Re: NEC-LIST:old question on non-physical output

My experience has been, for such dramatic errors:
1. Incorrect frequency card value (I build it in wavelengths then put in
the actual frequency, forget the FR card when it's in physical
dimensions, various other dumb stuff)
2. Acute bends near the source segments, especially if there is a radius
step
3. Not adhering to the segment length/radius rules at bends. Remember
that EK does not "work" at bends, so you need to be L/a>6 or so.
4. "Parasitic" elements (in a yagi, for example) not properly
terminated.
5. Lengthy horizontal wires too close to a perfect ground plane.

I don't know that NEC4 is more forgiving of the wire rules...the only
thing I know for sure is that horizontal wires near/in ground are much
better.

Generally, checking wire rules is straightforward. On the Unofficial
NEC Home Page is an old DOS program "necdraw" which is pretty good (I
personally worked with the developer way back when, too ;-)
It can do around 1000 segments.

I have a windoze version I've written that does 10,000 segments. Both
check all wire rules and color-code a wire-mesh representation of the
model.

Also...
6. Modelling a solid surface using a wire mesh without following
Ludwig's published rules for mesh size/wire radius etc.

Good Luck

Wayne Shanks wrote:
>
> I am generating some medium to large antenna files (800 segments)
>
> These antenna are generated automatically from a set of parameters. I
> do my best to make sure that I do not violate any wire rules, but even
> when I think there are no violations, I get strange results.
>
> For instance I may get negative port Z, or negative efficiency, or
> greater than 100% efficiency.
>
> sometimes I will have a reasonable feed Z and good efficiency, but the
> radiation pattern data is all -999.99 dB, Or the efficiency is ********
>
> Perhaps NEC4 is more forgiving of small segments, or maybe I just need
> to look into wire rule violations more.
>
> How should I interpret these strange simulation results?
>
> Wayne S
> --
> The NEC-List mailing list <nec-list_at_gweep.ca>
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