COMMAND RANGING & TELEMETRY UNIT CORTEX
CRT QUANTUM USER'S MANUAL
Ref. DTU 100042
Is.Rev. 5.17
Date: Dec.
03, 2021Sept. 30, 2021
This document is the property of Safran Data Systems.
It cannot be duplicated or distributed without expressed written consent.
3.6.10. INMARSAT / LMCO Tone Standards
3.6.10.1.General
The ranging procedure consists of a sequential transmission of four tones (1 major and 3 minor). Typically, the
minor tones are transmitted first, starting with the lowest frequency tone, followed by the major tone. On each
tone, a 6-second set time allows all ground and on-board receivers in the ranging loop to lock onto the signal and
the various PLLs to stabilize.
The tone order can be programmed as well as the number of measurements on each tone. Tone frequencies are
fixed. Ranging sequences with 2, 3 or 4 identical tones are accepted.
3.6.10.2.Tone Frenquencies
The frequency plan consists of four tones, derived by division from the 10-MHz reference clock:
Major tone 27,778 kHz (10
7
/360).
Minor tones 3968 Hz (27.778/7).
283 Hz (3968/14).
35 Hz (283/8).
P and Q factors for the INMARSAT and LMCO standards are « hard-wired » (not programmable):
Table 27: INMARSAT/LMCO Tone Standard. Tone Definition
3.6.10.3.Minor Tone Sub-Carrier
For reasons of modulation efficiency, the minor tones phase-modulate a 19-kHz sub-carrier (INMARSAT
standard) or a 27.778-kHz sub-carrier (LMCO standard). The default setting for the modulation index is 0.8
radian (can be adjusted in the Windows registry).
3.6.10.4.Ranging Sequence
Next figure illustrates the ranging measurement sequence:
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