Which propagation mode requires line-of-sight with the communicating station?

Which propagation mode requires line-of-sight with the communicating station?

• A. Low Frequency
• B. High Frequency
• C. Very High Frequency
• D. Ultra High Frequency

Answer: (C)

Line-of-sight is needed because higher-frequency radio waves travel in a straight path and don’t diffract around terrain or obstacles as easily as lower frequencies. Very High Frequency, which sits in the 30–300 MHz range, has wavelengths about 1 to 10 meters. At these frequencies, obstacles like hills, buildings, and trees block or weaken the signal more readily, so a clear direct path between transmitter and receiver is usually required for a reliable link. In contrast, lower frequencies (like those used for HF) can bounce off the ionosphere and travel beyond the horizon, reducing the emphasis on a direct line-of-sight path. Therefore, the propagation mode that requires line-of-sight is Very High Frequency.

Line-of-sight is needed because higher-frequency radio waves travel in a straight path and don’t diffract around terrain or obstacles as easily as lower frequencies. Very High Frequency, which sits in the 30–300 MHz range, has wavelengths about 1 to 10 meters. At these frequencies, obstacles like hills, buildings, and trees block or weaken the signal more readily, so a clear direct path between transmitter and receiver is usually required for a reliable link. In contrast, lower frequencies (like those used for HF) can bounce off the ionosphere and travel beyond the horizon, reducing the emphasis on a direct line-of-sight path. Therefore, the propagation mode that requires line-of-sight is Very High Frequency.