13 / 20

Which of the following elements influences the reception of VHF signals?

  • A

    Height of ionosphere.

  • B

    Twilight error.

  • C

    Altitude.

  • D

    Shoreline effect.

Refer to figures.
The VHF band extends from 30 MHz to 300 MHz. The frequency range normally used for Aeronautical Mobile Service (AMS) voice communication is defined between 118.000 and 136.975 MHz. This is a subpart of the VHF band. Any VHF transmission has the form of direct waves (space waves).

Space waves travel in a straight line. For efficient VHF transmissions, line-of-sight is required between the transmitter and the receiver. In other words, the straight line joining the transmitter and receiver must be relatively free of obstacles (i.e. mountains) since they might block the signal. Low level flight reduces greatly the range of reception, due to the presence of hills, mountains, bumps on the surface of the Earth and the roundness of the Earth itself. Consequently, high level flight provides better chances to establish communication on a VHF frequency. Therefore, a factor that affects the reception of a VHF signal is the altitude of the receiver.

Your Notes (not visible to others)



This question has appeared on the real examination, you can find the related countries below.

  • Austro Control