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.
3.3.4. Doppler Measurement
A single Doppler port is used for transmitting IF offset measurements or integrated phase measurements.
3.3.4.1. Sampling Mode
Elementary accumulated phases are sampled at the rate specified by the parameter « Doppler measurement
sampling rate » (every 100 ms to every 10 seconds). Phase generation period depends on the sampling rate
value.
If the sampling rate is a multiple of 10 ms, the accumulated phases are generated each 10 ms in order to take
advantage from raw data. Thus, Doppler measurement is based on exact values of phase.
If the sampling rate is not a multiple of 10 ms, the raw accumulated phases are sampled every 10 ms. To obtain
the accumulated phase at the desired date, an interpolation process is used.
3.3.4.2. Accumulated Phase Format
Elementary 32-bit phase values are accumulated in a 96-bit internal counter. The 21 least significant bits and the
11 most significant bits are discarded and the resulting 64-bit phase values are made available to remote
Doppler clients.
The accumulated phase resolution is
cycle (
radian = 0.175°).
Thus, the 64-bit phase counter capacity is:
(in seconds) where IF is the input IF frequency.
For example, at 70 MHz, the counter capacity is more than 4 years.
Samples are stored for further transmission, in a measurement block which size is programmable between 1 and
1000 elementary measurement(s). The first measurement in the block is time-tagged.
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