🌍 HF Propagation Predictor

How HF Propagation Works

High Frequency (HF) radio signals (3–30 MHz) propagate long distances by reflecting off the ionosphere — a layer of ionized particles in the upper atmosphere. The ionosphere has several layers (D, E, F1, F2) that vary in height and density depending on solar radiation.

Solar Flux Index (SFI) at 2800 MHz (10.7 cm) is the best predictor of ionospheric conditions. Higher SFI means more ionization, which supports higher frequencies. SFI > 100 is good for 20m; > 150 opens 15m and 10m consistently.

K-Index measures geomagnetic disturbance. Quiet conditions (K=0-2) are best for DX. Active conditions (K=4+) can cause absorption and reduce signal strength, especially on polar paths.

Seasonal effects: Winter nights have lower MUF (Maximum Usable Frequency) than summer. Daytime MUF is higher than nighttime. The equinoxes (March/September) often provide the best overall propagation.

Band Characteristics

• 160m (1.8 MHz): Groundwave and nighttime skywave. Very dependent on local noise. Best winter nights.
• 80m (3.5 MHz): Daytime groundwave, nighttime DX. Good for regional nets. Reliable but noisy.
• 40m (7 MHz): The "workhorse" band. DX possible day and night. Best at sunrise/sunset.
• 30m (10 MHz): Digital and CW band. Less crowded than 40m. Good for weak signal.
• 20m (14 MHz): Primary DX band. Open most of the day worldwide. Most active contest band.
• 17m (18 MHz): Often open when 20m is good. Less crowded. Good for DX during solar maximum.
• 15m (21 MHz): Strong solar dependence. Excellent during solar max, closed during min.
• 12m (24 MHz): Similar to 15m but less used. Good for contests when open.
• 10m (28 MHz): Most solar-dependent. Can be completely dead for years, then suddenly amazing.