Sailor Inmarsat B, SC4350, SA4415, ST4425 B, SP4360 Workshop Manual

SAILOR

Inmarsat B

Workshop Manual

W4400GB0

Inmarsat B

Workshop Manual

9905

9936

Please note

Any responsibility or liability for loss or damage in connection with the use of this product and the
accompanying documentation is disclaimed.

The information in this manual is furnished for informational use only, is subject to change without notice,
may contain errors or inaccuracies, and represents no commitment whatsoever.

This agreement is governed by the laws of Denmark.

Doc.no.: W4400GB0 Issue: D/9936

9936

CONTENTS

1 INTRODUCTION 1-1

1.1 SYSTEM COMPONENTS 1-2

1.2 TECHNICAL DATA 1-2

2 SYSTEM DESCRIPTION 2-1

2.1 ABOVE DECK EQUIPMENT 2-1

2.2 BELOW DECK EQUIPMENT 2-6

3 MODULE DESCRIPTION 3-1

3.1 ABOVE DECK EQUIPMENT 3-1

3.2 BELOW DECK EQUIPMENT 3-16

4 ACCESSORIES 4-1

4.1 SC4350 CONTROL UNIT 4-1

4.2 SD4360 DISTRESS BUTTON 4-1

4.3 H4394/95 VERITAS CONNECTION BOX 4-2

4.4 H4396 T-CONNECTION BOX 4-2

5 DISASSEMBLING, CONNECTORS, MODULE AND

SOFTWARE LOCATION 5-1

5.1 ANTENNA UNIT 5-1

5.2 TRANSCEIVER UNIT 5-17

5.3 HANDSET 5-25

5.4 CONTROL UNIT 5-25

6 SERVICE INTERFACE 6-1

6.1 ADE 6-2

6.2 ALARM 6-4

6.3 BOOK 6-4

6.4 BUTTONS 6-5

6.5 CAN 6-5

6.6 CASC 6-5

6.7 COURSE 6-7

6.8 CU 6-7

6.9 DATE 6-9

6.10 EXIT 6-10

6.11 GYRO 6-10

6.12 HELP 6-10

6.13 LES 6-11

6.14 LOG 6-11

6.15 MODEM 6-12

6.16 NUMERIC 6-13

6.17 PAX 6-13

6.18 POSITION 6-14

6.19 PRINTER 6-14

6.20 REGION 6-15

6.21 REMARK 6-16

6.22 SES 6-16

6.23 SNU 6-17

Inmarsat B

CONTENTS Inmarsat B

6.24 SPEED 6-18

6.25 SPS 6-18

6.26 STATUS 6-19

6.27 SU 6-20

6.28 TEST 6-20

6.29 TIME 6-22

6.30 VDP 6-23

6.31 VERSION 6-23

7 TROUBLE SHOOTING 7-1

7.1 BATTERY BACKUP 7-1

7.2 REAL-TIME CLOCK 7-1

7.3 EEPROM 7-1

7.4 INMARSAT IDs 7-2

7.5 +15V DC 7-2

7.6 FACTORY RESET 7-2

7.7 TX INHIBIT 7-2

7.8 DISTRESS BUTTON 1 7-3

7.9 DISTRESS BUTTON 2 7-3

7.10 TELEX INPUT 7-3

7.11 PRINTER INPUT 7-4

7.12 ADE INPUT 7-4

7.13 NMEA POSITION INPUT 7-5

7.14 SERVICE INPUT 7-5

7.15 NMEA GYRO INPUT 7-5

7.16 PRINTER ON-LINE 7-6

7.17 HEADING KNOWN 7-6

7.18 POSITION KNOWN 7-6

7.19 OCEAN REGION VALID 7-7

7.20 CONTROL UNIT FOUND 7-7

7.21 SCANBUS DATA TRANSMISSION 7-7

7.22 SCANBUS DATA RECEPTION 7-7

7.23 TU BUS 7-8

7.24 MODEM FOUND 7-8

7.25 MODEM ACTIVE 7-8

7.26 MODEM RX SU RATIO 7-9

7.27 SPS FOUND 7-9

7.28 SPS RX IF 7-9

7.29 SPS RX FILTER 7-9

7.30 SPS TX IF 7-10

7.31 SPS TX FILTER 7-10

7.32 SPS DSP 7-10

7.33 SPS OCXO 7-11

7.34 SPS RX S/N RATIO 7-11

7.35 ADE FOUND 7-11

7.36 DOWN CONVERTER LOCKED 7-12

7.37 TRACKING RECEIVER LOCKED 7-12

7.38 UP CONVERTER LOCKED 7-12

7.39 HPA FAILED 7-13

7.40 HPA TIMED OUT 7-13

7.41 HPA STOPPED 7-13

7.42 ADE READY 7-14

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CONTENTS Inmarsat B

9936

7.43 ADE IDLE 7-14

7.44 ANTENNA DIRECTION 7-14

7.45 ADE AZIMUTH RATE SENSOR 7-15

7.46 ADE ELEVATION RATE SENSOR 7-15

7.47 ADE CROSS-ELEVATION RATE SENSOR 7-15

7.48 ADE INCLINOMETER 7-16

7.49 ADE CONNECTION STABILITY 7-16

7.50 VDP RUNNING 7-17

7.51 VDP MODEM DETECTED 7-17

7.52 VDP CLOCK DETECTED 7-17

7.53 PAX FOUND 7-18

7.54 PAX RUNNING 7-18

7.55 PAX PHONE 1 ACTIVITY 7-18

7.56 PAX PHONE 2 ACTIVITY 7-19

7.57 PAX PHONE 1 PABX SETTING 7-19

7.58 PAX PHONE 2 PABX SETTING 7-19

7.59 PAX PHONE 1 LINE NOISE 7-20

7.60 PAX PHONE 2 LINE NOISE 7-20

7.61 SPS OCXO WARM 7-20

7.62 ADE FAILED 7-21

7.63 ADE CONTROL INPUT 7-21

7.64 ADE CONTROL OUTPUT 7-21

8 PERFORMANCE CHECK AFTER REPAIR 8-1

8.1 START-UP SEQUENCE 8-1

9 SERVICE 9-1

9.1 CHECK OF OCXO 9-1

10 PARTS LISTS 10-1

11 ABBREVIATIONS 11-1

CONTENTS

1 INTRODUCTION 1-1

1.1 SYSTEM COMPONENTS 1-2

1.2 TECHNICAL DATA 1-2

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1 INTRODUCTION

This manual describes the technical aspects of the Inmarsat B terminal. The purpose of the manual is
to provide the service technician with the knowledge about the system needed to locate faults and carry
out repair and performance checks after repair.

The contents of this manual have been structured as follows.

This chapter contains a brief description of the units of which a terminal consists, including accessories.
At the end of this chapter, technical specifications are listed.

Chapter 2 describes the system concept concerning antenna platform, its stabilisation and RF signal path
and finally the transceiver unit.

Chapter 3 is a technical description of the modules of which the antenna and transceiver unit consist.

Chapter 4 is a technical description of the accessories.

Chapter 5 concerns disassembling, connectors, module and software location.

Chapter 6 is a description of the commands in the service interface program, a software program which
is helpful during installation and trouble shooting.

Chapter 7 is a more detailed description of the self-test command and its use in locating faults.

Chapter 8 concerns performance checks after repair.

Chapter 9 describes preventive maintenance and how to adjust the system reference oscillator.

Chapter 10 contains the parts lists.

Chapter 11 is a list of the abbreviations used in this manual.

Note:

All descriptions of the ADE especially the ADE search are valid from ADE/TSP SW version 2.3.0 only.

1 INTRODUCTION Inmarsat B

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1.1 SYSTEM COMPONENTS

An Inmarsat B terminal can be supplied with various types of service and accessories. The drawing below
shows an installation with the various types of accessories.

ADE: The ADE (Above Deck Equipment) consists of a stabilised platform pointing the

antenna towards the satellite independent of the motion of the ship. Besides the
stabilisation including motors, sensors, tracking and stabilisation processor, the
platform also contains the main part of the RF equipment.

BDE: In the BDE (Below Deck Equipment) are placed the first/last part of the transmitter/

receiver consisting of a baseband UP and DOWN converter. Besides the interface
circuits for the various types of externally connected equipment, the BDE also
contains the signal processing, i.e. error correcting coding/decoding, voice coding/
decoding etc.

Handset: The control handset SC4345 is an integrated handset with display and keyboard used

when a voice call is in progress. A call is set up by entering the phone number from
the handset keyboard. A voice distress call can be started by removing the handset
from the hook and activating the distress button placed in the hook. Another function
of the handset is to use it as a control and set-up unit, where functions like the selection
of coast station and satellite can be carried out.

Control unit: The control unit SC4350 is a desk/bulkhead mounted keyboard and display with an

additional handset without keyboard and display.

Distress button: The distress button can be used to activate a voice or a telex distress alert. The kind

of distress alert the button is used for is selected during installation.

Connection
box: If there is a need for the connection of more than one handset or control unit, the

connection box is used. A maximum of five handsets or control units can be connected
to one transceiver unit which is possible by using four connection boxes.

Veritas: The Veritas connection box can be used as an interconnection box between the

transceiver unit and other system units using ship installation cables. Cables of that
type cannot be connected directly to the relatively small SUB-D connectors at the rear
panel of the transceiver unit.
Inside the Veritas connection box, to interface with ship installation cables, there is a
single printed circuit board containing SUB-D connectors to interface with the
transceiver unit and wire terminal blocks. Besides interfacing between transceiver
unit and ship installations, a gyro repeater is also included. The gyro repeater can be
used if there is no NMEA signal from the gyro of the ship.

1 INTRODUCTION Inmarsat B

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Inmarsat B

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SAT-B TRANSCEIVER

S.P. RADIO DENMARK

PABX Connection or

Push Button Telephone

32213E

Gyro NMEA

GPS NMEA

PABX

Heading Information

56/64 Kbit/sec.

Async./Sync.

Position Information

Personal

Computer

Heading Information

or Gyro

Distress Key

SD4360

Transceiver ST4425 Power Cable DC 24V

Compass

Keyboard

Telex

H1640

Maritime Computer

Connection

H4396

Box

Local Net

Matrix Printer

H1252

Control

Unit

SC4350

ABOVE DECK

BELOW DECK

SC4345

Control Handset

SAT-B Antenna

SA4415

Fascimile (G3)

Veritas

H4394/95

Connection Box

SAT-B Transceiver

ST4425C

can be replaced by Control Unit

All Control Handsets SC4345

SC4350 and vice versa.

Optional

Converter

Hard DiskOn / Off

1 INTRODUCTION Inmarsat B

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1.2 TECHNICAL DATA

Designation: SAT-B Ship Earth Station (SES) maritime class 1 with area group call capability and

normal tuning range, designed according to Inmarsat B System Definition Manual and
GMDSS requirements.

Configuration: SAT-B antenna SA4415

SAT-B transceiver, 24V ST4425 B/C
Control handset SC4345
Control unit, desk/bulkhead SC4350
Distress key SP4360

Interconnection: SAT-B antenna (ADE) to SAT-B transceiver (BDE):

Single coaxial cable (RG 214) up to 100 m carrying Rx/Tx IF signals (21.4/62.9 MHz),
data (4.8 kbit/s half duplex), 40.32 MHz reference signal and ADE power (40V DC).

SAT-B transceiver (BDE) to control handset and/or control units:
Multiconductor cable (8*0.25 mm2 + screen) up to 300 m implementing Scanbus
interface (LAN 76.8 kbit/s, ISOOSI 1-4), audio (Rx/Tx audio signal, 0 dBm) and power
(24V DC).

Services: Telephony incl. echo cancellation and DTMF signalling (APC vocoder, 16 kbit/s).

Telex (ITA-2, 50 baud).
Data communication (Hayes compatible (AT), 9.6 kbit/s).
Facsimile (CCITT group 3, 9.6 kbit/s).

Optional:
High speed data communication (56/64 kbit/s),

All modes available as duplex and fixed-originated simplex.

External I/F: Scanbus:

(DB-9 connector) Connection of control unit.

NMEA:
(DB-9 connector) Connection of 2-wire NMEA to GPS and GYRO.

DATA: (DB-9 connector) Connection of personal computer.

1 asynchronous serial (high speed) DTE/DCE port (9.6, 56, 64 kbit/s)
according to CCITT Rec. V.11 and X.27.

PC/Printer: (DB-15 connector) Connection of personal computer and printer.

1 asynchronous serial DTE/DCE port (50 baud telex and 9.6 kbit/s data)
according to CCITT Rec.V.24.
1 asynchronous serial DTE/DCE port (printer) according to CCITT Rec.
V24.

Alarm: (DB-15 connector) Connection of alarm unit and alarm indicating unit.

Phone1: (RJ-11 connector) 2W phone/PABX/FAX interface.
Phone2: (RJ-11 connector) 2W phone/PABX/FAX interface.

Antenna: Parabolic dish antenna for RHCP signals (21 dBi gain) with active stabilisation on 3

axes (azimuth, elevation and cross elevation) using rate sensors, inclinometers, and
signal strength tracking.

Transmission: 1626.5 - 1646.5 MHz (normal maritime tuning range, 20 kHz channel spacing for voice

communication).
EIRP = 25, 29, 33 dBW.

Reception: 1525 - 1545 MHz (normal maritime tuning range, 20 kHz channel spacing for voice

communication).
G/T = -4 dB/K.

Modulation: TX 24,132 kbit/s O-QPSK

RX 6 kbit/s BPSK, 24/132 kbit/s O-QPSK.

Coding: FEC convolution coding and 8 level soft decision Viterbi decoding (k = 7) and

(R = 1/2 , 3/4).
For high speed data, a sequential decoder with k = 36 and R = 1/2 is used.

Power Supply: Supply voltage: 24V DC +30/-10%.

Power consumption: TX/RX =250/120W

Environments: SAT-B antenna:

Temperature range: -25 to +55 °C.

SAT-B transceiver:
Temperature range: -15 to +55 °C.

Roll, pitch and yaw: ± 30° (T = 8 s), ± 10° (T = 6 s), ± 8° (T = 50 s)

Turning rate: ± 6 deg/s

Size and weight: SAT-B antenna:

H*W = 1410 mm * 1250 mm
M = 129 kg.

SAT-B transceiver:
H*W*D = 132 mm * 370 mm * 267 mm
M = 8.7 kg

Control handset:
H*L*B = 67 mm * 219 mm ‘ 70 mm
M = 1.2 kg

Control unit:
H*B*D = 100 mm * 200 mm * 120 mm
M = 0.8 kg

CONTENTS

2 SYSTEM DESCRIPTION 2-1

2.1 ABOVE DECK EQUIPMENT 2-1

2.1.1 PRINCIPLE OF STABILISATION 2-2

2.1.2 COMPONENTS OF THE STABILISATION SYSTEM 2-3

2.1.3 ANTENNA BEHAVIOUR DURING START-UP SEQUENCE 2-4

2.1.4 ANTENNA BEHAVIOUR DURING GLOBAL SEARCH 2-4

2.1.5 ANTENNA BEHAVIOUR DURING REGION SHIFT SEARCH 2-4

2.1.6 TRACKING ALGORITHM 2-5

2.1.7 COMMUNICATION, SETUP AND STATUS SURVEILLANCE 2-5

2.2 BELOW DECK EQUIPMENT 2-6

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2 SYSTEM DESCRIPTION

The two main parts making up a terminal are described in this chapter. The description of the antenna unit
(ADE) consists of two parts, one concerning the RF and one about the stabilisation. The other main part
of the terminal is the transceiver unit.

2.1 ABOVE DECK EQUIPMENT

The block diagram shown in fig. 2.1 concerns the RF part of the antenna unit.

35522A

Synthesizer

Tracking
Receiver

Converter

Down

Synthesizer

LNA

HPA

Diplexer

Converter

Up

Triplexer Conn. Board

SMPS

Rotary Joint

TSP

Sensor

Block

Motors

DMB
Transmitter Level
Power Control Voltage
Serial Comm. to SMPS

Signal Strength

Data RX/TX

Filter selc.

Frequency Selc.

21.4 MHz RX

10.08 MHz ref.

62.9 MHz TX

DMB

To Transceiver Unit

Fig. 2.1.

The RF part consists of a transmitter and a receiver part sharing a single antenna. The diplexer separates
transmitter and receiver signals to allow full duplex transmission without transmitter degrading receiver
performance.
The transmitter part consists of an UP converter which mixes a fixed intermediate frequency signal to a
signal in the transmitter band (1.6265 - 1.6465 GHz). The frequency selection is made by means of the UP
converter synthesizer. In the HPA (high power amplifier) the low level signal from the UP converter is
amplified before it enters the diplexer and antenna.
The receiver part consists of an LNA (low noise amplifier) and two receiver units, a DOWN converter which
is the counter part of the UP converter, and a tracking receiver which is a part of the tracking and stabilisation
system. The output signal from LNA is split out to both units. The DOWN converter and DOWN converter
synthesizer mix the receiver band (1.525-1.545 GHz) to a fixed intermediate frequency of 21.4 MHz. Due
to different service types, voice, high speed data etc., different receiver bandwidths are required. In the
DOWN converter three bandwidths can be selected on the final intermediate frequency.
The tracking receiver is always tuned to the NCSC channel in a given ocean region. The reason this channel
type is used, is that there is always a signal presented from the satellite, unlike other channel types where
service activation is used. The tracking receiver can be thought of as a frequency selective power meter
which measures the signal level on the channel which it is tuned to. It has its own synthesizer and covers
the entire receiver band. The tracking receiver output is a direct voltage which is used as input for the
tracking and stabilisation system.
As described in the previous chapter, a single coax cable between transceiver unit and antenna unit is used.
To make this concept work, a triplexer is used to distribute the signals from the transceiver unit to the
different modules in the antenna unit and to combine the different signals from the antenna unit to a
composite signal before it enters the cable.
To make the transceiver unit and antenna unit work together, data communication between them is
necessary. On the triplexer board a data receiver/transmitter is placed. The kind of data exchanged between

2 SYSTEM DESCRIPTION Inmarsat B

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antenna unit and transceiver unit is status and fail information from the antenna and configuration data.
Configuration data concerns frequency set-up of the synthesizer, DOWN converter filter selection, and
transmitter power level. The received data from the transceiver unit is processed by a microcontroller placed
on the tracking and stabilisation processor board, which also takes care of data in the opposite direction.

The tracking and stabilisation processor board is the heart of the antenna stabilisation system. To stabilise
the platform, tilt sensor and rata sensors are placed in different places on the platform. Those sensors
together with the tracking receiver supply input to the tracking and stabilisation processor board, which, as
output, controls the motors. In the following chapter the stabilisation system is described in detail.

The connection from the triplexer to the coax cable is made by means of a connection board and a rotary
joint. The rotary joint is used instead of a cable unwrap system. On the connection board, the main 40V
supply voltage from the transceiver unit is taken out and connected to the input of the switch mode power
supply (SMPS). The SMPS delivers different kinds of supply voltages to the modules. Besides those fixed
voltages, a microprocessor controlled voltage used to regulate the output power from the HPA is also
delivered.
If for some reason signals between transceiver unit and antenna unit are missing, a signal called

dead man’s

button

is activated, shutting the regulated voltage to the HPA, thus preventing the HPA from transmitting.

2.1.1 PRINCIPLE OF STABILISATION

The main objective of the stabilisation system is to keep the antenna pointing as accurately as possible
in the referenced pointing direction at any time under environmental conditions (ship yaw, pitch and roll).
To obtain this the antenna stabilisation system is based on three axis active stabilisation with closed loop
control of each axis. The individual axes are named azimuth (yaw/turning correction), cross elevation and
elevation (roll and pitch correction) as shown in fig. 2.1.1. Each axis uses a double sensor principal for
angular movement measurement (combined measurement of angular rate and absolute angle) and an
electrical motor as actuator. The angular rate is measured by means of angular rate gyros based on
oscillating piezoelectric crystals. For absolute angle reference the elevation (El) and cross elevation (Ce)
axes use a fluid based inclinometer, and the azimuth (Az) axis uses the ships gyro compass.

35972B

Az

Ce

El

Fig. 2.1.1.

2 SYSTEM DESCRIPTION Inmarsat B

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The controller function of the stabilisation system is performed by the tracking and stabilisation processor
board (TSP board).
In addition to the three axes contributing to the active stabilisation (Az, El and Ce) the antenna is equipped
with a horizontal axis holding a small sensor box. The sensor box holds several of the sensors for the
stabilisation system. Its main function is to make it possible to keep the working point of the inclinometer
sensor as close to the real horizontal level as possible under all antenna elevation reference angles. When
the elevation part of the pointing reference changes, the angle between the antenna disc and the horizontal
box will be changed into the same angle value in the opposite direction, thus keeping the sensor box
horizontal at all times.

2.1.2 COMPONENTS OF THE STABILISATION SYSTEM

Fig. 2.1.2 shows a block diagram of the stabilisation system.

Az rate sensor

El rate sensor

Inclinometer

Tracking receiver

Ce rate censor

Motor Driver

Motor Driver

Motor Driver

Motor Driver

Zero-mark det.

Horizontal

step motor

El axis

step motor

Az axis

step motor

Horizontal axis

DC motor

Brushless

TSP Controller

35973B

Fig. 2.1.2.

The stabilisation system can be divided into functional groups:

Azimuth axis:

Azimuth angular rate gyro sensor.
Fluxgate compass.
Ship gyro.
Azimuth step motor driver.
Azimuth step motor.

Elevation axis:

Elevation angular rate gyro sensor.
Elevation inclinometer (one axis of the dual axis inclinometer unit).
Elevation step motor driver.
Elevation step motor.

Cross elevation:

Cross elevation angular rate gyro sensor.
Cross elevation inclinometer (second axis of the dual axis inclinometer unit)
Cross elevation bldc motor driver.
Cross elevation bldc motor.

Horizontal axis:

Horizontal axis zero mark detector (optical fork).
Horizontal axis step motor driver.
Horizontal axis step motor.

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2.1.3 ANTENNA BEHAVIOUR DURING START-UP SEQUENCE

When the complete system, or just the ADE, has been reset or switched off and on, the ADE will initialize
and search for the satellite. The behaviour of the antenna during this process is described in this chapter.

1. Initialization

A few seconds after resetting, the horizontal axis will go to the bottom stop position. A knocking
sound will be heard for a few seconds. After this the axis will go up to the optical zero sensor.
Then the elevation axis will initialize in the same manner. Also from this axis a knocking sound
will be heard when it is in the bottom position. When the elevation axis has returned to horizontal
position, the cross-elevation axis will begin to move towards horizontal position. A high-fre­quency switch-mode sound can be heard when the cross-elevation axis moves. The antenna will
be ready after 2-3 minutes.
If the transceiver has received the position of the vessel, the fast search will begin.

2. Fast search

The elevation axis will move up to the calculated elevation angle of the chosen satellite, and the
azimuth will turn clockwise 360°. This rotation will last about 1-2 minutes. After the search, the
azimuth will go to the position with the highest signal level. This rotation will last less than 1
minute. Here a fine search will be performed.

3. Fine search

The fine search is a cross-shaped search, the centre of which will be in the expected direction of
the satellite. The angular speed of this search is lower than the speed of the fast search. First
the elevation axis will search vertically from 20° below the expected satellite position to 20°
above this position. Then it will search horizontally from 15° to the left of the expected position
to 15° to the right of it. Finally it will move back to the azimuth and elevation angles where the
highest signal levels were measured. The fine search will last 1-2 minutes.

The total start-up sequence will last 5-6 minutes.

2.1.4 ANTENNA BEHAVIOUR DURING GLOBAL SEARCH

If the modem cannot achieve synchronisation on the received NCSC signal within 5 seconds after the fast
search, a global search will start. In this search mode the azimuth will rotate slowly 360° clockwise, and
at the same time the elevation axis will move up and down in a zigzag shape. The elevation top of this zigzag
is 80° above the horizon and the elevation bottom is 5° above the horizon. After this the satellite dish is
turned to the direction where the highest signal level was measured. A ± 25° horizontal and vertical fine
search is performed around the direction whre the highest signal level was measured.

The total global search will last between 6-7 minutes.

2.1.5 ANTENNA BEHAVIOUR DURING REGION SHIFT SEARCH

The behaviour of the antenna during a region shift search depends on whether the position of the vessel
is keyed in manually or received directly from a GPS. In the following description, the values in square
brackets are those of a position keyed in manually, the other values are with a functional GPS connected
to the system.

If for some reason the signal between the satellite system and the ship is blocked by eg. a smokestack
or an other object on board or ashore, it can be necessary to change to an other region. Blocking objects
can cause the signal level to drop to a value where the system is still receiving from the satellite, but where
the quality of the signal is too poor to perform communication. This error may occur if for instance several
calls (Ship to shore) fail, or if only two LEDs are illuminated on the handset. In such cases the transceiver
can be shifted to an other region, in which case a region shift search is performed.

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When a region shift search is performed, the satellite dish first turns to the direction 15° [45°] to the left (or
right, depending on which is closer) of the expected position of the satellite. From this point it performs a
horizontal search to the point 15° [45°] to the right (or left, if the start position was right) of the satellite. After
this, a ± 15° horizontal and ± 20° vertical fine search is performed around the point where the highest signal
strength was measured. The total region shift search will take 1-2 minutes.

2.1.6 TRACKING ALGORITHM

For long term optimisation of the antenna pointing reference a step-track algorithm is included in the control
system for the antenna. The basic concept of the tracking algorithm is to measure the signal level around
the current centre of pointing by moving the reference in small measurement steps. At each measurement
point the reference position is fixed during an averaging time which is long enough to cover one to several
sea wave periods. After the averaging period the mean level is interpreted as the tracking level for that
reference point. This measurement is repeated several times at equally spaced points on each side of the
centre point before a decision is taken in which direction to move the centre. This procedure is repeated
on the elevation and azimuth axes one at a time until a new search is started. The size of the measurement
steps on the azimuth axis increases when the elevation reference angle increases.

2.1.7 COMMUNICATION, SETUP AND STATUS SURVEILLANCE

In addition to antenna tracking and stabilisation the TSP controller works as the central control unit in the
ADE and takes care of various setup and control tasks in the ADE.

Control data communication with the BDE:

Receiver, transmitter and tracking receiver channels.
Search initiation and sky slice parameters.
Ship gyro compass information.
Transmitter power level.
Antenna status information.

HPA setup and error reporting:

The TSP communicates with the microcontroller in the HPA unit. Power level infor­mation, burst length information and transmitter frequency range are sent to the HPA.
Status information and error codes are received from the HPA and reflected to the BDE
whenever needed.

Synthesizer setup:

The three synthesizer groups in the antenna (up converter, down converter and tracking
receiver) are all programmed by the TSP with configuration and frequency information.
The frequency programming parameters are calculated by the TSP based on the
channel numbers received from the BDE. In addition the TSP surveys the lock signals
generated by the synthesizers to detect if a synthesizer is unlocked. Unexpected
unlock situations are reported to the BDE.

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.
PAGE 2-6

9936

2 SYSTEM DESCRIPTION Inmarsat B

PAGE 2-7

9936

PAX board

The PAX board (phone and fax) contains hardware and software for interfacing with a fax machine and with
push button telephones like a stand-alone telephone or a PABX network.
The module also acts as an interface for data communication from a single terminal or a local network at
transmission rates of 9.6 or 64 kbit/s (64 kbit/s only possible if high speed data is implemented).

SMI board

The SMI (switch mode power supply and interconnection) board contains the system power supply. From
the ship, the main supply voltage of 24V DC is connected at the rear panel of the transceiver unit. And from
that, the switch mode power supply generates a number of different voltages not only for the modules in
the transceiver unit but also 40V DC for the antenna unit.

At the rear panel of the transceiver unit, a number of connectors are placed for externally connected
equipment. Those connectors are mounted on the board, from where they are connected to the respective
modules by means of ribbon cables.

CONTENTS

3 MODULE DESCRIPTION 3-1

3.1 ABOVE DECK EQUIPMENT 3-1

3.1.1 ANTENNA 3-1

3.1.2 DIPLEXER 3-2

3.1.3 LNA 3-2

3.1.4 DOWN CONVERTER 3-3

3.1.5 UP CONVERTER 3-4

3.1.6 HPA 3-4

3.1.7 TRACKING RECEIVER 3-5

3.1.8 TRIPLEXER 3-6

3.1.9 SYNTHESIZER FOR TRACKING RECEIVER 3-8

3.1.10 SYNTHESIZER FOR UP/DOWN CONVERTER 3-10

3.1.11 SWITCH MODE POWER SUPPLY 3-13

3.1.12 TSP 3-14

3.1.13 TILT SENSOR 3-15

3.2 BELOW DECK EQUIPMENT 3-16

3.2.1 SPS BOARD 3-16

3.2.2 MODEM BOARD 3-18

3.2.3 CSP/VDP BOARD 3-19

3.2.4 PAX BOARD 3-20

3.2.5 SMI BOARD 3-21

3.2.6 HANDSET 3-22

9936

Inmarsat B

PAGE 3-1

9849

3 MODULE DESCRIPTION

This chapter contains a description of the modules making up an Inmarsat B terminal, including modules
placed at the antenna unit and transceiver unit.

3.1 ABOVE DECK EQUIPMENT

3.1.1 ANTENNA

The antenna is a parabolic dish antenna as shown in fig. 3.1.

35971

SMA connector

Sub reflector

Fig. 3.1.

The diameter of the parabolic reflector is 90 cm and the feeder element is placed inside the plastic tube
in the focal point of the reflector. A small reflector with a diameter of 12 cm is placed at the end of the plastic
tube. The feeder element is a helical antenna operating in axial mode, thus creating a wave of circular
polarisation as required from Inmarsat. The wave is right handed. The helix is wrapped around a form of
polystyrene.
Inside the tube, a semi rigid coax cable connects the feeder element with the SMA connector at the bottom
of the parabolic reflector. This connector is connected to the diplexer through a highly flexible coax cable.

The following is a list of the most important antenna specifications:

Antenna gain: 20.9 dBi
Polarisation: Right handed circular
3 dB beam width: ± 7.5°
Side lobe level: More than 20 dB below main lobe
Axial ratio: Better than 2 dB

Inmarsat B

3 MODULE DESCRIPTION Inmarsat B

PAGE 3-2

9901

3.1.2 DIPLEXER

When a conversation is in progress via a satellite, the transmission mode is normally duplex which means
that the transmitter and receiver are active simultaneously. To prevent the HPA from overloading the LNA,
an interconnection device is used, i.e. a diplexer. Fig. 3.2 shows a block diagram of the diplexer.

Network

Coupling

TX Filter

Antenna Port

TX Port

RX Filter RX Port

35523A

Fig. 3.2.

The diplexer is a mechanical device, built up as two tenth-order band-pass filters connected to a coupling
network at the antenna port. The receiver path pass band is 1525 to 1545 MHz, and the transmitter path
pass band is 1626.5 to 1646.5 MHz.
Each filter is constructed of quarterwave resonators, the distance between them determining the coupling
coefficient. The tuning capacitors are made using screws in the top cover of the diplexer. Changing the
distance between a tuning screw and the resonator causes the top loading capacity to change, thus
changing the resonance frequency of the resonator as well.
The resonators are made of aluminium rods and the whole unit is silver plated to obtain a low insertion
loss. Furthermore, the device is sealed on the outside to avoid oxidation.
To obtain a low receiver noise figure, the LNA is placed in the diplexer. Interconnection between diplexer
receiver port and LNA input is made by means of a short piece of semi rigid cable. At antenna and TX
port, SMA connectors are used.

3.1.3 LNA

The main signal path in the LNA is constructed with four transistors and two helical filters as shown in
fig. 3.3.

Network

Matching

Down Converter

Tracking Receiver

1535 MHz 1535 MHz

Power

Divider

Bias Bias Bias Bias

Reg.

Voltage

Reg.

Voltage

BjtBjt BjtGaAs

35524

Fig. 3.3.

The semi rigid cable from the diplexer is soldered directly to the printed circuit board where it is connected
to a microstrip impedance matching network. The matching network acts as interconnection between
diplexer and the first gain stage to obtain a low noise figure. The first amplifier stage consists of a low noise
GaAs FET whereas the remaining three stages are based on junction transistors.
The two helical filters cover the maritime band, 1525 to 1545 MHz and ensure high immunity for out of
band signals. After the last filter, a microstrip power divider equally divides the signal to tracking receiver
and DOWN converter inputs.
The LNA is supplied with +18V DC from the tracking receiver through the coax cable which also carries
the RF signal.
In order to minimise gain variation over the entire temperature range, active bias network is used to keep
the current in each stage constant. The GaAs FET also uses a negative bias voltage which is made from
the +18V supply in a DC to DC converter based on pulse width modulation.

3 MODULE DESCRIPTION Inmarsat B

3.1.4 DOWN CONVERTER

The purpose of the DOWN converter is to convert an L-band signal to a fixed intermediate frequency of

21.4 MHz. A block diagram is shown in fig. 3.4.

20 kHz

10 kHz

100 kHz

Filter Module

Shift

Register

21.4 MHz

Data

Clock

Strobe

Lo-1 Lo-2

35525

Fig. 3.4

Down conversion takes place in two steps. The L-band signal is mixed to a first intermediate frequency
of 179.32 to 179.6325 MHz. The first IF signal is then mixed to 21.4 MHz. The reason why the first IF is
not fixed is that the frequency of the L-band synthesizer steps in 315 kHz. This is done to lower the close
in phase noise.

From the output of the LNA, the received signal is fed directly to RF input of the first mixer. The mixer is
a passive doubled balanced diode mixer with good large-signal properties. The local oscillator frequency
ranges from 1345.68 to 1365.525 MHz. The signal level from the synthesizer module is 0 dBm ± 3 dB and
is amplified in a MMIC to the required LO drive level of 10 dBm. To avoid power level variation of the local
oscillator input of the mixer, the compression point of the amplifier is approximately 10 dBm. Before
amplification takes place, the signal is filtered. The purpose of this filter is to attenuate spurious
frequencies which may add to the synthesizer module oscillator signal.

The first intermediate frequency consists of two double tuned band-pass filters separated by a dual gate
MOS-FET amplifier. The total power gain including filter losses is approximately 8 dB. The power gain
is temperature compensated by means of an NTC resistor in the bias network of the MOS-FET transistor.

The final down conversion to second IF at 21.4 MHz takes place in the second. This mixer has the same
properties as the first one. The second local oscillator amplifier amplifies the synthesizer signal from

-20 dBm to the required level of 10 dBm. The amplifier is built up as a two stage tuned transistor amplifier
with a 3 dB attenuator separating the transistors. The selectivity is formed by the tuned impedance
matching networks. This amplifier also has a compression point of approximately 10 dBm.

Due to the different types of services (voice, high speed data, telex etc.) different receiver bandwidths are
required. In the DOWN converter it is possible to select between three different crystal filters, i.e. 10, 20
and 100 kHz. Those filters are located on another PCB together with buffer stages and filter selection
circuits. The filter selection is made by means of switch diodes which are controlled by a TTL shift register.
Three control signals (data, clock and strobe) to set up the shift register are supplied from the TSP board.
The filter module buffer stages have two purposes, to amplify the signal and to serve as interconnection
between the filter module and the main board.

Finally the signal is amplified in a two stage dual gate MOS-FET amplifier, and a common collector stage
takes care of the impedance matching to a 50 ohm load.

All internal supply voltages (+15, -12 and 5V) are made by means of integrated voltage regulators.

PAGE 3-3

9901

3 MODULE DESCRIPTION Inmarsat B

3.1.5 UP CONVERTER

The input signal to the UP converter is mixed in two steps to cover the frequency band from 1626.5 to

1646.5 MHz.

Lo-1 Lo-2

Output to HPAInput from Triplexer

62.9 MHz

ATT

150 MHz 150 MHz

ATT

1636.5

35526

Fig. 3.5.

The input signal to the UP converter is filtered to attenuate out-of-band signals before the first frequency
conversion. Between the filter and first mixer, a 3 dB attenuator is used to improve termination. The mixer
is a passive double balanced diode mixer. Second IF is at 150.1 to 150.415 MHz. Second IF is built up
as band-pass filter, a BJT amplifier, another band-pass filter and finally an attenuator. The amplifier is
temperature compensated to minimise gain variations and includes a gain adjustment to set up the overall
gain of the UP converter. The final frequency conversion to L-band takes place in the second mixer. The
RF signal at the output of the mixer is filtered with a helical filter to reduce out-of-band spurious. The final
amplification takes place in an MMIC.
The two local oscillator signals are delivered by the UP converter synthesizer. The frequency of the first
LO is 213.0025 to 213.315 MHz. To obtain the required drive level of 7 dBm to the mixer LO port is used
a buffer built up with two transistors. The last stage is driven into compression to maintain a constant
power level to the mixer. To minimise intermodulation products, a bandpass filter between the two
transistors attenuates unwanted signals.
The frequency range of the second local oscillator is 1776.915 to 1810.620 MHz. The buffer stage
consists of a bandpass filter and an MMIC which is also driven into compression at a power level of 7 dBm.
All internal supply voltages are +15V DC and generated by means of integrated voltage regulators.

3.1.6 HPA

When mounted in the ADE, the HPA is placed in a separate, enclosed cabinet. The block diagram in
fig. 3.6 shows the main parts of the HPA.

Power Module

M Controller

DMB

1635.5 1635.5

Power

Det.

Senser

Temp.

EE-Prom

Clock

Data

Strobe

Clock

Data

Strobe

Data

+28V DC

SMPS

TSP

Input from

UP Converter

Output to

Diplexer

Directional

Coupler

35527

Fig. 3.6.

PAGE 3-4

9901

3 MODULE DESCRIPTION Inmarsat B

PAGE 3-5

9901

To reject out of band signals, a helical filter is placed at the input of the HPA. The output signal from the
UP converter can vary approximately 17 dB depending on the length of the cable between BDE and ABE,
temperature variations and AM fluctuations in the different digital modulation forms used. To remove
variations in the signal power, the signal is amplified in a two-stage amplifier built up around two integrated
amplifiers. The amplifiers are driven into compression, thus removing the power variation. A second
helical filter is located after the amplifier stages to attenuate the harmonic contents of the signal.
The final amplification is performed in the power amplifier, which is an integrated amplifier. The output
power can be controlled by varying the +28VR DC supply voltage to the power amplifier. The power
regulation facility serves two purposes: transmission at three predefined power levels and correction of
each power level due to temperature variations and parameter spread of the components.
From the directional coupler at the output of the HPA, a small part of the transmitter signal is taken out,
and a power detector built up around a Schottky diode converts the signal to a direct voltage which is
proportional to the transmitter power. The DC voltage is sampled by means of an A/D converter inside
the microcontroller.
A circulator at the output of the directional coupler is used to protect the power module if for some reason
the transmitter power is reflected back into the power module.
A sensor monitors the instantaneous temperature of the module, and its output is connected to a
microcontroller.

The microcontroller is connected to an A/D converter in the switch mode power supply which regulates
the +28VR DC and thus the transmitter power. If for some reason a burst in burst mode transmission
becomes too long, the output power or the temperature becomes too high, the microcontroller forces the
switch mode power supply to shut down the +28VR DC supply voltage and thus the transmitter power.
The interconnection between the microcontroller and the switch mode power supply is a serial
connection.
If a fail condition arises, an error code is transmitted to the TSP board, from where it is sent to the system
processor in the transceiver unit.

During a call, the TSP receives information concerning transmission, i.e. burst or continues mode and
power level. That information is given to the microcontroller in the HPA, from where the A/D converter in
the SMPS is controlled.

3.1.7 TRACKING RECEIVER

The tracking receiver can be considered as an ordinary receiver whose detector delivers a direct voltage
proportional to the received signal level.
The input signal to the tracking receiver is taken from a power divider located at the LNA. The coax cable
between LNA and the tracking receiver is also used to supply the LNA with DC power. In fig. 3.7 a block
diagram is shown.

Lo-1

To TSP

134 MHz 134 MHz

6 dB

Lo-2

10.7 MHz

ATT

10.7 MHz

DC

IF1 IF2

AGC

Level

Converter

35528

Fig. 3.7.

The receiver is built up as a double conversion receiver, with a first IF of 133.96 to 134.27 MHz. The
second IF is fixed at 10.7 MHz. The reason why the first IF is not fixed is that the frequency of the L-band
synthesizer is changed in step of 315 kHz. This is done in order to lower close in phase noise.
The DC block between tracking receiver input and first mixer adds an 18V supply voltage to the coax cable
up to the LNA and makes sure that the DC voltage does not reach the mixer input.
The first mixer, a double balanced diode mixer, down converts the L-band signal to first IF where two
double tuned bandpass filters separated by a dual gate MOS-FET amplifier reject image frequencies. The
final down conversion to 10.7 MHz is made by means of a mixer of the same type as the first one. At second

3 MODULE DESCRIPTION Inmarsat B

PAGE 3-6

9901

IF, adjacent channel selectivity is obtained in a crystal filter. Between the mixer and crystal filter, a 6 dB
attenuator is used to improve the termination impedance of the mixer IF port.
Second IF consists of two integrated amplifiers of which the first has fixed and the second variable gain
controlled by a DC voltage. After that a crystal filter limits the noise bandwidth before the final amplification
in a two-stage transistor amplifier.
A diode detector converts the IF signal to a DC voltage proportional to the signal strength. An AGC circuit
ensures that the detector voltage is constant by regulating the gain of the second IF2 amplifier. The
voltage regulating the gain is used as an indicator of the signal strength. When the input power for the
tracking receiver changes from minimum to maximum, the AGC voltages change by approximately 0.5V.
A level converter is used to give a 0-5V change for the same input power variation. This signal is connected
to the TSP board.

The module uses +15 and -12V supply voltages generated by integrated voltage regulators.

3.1.8 TRIPLEXER

The main function of the triplexer is to combine and distribute signals in the coax cable between ADE and
BDE to and from the different modules placed on the antenna unit. A block diagram of the triplexer is
shown in fig. 3.8.

:4

40.32 MHz

21.4 MHz

87 MHz

Circuit

FM-IF

Slicer

Data

OSC.

99 MHz

Vector

Modulator

150 kHz

150 kHz

Phase

Control

OSC.

150 kHz

Combiner

Splitter/

Converter Synthesizer

10.08 MHz to UP/Down

10.08 MHz to Tracking
Receiver Synthesizer

62.9 MHz output to
UP Converter

21.4 MHz input
from Down Converter

Data to TSP

Data from TSP

To Connection Board

35529

Fig. 3.8.

The input block consists of a number of baluns separating the different types of signals from the BDE and
combining the signals to the BDE. The different types of signal are listed below:

40.32 MHz reference signal

In the BDE is placed a stable oscillator which is used to derive the reference frequencies for the
synthesizers, among other things. The oscillator frequency is 10.08 MHz but is multiplied by a factor four
before entering the coax cable. This signal is taken out of the combiner/splitter block and filtered in a
bandpass filter with a center frequency of 40.32 MHz. The signal amplification takes place in an integrated
circuit and two discrete transistors. The last transistor is a switch transistor converting the signal to a level
suitable for TTL circuits. After level conversion, the frequency is divided by a factor four to obtain the
original reference frequency of 10.08 MHz. The divider circuits are built up around two d-type flip-flops.
The 10.08 MHz signal is now amplified and finally split out to two SMB connectors. From those
connectors, the reference frequencies for the tracking receiver and UP/DOWN converter synthesizer are
taken.

3 MODULE DESCRIPTION Inmarsat B

PAGE 3-7

9905

62.9 MHz UP converter signal

The transmitter signal from the BDE, which is a 62.9 MHz intermediate frequency signal, is taken out of
the combiner/splitter block and is fed directly to an SMB connector where the input of the UP converter
is connected.

21.4 MHz DOWN converter signal

The output signal from the DOWN converter enters the triplexer board in an SMB connector and is then
low-pass filtered before entering the combiner/splitter block.

Data receiver/transmitter

As described in the previous chapter, data communication between ADE and BDE is necessary. On the
triplexer board, a complete 4800 bit/s data receiver /transmitter is placed. The data receiver/transmitter
is built up as an FSK (frequency shift key) modem where a 99 MHz transmitter carrier is shifted ± 150 kHz
in frequency depending on the data bit (one or zero). The receiver is based on the same principle except
that the centre frequency is 87 MHz. The data receiver is built up around an integrated circuit which is
a complete FM IF subsystem. The integrated circuit contains a mixer which converts the 87 MHz receiver
signal to an intermediate frequency of 12 MHz. The needed local oscillator signal is taken from the 99 MHz
crystal oscillator. The 12 MHz FSK modulated IF signal is demodulated in an frequency discriminator.
After demodulation the signal is led to a data slicer reconstituting the data shape. The serial bit stream
from the data slicer is connected to the TSP board. The data transmitter is built up around an integrated
vector modulator. The modulation is generated through a 150 kHz I/Q signal, the phase of the Q signal
switched 0 or 180° depending on the I signal controlled by the bit stream to be transmitted. The I and Q
signals are square waves, but low-pass filters attenuate the harmonic contents to generate low distortion
sine and cosine signals as vector modulator input.

3 MODULE DESCRIPTION Inmarsat B

PAGE 3-8

9901

3.1.9 SYNTHESIZER FOR TRACKING RECEIVER

The two local oscillator signals used in the tracking receiver are generated on this synthesizer module.
The first local oscillator which is used to mix the receiver frequency to first IF is called L-band synthesizer
and the other is called VHF synthesizer.
The frequency coverage of the two synthesizers is listed below:

L-band synthesizer: 1391.040 - 1410.885 MHz in steps of 315 kHz
VHF synthesizer: 144.66000 - 144.97375 MHz in steps of 1.25 kHz

A block diagram of the synthesizer module is shown in fig. 3.9.

LOOP 1

PD:32 VCO

:N :64/65

:A

PD:126 VCO

:N

:A

:20/21

:A

:N :20/21

:128 PD VCO

VHF

L Band

Lock

det.

LOOP 2

10.08 MHz

from Triplexer

To TSP

from PLL

Lock Signals

35530

Fig. 3.9.

L-band synthesizer

The L-band oscillator is based on a voltage controlled oscillator (VCO) with good close-in phase noise
properties. Frequency stability is obtained using a PLL circuit where the VCO is locked to the highly stable
reference frequency supplied from the triplexer board.

3 MODULE DESCRIPTION Inmarsat B

PAGE 3-9

9901

The integrated PLL circuit contains phase detector, divider for reference frequency, divider with modulus
two architecture and built in L-band prescaler with a division ratio of 64/65.
The 10.08 MHz reference frequency is divided by 32 in the reference divider to obtain a frequency
resolution of 315 kHz.
The loop filter is an active low-pass filter built up around a low noise operational amplifier. The output
signal from the VCO is amplified in two integrated L-band amplifiers (MMIC). The purpose of the amplifiers
is not only to obtain the required signal level but also to isolate the frequency determining components
in the VCO from the rest of the circuits.

VHF synthesizer

The VHF synthesizer is also based on PLL technology but because of the high frequency resolution of

1.25 kHz and demands for low phase noise, a dual loop synthesizer is used. The two loops are built up
as conventional synthesizers with the exception that loop 1 contains a mixer.
The reference divider in loop 1 is 126, giving a frequency resolution of 80 kHz, and for loop 2 it is 128,
giving a frequency resolution of 78.75 kHz.
When the divider in the feed back loop of loop 1 is incremented by 1, the output frequency of the VHF
synthesizer is increased by 80 kHz. If at the same time, the divider in the feed back loop of loop 2 is reduced
by one, the output frequency of the VHF synthesizer is decreased by 78.75 kHz. The resulting change
of frequency at the output of the VHF synthesizer is therefore only 1.25 kHz.

The integrated PLL circuits used in loop 1 and 2 do not include the prescaler. Therefore, external
prescalers with a division ratio of 21/22 are used. The loop filters are of same type as the one used in the
L-band synthesizer.
The VCO’s are a Colpitts-Clapp type, built up with BJT’s . Before the amplified VCO signals enter the loop
mixer, they are low-pass filtered to attenuate the harmonic contents. Loop mixing takes place in a passive
double balanced diode mixer, and at the output the mixer, a low-pass filter removes the sum frequency.

For initialization and selection of frequencies, the PLL circuits need three signals each: clock, data and
strobe. The strobe signal is used for chip selection and therefore three separate wires are used. The clock
and data signals are the same for the three PLL’s, the strobe signals determining which one is loaded with
data. The strobe, data and clock signals are generated from the TSP board.

Each of the three PLL’s has a built in lock detector which indicates when a VCO is unlocked. These signals
are combined in a lock indicator circuit which indicates if one or more VCO’s are unlocked. The lock
condition is signalled to the TSP board, which sends this information to the transceiver unit. The lock
indicator is also connected to a led placed on the synthesizer board, which is lit when a VCO is unlocked.

The supply voltages (+18V, +8V, -15.5V) from the SMPS are converted to +15V, +5V and -1.25V by
standard voltage regulators but the more critical supply voltages to VCO’s and phase detectors are made
by discrete components to lower the noise level.

3 MODULE DESCRIPTION Inmarsat B

PAGE 3-10

9901

3.1.10 SYNTHESIZER FOR UP/DOWN CONVERTER

The UP and DOWN converter synthesizers are two separate units but placed on the same printed circuit
board.

UP converter synthesizer

The two local oscillator signals used in the UP converter are generated on this synthesizer module. The
first local oscillator which is used to mix the transmitter frequency to first IF is named VHF synthesizer
and the other is named L-band synthesizer.
The frequency coverage of the two synthesizers are listed below:

L-band synthesizer: 1776.915 - 1810.620 MHz in steps of 315 kHz
VHF synthesizer: 213.0025 - 213.3150 MHz in steps of 2.5 kHz

A block diagram of the UP converter synthesizer is shown in fig. 3.10.

LOOP 1

PD:32 VCO

:N :64/65

:A

PD:63 VCO

:N

:A

:20/21

:A

:N :20/21

:64 PD VCO

VHF

L Band

Lock

det.

LOOP 2

10.08 MHz

from Triplexer

To TSP

from PLL

Lock Signals

35534

Fig. 3.10.