Topband: radial length

[Richard (Rick) Karlquist]

I have a 230 foot diameter ground screen having 3'x3' squares.
When I first built it, I put a 40 meter
vertical in the middle of it and drove it against the
center junction of the grid.  The drive impedance read
70 ohms.  To get it down to 36 ohms, I had to install
64 radials, 25 feet long.  An interesting aspect of
this experiment is that the field strength was the
same with no radials or 64 radials, only the impedance
changed.  BTW, I tried 120 radials, but there was
virtually no change in the impedance vs 64 radials.

So I think the answer to this "paradox" is that you
need very close radial spacing close to the antenna
where the current density is highest.  Farther out it
is OK to have greater spacing.

Rick N6RK