Real-time ionospheric indices: estimated foF2, MUF(3000) and K-index for HF propagation from Romania. Real-time data from NOAA Space Weather Prediction Center.
| Band | Frequency | Day | Night | Notes |
|---|---|---|---|---|
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Estimated conditions based on calculated foF2, SFI and K-index. Actual values may vary.
SFI and K-index data from NOAA Space Weather Prediction Center · foF2 calculated with simplified CCIR model for latitude 47N
The critical frequency of the F2 layer — the highest frequency at which radio waves sent straight up are reflected back. Typical values: 3–15 MHz. The higher it is, the "denser" the ionosphere.
The maximum usable frequency for a 3000 km path via the F2 layer. Calculated from foF2 with the obliquity factor (~3×foF2). A guide to the best HF band for DX.
The global geomagnetic activity index, on a 0–9 scale. Kp < 3 = good HF conditions. Kp ≥ 5 = geomagnetic storm — propagation can be badly affected.
The solar flux at 10.7 cm — an indicator of solar activity and ionospheric density. Typical values: 70–300 sfu. High SFI = denser ionosphere = higher foF2 = higher MUF.
| Layer | Altitude | Active hours | HF propagation effect | Parameter |
|---|---|---|---|---|
| D | 60–90 km | Daytime only | Absorption — worsens propagation on 160m–40m during the day | — |
| E | 90–150 km | Daytime, sporadic Es | Reflects 1–5 MHz; sporadic Es can allow unexpected DX on VHF | foE, foEs |
| F1 | 150–250 km | Daytime (summer) | Reflection at medium-high frequencies (4–7 MHz) | foF1 |
| F2 | 250–600 km | Permanent | The main DX layer — reflects 3–15 MHz, intercontinental distances | foF2, hmF2, MUF |