- Ray trace (blue line): The center of the transmitted signal beam, following the path that the signal takes from the antenna, through the ionosphere, and back to Earth. The brightness of the ray indicates relative signal strength — a brighter ray means a stronger received signal.
- Signal lobe (blue shaded region): A simplified representation of the angular spread of the transmitted signal around the center ray. In this display the lobe is intentionally narrow (approximately 20°) for visual clarity. In reality, antenna radiation lobes can be significantly wider, covering a much greater area of the Earth's surface than depicted here.
- Lobe opacity: The transparency of the lobe directly represents signal strength. A bright, opaque lobe indicates strong propagation; a faint, nearly invisible lobe indicates a weak or marginal signal. When the D-layer is absorbing, the lobe fades to zero inside the layer, representing signal loss.
- Takeoff angle: The angle above the horizon at which the signal leaves the antenna. Lower angles produce longer skip distances (DX). Higher angles produce shorter, more regional paths. Note: the takeoff angle shown on the canvas is vertically exaggerated for illustrative clarity and does not represent the true geometric angle to scale.
- Skip zone (green shaded band): The region between the end of ground wave coverage and the first skip landing point. Stations in this zone cannot hear your signal via either ground wave or sky wave — it is a "dead zone" for communication.
- Ground wave (amber line): The portion of the signal that travels along the Earth's surface. Range decreases sharply with increasing frequency.
- Skip distance / Max range: Shown in the status bar. Skip distance is the one-hop landing distance. Max range includes all selected hops. Both are in miles.
- D layer (blue band): Present only during daylight hours. Absorbs lower-frequency signals (40m–160m) heavily near midday. Opacity of the layer is fixed — absorption effects are shown only through signal strength (lobe/ray opacity).
- Above MUF (red dashed line): When the selected frequency exceeds the Maximum Usable Frequency, the signal passes through the ionosphere and is lost to space. No skip propagation occurs.
- SFI (Solar Flux Index): A measure of solar radio emission at 10.7 cm wavelength, correlated with ionospheric density. Higher SFI generally improves HF propagation on higher bands while worsening D-layer absorption on lower bands during the day.
- Top-down map: Shows the geographic coverage of your signal from the TX location (blue marker). The amber dashed circle shows ground wave coverage. The red dashed circle marks the inner edge of the skip zone (signals cannot land closer than this). The first blue circle marks the first-hop landing zone (where the signal first returns to Earth). Additional blue rings show second, third, and fourth hop landing zones, fading with each hop to indicate signal loss. Open and close the map using the arrow control in the bottom bar of the display. Click anywhere on the map to relocate the TX, or type a Maidenhead grid square and press Go.
⚠ Model Disclaimer: This visualizer is intended to illustrate general principles of HF ionospheric propagation for educational purposes. The physics model is substantially simplified. Actual propagation is affected by geographic latitude, season, solar cycle phase, geomagnetic conditions, terrain, and many other factors not modeled here. Predicted skip distances, signal strengths, and band openings may differ significantly from real-world operational experience. Do not use this tool for operational planning or contest strategy.