Topband: Question - optimum number of radials

[Tom W8JI]

> Jerry Sevick, W2FMI, has an interesting comment about the "120" number in
> his book, "The Short Vertical Antenna and Ground Radial."  At the end of
> the first chapter he notes:
>
> "...it should be mentioned that the world standard for the number of
> radials to be used with verticals in the AM broadcast band is 120.  This
> number was based on the classic paper published in 1937 by Brown, Lewis,
> and Epstein.  During the course of a business meeting with Dr. Brown, I
> asked him how he and his colleagues arrived at the 120 radial
> figure--because I was quite sure 100 would work as well.  His answer was
> interesting.
>
> "He said that he and the others had been thinking in terms of 100 radials,
> but the farmer who plowed in 100 radials had wire left over because copper
> is soft and stretches easily.  When he asked what to do with the extra
> wire, the farmer was told to plow it in.  The result was a world standard
> of 120 radials."

That's an interesting story, but the story-teller must never have looked at 
the papers.
BL and E used 113 radials maxium, not 120.

Brown, Lewis, and Epstein's papers are all over the web, if you search for 
them.

The FCC says:

"At the present development of the art, it is considered that where a 
vertical radiator is employed with its base on the ground, the ground system 
should consist of buried radial wires at least one-fourth wave length long. 
There should be as many of these radials evenly spaced as practicable and in 
no event less than 90. (120 radials of 0.35 to 0.4 of a wave length in 
length and spaced 3° is considered an excellent ground system and in case of 
high base voltage, a base screen of suitable dimensions should be 
employed.)"

So you see, the FCC requires 90 radials unless you prove you can make 
efficiency with fewer. They do not say 120 quarter wave radials, they 
require 90 1/4 wave or longer, and say 120 radials .35 to .4 wl is 
"considered excellent".