HF Propagation Map

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).

Open Source

This tool is open source under the GNU GPL v3. The code, the propagation model and the scripts used to validate it against ionosonde and WSPR data are all on GitHub: github.com/gauthig/propagation. Issues and pull requests are welcome.

Propagation Model

• foF2 (critical frequency) is estimated from SFI and the sun's elevation at each reflection point — so time of day, season, and latitude all count — with the F2 layer lagging the sun, starting to ionize before ground sunrise, boosted near the equator and reduced at high latitudes. Its constants were fitted to 16,200 real ionosonde soundings from 12 stations worldwide (typical error under 1 MHz at mid-latitudes).
• MUF = foF2 × M-factor, where the M-factor comes from curved-earth hop geometry: ~1 for short hops, rising to ~3.4 for a 3,500 km hop. Longer paths are split into equal hops.
• Multi-hop paths are evaluated at each reflection point along the great-circle path; the weakest hop limits the path MUF.
• The MUF is a median estimate; the real ionosphere varies about ±14 % day to day (measured). Strength is the probability the band is open on the path today: 50 % at the median MUF, ~10 % at 1.2× the MUF, ~95 % at 0.8×.
• After sunset the F2 layer fades gradually (about 2 hours at mid-latitudes, much longer near the equator) rather than switching off, so bands like 20m stay open into the evening toward the Pacific.
• Auroral absorption: paths whose hops touch the auroral zone (around 68° geomagnetic latitude, moving toward the equator as the K-index rises) lose signal. This is why the polar route from the US West Coast to Europe, over Hudson Bay and Greenland, is usually shown closed.
• Checked against a week of real WSPR reception from Southern California on 20m and 40m: paths the map colors were heard about 5–10× more often than paths it leaves dark.
• Greyline: when both your QTH and the far end are in twilight, the path gets a modest boost — less absorption and a slightly higher MUF along the terminator. Tick Show greyline to see the twilight band (violet), the terminator (dashed line) and the point where the sun is overhead (yellow dot). When your QTH is inside the band, the far parts of the band are your greyline paths.
• D-layer absorption weakens each hop in daylight — strongest at low frequencies and high sun. This is why 80m/40m fade over long daytime paths while 20m stays open.
• Geomagnetic activity (K-index) applies a uniform penalty to all paths.

Antenna Model

• Vertical (baseline): assumed to be a resonant λ/4 vertical cut for whichever band you select, with a good radial field (about 30 or more on-ground radials, ~10 Ω ground loss). That is the usual standard. With its image in the ground, it performs much like a λ/2 vertical dipole. It is omnidirectional and has no height setting. Over average soil it is the 0 dB reference every antenna is compared against; this is also the map you see with "Use antenna" unticked.
• 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.
• Elevated GP (Zero Five 10–80m): a 43 ft radiator with six 130-inch radials, base 4–12 ft above ground, fed through a 4:1 UnUn and 100 ft of RG-213 to a tuner in the shack. Modeled in the NEC2++ antenna simulator over the chosen soil, band by band as it actually behaves, and compared at every takeoff angle with the reference λ/4 vertical over average soil. Over average soil it is weak on 80m (about −7 dB, mostly coax loss at the very high SWR) and about −2 dB on 60m. It is even to about +2 dB on 40m–17m at low angles, with 20m the standout. On 12m–10m it splits into high-angle lobes ("cloud-warmer"). Base height (4–12 ft) changes it by roughly 0.5–2 dB, depending on band.
• Takeoff angle per path is estimated from curved-earth geometry using the F2 layer height (300 km) and per-hop distance (minimum 3°).
• Soil applies to every antenna. Each is measured against one fixed reference, a λ/4 vertical over average soil, so poor ground is worse for all of them. Choices: very poor 0.001 S/m (city), poor 0.002 (desert, rocky), average 0.005 (pasture, clay), good 0.030 (farmland), salt water 5 S/m. Vertical antennas care most about soil, because their low-angle signal depends on the ground reflection: at a 10° takeoff a λ/4 vertical runs from about −3 dB on very poor ground to +7 dB at the shoreline. Horizontal dipoles and beams change by only a few tenths of a dB.
• Dipole / hex beam height sets the elevation lobes through the ground reflection: a dipole λ/2 up peaks around 30°, and one wavelength up has a null at 30°. (Before version 2609.008 the model treated every dipole as half its real height.)
• The readout next to the band-plan button shows the dB the map applies for your antenna, soil and height at 10° and 20° takeoff, in its best direction, compared with the reference.
• All antennas assume resonance on the selected band (the Zero Five is modeled as it actually behaves on each band).

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 — Marginal. Near the MUF edge or weakened by absorption. Noisy but workable.
• Yellow — Good probability.
• Lime / Green — Prime operating range. The ionosphere supports the path with little absorption.
• No color — Band closed on that path, or open on fewer than about 1 day in 8 (strength below 0.12).

Skip Zone

The gray dashed circle shows the estimated minimum skip distance — where your signal first returns to Earth, in the most favorable direction. Locations inside it normally cannot be reached via skywave on the selected band (ground wave covers only the first few tens of km). Faint red inside the circle marks occasional openings when the ionosphere runs above its median. No circle means the band reaches all the way in (NVIS).

Data Collection

HF Propagation collects only what is necessary to provide the service: your amateur radio callsign, a salted password hash (never the plaintext password), and optionally your email address for password resets.

Data Use

All collected data stays within this application. It is used solely to:

• Save your personal settings (QTH location, band preferences)
• Track aggregate application usage statistics (not linked to individual users)
• Send password reset notifications when you request them

Data Sharing

No data will be sold, transferred, or provided to any third party under any circumstances. Your callsign and any personal information you provide remains within this program only.

Email

If you provide an email address it is stored securely and used only for password reset notifications. It will never be used for marketing or shared with any third party.