Satellite Doppler Shift Calculator

What It Does

The Satellite Doppler Shift Calculator computes the maximum doppler frequency shift for a spacecraft passing over a ground station, using Δf/f = v_rel/c. Input the spacecraft's relative velocity (or orbit altitude for a quick estimate using the maximum line-of-sight rate) and the carrier frequency, and the calculator returns the maximum doppler offset and the doppler rate (Hz/s) at closest approach. Supports LEO, MEO, GEO, and lunar geometries.

Key Features

• Maximum doppler shift in Hz from carrier frequency and relative velocity
• Doppler rate (Hz/s) at closest approach for receiver loop bandwidth sizing
• Quick LEO/MEO/GEO presets with typical maximum line-of-sight velocities
• Both transmit-side and receive-side doppler computation

Why It Matters

Doppler shift is the difference between a working downlink and a silent pass. A LEO satellite at 7.5 km/s produces a doppler shift of about 50 ppm, which on an X-band downlink at 8.4 GHz means ±420 kHz of carrier offset — well outside the lock range of most narrow-bandwidth receivers without doppler tracking. The doppler rate matters too: a fast LEO pass can drift 20 kHz/sec at closest approach, demanding fast loop bandwidths in the demodulator. Sizing both at design time keeps your downlink from dropping at the worst possible moment.

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