[TowerTalk] Raised Radial Spacing

[Jim Lux]

As noted in another email, radials buried, on, or near the ground are likely not identical, (different soil properties if nothing else, but also “other stuff near by”, unless you’re out in flat farmland that is very uniform. 

But the point that Jim makes is valid nonetheless - more radials is better, especially short ones.  Close to the antenna is  where the current density is highest, and what radials essentially do is make your soil “more conductive”.

Turns out, the radials don’t even have to be connected to anything to still make a difference.  They still reduce the ohmic loss of the soil.   

Let’s take a practical example: Let’s say we’re looking at a 1 meter cube of soil with 0.005 S/m conductivity.

The resistance of that cube is R = length/Area * 1/0.005 -> I’ve chosen 1 meter cube, so Length/area = 1, so the resistance (if you had a big perfect conductor 1m square on each end) is 200 ohms. 
Just about *any* wire you put in that lump o’ soil between the ends will make the resistance less. 

What I’ve not looked for recently is whether anyone has modeled whether the direction of the wire or whether just dumping chopped up wire into the soil works. 

Notable exception - the proverbial salt marsh - Salt water has a conductivity around 5 S/m - That’s 0.2 ohms for our 1 meter cube… 

(this is for the near field stuff, which is what radials are all about - far field is driven more by the “reflection coefficient” which is polarization and angle sensitive - so water content (epsilon r of 80) has a huge effect.  )

I note there’s a  nice short paper by Rutledge and  Muha  dipoles on a dielectric medium (e.g. soil) that shows that for a dipole laying on the surface, about 5 x the power goes into the soil as radiates.  
 
D. B. Rutledge and M. S . Muha, “Imaging antenna arrays,” IEEE Trans. Antennas Propagar., vol. 30, pp. 535-540, 1982
Scrounging around might find a copy that’s not paywalled at IEEE.  



On Sat, 25 Oct 2025 03:41:07 -0700, Jim Brown <jim at audiosystemsgroup.com> wrote:

On 10/24/2025 4:03 PM, Dale Dean wrote:
> Any other suggestions?



Rudy's work was an important light-bulb for me, AND for all of ham
radio. Why are more radials better? The earth couples to radials as
series R. Loss in that R is I squared R, as the number of radials
increases, the current in each divides between them. That is a LINEAR
relationship, but power is I SQUARED. So loss drops in proportion to the
number of identical radials (equal current distribution).

A similar relationship happens with chokes in series, which linearly
increases both their power handling and their choking impedance.

73, Jim K9YC

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