tools / RF & SDR
Doppler Shift Calculator
Enter a carrier frequency and a relative speed and get the Doppler shift. It comes up everywhere I work: catching a satellite pass with an SDR, tracking a fast vehicle, or understanding why a GPS receiver has to hunt across a shifted L1 carrier.
Use the speed component along the line between the two ends, not raw ground speed.
How it works
The shift
Doppler shift is frequency times relative velocity over the speed of light (Δf = f·v/c). Closing speed raises the frequency, opening speed lowers it. The higher the carrier, the bigger the shift for the same speed.
FAQ
How much does GPS Doppler shift?
GPS L1 sits at 1575.42 MHz. At 100 m/s of line-of-sight speed the shift is about 525 Hz, and a low satellite pass can swing several kHz, which the receiver has to track.
Do I use ground speed or line-of-sight speed?
The component along the line between transmitter and receiver. Motion straight across the path produces no shift at that instant.
