Traces multiple rays across a range of elevation angles simultaneously. This produces a "fan" of rays departing the transmitter, showing how signals at different departure angles propagate through the ionosphere. Useful for visualizing overall propagation geometry and skip zones.
Finds the specific elevation angle (or other parameter) needed to reach a target ground range. Uses bisection search to converge on the right launch conditions. Quick mode bisects a single variable; Advanced mode sweeps multiple parameter combinations and finds the best match for each.
The radio wave operating frequency. Higher frequencies penetrate deeper into the ionosphere before refracting. Frequencies above the Maximum Usable Frequency (MUF) will punch through the ionosphere entirely and escape into space. Typical HF range: 2–30 MHz.
The Earth's magnetic field splits radio waves into two characteristic modes:
Controls the departure angles of the ray fan, measured from the horizon upward. Low angles (5–15°) produce long-range "skip" propagation. High angles (60–89°) go nearly vertical. The step size determines how many rays are traced in the fan.
The peak plasma frequency of the F2 layer — the densest part of the ionosphere. A vertically-incident wave at this frequency will just reflect. Oblique rays can reflect at higher frequencies (up to ~3× foF2). Typical daytime values: 5–12 MHz; nighttime: 2–6 MHz.
The altitude of maximum electron density in the F2 layer. Higher hmF2 generally means longer skip distances because rays refract in a wider arc. Typical values: 200–400 km. Varies with solar activity, season, and time of day.
Controls how "thick" the ionospheric layer is — the vertical distance over which electron density drops by a factor of e (~2.718). Larger scale heights produce a broader, more gradual density profile. Smaller values create a sharper, thinner reflecting layer. Typical range: 50–150 km.
The electron cyclotron frequency in the Earth's magnetic field — the frequency at which free electrons spiral around geomagnetic field lines. Determines the strength of magneto-ionic splitting between O and X modes. Typical surface value: 0.8–1.4 MHz; decreases with altitude.
Select Fan Sweep to visualize many rays at once, or Target Location to find how to reach a specific ground range.
Adjust the transmitter frequency. Start with 10 MHz for a typical HF scenario. Lower frequencies reflect more easily; higher frequencies reach farther or escape.
Adjust foF2 (critical frequency), hmF2 (layer height), and Scale Height to simulate different ionospheric conditions. Defaults represent a typical daytime mid-latitude ionosphere.
Click ▶ Trace Rays (Fan mode) or 🎯 Find Path (Target mode). Rays will be computed instantly in your browser via WebAssembly.
Click and drag to pan. Scroll wheel to zoom. Hover over any ray for detailed info. Double-click to reset the view.
Check multiple boxes in any group (modes, density models, magnetic models, etc.). Each combination becomes a separate trace group with its own color.
Click the 🔀 button next to any numeric parameter to enable a sweep range. Set min, max, and step to generate multiple traces across that parameter space.
The badge on the Trace button shows how many configurations will be run. Keep it under 50 for best performance.
Enter the desired ground range in km. The map will auto-zoom to show the transmitter and target. A pink marker shows the target location on the globe.
In Quick mode, pick which parameter to bisect (elevation, frequency, foF2, etc.). The search will find the value that lands a ray closest to your target.
Advanced mode sweeps multiple ionospheric parameters and bisects elevation for each combo, ranking all results by accuracy. Great for finding optimal propagation conditions.
After a fan trace, export your rays as KML (for Google Earth) or GeoJSON (for GIS tools). Exports include 3D coordinates with altitude for each ray point.