HF Propagation

What it does

Shows estimated HF skywave propagation probability from your QTH across the globe, based on current solar conditions and your antenna setup. Color indicates how open the selected band is toward each location — from deep red (marginal) to bright green (prime operating range).

Propagation Model

• foF2 (critical frequency) is estimated from SFI, latitude, and local solar time using an empirical formula aligned with ITU/CCIR ionospheric tables.
• MUF = foF2 × M-factor. M-factor scales with hop count: 3.2 (1-hop, <2,000 km), 3.7 (2-hop), 4.1 (3-hop).
• Multi-hop paths are evaluated at each reflection point; the weakest hop limits the path MUF.
• The nominal MUF is a median estimate — the band is open ~50 % of the time at exactly that frequency. The strength curve extends ±35 % around the MUF to model natural foF2 variability.
• Geomagnetic activity (K-index) applies a uniform penalty to all paths.

Antenna Model

• Vertical (baseline): Omnidirectional. λ/4 height = factor 1.0. Shorter reduces efficiency; longer shifts the pattern upward.
• Dipole: Figure-8 pattern broadside to the wire (sin² azimuth). Elevation pattern follows the ground-reflection lobe model F(θ) = |sin(π·h/λ·sin θ)|. Higher = better low-angle DX radiation.
• Hex Beam: ±30° beamwidth, ~6 dBd forward gain, ~19 dB front-to-back. Valid on 20m–10m only (design frequency range). Same elevation model as dipole.
• Takeoff angle per path is estimated geometrically from the F2 layer height (300 km) and per-hop distance.
• All antennas assume resonance on the selected band and average ground (σ ≈ 5 mS/m).

Solar Data Sources

• Primary: hamqsl.com XML feed — SFI, K-index, A-index, SSN, and per-band conditions. Cached for 10 minutes.
• Fallback: NOAA SWPC JSON endpoints (planetary K-index + monthly solar cycle indices) if hamqsl is unreachable.
• If both sources fail, the last cached values are used and marked [STALE].

Color Scale

• Red — Very low probability. Band is marginal; natural variability may still allow contacts.
• Orange — Below optimum frequency (below FOT). Noisy but workable.
• Yellow — Good probability. Near or above the FOT.
• Lime / Green — Prime operating range. Frequency is in the FOT–MUF window.
• No color — Band closed at that path (ionosphere cannot support propagation).

Skip Zone

The gray dashed circle shows the estimated minimum skip distance — where your signal first returns to Earth. Locations inside this circle cannot be reached via skywave on the selected band.