Where does your HF signal actually land?

This maps where an HF (shortwave) signal launched from your station returns to earth — the near-in reach, the dead skip zone, and the hop rings out to DX. It runs entirely on your device, so it works with the internet down.

Reading the map

The shading is the predicted signal-to-noise at each spot — brighter is stronger:

• Green — reliable, a strong signal.
• Yellow — marginal: weak but workable.
• Blue — absorbed: the daytime D-layer is soaking up a low band (160/80m by day). Alive again at night; it sweeps with the day/night line.
• Clear (no shade) — no path: the skip zone (too close for this band) or above the MUF (the signal shoots through into space).
• The darkened region is night; the soft line across it is the terminator (the “gray line”). It moves as you change the time.

Because your antenna’s elevation gain is in the calculation, coverage responds to it: a low dipole is strong close-in (NVIS) but weak for DX, while a vertical is weaker close-in and reaches farther. Raise or lower the antenna and the reach changes.

Controls

• Band, time, month, sunspot number set the ionosphere. Season and time of day matter enormously — winter daytime opens the high bands, night opens the low ones.
• Antenna is where it gets personal. Height sets the take-off angle: a low wire fires straight up (NVIS/regional), a high one fires low (DX) — and because that depends on height in wavelengths, the same antenna behaves differently band to band. Type picks the pattern (dipole, EFHW, wire, vertical, mag loop, Yagi); orientation matters for the directional ones (a dipole is broadside to the wire, a beam points where you aim it).

How it works

Ionospheric MUF from the ITU-R P.533 F2-layer method over the CCIR monthly maps (the physics behind VOACAP), then a P.533-style link budget for each spot: free-space spreading + D-region absorption + ground-reflection loss, minus your antenna’s elevation gain, against an HF noise floor — giving a signal-to-noise the map colors by. The MUF and skip geometry are rigorous; the field-strength and noise terms are faithful approximations (the full P.533 uses absorption and noise tables we don’t bundle offline), so treat the exact SNR edges as relative, not absolute.