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.
3.3.1.3. FM demodulation
3.3.1.3.1. FM Discriminator
The number of periods of the FM discriminator can be configured between 1 to 16. The output amplitude
depends on the selected Pre-Detection filter and the discriminator number of periods.
Let us take the example of an input IF carrier which is FM modulated by a pure sub-carrier, this signal being in
the Pre-Detection filter bandwidth. -to-polar converter is:
Where:
is the sample time index,
is the number of bits on which the phase and the frequency are coded,
is the pulsation of the Center Frequency transposing synthesizer-NCO,
is the pulsation of the input signal carrier,
is the pulsation of the input modulation sub-carrier,
is the sampling frequency,
is the frequency of the input modulation sub-carrier,
is the FM frequency deviation.
The frequency output f(n) of the differentiator, where is the differentiator delay, is:
The frequency output
normalized on Full Scale is :
The level of the sub-carrier on frequency output is (expressed in dBFS):
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