addressed in these slides for a talk I did at Visalia and Pacificon 
about ten years ago. http://k9yc.com/160MPacificon.pdf

I published a modeling study of this about ten years ago. It was written 
for NCJ, but ARRL's graphics department complained about the number of 
graphs (which are crucial to understand it). It's here.

http://k9yc.com/AntennaPlanning.pdf

73, Jim K9YC