Topband: Ground Radials Yet Again

[K9AY]

Yes, a wire on ground has a velocity factor determined by the dielectric 
constant of the earth below it, as well as the air above it. But it doesn't 
matter when we have many wires working together as a radial system.

1. The purpose of radials is to provide a low loss conducting path for the 
return currents (the "ground image" of the vertical).

4. When you have a sufficient number of radials that the RF currents are 
well-shielded from the lossy earth below, the velocity factor goes away, 
since the RF currents are only flowing on the "top" side of the 
counterpoise, where air is the dielectric.

3. For a typical vertical, the current density is highest immediately 
adjacent to the base of the vertical, diminishing with distance according to 
a cosine function. Handling the higher close-in currents is the reason for 
using a larger number of short radials -- BUT -- using just short radials is 
recommended only when you are limited by space or resources and cannot (or 
choose not to) install longer radials.

I think this discussion started with a question about trading a small number 
of long radials for twice as many short ones. Why remove any radials? If 
circumstances prevent the addition of longer radials (the best case 
scenario), then simply add more short radials to the existing system and 
keep the performance contribution of the longer radials.

73, Gary
K9AY