Also I do know there are differences between NEC 2, NEC4.1 and NEC 4.2
on how each of them handles conductors on or near earth. NEC 2 does not
deal accurately (?) with wire close ( some small fraction of a
wavelength or less) to earth. NEC 4.1 does and "adequate" job with wires
"on the ground" and possibly buried to some degree. Reportedly Rudy,
N6LF found errors with the ground model and worked with Jerry/Gerry (?)
Burke and supposedly that led to NEC4.2 . I do not have exact knowledge
of what those errors were or how they affected what conditions and to
what degree though I am told that for most things we deal with at HF
that it wasn't significant. I have had recent conversation Rudy on
other topics related to measuring ground characteristics using a OWL
probe and good VNA but we did not get into the various releases on NEC
in the process
STILL: I would like to get BACK TO MY ORIGINAL QUERRY
HAS ANYONE OUT THERE ACTUALLY USED THE new NEC 5.0 windows executable as
supplied by Lawrence Livermore Labs?
Dave
NR1DX
On 3/12/2021 10:04 AM, Lux, Jim wrote:
On 3/11/21 11:57 PM, M�ximo EA1DDO_HK1H wrote:
Hi Jim,
As far as I know, for Cubical Quads, MiniNEC (Mmana) gets more
accurate results than NEC2/4.
I haven't tested myself but it's what I remember to read somewhere else.
Do you know how NEC5 performs on same Cubical Quads?
Thanks
73, Maximo - EA1DDO
No idea off hand, since I don't use MiniNEC or MMANA. A lot of the
issues reported with NEC are for NEC2, which has problems where wires
join at acute angles, and with numerical precision with very short
segments.� NEC4 doesn't have those problems.� I would *think* that
NEC4 would do fine on a cubical quad - it's wires, it's simple,
there's no "rapid changes in diameter" or "wires of radically
different cross size connected at an angle" or "wires connecting to
surfaces".
Both are method of moment codes, so the basic solution approach is the
same. The differences are in how they represent the current along each
segment.� NEC4 is significantly better when dealing with transitions -
For all the codes, they make an assumption of what the current
distribution along a segment is - flat, sloped, typically, some sort
of A + B*sin() + C*cos().�� What NEC4 did is change this a bit to
A+B*sin()+C*(1-cos()) to improve the numerical performance for very
short segments.� With NEC2, if you took a dipole and made it
successively smaller and smaller segments, at some point, the solution
blew up - too many equations with terms that are either 1.000000001 or
0.00000001 and even with double precision it didn't work.
The other significant difference from NEC2 to NEC4 is a difference in
where the "current filament" is considered to exist. In both versions,
the current is assumed to be entirely along the axis of the segment
(there's no "around the segment" current flow).� In NEC2, the current
is assumed to be at center of the wire, but in NEC4, it's on the
surface of the wire.� For long straight uniform wires, this makes no
difference, but on a step or at a corner, or where wires are close
together, it does make a difference.
https://physics.princeton.edu/~mcdonald/examples/NEC_Manuals/NEC4TheoryMan.pdf
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