How does RF LOS differ from visual LOS?

• A. RF LOS does not require line of sight.
• B. RF LOS is accompanied by a Fresnel zone, a series of concentric ellipsoid-shaped areas around the visual LOS path.
• C. RF LOS and visual LOS are identical concepts.
• D. RF LOS is only relevant for microwave frequencies.

Answer: (B)

The main idea being tested is that radio frequency links rely on more than just a straight line between transmitter and receiver. In RF propagation, energy doesn’t travel as a single line; it occupies a surrounding volume called the Fresnel zones. The first Fresnel zone is an ellipsoidal region around the direct line-of-sight path. For a reliable RF link, this zone should be clear of obstructions because objects within it cause diffraction and weaken the signal, even if the direct path looks unobstructed.

Thus, RF line of sight differs from visual line of sight because visual LOS just asks whether the direct path can be seen, while RF LOS includes maintaining clearance of the Fresnel zone around that path to minimize diffraction loss. The other statements are not accurate: RF links still need a path, RF LOS isn’t identical to visual LOS, and Fresnel zones apply across RF frequencies (not only microwave).