A program for visualizing NEC2 input and output data

Xnecview is a program for visualizing the input and output files of the NEC antenna simulation software. It runs on Linux/Unix systems with the X window system.

The most recent version is version 1.37, which was released January 12th, 2020. Its source code and documentation can be downloaded as a .tgz-file. This version contains only minor improvements and bugfixes, compared to the previous versions; version 1.32 introduced drawing the radiation pattern as an opaque surface rather than a wire grid.
An RPM file for easy installation on RPM-based Linux distributions of some xnecview version is made available by F6FGZ on his web page. Furthermore, several versions of xnecview packaged as .deb files are available in the Debian project.

Below, some screenshots are shown to demonstrate Xnecview's capabilities. As an example a model of a logarithmic periodic ("log-per") antenna is used.

[xnecview window showing antenna structure]
Here, the structure of the antenna is shown. This picture can be rotated and zoomed. Note that the tag numbers of the wires are shown, so it is easy to identify which wire should be changed if one has made a mistake.

[xnecview window showing radiation pattern]
In this picture, the radiation diagram of the antenna has been superimposed: the red mesh. The farther this is from the center point in a given direction, the stronger the antenna radiates in that direction. Of course, this picture can also be rotated. Furthermore, slices through the XY, XZ and YZ planes can be shown, and four different gain scales are available: linear in power, linear in voltage, ARRL-style, and logarithmic with -40 dB at the center. The above example uses the logarithmic gain scale. Note the side and back lobes.

[xnecview window showing graphs of gain etc. vs. frequency]
If the NEC output file contains output data for several frequencies, an additional window is opened showing selected data as a function of frequency. In this example, graphs of the gain, front/back ratio, and SWR of the antenna are shown. Note that the log-per is indeed a broad-band antenna: this one is usable from about 30 MHz to about 55 MHz. The vertical (cyan) line indicates the frequency at which the other window is showing the radiation pattern; 44 MHz in this case.

[xnecview window showing current distribution]
NEC also calculates the distribution of current on the wires of the antenna. The above picture shows how Xnecview visualizes the currents on our log-per example at 44 MHz. The thickness of the wires indicates the amplitude of the current, while the colour indicates the phase. We see that several elements in the middle of the array are carrying the largest currents. Furthermore, we see that they have approximately the same colour: their contributions to the forward radiation of the antenna are almost in phase, so they don't cancel. (note that in the above picture, the phase has been corrected for the distance along the X axis; see the Xnecview manual page for more details on this).

In the above picture, the time-dependence of the currents is indicated by their colour, which represents the phase difference between them and the source. Obviously, other quantities of interest, such as the charge distribution and the electric and magnetic fields in the neighbourhood of the antenna, are also time-dependent. It is quite hard to show those quantities in the same way (i.e., by colours), so a new facility has been integrated into Xnecview version 1.30: animation. Because of the size of the file, an example of this has been put on a separate page.

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