What frequency range is considered "line of sight" for RF signal propagation?

The frequency range categorized as "line of sight" for RF signal propagation is primarily found within the UHF band. Line of sight propagation occurs when a transmission is capable of being received directly by the receiver without significant obstruction. UHF, which typically ranges from 300 MHz to 3 GHz, is effective for this type of communication due to its relatively short wavelengths, allowing radio waves to travel in a straight line. This characteristic enables UHF signals to maintain a clear path between transmitter and receiver, making it suitable for applications such as television broadcasts, mobile phones, and two-way radios.

In contrast, the other frequency ranges—VHF, HF, and LF—exhibit different propagation characteristics. VHF, although capable of line of sight communication, is characterized by a longer wavelength and is often used for radio and television broadcasts where covering larger areas is essential. HF operates primarily below 30 MHz and is more influenced by atmospheric conditions and can propagate over long distances using skywave propagation. LF, which covers frequencies from 30 kHz to 300 kHz, typically has very long wavelengths and primarily supports very low frequency applications, like navigational signals, but does not support line of sight propagation effectively.