Question 6A449

Radio waves in the Very High Frequency (VHF), Ultra High Frequency (UHF), and microwave bands primarily propagate via line-of-sight (LOS). This means they travel in a straight line from the transmitting antenna to the receiving antenna, much like visible light. The reason for this behavior is that their wavelengths are too short to be significantly refracted or reflected by the Earth's ionosphere, which is the primary mechanism for long-distance skywave communication at lower frequencies (like HF). Additionally, these higher frequencies tend to be blocked by obstacles such as buildings, terrain, and even the curvature of the Earth, rather than diffracting around them effectively. The frequency range of approximately 50 MHz to 30,000 MHz (30 GHz) directly corresponds to these bands: * VHF: 30-300 MHz * UHF: 300 MHz - 3 GHz * Microwave: Frequencies above 1 GHz, often considered from 3 GHz upwards. Therefore, both the descriptive band names (VHF, UHF, microwave) and the associated frequency range (50-30,000 MHz) correctly identify frequencies that exhibit substantially line-of-sight propagation.