[TowerTalk] NEC 5.0 ???

[Máximo EA1DDO_HK1H]

Some gents wrote about that in the past.

Just wondering if NEC5 has resolved those issues on NEC4, and overpassed MiniNEC, all of that from the loop (Quad) antenna.

Perhaps for Yagi or verticals is a different situation.



Mr Cebik. W4RNL (SK)



http://www.antentop.org/w4rnl.001/fd.html



MININEC's achievement of reasonable convergence of results and NEC-4's inability to achieve converged results suggests that the NEC-4 results are less trustworthy than those of MININEC.

It is clear that, for a loop of a given size, NEC-4 will yield lower gain numbers and higher feedpoint values than MININEC. Otherwise expressed, NEC-4 will call for a loop of smaller dimensions to approach resonance.





Mr. Roger W8IO



http://wb0dgf.com/mininec.htm



You might ask - why care about MININEC when we have NEC-2 and NEC-4 available. MININEC does have certain advantages when compared to either NEC2 or NEC-4.  Some of them include close-spaced wires, close-spaced wires of different diameters,  tapered-diameter elements, different diameter wires joined at an angle, and placing sources at a wire junction.



Thank you



73, Maximo - EA1DDO







-----Original Message-----
From: Lux, Jim [mailto:jim at luxfamily.com]
Sent: viernes, 12 de marzo de 2021 15:04
To: Máximo EA1DDO_HK1H; towertalk at contesting.com
Subject: Re: [TowerTalk] NEC 5.0 ???



On 3/11/21 11:57 PM, Máximo 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