Chapter 2: Basic Principles of HF Propagation
In this chapter, the basics of HF propagation are discussed to provide a foundation for understanding how radio waves travel over long distances using the ionosphere. Here are some key points covered in this chapter:

Overview of HF Radio Waves:
- Frequency Range: HF radio waves fall within the frequency range of 3 to 30 MHz.
- Skywave Propagation: HF waves can be refracted by the ionosphere, allowing them to “bounce” back to Earth, enabling long-distance communication. This is known as skywave propagation.
- Groundwave Propagation: HF waves can also travel along the Earth’s surface for shorter distances. This is known as groundwave propagation.
- Ionospheric Layers: The ionosphere, an electrically charged layer of the Earth’s atmosphere, plays a crucial role in HF propagation. It consists of several layers that vary in density and altitude, affecting how radio waves are refracted.
- Critical Frequency: The critical frequency is the maximum frequency that can be used for skywave propagation at a specific angle of incidence.
- Maximum Usable Frequency (MUF): The highest frequency that can be used for skywave propagation between two points on Earth at a specific time.
- Skip Distance: The skip distance is the shortest distance between a transmitter and the point where the skywave is first returned to Earth.
Frequency Range: HF radio waves fall within the frequency range of 3 to 30 MHz.