What frequency range is commonly used for long-distance communications?

The choice of High Frequency (HF) for long-distance communications is based on its unique propagation characteristics. HF radio operates in the frequency range of 3 to 30 megahertz (MHz) and is particularly effective for long-distance communication due to the ability of HF waves to be reflected off the ionosphere. This ability to bounce signals off the ionosphere enables HF communications to cover vast distances, often reaching beyond the horizon, making it ideal for maritime, aviation, and international communication purposes.

HF frequencies are less susceptible to the atmospheric interference that affects other frequency ranges, providing clearer signals over long distances. This characteristic is why HF is widely used for various applications, including amateur radio, maritime communication, and emergency services.

In contrast, other frequency ranges like Medium Frequency (MF), Extremely Low Frequency (ELF), and Very Low Frequency (VLF) serve different purposes and have limitations concerning long-distance communications. For instance, MF is commonly used for AM radio broadcasting but is more limited in range compared to HF. ELF and VLF are utilized primarily for specific communication needs, such as submarine communications, but they do not provide the same level of flexibility and range for general long-distance communication as HF does.