H12-311_V3.0 · Question #213
When installing a long-distance point-to-point radio frequency communication link, if the distance between the transmitting and receiving antennas exceeds how many kilometers, the influence of the…
The correct answer is D. 11.3km. Option D (11.3 km) is the standard threshold used in telecommunications engineering for point-to-point RF link design. Beyond this distance, the Earth's bulge along the signal path becomes large enough to obstruct or significantly attenuate the direct signal, and engineers must…
Question
When installing a long-distance point-to-point radio frequency communication link, if the distance between the transmitting and receiving antennas exceeds how many kilometers, the influence of the curvature of the earth needs to be considered?
Options
- A3.3km
- B5.3km
- C7.3km
- D11.3km
How the community answered
(36 responses)- A3% (1)
- B6% (2)
- C6% (2)
- D86% (31)
Explanation
Option D (11.3 km) is the standard threshold used in telecommunications engineering for point-to-point RF link design. Beyond this distance, the Earth's bulge along the signal path becomes large enough to obstruct or significantly attenuate the direct signal, and engineers must apply Earth-curvature correction factors (using an effective Earth radius, typically k = 4/3) when calculating clearance for the Fresnel zone.
Options A (3.3 km), B (5.3 km), and C (7.3 km) are distractors that represent plausible-sounding but incorrect thresholds - at those shorter distances, the geometric effect of Earth's curvature on the signal path is negligible and can safely be ignored in link budget calculations.
Memory tip: Think "11.3 = Earth curve concern" - the number 11 looks like two antenna towers, and once you need two towers far enough apart (beyond 11 km), you must "curve" your calculations to account for the Earth between them.
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