Question
What is Doppler shift in reference to satellite communications?
Answer Options
- A) A change in the satellite orbit
- B) A mode where the satellite receives signals on one band and transmits on another
- C) An observed change in signal frequency caused by relative motion between the satellite and Earth station
- D) A special digital communications mode for some satellites
Correct Answer: C
Explanation
Doppler shift is a common phenomenon in physics where the frequency of a wave appears to change when the source of the wave is moving relative to the observer. This is the same effect that causes a train whistle to drop in pitch as it passes you.
In satellite communications, Doppler shift is an observed change in signal frequency caused by the relative motion between the satellite and Earth station. As the low-Earth orbit (LEO) satellite approaches, the frequency appears higher; as it moves away, the frequency appears lower. Operators must constantly adjust their radio frequency to compensate for this shift.
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