Modeled #14 AWG, copper conductor, 32ft monopole, 29 radials of 25ft, and
base 6" above (nominal lambda/1000) Sommerfeld/Norton ground of Er = 13,
sigma = 0.013 S/m at 1.8 MHz. All segments 6".

NEC2 computes:
Zin = 2.87 - j1358 Efficiency 92%

RADIALS2 computes (with radials 1mm below ground):
Zin = 1.55 - j1310 Efficiency 23.5%

Not a large amount of difference, but thought I had gotten closer results
with a different monopole, but seem to have deleted the code (Not sure why
such a large difference in efficiency). NEC2 is supposed to provide a
reasonable approximation of a buried radial monopole when at about
lambda/1000 above ground. Be interested in any comments, and what NEC4
provides if anybody has it.

73,

Frank

"Roy Lewallen" wrote in message
...
Reg Edwards wrote:

The only program I am reasonably familiar with is the several years old
free
EZNEC. I don't know whether it has been updated or not and I make very
little use of it. Come to think of it, I don't make much use of my own
programs either.

Regarding shallow buried radials in conjunction with a vertical, have you
tried my recent program RADIALS2 ?

It is intended to demonstrate performance of the radials themselves in a
given ground rather than antenna performance. Which I suspect is the
reverse
of NEC-4.

As you probably know, the effects of above-ground radials change very
rapidly as they get within a few inches of the ground surface. But once
in
the ground they tend to remain static.

RADIALS2 uses an entirely different, unconventional form of performance
analysis. If other programs don't take soil permittivity into account at
HF,
predictions must lose accuracy. Are the inputs and outputs of NEC-4 in a
form suitable for a direct comparison with my simple program?

Yes. I made a few comparisons long ago, shortly after you introduced your
program, and found major disagreement. NEC-4 approximately agrees with the
measurements made long ago by Brown, Lewis, and Epstein (whom I know
you've never heard of), once you make reasonable assumptions of ground
conductivity and dielectric constant. Your program gives very different
answers. At the time, I concluded that there's considerable coupling
between radials, which your program doesn't seem to account for.
Interested readers should look in the google archives for postings in this
group on the thread "Ground Radials" in July 1998 and "Evaluation of G4FGQ
Freeware Antenna Software" in September 1998.


But in view of the large uncertainties involving ground conditions,
accuracy
is not worth making much of a song and dance about.

True, but in the past, you've used the results from your program to reach
conclusions about radial systems that I didn't, and don't, believe to be
valid. (See the threads mentioned above.) I don't think it's wise to draw
conclusions from a program that gives results which are demonstrably very
different from the only measurements regarded to be reasonably well made.

Roy Lewallen, W7EL