🌎 HF Propagation Conditions

Real-time solar-terrestrial data and HF band conditions. Data sourced from NOAA SWPC, updated every 10 minutes.

SFI142

Kp0.67

X-RayA0

Solar Wind449 km/s

Bz3.7 nT

⬆ Highest Available Frequency (MUF)

MUF contour map — updated hourly. Source: hamqsl.com / NOAA SWPC

22 MHz

Estimated Maximum Usable Frequency for 3000 km path from Beijing (40°N)

~11 MHz at night

MUF (Maximum Usable Frequency) is the highest frequency that can be used for skywave communication over a given path. Frequencies above the MUF pass through the ionosphere into space. Use frequencies at 80-90% of the MUF for best results.

Current foF2 estimate: 7.2 MHz (critical frequency of F2 layer. MUF ≈ foF2 × 3 for 3000 km hop.)

⬇ Lowest Available Frequency (LUF)

3.5 MHz

Estimated Lowest Usable Frequency
d_layer_absorption_label Normal

LUF (Lowest Usable Frequency) is the lowest frequency that can penetrate the D-layer without being absorbed. Frequencies below the LUF are absorbed by the D-layer before reaching the F-layer for refraction.

Band	160m	80m	40m	30m	20m+
Frequency	1.8 MHz	3.5 MHz	7 MHz	10.1 MHz	14+ MHz
Passes D-Layer?	NO	YES	YES	YES	YES

🌏

D-Layer Absorption

The D-layer (60-90 km altitude) absorbs HF signals during daylight. Absorption is driven by solar X-ray and UV radiation. Higher X-ray flux = stronger D-layer = higher LUF.

Current X-ray class: A0 — Normal

🌱 Ionospheric D-Layer Absorption — NOAA SWPC Boulder, CO

Solar-terrestrial data dashboard — includes D-region absorption indicators

D-Region Absorption Prediction

Parameter	Value	Impact
GOES X-Ray Flux	A0	Normal
Solar Wind Speed	449 km/s	Normal
bz_imf	3.7 nT	Northward — stable
kp_index_label	0.67	Quiet

D-Layer absorption occurs at 60-90 km altitude. It is strongest during daylight hours and increases dramatically during solar flares (M and X class). During major flares, HF communication below 10-15 MHz can be completely blacked out on the sunlit side of Earth. This is called a Short Wave Fadeout (SWF).

Data sourced from NOAA Space Weather Prediction Center, Boulder, Colorado USA. The hamqsl dashboard above consolidates NOAA SWPC, Space WX Canada, and Lowell GIRO Data Center measurements.

☀ Real-Time Sun Surface — NASA Solar Dynamics Observatory

Sun surface - HMI Intensitygram showing sunspots

▶ Click image for full 4096×4096 resolution — SDO/HMI Continuum Intensitygram (white light). Dark spots = sunspots. Updated every 15 min. Source: NASA SDO

Sunspots & Solar Activity

111

Estimated Sunspot Number (from F10.7 cm flux)

Sunspots are regions of intense magnetic activity on the Sun's surface (photosphere). They appear dark because they are cooler (~3500°C vs ~5500°C surroundings). More sunspots = higher solar activity = better HF propagation on higher bands.

Click image for full 4096×4096 resolution — SDO/HMI Continuum Intensitygram (white light). Dark spots = sunspots. Updated every 15 min. Source: NASA SDO

Solar Cycle 25 is currently approaching its maximum (predicted 2025-2026). Sunspot numbers above 100 are common during solar maximum, enabling excellent propagation on 15m, 12m, 10m, and 6m bands.

Last updated: 2026-06-09T21:24:45+00:00 UTC — SFI/MUF/LUF computed from NOAA SWPC data