Re: NEC-LIST: Currents

Yes, it it true. The NEC manuals are the best I have ever seen. I
wasn't trying to disparage them. I'm sorry if I gave that impression.
Rob.

Jim Lux wrote:
>
> The segment current in NEC is the current in that segment, with the
> excitation of the antenna being whatever you specified on the EX card. If
> you look at the segment that corresponds to the feedpoint, you'll see that
> the current in that segment is the same as the feedpoint current in the
> "feedpoint" section of the output. The apparent Z and Y are just calculated
> by current and voltage (Z=E/I, Y=I/E).
>
> As for finding the answer in the source code... I'd have looked in the
> program documentation, particularly Part 1 and Part 2, which describe in
> quite some detail how NEC works, what it computes, etc. While well
> documented code is a "good thing", one shouldn't expect the entire theory of
> operation, nor the "how to use it" to be in the comments. I've found the
> comments in the NEC code fairly complete, assuming one knows what the
> program is trying to do (i.e. solve the general method of moments problem)
> and how it does it. Also, don't forget that NEC was written in the early
> 80's, in a development environment that differs quite substantially from
> what is "usual" today. To have the theory separately documented from the
> code would be (and still is) standard practice, if only because the theory
> and program design would have to go through design reviews before
> implementation.
>
> There is also a certain expection of sophistication and knowledge on the
> part of the creators of NEC2. That is, they probably assumed that the
> original intended users of NEC2 would be knowledgable about
> method-of-moments, antenna simulation theory, etc. I doubt that the original
> authors ever expected that thousands of people would be running dozens of
> NEC2 models on PC's at home. In 1981, running a 1000 segment model would
> have required some serious (and very expensive) computer resources: I sure
> wouldn't have been running it on my CP/M Z80 machine with 48K of RAM. The
> "mass market" use of MoM codes has been greatly facilitated by later
> products like EZNEC, 4nec2, etc.etc.etc. which, to a certain extent, reduce
> the need to understand EM modeling theory. This is, as always at the risk
> that you'll "get bit" by some inherent limitation... There have been some
> good articles over the years in the amateur radio literature about
> understanding the limitations of MoM codes, etc.
>
> I think that the endurance of the basic NEC2 code is a testament to the
> design process which created it in the first place. There aren't many other
> software packages that are 20+ years old that are being run by casual users
> in a form substantially unchanged from the original.
>
> ----- Original Message -----
> From: "Rob" <rob_at_pythonemproject.com>
> To: "Pat Foster" <prf_at_maasdesign.co.uk>; <nec-list_at_gweep.ca>
> Sent: Saturday, December 07, 2002 8:33 AM
> Subject: Re: NEC-LIST: Currents
>
> > ASAP will do this, and give you a nice list. You'd have to look at the
> > code. I believe the current from a 1V rms source into Zin at the
> > antenna terminals is the default source, which then gives/prints the
> > mag/phase current on each segment. The current is what the matrix
> > routine solves for. Thats a big plus for readable source code.
> >
> > I think NEC does the same, but its not a symmetrical matrix like ASAP,
> > so LU decomposition is used to solve it. Eznec gives a nice relative
> > plot of all of the currents, so thats what I use when I want a pretty
> > picture of antenna currents.
> >
> > Rob.
> >
> > Pat Foster wrote:
> > >
> > > It is possible to output the currents on all segments of a structure in
> NEC.
> > > But exactly what current is being output? I have hunted through the code
> but
> > > have not had much joy.
> > >
> > > Regards
> > >
> > > Pat Foster
> > >
> > > ***********************************
> > > MAAS
> > > Microwave and Antenna Systems
> > > 16 Peachfield Road
> > > Malvern
> > > WORCS WR14 4AP
> > > Tel (44) 1684 574057
> > > FAX (44) 1684 573509
> > > email prf_at_maasdesign.co.uk
> > > ***************************************************
> > > See our Home Page at http://www.maasdesign.co.uk/maas
> > > ***************************************************
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> >
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> >
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