The range limitation of TACAN reception is based on

• A. Inverse square law
• B. Line of sight
• C. Atmospheric refraction
• D. Ground conductivity

Answer: (B)

Line of sight governs TACAN range. TACAN uses UHF signals that travel in straight lines and are blocked by the Earth's curvature, so the practical limit is the radio horizon between the ground station and the aircraft. The distance you can reach grows with height of both antennas, since higher points see farther over the curve. A handy rule is that the usable distance is roughly 1.23 times the sum of the square roots of the transmitter and receiver heights (in feet), giving nautical miles. The inverse square law describes how power falls off with distance, but it doesn’t set the actual usable range for a line-of-sight system like TACAN; once the path is geometrically blocked, reception is lost regardless of power. Atmospheric refraction and ground conductivity have some minor effects, but they don’t define the fundamental range limitation.