Tropospheric ducting can allow VHF/UHF/microwave signals to travel?

  • ABeyond the normal radio horizon
  • BOnly through underground conductors
  • COnly vertically upward
  • DOnly within an antenna feed line
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Correct Answer: A. Beyond the normal radio horizon
Explanation: Strong refractive-index gradients can trap radio waves in atmospheric ducts and extend propagation beyond the normal horizon.
Reference: Standard antenna and wave propagation: tropospheric propagation