Topband: Radial system gain

Tom Rauch w8ji at
Sat Sep 30 15:20:53 EDT 2006

> Aren't all these figures ground wave? That's quite useful 
> for broadcasters, as that's where the consumer radios are, 
> but do we know by measurement of some kind what the 
> results would be at even 5 degrees, so we are not dealing 
> with any possible ground proximity effect that does not 
> map to the useful (for us) skywave?

Yuri brought up the point that the large ground system aided 
low wave angles, giving four square gain from an omni 
antenna. The fact is there just isn't that much power being 
wasted close to the antenna once we have anywhere close to 
50 radials.

The Fresnel zone of a vertical extends out several 
wavelengths. What we do to the ground in the near field, 
assuming we don't make the ground system a radiating 
element, only affects the overall efficiency of the system. 
Even 1/2 wave out is not enough to affect the low angle 
problems associated with a vertical. It's the conductivity 
over the first few miles that changes low angle skywave 
propagation on 160, not what we do within a few hundred 
feet. Within a few hundred feet we just change efficiency.

I believe N6RK did some measurements, and there have been 
professional measurements that support this. Certainly 
geometry and Method of Moments programs do.

> Anyone ever do that or something similar with 160 or high 
> broadcast verticals to see if the modeled efficiencies 
> hold for skywave?

This has always been of interest Guy, even with AM 
broadcast. The large clear channel 50kW and larger AM 
transmitters were always concerned about laying down maximum 
signal on skywave. Smaller local stations with directional 
patterns also have to protect skywave. It was never 
neglected in AM service. It simply became unimportant 
because it is meaningless.

We have to go out a very large distance in wavelengths to 
affect low angle signals, and higher angle signals aren't 
affected much by any change once a minimum number or radials 
are used. For skywave at high angles our local conductivity 
doesn't mean much. All the radials do is change the overall 
efficiency. To change the wave angles that earth losses 
affect the ground has to be changed several wavelengths from 
the antenna. That's why all through history no one has 
worried about changing what they cannot change. At upper HF 
with a tight pattern vertically polarized directional array 
it becomes practical to go out several wavelengths with a 
grid of parallel wires and affect skywave pattern and gain. 
On 160 meters it isn't reasonably possible, and it certainly 
can't occur just by adding more wire where it already isn't 

We already know, or should know, that once radials of 
reasonable length are spaced .025 to .05 wavelengths at the 
open ends adding more wire in between those wires is a total 
waste of copper. It already looks like a sheet. Our only 
choice for pattern enhancement, which can only occur at very 
low angles, is going out thousands of feet with wires spaced 
ten feet apart or moving next to a large body of salt water.

73 Tom 

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