2
SYSTEM DESCRIPTION
Inmarsat B
2.2
BELOW DECK EQUIPMENT
The below deck equipment or transceiver unit as it is called consists of five printed circuit boards (modules)
as shown in fig. 2.3.
Pax
CSP/VDP
Modem
SPS
Rear Panel Connectors
SMI
SMPS
35974
Fig. 2.3.
SPS board
The SPS (signal path and synthesizer) board is the interface between the analogue RF parts at the antenna
unit and the digital signal processing in the transceiver unit. The receiver IF of 21.4 MHz is converted to
baseband, sampled and processed in a digital signal processor.
The transmitter part consists of a quadrature mixer where two baseband data signals are up converted and
combined to a 62.9 MHz IF signal. The baseband signals are generated in the modem module.
A data receiver and transmitter for communication with the antenna unit is also placed at this board.
All critical frequencies are derived from the system reference oscillator. The oscillator is a crystal oscillator
built into an oven.
The RF input/output to/from the SPS board is a single coax connection. Therefore, a combiner/splitter
circuit is used to combine the RF signals to be sent to the antenna unit and the split-out received RF signal
to the respective blocks which are to use them.
Modem board
The purpose of the modem board is to code data flow sent from the terminal to the satellite and decode data
flow received from the satellite. Coding is used to make it possible to detect and correct bit errors, thus
increasing the quality of the communication.
To increase the security, data bits are scrambled. Scrambling and descrambling takes place in the modem.
Data flow is transmitted/received in frames. The contents of a frame, besides the data to be transmitted
or received, are bit sequences helping the modem to synchronise. The modem takes care of the frame
format in both the receiver and the transmitter directions.
CSP/VDP board
The CSP/VDP board consists of two functionally separate parts. The CSP (control and signalling processor)
is the main processor in the system and takes care of the satellite protocol, man/machine and external
equipment interfaces.
The VDP (voice and data processor) is a digital signal processor which handles voice coding and decoding
and is the interface between modem and the PAX module for data and fax services.
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Содержание Inmarsat B
Страница 1: ...SAILOR Inmarsat B Workshop Manual W4400GB0 ...
Страница 2: ...Inmarsat B Workshop Manual 9905 ...
Страница 7: ...CONTENTS 1 INTRODUCTION 1 1 1 1 SYSTEM COMPONENTS 1 2 1 2 TECHNICAL DATA 1 2 9849 Inmarsat B ...
Страница 46: ...4 ACCESSORIES Inmarsat B PAGE 4 3 Inmarsat B 9849 Diagram Veritas connection box ...
Страница 124: ...CONTENTS 8 PERFORMANCE CHECK AFTER REPAIR 8 1 8 1 START UP SEQUENCE 8 1 9936 Inmarsat B ...
Страница 127: ...CONTENTS 9 SERVICE 9 1 9 1 CHECK OF OCXO 9 1 9936 Inmarsat B ...
Страница 129: ...CONTENTS 10 PARTS LISTS 10 1 9901 Inmarsat B ...
Страница 133: ...CONTENTS 11 ABBREVIATIONS 11 1 Inmarsat B 9849 ...