In a link budget, doubling distance increases path loss by approximately how many decibels?

• A. About 3 dB
• B. About 6 dB
• C. About 9 dB
• D. About 12 dB

Answer: (B)

Doubling the distance increases path loss by about 6 dB because free-space path loss scales with the square of the distance. In the Friis equation, received power is proportional to (1/d)^2. So when distance goes from d to 2d, the received power drops by a factor of (1/2)^2 = 1/4. A drop to one quarter corresponds to a loss of 10 log10(4) ≈ 6.02 dB. That’s why the path loss in a link budget increases by roughly 6 dB when distance doubles. The other values would reflect different power factors (e.g., a factor of 2 in power for 3 dB, a factor of 8 for 9 dB, etc.), which don’t occur from simply doubling distance in free space. In real links, additional losses or gains can adjust this, but the canonical result for free-space doubling is about 6 dB.