Question T3C08
From subelement T3 - T3C
What causes tropospheric ducting?
Why is this correct?
Tropospheric ducting occurs when temperature inversions create atmospheric layers where cooler air gets trapped below warmer air in the troposphere. This forms a 'duct' that can guide VHF and UHF signals for hundreds of miles beyond normal line-of-sight range. Lightning (A), solar activity (B), and storm updrafts (C) don't create the stable layered atmospheric conditions needed for ducting.
Memory tip
Weather-related propagation effects follow predictable patterns: temperature inversions affect the troposphere (lower atmosphere), while solar phenomena affect the ionosphere (upper atmosphere). Remember that ducting needs stable atmospheric layering, not chaotic weather events.
Learn more
Tropospheric ducting demonstrates how atmospheric conditions can extend frequency privileges beyond normal coverage areas. In practical operation, ducting often occurs during high-pressure weather systems when temperature inversions are stable. This propagation mode is particularly valuable for VHF/UHF emergency communications when repeaters are unavailable, as it can provide direct simplex contacts across much greater distances than typical line-of-sight limitations would allow.
Think about it
Why do you think stable atmospheric layering creates better signal propagation than turbulent weather conditions like storms or high winds?