What frequency band is primarily used for sky wave propagation?

Sky wave propagation primarily utilizes the High Frequency (HF) band because HF frequencies, typically ranging from 3 to 30 MHz, are capable of reflecting off the ionosphere, allowing radio signals to travel over the horizon and reach distant locations. This phenomenon is dependent on the frequency of the signal and the ionospheric conditions, which can vary at different times of day and during different seasons.

The ionosphere is a layer of the Earth's atmosphere that becomes ionized by solar radiation, and it plays a crucial role in bending HF signals back to Earth, enabling communication over long distances without the need for satellites or repeaters. This characteristic of HF frequencies makes them particularly valuable for aviation, maritime, and long-range communication applications.

While the Very Low Frequency (VLF) and Low Frequency (LF) bands can also have some ground wave propagation capabilities, they are not typically effective for long-distance sky wave communication due to their longer wavelengths. Ultra High Frequency (UHF), on the other hand, primarily relies on line-of-sight propagation and is generally not suited for sky wave transmission, making HF the most appropriate choice for this form of propagation.