🌞 Solar Weather Dashboard

Understanding Solar Indices for Ham Radio

Sunspot Number (SSN): A count of visible sunspots on the solar disk. Higher numbers mean more active regions, which produce more ionizing radiation. Good for HF propagation on higher bands (15m, 12m, 10m). Typical range: 0–200+.

Solar Flux Index (SFI): Measured at 2800 MHz (10.7 cm wavelength). This is the most reliable single indicator of HF propagation. Values above 100 are good for 20m DX; above 150 opens 15m and 10m consistently; above 200 is excellent for all HF bands.

K-Index: A 3-hour measure of geomagnetic disturbance. Ranges from 0 (quiet) to 9 (extremely disturbed). K=0-2 is excellent; K=3 is moderate; K=4+ degrades HF propagation, especially on polar routes. K=7+ can cause a total blackout on higher latitudes.

A-Index: A daily average of geomagnetic activity. A=0-7 is quiet; A=8-15 is unsettled; A=16-29 is active; A=30-49 is stormy; A=50+ is a severe storm. High A-index means auroral absorption and unstable propagation.

X-Ray Flux: GOES satellite measurement of solar X-ray output. Used to classify solar flares: C-class (minor), M-class (moderate), X-class (extreme). An X-class flare can cause immediate HF blackout on the sunlit side of Earth for 15–60 minutes.

Band Conditions Guide

• 160m/80m: Generally open night hours regardless of solar conditions. Quiet geomagnetic conditions improve reception.
• 40m: Open day and night. Good for DX when solar flux is moderate (SFI > 70). Best at sunrise/sunset.
• 30m: Digital and CW band. Good for weak signal work. Less affected by solar conditions than higher bands.
• 20m: The "DX band." Open most of the day when SFI > 80. The most reliable long-distance band.
• 17m/15m: Require SFI > 100 for consistent openings. Best during solar maximum and daytime hours.
• 12m/10m: Need SFI > 130–150. Can be completely closed during solar minimum. When open, provide excellent long-distance propagation with low noise.
• 6m: Sporadic-E in summer, F2 during solar maximum. Very dependent on solar activity.