Variables
Description
What is this formula?
The Doppler Shift calculates the frequency change observed when there is relative motion between a transmitter and a receiver. As the distance between them changes, the received frequency differs from the transmitted frequency.
When to use it
Use this formula when analyzing mobile communications, satellite links, radar systems, aircraft communications, vehicle tracking systems, and wireless networks involving moving objects.
Example
A vehicle moves directly toward a transmitter at 30 m/s while receiving a carrier frequency of 900 MHz.
Formula:
fd = (v*fc)/c
Substitution:
fd = (30*900000000)/(299792458)
Result:
fd = 90.06 Hz
The received signal experiences a Doppler shift of approximately 90 Hz.
Applications
Cellular communications, satellite communications, radar systems, GPS receivers, aircraft communications, vehicle tracking, wireless networking, and mobile radio systems.
Note
This formula is an approximation valid when the relative velocity is much smaller than the speed of light and the motion is purely radial. The complete Doppler equation includes the angle between the direction of motion and the propagation path. For relativistic velocities or non-radial motion, more general Doppler models should be used.