3
MODULE DESCRIPTION
Inmarsat B
I and Q baseband signals taken out of the IF ports of the mixers are amplified by operational amplifiers
before they are filtered in low-pass switch capacitor filters. Those filters are of the same type as those used
in the transmitter part. The cut off frequency of the filters is selected by the frequency of the RX-SC
synthesized oscillator. The output signals of the switch capacitor filters are further amplified before they
are sampled in two 12 bit analogue to digital converters. The data format out of these A/D converters is
a 12- bit parallel format converted to a serial bit stream in a 24 bit shift register. This serial bit stream
representing the sampled I and Q signals is clocked into the digital signal processor.
Data receiver
From the quadplexer, the data signal transmitted from the triplexer at the antenna unit is filtered out in
a 99 MHz bandpass filter. The data receiver is built up around the same FM integrated subsystem where
an 87 MHz crystal oscillator is used to down convert the 99 MHz data signal to a 12 MHz IF before the
data bit is recovered in the FM detector. The 4800 baud data stream is transferred to the CSP/VDP board.
Data transmitter
The data transmitter is built up as an FSK modulator equal to the one placed on the triplexer board. The
data stream which is received from the CSP/VDP board is modulated into a carrier of 87 MHz with a
frequency shift of ± 150 kHz. A high-pass filter with a cut off frequency of 83 MHz increases the isolation
between the 62.9 MHz transmitter signal and the vector modulator in the data transmitter to lower
intermodulation products. Finally the signal level from the data transmitter is amplified before it enters the
quadplexer.
Reference oscillator
Due to the rigorous frequency accuracy requirement over a relatively wide temperature range, an oven
controlled crystal oscillator of 20.16 MHz is used to derive all critical reference frequencies.
A frequency doubler generates a 40.32 MHz signal to the ADE.
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Summary of Contents for Inmarsat B
Page 1: ...SAILOR Inmarsat B Workshop Manual W4400GB0 ...
Page 2: ...Inmarsat B Workshop Manual 9905 ...
Page 7: ...CONTENTS 1 INTRODUCTION 1 1 1 1 SYSTEM COMPONENTS 1 2 1 2 TECHNICAL DATA 1 2 9849 Inmarsat B ...
Page 46: ...4 ACCESSORIES Inmarsat B PAGE 4 3 Inmarsat B 9849 Diagram Veritas connection box ...
Page 124: ...CONTENTS 8 PERFORMANCE CHECK AFTER REPAIR 8 1 8 1 START UP SEQUENCE 8 1 9936 Inmarsat B ...
Page 127: ...CONTENTS 9 SERVICE 9 1 9 1 CHECK OF OCXO 9 1 9936 Inmarsat B ...
Page 129: ...CONTENTS 10 PARTS LISTS 10 1 9901 Inmarsat B ...
Page 133: ...CONTENTS 11 ABBREVIATIONS 11 1 Inmarsat B 9849 ...