A 3D, physics-accurate visualiser for HF antenna radiation patterns, powered by NEC-2 compiled to WebAssembly.
Pick an antenna, set your frequency, height and ground, and see the pattern it actually radiates — in 3D, with elevation and azimuth cuts, SWR across the band, and a comparison mode for putting two configurations side by side. The NEC-2 engine runs entirely in your browser; nothing is uploaded, and there is nothing to install.
Open www.gain.observer. That's it — it runs on phones, tablets and desktops, and works offline once loaded.
Keyboard shortcuts:
t— toggle dark/light themeu— toggle metric/imperial unitsm— toggle between normal and comparison mode
Dipoles, inverted-V, sloping-V, inverted-L, vertical whips, folded dipoles,
delta loops and terminated deltas, from 1.8–30 MHz, over real ground.
docs/antenna-spec.md describes the geometry and physics of each in detail.
This is a hosted application first. The source is open under GPL v3 and you are welcome to read, fork or run it, but it is built and maintained to be used at the link above rather than self-hosted, and the documentation is written with that reader in mind.
It is GPL v3 because it statically links nec2c (by N. Kyriazis), which is
itself GPL v3. See LICENSE for the full text.