Which propagation mode dominates the VHF and UHF bands?

Which propagation mode dominates the VHF and UHF bands?

• A. Near-field coupling
• B. Ground wave
• C. LOS
• D. Sky wave

Answer: (C)

Line-of-sight propagation dominates in the VHF and UHF bands. As frequency rises, the ground-wave component becomes negligible because surface waves attenuate quickly, so signals don’t follow the ground well. The ionosphere also stops acting as a good reflector at these higher frequencies, so sky waves don’t reliably bounce back to the Earth for long-distance links. That means most VHF/UHF communication travels in straight lines between transmitter and receiver, limited by the horizon. To reach beyond that line-of-sight, you typically need taller antennas, repeaters, or satellites. Near-field coupling is only a concern at very short ranges, not for typical VHF/UHF communications.

Line-of-sight propagation dominates in the VHF and UHF bands. As frequency rises, the ground-wave component becomes negligible because surface waves attenuate quickly, so signals don’t follow the ground well. The ionosphere also stops acting as a good reflector at these higher frequencies, so sky waves don’t reliably bounce back to the Earth for long-distance links. That means most VHF/UHF communication travels in straight lines between transmitter and receiver, limited by the horizon. To reach beyond that line-of-sight, you typically need taller antennas, repeaters, or satellites. Near-field coupling is only a concern at very short ranges, not for typical VHF/UHF communications.