What is the formula for VHF range based on the height of the antenna?

The formula for VHF range is derived from the height of the antenna and is conventionally expressed as VHF range (in nautical miles) equal to a constant multiplied by the square root of the height of the antenna (in feet). This relationship indicates that as the height of the antenna increases, the range of VHF communication also increases, as a higher antenna can transmit signals over a greater distance due to reduced signal obstruction by the Earth's curvature.

The correct choice indicates that this relationship is approximately 1.25 times the square root of the antenna height. This multiplier reflects empirical measurements and is used in practice to provide a reliable estimate of how VHF range changes with antenna height.

The other potential choices, while based on the same underlying principle, deviate from this specific empirical correlation, which has been established through testing and observation in the field of aviation communications. Hence, the choice of 1.25 as the factor captures the most accurate approximation of VHF range based on antenna height according to established guidelines.