COMMAND RANGING & TELEMETRY UNIT CORTEX
CRT QUANTUM USER'S MANUAL
Ref. DTU 100042
Is.Rev. 5.17
Date: Dec.
03, 2021Sept. 30, 2021
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It cannot be duplicated or distributed without expressed written consent.
3.6.3.5.3. Carrier Doppler Shift in Non-Coherent Mode
In non-coherent mode, the Doppler shift on the received carrier frequency depends on the operating mode: one-
way RF lock or two-way RF lock.
Besides, because the transponder locally generates the downlink carrier, the actual downlink frequency is
unknown and it can exist a frequency bias of several kHz, due to on-board oscillators drift, with respect to the
expected downlink frequency.
Consequently, contrary to the coherent mode case, there isn’t an exact a priori knowledge of the ratio between
the carrier Doppler shift and the tone Doppler shift. This ratio:
can only be approximated, using the expected value of the transponder downlink frequency. It also depends on
the tracking mode.
Example: Let us consider the following system:
Spacecraft Mode : Non-Coherent Two-way RF lock
Expected Downlink Carrier : 2250 MHz
Ranging Tone Frequency : 0.5 MHz
Downlink Frequency Bias : 20 kHz
The approximated Carrier Doppler shift / Tone Doppler shift ratio values:
whereas its real value is:
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