[TowerTalk] COUNTERPOISE for Dipoles

[K3BU@aol.com]

In a message dated 8/12/2000 5:10:25 PM Eastern Daylight Time, 
w8ji@contesting.com writes:

>Low full wave loops have almost zero gain over a dipole. Any 
>advantage is in the minds of the owner.

Not as NVIS or straight up. Just like dipole, full wave loop adds some 
"stacking gain".

>The reason they have almost no gain is the "focus" the energy by 
>nulling signals slightly on a line through the plane of the loop. 
>Since earth already produces a null at that angle, the loop can not 
>have gain because there is no energy to remove and redirect.    

This is when looking at horizon, and not as discussed for "straight up" 
antennas, which at angles over about 20 degress will beat verticals.

>  Think of the earth as the screen reflector in a dipole backed by a 
>  screen. The better the reflector the more gain because less energy 
>  is turned to heat. When the dipole is close to earth, the reduction 
>  of loss can improve the signal at every angle...not just straight up.
>  

How can we think of "plain" earth as a screen reflector when we are told that 
RF penetrates earth, lower the frequency, more penetration. How is the 
"screen" defined? Thick screen? Variable depth screen? Where is the 
reflection taking place?

By placing radials, resonant dipoles or screen on the surface of earth we 
define the reflection plane and enhance the antenna performance. I used to 
sprinkler the heck out of the ground around the tower before the contest. 
Seemed to help signal. (No "scientific" measurements.)

As team vertical 6Y2A etc. proved, verticals with two elevated and resonant 
radials placed over or next to "perfect" ocean ground are unbeatable. The 
closest inland situation would be to have few elevated radials over ground 
screen (plane, radials, dipoles, salty marsh). That also helps horizontal 
antennas by defining reflection surface, instead of mushy "RF sponge" that 
earth sometimes is.

There are two things that come to play with vertical antennas: the reflective 
"ground screen" and antenna's counterpoise (the other half). By using 
elevated radials over ground screen we take advantage of both and maximize 
the performance of the antenna. 

Yuri, K3BU

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