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Why do VHF radio signals used for communication and navigation have a limited range?
  • A
    Ground waves are absorbed by the Earth’s surface.
  • B
    Direct waves interfere with ionosphere waves.
  • C
    Sky waves are refracted from the D-layer.
  • D
    Because of the curvature of the Earth.

An aircraft uses a range of radio frequencies to navigate to its destination and communicate with air traffic control. Aircraft short range communication uses VHF band between 118 MHz and 137 MHz to talk with air traffic control.

These VHF frequencies have a line of sight capability, meaning that they travel in a straight line whilst the surface of the Earth is a downward-curved surface (declination), relative to the signal. Eventually, at a certain distance, the receiving aircraft will fall out of the line-of-sight of the transmitter – because the signals normally do not follow the curvature of the Earth

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