Question 44G5

VHF transmissions are called "line of sight" because their radio waves travel largely in straight lines and do not significantly follow the Earth's curvature or reflect off the ionosphere. However, this "radio line of sight" is usually much further than the *visual* line of sight from a bridge. Radio waves can travel beyond what the human eye can see, especially with elevated antennas, due to a phenomenon called the radio horizon, which extends slightly past the optical horizon due to atmospheric refraction. Therefore, VHF communications are effective with stations that are not necessarily within direct visual range, making D the correct answer. Regarding the other options: * **A) and C):** Antenna height (for both vessel and coast stations) significantly affects the radio horizon and thus the radius of propagation for VHF. Higher antennas extend the range. * **B):** While 10 NM might be a common practical working range for some vessel-to-coast station communications, it's not a universal limit imposed by the "line of sight" principle; actual range can be much greater depending on antenna heights and power.