There are two major differences between EZNEC and EZNEC/4. The first is
that EZNEC/4 is one of the two EZNEC pro programs, the other being
EZNEC-M. These programs are intended for professional use (although some
amateurs have bought them) and cost several times as much as the
standard version of EZNEC. The added features of the pro versions are
10,000 segment capability, the ability to read and write description
files in NEC format, ground wave analysis, automated rectangular wire
grid creation, and a way to do advanced replication, rotation, and
translation of groups of wires. EZNEC-M is identical to EZNEC/4 except
that EZNEC-M only has an NEC-2 calculating engine, while EZNEC/4 gives
you the choice of NEC-2 or NEC-4. And the availability of an NEC-4
calculating engine is the second difference between EZNEC and EZNEC/4,
since EZNEC has only NEC-2.

The most striking advantage of NEC-4 over NEC-2 is that it allows the
modeling of buried conductors. It also is relatively free of the error
NEC-2 creates when modeling connected wires of dissimilar diameters, and
will hold up better at the edges of calculation capability. For example,
it'll handle loops which are a bit smaller than the smallest that NEC-2
can manage. For most models above ground, though, NEC-2 and NEC-4 will
give you virtually identical results.

NEC-4 has some additional capabilites which I haven't yet implemented in
EZNEC/4. These include the ability to include the effect of wire
insulation, and the ability to define the conductivity and permittivity
of the primary medium (fixed at free space for NEC-2). It also does some
checking of the geometry for errors such as overlapping or crossing
wires. EZNEC/4 does have it run these checks.

NEC-2 is public domain software -- anyone can get it and use it for any
purpose, free. It's on the Web as both source code and compiled for a
number of platforms. But NEC-4 is copyrighted by the University of
California, and is not free. Any U.S. citizen can buy it for use within
the U.S. I believe the cost is still $850, although there's a discount
for universities, and some military and defense groups can get it free.
I sell EZNEC/4, which includes an NEC-4 calculating engine, only to
people and organizations whom I've confirmed have a valid NEC-4 license,
via confirmation from the issuing agency. (You don't need to have NEC-4
in order to run EZNEC/4, but you must have purchased it before I'll sell
EZNEC/4 to you.) EZNEC/4 is $600 on top of the $850 NEC-4 fee, so no, an
upgrade from EZNEC isn't a viable choice for the vast majority of hobby
users.

NEC-3 was a forerunner of NEC-4, and was sort of a first attempt at
implementing NEC-4's advanced features. It had a number of shortcomings
which were fixed in NEC-4. NEC-4 wasn't available to the public for a
number of years, and NEC-3 was never made available to the public.

If anyone is seriously interested in purchasing NEC-4, drop me an email
and I'll be glad to tell you whom to contact.

Roy Lewallen, W7EL

wrote:
Roy, this brings up a question , and am curious about-- Just what are the
differences between EZNEC and EZNEC -4 ? Have had copies of Elnec, thru
EZNEC, and you keep doing great job improveing each one, but keep hearing
about NEC-4 (as opposed to NEC, and NEC-2), and am curious (no puns
intended), as to what are the major advantages of NEC-4 over NEC, and NEC-2
(what ever happened to NEC-3?) Is it worth upgradeing to, or, of interest
only to someone doing complex arrays ? I'm sure others would also be
interested, as am not in a position to get engineering tomes (am retired),
but am curious. Kinda like a teacher that was at Oregon Institute of
Technology (last name of "Barber"), who ran a company that built antennas
for military planes - turned out a curtain, so if part of hull was shot, the
rest of the hull would radiate! Wished I had more oppurtunity when still in
K.Falls to pump him, but they cut his teaching position. Guess you the
expert to ask, now-- Jim NN7K