Understanding Solar Data
Solar data tells you what to expect on the bands. Here's how to read and use it.
Key Solar Indices
Solar Flux Index (SFI)
The SFI measures radio noise from the sun at 2800 MHz. It correlates with ionization levels.
| SFI | Conditions | What It Means | |-----|------------|---------------| | <70 | Poor | 10m/12m probably closed, 15m weak | | 70-90 | Fair | 20m should be good, 15m sometimes | | 90-120 | Good | 15m often open, 10m possible | | 120-150 | Very Good | 10m can be excellent | | >150 | Excellent | All HF bands potentially great |
Sunspot Number (SSN)
More sunspots = more solar activity = better propagation. We're in Solar Cycle 25, which is performing well.
A-Index (Planetary)
The A-index measures geomagnetic stability over 24 hours. Lower is better for HF.
| A-Index | Conditions | |---------|------------| | 0-7 | Quiet (good) | | 8-15 | Unsettled | | 16-29 | Active (degraded) | | 30-49 | Minor storm | | 50+ | Major storm (poor) |
K-Index
The K-index is similar to A but measured every 3 hours. More responsive to current conditions.
| K-Index | Conditions | |---------|------------| | 0-1 | Quiet (excellent) | | 2-3 | Unsettled (good) | | 4 | Active (fair) | | 5+ | Storm (poor to bad) |
Band Condition Indicators
Many sites show conditions like "GOOD" or "POOR" for each band. These are estimates based on solar data. They're helpful but not always accurate.
Day vs Night
Conditions are different depending on time:- Daytime: Higher bands (10m-20m) tend to be open
- Nighttime: Lower bands (40m-160m) tend to be better
Path-Specific
Conditions vary by direction. Europe might be open when Asia is not.Solar Events That Affect Propagation
Solar Flares
Intense bursts of radiation. Effects:- X-class flares can cause radio blackouts on the daylight side
- Usually recover within hours
Coronal Mass Ejections (CMEs)
Clouds of solar material. If Earth-directed:- Can cause geomagnetic storms
- Usually 1-3 days after the flare
- Can disrupt propagation for days