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Author Topic: Tutorial for writing nec input files  (Read 2165 times)
KK4EOF
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Posts: 11




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« on: January 22, 2012, 08:26:28 PM »

I looked over this forum back to November of 2011 and didn't see this question asked, so I thought that it might be safe to ask:
Does anyone have a source of tutorial or other good explanatory documentation on how to write nec input files?  I'm running
Debian/Gnu linux, and have xnec2c installed.  It sounds like users of eznec have text input widgets that they can use to just
type in element lengths and so forth, but xnec2c doesn't have anything like that and I have to learn how to create nec input
files if I want to do modelling.  I have read a few things and have a clue, but I'd like some thorough explanations so I don't make
mistakes that take me months to figure out.

I made a couple of shortwave listening dipoles over the years but have only recently gotten my ham license, and now I have to
make antennas that I can use for transmitting, and that looks to be a lot more exacting than just receive antennas.  So, time to
learn a lot more stuff.......
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W6RMK
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Posts: 649




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« Reply #1 on: January 22, 2012, 08:35:39 PM »

Have you looked at the example files that come with the NEC distribution?

But basically, there's two parts... defining the geometry (GW cards for the most part, although GM can save a lot of hassle with things like arrays, grids, ground radials and the like)

Then there's the "what do you want to see for output"  The FR, the RP cards are the ones here.  The LD cards for using "real materials".  TL or NT for transmission lines and matching networks.

But, if you're slogging it out with bare NEC, it's worth it to look for helper utilities to deal with geometry entry.  I've written a lot of Basic, VB, and Matlab scripts over the years to generate GW cards.

There are some spreadsheet (Excel) things out there to help with the geometry. google around for AC6LA's MultiNEC (I think).... it might run under OO.
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WB6BYU
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Posts: 13005




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« Reply #2 on: January 22, 2012, 09:13:20 PM »

Spend some time going through the website of the late W4RNL:

http://www.cebik.com/content/radio.html

Yes, you have to register for free, but he has a lot of information on modeling
(along with a huge quantity of other antenna information.)  Besides the list
of articles on the main site, his series on antenna modeling for Antennex
magazine is here:

http://www.antennex.com/w4rnl/index.htm
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VK2FXXX
Member

Posts: 102




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« Reply #3 on: January 25, 2012, 04:53:30 AM »

http://ebookbrowse.com/tutorial-4nec2-english-homepage-pdf-d79246852

http://wireless.ictp.it/school_2005/download/nec2/nec_part1.pdf

http://wireless.ictp.it/school_2005/download/nec2/nec_part2.pdf

http://wireless.ictp.it/school_2005/download/nec2/nec_part3.pdf

http://wireless.ictp.it/school_2005/download/nec2/nec_part4.pdf


That lot should get you started.
Enjoy.
Brendan.
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KK4EOF
Member

Posts: 11




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« Reply #4 on: January 27, 2012, 10:18:15 PM »

Thank you both for the links.  I'll have to wait a week or two to register for the antennex website
but I have downloaded the pdfs and am looking at them now.  I can't let myself get too distracted
because I'm studying for the extra class exam on the first week of February, and it's proving to be
a lot of work.   Once I'm past that I will be more comfortable with spending time on the stuff I want
to play with...
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AE5QB
Member

Posts: 265




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« Reply #5 on: January 28, 2012, 05:00:32 AM »

Another option is using a visual oriented version like 4nec2 by Arie Voors.  http://home.ict.nl/~arivoors/Home.htm  His version has a couple of quirks but being able to draw your antenna while seeing it in a 3-D modeling environment goes a long ways towards understanding what is going on.  With his version you can draw your antenna and then switch to a NEC input view and see the cards that were generated.  I have learned a lot (but I am no expert) from using Arie's version.  Warning, it is addicting. 

Also, be advised that the free versions are based on the NEC 2 engine which isn't the most accurate engine and has a number of limitations.  The NEC 4 engine is much better but you must purchase a license to use it for about $350, if I remember  correctly.
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