Band Conditions & Propagation
Real-time solar and geomagnetic data for HF radio propagation.
Understanding the Indices
Solar Flux Index (SFI)
Measures radio emissions from the sun at 2800 MHz. Higher values mean better HF propagation. Above 100 is good, above 150 is excellent. Values below 70 indicate poor conditions on the higher HF bands.
Sunspot Number (SN)
Correlates directly with SFI. More sunspots mean more UV radiation hitting the ionosphere, creating stronger ionization layers. This is the primary driver of HF propagation quality across the 11-year solar cycle.
A-Index
Measures geomagnetic activity over the past 24 hours on a scale of 0–400. Lower is better for HF. Under 10 is quiet, 10–20 is unsettled, and above 30 often means degraded conditions or blackouts on the polar paths.
K-Index
Short-term (3-hour) geomagnetic disturbance index on a scale of 0–9. Under 3 is good for HF propagation. Values of 5 or above indicate a geomagnetic storm that can cause signal absorption and aurora on VHF.
Band Conditions
The widget shows Good, Fair, or Poor for each HF band based on current solar and geomagnetic data. Conditions are shown separately for day and night paths, since propagation characteristics differ significantly between sunlit and dark ionospheric regions.