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xnec2c-optimize

xnec2c-optimize is an optimization framework to tune antenna geometries with xnec2c.

Why tune our antenna? High gain and low VSWR, of course!

  1. Before and after graphs
  2. Getting Started
  3. Writing NEC2 files with Perl

Examples

Optimization

Before:

  • 9.3 - 10.9 dB gain.
  • Huge 23.31 VSWR at 148 MHz, lets fix that. before xnec2c-optimize

After:

  • 10.81 - 11.3 dB gain!
  • 1.25 VSWR, hurray! (Note that the graph scale changed) after xnec2c-optimize

Writing NEC2 files with Perl

From the 2m dipole example:

use lib 'lib';

use NEC2;

my $nec = NEC2->new(comment => "half-wave 2-meter dipole");

my $ns = 21; # number of segments

$nec->add(
        GW( tag => 1, ns => $ns, z2 => 1),
        EX( ex_tag => 1, ex_seg => int($ns/2) ),
        RP,
        NH,
        NE,
        FR(mhz_min => 140, mhz_max => 148, n_freq => 10),
        );

$nec->save('dipole-2m.nec');

print $nec;

Getting Started

  1. Install the latest version of xnec2c from here: https://www.xnec2c.org/

    • xnec2c v4.4.12 or later is recommended.

  2. Install the following perl modules with cpanm using these commands:

    • Ubuntu: sudo apt install cpanminus build-essential
    • CentOS: 
      yum install perl-App-cpanminus
yum groupinstall "Development tools"

  3. Install the dependencies with this command:

    cpanm PDL::Opt::Simplex::Simple PDL::IO::CSV Linux::Inotify2 Time::HiRes Math::Vector::Real Math::Matrix Math::Trig

  4. See yagi.conf for an example to get started. Just run this:

    ./xnec2c-simplex.pl ./examples/yagi.conf

More detail

Now xnec2c-simplex does most of the work below automatically, so here is more information if you need it:

Open xnec2c -j NN examples/yagi.nec where NN is the number of CPUs you have available on your system.

  • From the main window: select View->Frequency Plots
    • From the Frequency Data Plots window: Enable a graph, like VSWR. Configure whatever you would like to see during optimization.
    • Click the triangular "Play" button to run a frequency sweep. This setting must be active in order for the optimizer loop to function.
  • From the main window:
    • Click "File->Optimization Settings->After calculation, write <file>.csv".
    • Click "File->Optimization Settings->Reload and write data on .NEC file changes".
  • Optimization will then begin!

See also: https://www.xnec2c.org/#Optimization

-Eric, KJ7LNW