Using the most appropriate HF radio frequency is crucial when establishing contact with STORADIO. The HF Propagation Forecast will help you choose the most appropriate HF frequency given: the time of day/night, the atmospheric conditions and geographic location, by showing the most suitable HF frequency for communication with us. Choose the chart diagram that is closest to your geographical location. General rules: The higher the sun, the higher the frequency. The lower the sun, the lower the frequency. The longer the distance, the higher the frequency. The shorter the distance the lower the frequency.