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Which aeronautical radio frequency band uses refraction within ionospheric layers?
  • A
    HF
  • B
    VHF
  • C
    UHF
  • D
    VLF

Refer to figure.
Long-distance communication works on skywave propagation, where radio waves are directed at an angle to the sky so they refract back to earth from the ionosphere. By this method it is given that frequencies in the High Frequency (HF) band can travel beyond the horizon, following the curvature of the earth, and can be received at long distances.

Because of the refraction and reflection properties of the HF band, these frequencies are also good for transmission in mountainous terrains which prevent line of sight communications.

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