From the information I have heard and the comparisons I have done on
several occasions there is very little difference between NEC2 and NEC4
for wires close to the ground. Of course NEC2 won't handle anything
below ground. I don't know exactly what the lower limit of height is
when NEC2 flames out. However N6LF shows a plot in his article for a
450 ft BOG 1 inch above ground. His analysis was done in NEC4-2. I can
closely generate the same thing in NEC2. The pattern is almost
identical, with only a small difference in the elevation angle of that
little low angle null in the back half of the pattern. I got 1 dB less
forward gain that he did and the RDF was 12, same as he got. Close
enough for me.
Jerry, K4SAV
On 5/14/2016 5:37 PM, Carl Luetzelschwab wrote:
Mike W0BTU commented:
"But I thought that it was a well-established fact that NO antenna modeling
software does well with antennas close to the ground".
Yes, I believe that's true with the NEC-2 computational engine. The NEC-2
engine is readily available to the public.
The NEC-4 computational engine addresses antennas very close to ground,
buried antennas and antennas connected to non-perfect ground. The NEC-4
engine requires a license from Lawrence Livermore National Labs - it is
$300 for US Non-commercial entities. This does *not* include the antenna
analysis software.
N6LF used NEC-4.2 (with EZNEC Pro4 v6) in his article that I recently
cited, and his results were very good for what he simulated and measured
(one buried antenna, one antenna very close to ground and a vertical wire
with a ground rod).
Of course just having the NEC-4 engine doesn't guarantee success, as N6LF
pointed out. You must have an accurate model of your ground conditions, you
must obey the wire rules, you must have accurate dimensions for the
antenna, and if it's wire you should include the insulation, too.
That's my two cents worth.
Carl K9LA
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