Steve, W9HJW wrote:
"Something like .05 wavelength (between ends of buried radials) rings a
bell, but I`m not sure."

That would depend on the length and number of radials. But, the .05
number may be significant in the case of 120 radials. 120 radials is an
FCC standard. Spacing is 3-degrees.

In a right triangle, the side opposite an angle is equal to the tanget
times the adjacent side length. For a 3-degree angle, difference between
the adjacent side and hypotenuse lengths is insignificant.

The tangent of 3-degrees is .05. The distance between radials spaced by
3-degrees is therefore very nearly .05 times the length of the radial.
That`s my guess as to the source of Steve`s .05 number.

Best regards, Richard Harrison, KB5WZI