Why is HF used for long range communication?

HF, or high frequency, is used for long-range communication for several reasons:

1. Propagation: HF signals can travel long distances by refracting off the ionosphere. This is known as skywave propagation. The ionosphere is a region of charged particles in the upper atmosphere that can refract radio waves back down to Earth. The strength of the signal can vary depending on the time of day, season, and solar activity.
2. Penetration: HF signals can penetrate through obstacles such as buildings and trees. This makes it useful for communication in remote areas or in situations where line-of-sight communication is not possible.
3. Availability: HF frequencies are allocated globally and can be used for long-range communication without the need for infrastructure such as satellites or cables.
4. Efficiency: HF transmitters can transmit at relatively low power levels and still achieve long-range communication. This makes it a cost-effective option for long-range communication.

Overall, HF communication is a cost-effective way to communicate over very long distances, especially in remote areas or in situations where other forms of communication are not available. However when there are erratic changes in the ionospheric conditions due geomagnetic storms HF communication can become quite unreliable.