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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:
The approximated Carrier Doppler shift / Tone Doppler shift ratio values:
whereas its real value is:
© Safran Data Systems
COMMAND RANGING & TELEMETRY UNIT CORTEX
CRT QUANTUM USER'S MANUAL
Spacecraft Mode
Expected Downlink Carrier
Ranging Tone Frequency
Downlink Frequency Bias
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f
dop_carrier
2f
dop_tone
:
Non-Coherent Two-way RF lock
:
2250 MHz
:
0.5 MHz
:
20 kHz
2250
= 2250 =
2 × 0.5
2250 + 0.02
= 2250.02 =
2 × 0.5
Safran Data Systems
.
Ref.
DTU 100042
Is.Rev.
5.17
Date:
Dec.
03, 2021Sept. 30, 2021
Page 160
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