It's possible to run a near field analysis using MININEC type ground
with some v. 4.0 and all v. 3.0 and earlier versions of EZNEC. However,
the results will be wrong. The problem with using near field analysis
and MININEC type ground was discovered while v. 4.0.27 was current, and
the restriction preventing that combination was introduced at v. 4.0.28
in August 2006. So only v. 4.0.28 and later programs have this
restriction. Please see the last paragraph of this posting for remedies.

In EZNEC v. 4.0.28 and later, the NF Tab button is greyed out whenever a
MININEC-type ground is specified. If it's clicked, you'll see a message
that near field analysis is disabled when MININEC-type ground is
specified. If you click Help in the message window, it'll open the
manual topic which discusses real ground types. There, you'll find:

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Near field analysis is disabled when MININEC-type ground is selected.

Tests have shown that, because of the fundamental way NEC does
calculations, near field analysis with MININEC-type ground can produce
significantly erroneous results, particularly in the vicinity of a wire
which is connected to ground. This is really a contrived situation
anyway, because the only way to achieve a ground connection for a real
antenna comparable to the MININEC-type ground model is to install a
radial system. This will alter the ground conductivity and local fields,
so the MININEC-type ground model isn't really representative of
conditions near a grounded wire in any case. Use some other ground type
for near field analysis.

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If the conclusion that EZNEC near field results differ from the FCC
ground wave predictions is based on a near field analysis with
MININEC-type ground, I'm not surprised at the disagreement. The analysis
should be redone with a large number of radials just above the ground,
and High Accuracy ground used instead of MININEC-type ground.

Two reminders:

1. As explained in the EZNEC manual, "near field" analysis isn't
restricted to the near field. It's actually "total field" -- including
ground wave -- and is accurate at any reasonable distance. The "near
field" nomenclature is carried over from NEC.
2. The EZNEC ground model is flat and infinite in extent. So the
predicted direct line field begins deviating from actual field values
where the curvature of the Earth becomes a significant factor.

Anyone using EZNEC v. 3.0 and earlier should avoid using the combination
of near field analysis and MININEC-type ground. Anyone using v. 4.0
should update his program to the last revision of that version, 4.0.39.
You can find instructions on updating in the manual, Support/Updates
(Maintenance Releases). To determine which revision you have, click Help
in the main program window, then About EZNEC. I strongly recommend that
v. 5.0 users periodically check for updates.

Roy Lewallen, W7EL