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Which statement is true about the use of the Doppler effect in a Doppler VOR?
  • A
    By using the Doppler effect it is possible to determine the range of the aircraft from the VOR station more accurately.
  • B
    The Doppler effect is used to create a signal which is received by the aircraft’s VOR-receiver as an amplitude modulated signal.
  • C
    The Doppler effect is used to create a signal which is received by the aircraft’s VOR-receiver as a frequency modulated signal.
  • D
    By using the Doppler effect it is also possible to determine the aircraft’s approach speed to the VOR.

Doppler VOR is an evolution of CVOR and provides improved signal quality and accuracy by reducing scalloping errors. The reference signal of DVOR is amplitude-modulated and the variable signal is frequency-modulated, exactly the opposite of CVOR. The frequency-modulated signal is less prone to interference, when compared to the amplitude-modulated signal, which makes the rotating variable signal FM make direction determination more accurate.

The Doppler effect is generated by electronically-rotating the variable signal. Via this set of circular elements, the variable signal is emitted in a rotating sequence at 30 revolutions per second. When the signal is heading towards a receiver a positive doppler shift is experienced and the received frequency is slightly higher, when it is moving away, it is slightly lower.

Doppler effect, in a VOR, is not used to detect velocity. The VOR does not measure range.

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