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xnec2c

Interactive antenna modelling — NEC2 with a live graphical front end

What it does

Models an antenna as a wire structure and computes what it does: radiation pattern in 2D and 3D, gain, feedpoint impedance and SWR against frequency, current distribution along each wire, near fields. It runs the NEC2 engine continuously as you change a parameter, so the pattern redraws while you drag rather than after a batch run.

Why you would want it

Antenna design is iterative and the interesting part is what happens when you move something. Batch NEC -- edit a card deck, run, plot, repeat -- makes that loop slow enough that people stop exploring. This makes it immediate, which is why it is the tool most Linux operators actually use for modelling rather than the one they mean to learn.

Before it will work

A NEC input file describing the geometry. Writing one from scratch means learning the card format; starting from one of the shipped examples and changing it is the usual and faster route.

How it installs

  • apt: xnec2c

Known problems

NEC2 has real modelling rules -- segment lengths relative to wavelength and to wire diameter, junction handling, ground models -- and violating them produces output that looks fine and is wrong. The program will warn about some of it and not all. A model is not a measurement: it does not know about your mast, your feedline, the house, or the ground under it, and the difference between a modelled and a built antenna is usually those things rather than an error in the model.

Keeping it current

  • probe: apt policy
  • strategy: apt_upgrade

Where to get help with the software itself

Now maintained by Eric Wheeler, KJ7LNW, after the original author Neoklis Kyriazis, 5B4AZ. GitHub issues at the URL above.

Source: catalog/packages/xnec2c.yaml