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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.
Where:
The frequency output f(n) of the differentiator, where �� is the differentiator delay, is:
�� ( �� ) =
The frequency output ��
��
��������
The level of the sub-carrier on frequency output is (expressed in dBFS):
© Safran Data Systems
COMMAND RANGING & TELEMETRY UNIT CORTEX
CRT QUANTUM USER'S MANUAL
��
��
�� ( �� ) =
[ ( ��
����
��
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.
��
��
��
{ ( ��
)
− ��
+
��
����
����
��
��
(��) normalized on Full Scale is :
��������
��(��
− ��
)
�� × ∆��
��
����
( �� ) =
+
��
��
��
��
⁄
��
( ��
) = ����������
��
��������
����
����
This document is the property of
It cannot be duplicated or distributed without expressed written consent.
��
∆��
��
− ��
)
+
������ (
��
����
��
��
��
��
����
∆��
��
��
× (−��)������ [��
×
����
��
��
��
����
��
��
����
������ [��
��]
��
��
×
× (−��) ������ [��
��
⁄
����
��
��
��
��
��
�� × ∆��
[
] − �� + ����������
����
��
��
⁄
��
Safran Data Systems
.
Ref.
DTU 100042
Is.Rev.
Date:
Dec.
03, 2021Sept. 30, 2021
-to-polar converter is:
)] + ��(��)
��
��
��
] ������ [��
(�� +
) ×
]}
����
��
��
��
��
��
(�� +
) ×
]
����
��
��
��
��
����
������ [��
��]
��
��
{
}
��
����
��
��
��
��
5.17
Page 30
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