Editing SimTX API/Tracking and pointing (section)

== Doppler correction ==
A satellite's signal is shifted by up to a few kilohertz at VHF and UHF during a pass, depending on its speed towards or away from the station.
* '''Receivers:''' with <code>doppler_correct</code>, the receiver's tuning is shifted by the target's downlink Doppler at the receiver's centre frequency, so the satellite's signal stays at a fixed offset in the IQ passband.
* '''Transmitters:''' with <code>doppler_correct</code>, the carrier is pre-corrected for the uplink Doppler at emission time, so the signal arrives on frequency at the satellite.

The correction is geometric. The small ionospheric Doppler (below about 2 Hz at 70 cm) remains. Doppler shifts of moving stations are always simulated, whether or not a session corrects for them.

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