[K3PZN-List] Antenna analysis correction

[Peter Morton]

At the Monday night meeting during the Radio Canada International Transmitter Site presentation, I was demonstrating 4NEC2 antenna analysis software.  I showed a 20 meter dipole at 35 ft. and then lowered it to 17.5 ft. to show the pattern change.  I stated that the dipole was at one wavelength above ground and lowered to a half wavelength.  35 ft. is actually about a half wavelength and the dipole was lowered to about a quarter wavelength where we observed the pattern approach that of a pattern that might be used for NVIS (Near Vertical Incidence Skywave) operation.

Many expressed interest in the 4NEC2 software.  Here is a link to the website were it may be downloaded for free:

    http://home.ict.nl/~arivoors/

Wikipedia has a good description of NEC (Numerical Electromagnetics Code) history.  See:

    http://en.wikipedia.org/wiki/Numerical_Electromagnetics_Code

NEC-2 is in the public domain but has some limitations.  For example I get warnings messages when I space two conductors very close together to form an open-air transmission line.  It also does not handle well tapered conductors such as elements of a yagi where the elements are made up of different diameter sections of aluminum tubing, although approximations work quite well.

NEC-4 is a much improved version that permits closely spaced conductors and tapered conductors, and other improvements.  NEC-4 remains proprietary with the Lawrence Livermore National Laboratory and the University of California, so it costs money.

L.B. Cebik, W4RNL, (SK) has a great antenna modeling web site along with other amateur-radio subjects.  His page on the various NEC modeling programs available is very informative.  Since L.B.'s death last year, the site has been taken over by the publisher of antenneX magazine, Jack L. Stone, so you are now required to register for free access to L.B.'s original site.  See:

    http://cebik.com

Once you have registered and logged in, click on "Tales and Technicals" and then on "Antenna Modeling Programs"

Here is another site that has various antenna modeling software packages described, and software may be downloaded.  (It appears now to be a bit out of date, but a lot of info is available.)

    http://www.si-list.net/swindex.html

Hope this helps.

-Pete, W3GVX