T8B07 With regard to satellite communications, what is Doppler shift?
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 the earth station
D. A special digital communications mode for some satellites
- C. An observed change in signal frequency caused by the relative motion between the satellite and the earth station
- Doppler shift or Doppler effect describes the way the downlink frequency of a satellite varies by several kilohertz during an orbit due to its motion relative to the receiving station. As the satellite is moving toward the receiving station, the frequency of the satellite’s signal will increase by a small amount. After the satellite passes overhead, the frequency of the signal will begin to decrease. This is the same effect that causes the sound of a vehicle’s horn or whistle to change pitch as it moves past you. [Ham Radio License Manual, page 6-32]