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.
3.3.4.6.2. Error Due to Floating Representation
The floating representation may generate an error in
(for example, 0.1 + 1.49x10
-9
s in the case
of 0.1s programming), which could have generated an error on Doppler estimation of
.
But this floating representation is converted into double, owing to rounding processing, so that this error is not
added to the previous one (provided that the programmed sampling period does not have more than 5 digits in its
fractional part).
3.3.5. Diversity Combining
3.3.5.1. General
The CORTEX CRT Quantum allows to combine two IF signals from two different polarizations, in post-detection
or pre-detection mode. This processing is available when the IF Receivers are in Video mode (PM or FM
demodulations) or PCM mode (direct PCM demodulation).
Two operating modes are supported:
Automatic selection of the best telemetry channel (no combination),
Combination of the two signals, with up to 3-dB gain when both signals have the same
level.
Maximum fading rates that can be tracked using the diversity combiner are:
Post-detection PCM mode: 10 dB/s
Post-detection video mode: 20 dB/s
Pre-detection PCM or video mode: > 30 dB/s
These maximum values are determined by combining two signals derived from the same source, one with
variable SNR and one with fixed SNR, as in depicted in the graph below. Then, the maximum fade rate is defined
as the value for which the SNR of the combined signal is not worse than the SNR of channel B.
These results have been obtained in the following configurations:
PCM signal: QPSK NRZ-L 4 Mbps, predetection filter 10 MHz
Video signal: PCM/PSK/PM NRZ-L 600 kbps, S/C 2 MHz, predetection filter 10 MHz
Diversity combiner: Combining mode “Combining”
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