[TowerTalk] Radial Ends Buried???

[Jim Brown]

On 11/18/2022 12:45 PM, John Langdon wrote:
> If you have really poor soil you could mount
> the vertical on a copper disc with a radius of 1/4 or 1/4 wavelength and it
> still wouldn't radiate as effectively as one with a few radials over
> excellent soil. 

Not quite. Soil conductivity affects signal strength two ways. First, 
with return current in the earth surrounding the antenna, or the field 
coupled to the earth by current in the radials. That's a direct 
subtraction from TX power. The reason that more radials reduces that 
loss is that power is I squared R, and as current divides between more 
radials, I becomes smaller.

The second effect of lossy soil is in the far field, and in the strength 
of the first reflection summing with the direct. We have no control over 
that.

   --
Elevated radials work because they "protect" the antenna
> from the lossy ground.

YES.

> The only reason I can think to put ground rods at the end of radials is to
> spread out a lightning strike over a greater area in rocky soil, 

That doesn't help because the radial is an inductance in series with the 
rod. And it's a TERRIBLE idea, because for current distribution on the 
radial to be ideal, the far end of the radial needs to be open. AND the 
capacitive coupling between radials and earth will lower the impedance 
to earth for a strike, which is NOT a DC event, but rather an RF event, 
because it is a spike of fairly short duration. IEEE studies have shown 
that the energy in lightning is broadly centered in a 2-decade range 
above and below about 1 MHz.
> or perhaps
> to make sure they don't roll up and come in contact with a mower.

Ground staples are a better solution. Many OTs have observed that 
on-ground radials will quickly be overgrown by grass and other growing 
things. I don't have anything approaching a lawn, but I've got lots of 
things coming out of the ground, and radials that have been there for a 
while are pretty hard to find.

73, Jim K9YC