Which frequency spectrum is not LOS?

Which frequency spectrum is not LOS?

• A. LF, MF, HF
• B. VHF, UHF
• C. SHF
• D. EHF

Answer: (A)

Low-frequency bands have propagation modes that don’t rely on a direct line-of-sight. LF and MF signals travel as ground waves along the Earth's surface and can diffract around obstacles, while HF signals can bounce off the ionosphere (skywave) and return to Earth far beyond the horizon. These behaviors allow communication over long distances even when the transmitter and receiver aren’t in a direct line-of-sight. In contrast, higher-frequency bands tend to propagate in straight lines and are limited by terrain and obstacles, making line-of-sight the dominant requirement for reliable communication. That’s why the lower-frequency spectrum is the one not confined to LOS.

Low-frequency bands have propagation modes that don’t rely on a direct line-of-sight. LF and MF signals travel as ground waves along the Earth's surface and can diffract around obstacles, while HF signals can bounce off the ionosphere (skywave) and return to Earth far beyond the horizon. These behaviors allow communication over long distances even when the transmitter and receiver aren’t in a direct line-of-sight.

In contrast, higher-frequency bands tend to propagate in straight lines and are limited by terrain and obstacles, making line-of-sight the dominant requirement for reliable communication. That’s why the lower-frequency spectrum is the one not confined to LOS.