section_3

Spacetrack 4000Spacetrack 4000

Section 3Section 3 Field Technician's Field Technician's

ManualManual

Data Marine Systems Ltd Spacetrack Field Tech Manual

Rev: 04.1 Section 3 - 1

TABLE OF CONTENTS

TABLE OF CONTENTS..........................................................................................................................................1

3.1 EQUIPMENT OVERVIEW ...............................................................................................................................3

3.1.1 ADU MODULE ............................................................................................................................................. 3 3.1.2 COARSE AZIMUTH AND GIMBAL ASSEMBLY ......................................................................................... 4 3.1.3 PEDESTAL WIRING...................................................................................................................................... 5 3.1.4 BDU MODULE .............................................................................................................................................. 6

3.1.4.1 Spacetrack 4000 Antenna Controller Module Layout ...............................................................6 3.1.4.2 Below Deck Interface Panel .............................................................................................................7

3.1.5 SENSORS......................................................................................................................................................... 8 3.1.6 TECHNOLOGY OVERVIEW .......................................................................................................................... 9

3.1.6.1 Control System Overview..................................................................................................................9 3.1.6.2 Satellite Orbital Mechanics. ............................................................................................................9

3.1.7 CONTROL SYSTEM OPERATION ............................................................................................................. 12 3.1.7.1 Operation...........................................................................................................................................12

3.1.7.1.1 Sensors ......................................................................................................................................... 12 3.1.7.1.2 Normal and Instrument Angles................................................................................................. 12 3.1.7.1.3 Sensor Processing. ..................................................................................................................... 12

3.1.7.1.3.1 The Torque Loop................................................................................................................. 13 3.1.7.1.3.2 The Velocity Loop............................................................................................................... 13

3.1.7.1.4 Motors .......................................................................................................................................... 13 3.1.7.1.5 Inertia ............................................................................................................................................ 13 3.1.7.1.6 System modes .............................................................................................................................. 14

3.1.7.2 Satellite Acquisition........................................................................................................................16 3.1.7.2.1 Tracking Sources. ....................................................................................................................... 16 3.1.7.2.2 Input Attenuation and Acquisition Threshold...................................................................... 17

3.1.7.2.2.1 Setting the Attenuation and Threshold Manually......................................................... 17 3.1.7.2.3 Acquisition Angles. ................................................................................................................... 17

3.1.7.2.3.1 Modem CD............................................................................................................................ 18 3.1.7.3 Satellite Tracking. ...........................................................................................................................19

3.1.7.3.1 Polar Tracking.............................................................................................................................. 20 3.1.7.3.1.1 Linear Polar Tracking .......................................................................................................... 20 3.1.7.3.1.2 Circular Polar Tracking........................................................................................................ 20

3.1.7.3.2 Scan Parameters. ......................................................................................................................... 20 3.1.7.3.2.1 Search Parameters................................................................................................................ 21 3.1.7.3.2.2 Lock Parameters................................................................................................................... 21 3.1.7.3.2.3 Track Parameters.................................................................................................................. 22

3.1.7.4 Active Weights...................................................................................................................................24 3.1.7.4.1 Active Weights........................................................................................................................... 25

3.1.7.5 System Log.........................................................................................................................................26 3.1.7.6 Auxiliary Communication Port. ....................................................................................................26

3.2 ASSEMBLY AND INSTALLATION............................................................................................................27

3.2.1 SITE SURVEY.............................................................................................................................................. 27 3.2.2 ASSEMBLING THE PLATFORM ................................................................................................................. 27 3.2.3 DECK INSTALLATION ............................................................................................................................... 28 3.2.4 ASSEMBLING THE BDU............................................................................................................................. 29 3.2.5 ELECTRICAL CONNECTIONS.................................................................................................................... 29 3.2.6 ECLIPSING HEADINGS CHART .................................................................................................................. 30 3.2.7 INSTALLATION CHECKLIST ..................................................................................................................... 30 3.2.8 DEMOBILISATION ...................................................................................................................................... 30

3.3 INITIALISATION............................................................................................................................................30


Section 3 - 2 Rev: 04.1

3.3.1 INITIALISING THE SYSTEM ...................................................................................................................... 31 3.3.2 SETTING THE COARSE AZIMUTH........................................................................................................... 32

3.3.2.1 Set the coarse azimuth limit switch...............................................................................................33 3.3.2.2 Set the coarse azimuth ADT............................................................................................................33

3.3.3 MECHANICAL UNWRAP LIMIT ............................................................................................................... 34 3.3.4 SETTING THE GIMBAL MOTOR POTENTIOMETERS ........................................................................... 34 3.3.5 BALANCING THE PLATFORM................................................................................................................... 35

3.3.5.1 Platform Balance..............................................................................................................................35 3.3.5.2 Gimbal Balance. ...............................................................................................................................37

3.3.6 SETTING THE INERTIAS ........................................................................................................................... 37 3.3.7 SETTING UP THE RF EQUIPMENT .......................................................................................................... 37 3.3.8 SET-UP THE TRACKING RECEIVER......................................................................................................... 38 3.3.9 SETTING THE SIGNAL THRESHOLD........................................................................................................ 38 3.3.10 LOCK-ON TEST ......................................................................................................................................... 39 3.3.11 INITIALISATION CHECKLIST ................................................................................................................. 39

3.4 TROUBLESHOOTING...................................................................................................................................39

3.4.1 ERROR MESSAGES....................................................................................................................................... 40 3.4.2 FAULT FINDING ......................................................................................................................................... 42 3.4.3 CHECKING INDIVIDUAL SYSTEM COMPONENTS.................................................................................. 47

3.4.3.1 ADU/BDU Comms Link ...................................................................................................................47 3.4.3.2 Gimbal Motor....................................................................................................................................48 3.4.3.3 Coarse Azimuth Motor....................................................................................................................49 3.4.3.4 Motor Pots.........................................................................................................................................50 3.4.3.5 Coarse Azimuth ADT........................................................................................................................51 3.4.3.6 Velocity Sensors ...............................................................................................................................51 3.4.3.7 Inclinometers.....................................................................................................................................51 3.4.3.8 ADU Module Power.........................................................................................................................52 3.4.3.9 BDU Module Power.........................................................................................................................52 3.4.3.10 Internal Tracking Receiver..........................................................................................................52

3.4.4 CHECKING SENSOR AND MOTOR POLARITY........................................................................................ 53

3.5 COMPONENT REPLACEMENT..................................................................................................................54

3.5.1 REPLACING AN INCLINOMETER BLOCK ................................................................................................ 54 3.5.2 REPLACING A GIMBAL MOTOR POTENTIOMETER ............................................................................. 54 3.5.3 REPLACING THE COARSE AZIMUTH ADT............................................................................................ 55 3.5.4 REPLACING THE COARSE AZIMUTH MOTOR....................................................................................... 55 3.5.5 REPLACING THE COARSE AZIMUTH LIMIT SWITCH .......................................................................... 55 3.5.6 REPLACING A GIMBAL MOTOR .............................................................................................................. 56 3.5.7 REPLACING THE ADU MODULE............................................................................................................. 56 3.5.8 REPLACING THE BDU MODULE ............................................................................................................. 56 3.5.9 REPLACING THE RF EQUIPMENT ........................................................................................................... 57

3.6 MAINTENANCE...............................................................................................................................................57

3.6.1 LUBRICATION ............................................................................................................................................. 57 3.6.2 INSPECTION FOR LOOSE BOLTS............................................................................................................... 58 3.6.3 CORROSION PREVENTION......................................................................................................................... 58 3.6.4 ADU MODULE CARE ................................................................................................................................ 58



3.1 EQUIPMENT OVERVIEW

This Field Technician's Manual is provided as a guide to the installation, maintenance, and troubleshooting of the Spacetrack Stabilised Antenna Platform. This manual is intended to be used in conjunction with Section 1 - Radio Operator's Manual and the Appendices, which includes drawings.

The primary function of the Spacetrack system is to keep an antenna, mounted on a moving vessel such as a ship at sea, pointed very accurately at a satellite as the vessel moves underneath it.

In a typical installation, Spacetrack hardware is located in the following places:

THE SHIP'S DECK

A radome is located on the ship's deck, and contains the majority of the hardware, including the Stabilised Platform. This is controlled by the ADU (Above Deck Unit) electronics, Antenna, Antenna Feed, and Radio Equipment, as shown in Figure 1 and as described in Sections 3.1.1 through 3.1.5, below. In general, ship's personnel will not be required to work on equipment located in the radome.

THE RADIO ROOM

The satellite communications rack, which is usually in the Radio Room, will contain the BDU (Below Deck Unit) and the associated communications equipment. The BDU controls the Spacetrack Stabilised Antenna and consists of the Spacetrack 4000 Interface. Figure 2 shows a typical BDU module. Ship's personnel may be required, in exceptional circumstances, to use this module to help the Stabilised Platform re-acquire a lost Satellite Signal.

Each Spacetrack terminal is individually configured to the specific requirements of the customer, and while this manual explains the most common Spacetrack configurations, there may be circumstances where the terminal design varies slightly from the description given.

3.1.1 ADU Module

Figure 4 shows the ADU Module, which is attached to the platform side rail. Note: The module contains velocity sensors and must therefore be oriented on the system correctly. A small diagram on the front of the module indicates the direction in which it should be mounted on the side rail.

The three external circular connectors are for connecting the mains power, signal wiring and motor power. Always ensure when connecting the cables to the module, that the connectors are fully screwed onto the module. There may also be a fourth connector, depending on hardware revision, which is used to control the active weights.



The module electronics are fully protected from the harsh marine atmosphere when the lid is sealed. A silica desiccator removes any moisture that might be present inside the module. An indication of the amount of moisture that the desiccant has soaked up is shown on the front of the module. The indicator shows a 30 and 50-percentage value, which will change colour according to the moisture content of the desiccant. Blue indicates that the moisture content is below 50 percentage while pink indicates that it is above this value. If the 50 value turns pink the module should not be stored in cold and damp locations.

Fans located on the top and bottom edges of the module ensure a flow of air through the module. This keeps the power components operating temperature, at a reasonable level. This air however, does not come in contact, with any of the signal electronics.

An Earth strap is located next to J3, the mains input, which should be securely bonded to the Spacetrack frame.

The module electronics processes the information from the various sensors in the system and passes the information to the BDU. The module also provides the signals to drive the system motors on command from the BDU. Three velocity sensors inside the module sense velocity in the azimuth, elevation and polar axis.

Since the velocity sensors within the module may be damaged by mechanical shock, a device on the module indicates if the module has been subject to excessive shock. If the shock indicator is red the module should be rejected.

Note: As the module electronics are sealed from the atmosphere and contain no user serviceable parts, do not remove the module lid. If a problem with the ADU module is suspected, it should be replaced with a complete new module, and returned to DMS for failure analysis. DMS will not honour any warranty claim if the module has been opened by non DMS personnel.

3.1.2 Coarse Azimuth and Gimbal Assembly

The pedestal provides the mechanical interface to the vessel on which the Spacetrack is mounted. Attached to the pedestal is the coarse azimuth drive assembly which provides a large range of motion in which the much more accurate gimbal motors can control the stabilised platform (see Figure 1)

Connected to the coarse azimuth drive assembly is the coarse azimuth Angular Displacement Transducer (ADT) which provides the coarse azimuth axis angular position information.

The coarse azimuth motor drives around the gimbal support tower, which supports the gimbal. The gimbal provides the necessary degrees of freedom to stabilise the platform, on which the antenna is mounted. Three motors on the gimbal move the platform in azimuth (side to side), elevation (up and down), and polarisation (rotation about the axis parallel to the antenna bore sight).



By controlling the platform in the three axes the antenna can be pointed very accurately at geosyncronous satellites (geostationary or inclined satellites), permitting a communications link to be maintained regardless of the vessel’s motion.

The gimbal motors are driven by a high frequency PWM (Pulse Width Modulation) signal, the duty cycle is proportional to the amount of torque desired. The coarse azimuth motor is also driven by a PWM signal.

An inclinometer module (see Figure 17) and a wiring interconnection plate (see Figure 6) are attached to the gimbal support tower. The inclinometer module houses the two inclinometers (see Section 3.1.5), and a power resistor for the coarse azimuth motor.

A wiring interconnection plate provides a means of easily connecting the cable loom, which runs along the platform arms and gimbal, to the sliprings (or to the baseplate junction boxes, if no sliprings are present).

If the system does not have slip rings, (i.e. the cables go straight through the centre of the pedestal), the coarse azimuth movement is limited to a physical maximum rotation of ±350 degrees from the centre line of the vessel, before a cable unwrap occurs. The exact unwrap points are set as a parameter in the control software (see Section 4.1.2.2.8 for details). The transducer shaft is geared, so that as the Gimbal Support Tower rotates 360 degrees, the transducer shaft only rotates 170.53 degrees. There is also a Coarse Azimuth Limit Switch - a trip switch, which is normally on, and which is switched off by a pin on the ADT gear cog. A secondary mechanical limit stop is fitted as a fail-safe assurance that the platform will not over-wrap its cables.

The system is simplified if it is supplied with sliprings. Each cable passing through the pedestal is connected to a pair of rings that are electrically connected, but can slide over one another. This allows the Gimbal Support Tower to rotate without the requirement for cable unwrapping. On these systems the coarse azimuth ADT shaft rotates the same amount as the Gimbal Support Tower, there are no limit switches, mechanical stops, and the unwrap feature is unnecessary.

3.1.3 Pedestal Wiring

See Figure 6 for details of the gimbal cable loom. Figures 7A and 7B details the pedestal wiring and Figure 10 details the cross deck wiring from the BDU to the pedestal.

The ADU interface panel is located on the gimbal support tower, which, provides connections for the radome mains supply and the communications link to the BDU. The cross deck co-axial transmit, receive and spare cables are also terminated on an interface plate with N type connectors.

The interface panel also serves to provide a connection for the M & C console. This allows system operation and diagnostic functions to be performed in the radome.



3.1.4 BDU Module

Figure 2 shows the BDU Module, which is normally installed in a 19 inch rack in the Radio Operator's room. Other communication equipment may also be mounted in this rack. The BDU module requires full length support when mounted in the rack.

The BDU Module is an integral part of the Spacetrack system. It must therefore remain switched on and connected for the system to operate.

The BDU module provides the user interface to the system through a membrane front panel keyboard/LCD; and also through a monitor and control serial connection to a console. The BDU controls the tracking platform, processing the navigation and feedback signals to maintain a communications link.

3.1.4.1 Spacetrack 4000 Antenna Controller Module Layout

The front of the enclosure has a membrane keypad and a LCD display. The LCD panel displays information to the user and also allows the user to change, in conjunction with the keypad, the system parameters and operation. When idle the module displays the system mode, the received AGC level, and also the time and date.

The rear of the enclosure has two male BNC connectors, one IEC mains connector and two D type interface connectors. See Figure 8 and Section 3.5 for details of how to wire the unit into the system. The connector functions are as follows:

• 70MHz BNC Connector - Receiver Input. This input is used to provide the satellite feedback signal, which allows the system to determine where the peak AGC signal is, and so maintain the best signal level. The 70MHz input may be derived from the external communications equipment and is usually the main system IF frequency. The user may select a wide bandwidth or a narrow bandwidth detector.

• L Band BNC Connector - Receiver Input. The system may also accept a L Band signal to track with. The L Band signal is down converted to 70 MHz and processed using either the narrow or wide band detector.

• IEC Mains Connector - Mains input. Provides power to the module.

• Interface - This connector is used to interface the BDU module to the ship’s electronics and ADU, via the below deck interface panel. The below deck interface panel expands the D type connections to terminal blocks grouped in the appropriate functions.

• M&C - This connection provides an interface to the monitor and control console, which allows the user to control the system remotely using a serial terminal.



3.1.4.2 Below Deck Interface Panel

The interface panel expands the interface connector on the back of the BDU module to terminal blocks, which provides a more convenient connection to the module.

• CN1 – Interface. This connector is connected to the BDU module interface connector, and is the expansion cable.

• CN2 – Cross Deck Cable. This connects to the ADU and must always remain connected for the system to function. If this link is not present, the ADU will switch off the power to all the motors on the stabilised antenna. The link uses two balanced pairs (RS422 signal levels) and three RS232 monitor and control wires, see Appendix E, the table of connections for core assignment. The two balanced pairs are –

1. Transmit to ADU (ADU A & ADU B).

2. Receive from ADU (ADU Y & ADU Z).

The transmit and receive data rate is 38400baud, which is optically isolated.

The RS232 lines are not necessary, if system control in the radome is not required. See Figure 10 for cross deck connection details.

• CN4 – Stepper. This connection provides an interface to a gyro compass, allowing the vessel heading information to be automatically updated. It will accept a positive or negative referenced gyro output. See Figure 9 for details of how to connect to a gyro compass.

• CN5 - NMEA. This optional connection provides an interface to the host vessel’s NMEA data sources. The NMEA data sources provide position and heading information to the system in a digital format. The system can accept either RS232 or RS422 data format, the selection is performed by the user in software, or by the system automatically on boot. See Figure 9 and 23 for details of how to connect to NMEA sources to the system.

• CN6 - AGC. If an external dc voltage is available, which is proportional to the signal level received from the satellite; this may be connected to the AGC input to allow the system to track. The system accepts dc levels of 0 to +10V. See Figure 22 for connection details.

• CN8 – Misc. The Miscellaneous connector is used to provide status information to external equipment and also to control the operation of the tracking platform. See Figure 22 for connection details. The provided signals are:

1. Modem CD. To enable the system to discriminate between closely located satellites, it is possible to connect the modem demodulator lock signal to the interface panel. When the system locks onto the correct satellite, the modem will also lock onto the down converted signal, indicating through the demodulator locked output that the correct satellite has been acquired. To use the modem CD input, connect the demodulator locked, (normally open connection), to the modem CD signal and ground connections on CN8. See Section 3.1.7.2.3.3.



2. Track Out. The track out signal is a logic level output which indicates when the control system is in track mode.

3. Error Out. The error out signal is a logic level output, which indicates when the system has an error active. This signal may be interfaced into an external monitoring system or DCS.

• CN9 – Aux Port. The auxiliary port is a spare RS232 format serial port, which may be used to access remote equipment through the M&C console. See Figure 22 and figure 8 for connection details.

• CN10 – M&C input Connector. The M&C connector is used to attach the interface panel to the control module.

• CN11 – M&C Connector. The M&C connector is used to attach a console to the system. See Figure 19 for connection details.

3.1.5 Sensors

With all options installed, there are ten sensors providing information to the control system.

• Three Velocity Sensors - azimuth, elevation and polar. These are located in the ADU Module (See Section 3.1.1) and produce a voltage proportional to their angular velocity.

• Three Gimbal Motor Potentiometers - fine azimuth, elevation and polar. The ADT’s couple with each gimbal axis, and feedback the exact angular positions of the motors. They must be initially set so that the system has a central position reference. (See Section 3.3.4 for details on how this is achieved).

• A Coarse Azimuth Angular Displacement Transducer (ADT) - This is located in the centre of the pedestal just beneath the gimbal support. The sensor is powered by +15V, -15V and a precision voltage reference of +10V. The sensor returns a 0 to +10V signal proportional to the rotation of the gimbal support.

• Two Inclinometers - roll and pitch. These are located on the inclinometer module attached to the left gimbal support arm and return a voltage proportional to their angle relative to the local horizon.

• An Optional Feed Motor Potentiometer - If an active feed is fitted, the potentiometer connects to the motorised feed arrangement and returns a voltage proportional to the angular position of the OMT assembly.



3.1.6 Technology Overview

3.1.6.1 Control System Overview

The minimum distance from the surface of the Earth to a satellite in geosynchronous orbit is 36000 km. This distance is measured relative to a location on the Earth’s surface directly below the satellite. Moving 1km from this reference point, the change in angle required, to remain pointed at the satellite alters by less then 2/1000’s of a degree. On the other hand, the half power beam width of a 2.4 meter Ku band antenna (a typical configuration for a Spacetrack system) is 0.3°. What this illustrates is that, if an Earth based antenna points 0.15° away from the satellite, the received signal power will be half the power that would be received, if the antenna was pointing directly at the satellite. This highlights that, rotation is more critical in terms of stabilising the antenna than linear motion. Linear motion only plays a part in the forces acting on the stabilised platform, which act through the gimbal centre. If the centre of gravity for the platform is not at the physical gimbal centre then the linear motion of the pedestal will result in a rotational force on the platform. The platform, must therefore, be carefully balanced.

Once the platform is balanced, it will maintain its orientation due to inertia. The forces disturbing this equilibrium are friction and residual imbalances. This is where the Spacetrack control system takes effect. The antenna is stabilised by measuring platform rotation and applying a counter balancing force. The gimbal motors are free floating until a counter balancing force is required and demand signals are applied to them.

The signals from the velocity sensors and the motor potentiometers are combined, which gives the control system the information necessary to stabilise and position the antenna.

There is actually a great deal more to Spacetrack stabilisation. In fact, the Spacetrack system actively tracks the satellite position by monitoring a beacon or automatic gain control (AGC) signal from the satellite, continuously seeking to maximise the signal level.

There are three steps involved in tracking the satellite. These are: moving to the general orientation to find the satellite, performing an expanding spiral search centred on the presumed orientation and locking onto the satellite once the AGC signal exceeds the threshold value.

3.1.6.2 Satellite Orbital Mechanics.

Satellites may be placed along many different paths, or orbits, as they revolve around the Earth. The plane of these orbits can be equatorial, polar, or inclined. A polar orbit has a plane that is more or less parallel to the Earth’s polar axis, while the plane of a geostationary orbit is equatorial in nature, lying parallel to the Earth’s equator. Orbits that are offset in degrees from the Earth’s equatorial plane are called inclined orbits.

The communications satellites in geostationary orbit are located above the equator, in an assigned nominal orbit, and revolve around the Earth at the same



rate as the Earth rotates on its axis. To an observer, or satellite antenna, on the ground these satellites appear to be stationary. However, geostationary satellites are constantly being subjected to forces such as the gravitational attraction of the Sun and the Moon, the radiation force from sunlight, (the solar wind); and the Earth’s gravitational field, all of which create a tendency for any stationary satellite to drift away from its assigned subsatellite point over the Earth’s equator.

Geostationaryarc

subsatellitepoint

internationaldate line

meridian

The satellites stay in geostationary orbit, due to the interaction of the Earth’s gravitational pull and the satellite’s momentum. The satellite’s rotational momentum produces a centrifugal force, which would, if unchecked, throw the satellite away from the Earth. This centrifugal force is balanced by the gravitational pull of the Earth on the satellite.

Under normal conditions, the satellites use station keeping manoeuvres to keep the satellite located within a box, which is usually dimensioned ±0.1 degrees in the North/South direction and ±0.05 degrees in the East/West direction.

As the satellites age, their store of onboard fuel decreases. To extend the satellite’s operational life, the satellite operators often change the satellite’s orbit to an inclined orbit. Inclined orbits use less fuel as the satellite is only restricted in the East / West direction. The North / South direction is allowed to wander, the amount of movement is termed the satellite inclination. Inclined orbits use much less station keeping fuel as the majority of fuel is expended in counteracting the Sun / Moon pull, which produces the North / South movement. The East / West position must be strictly maintained to ensure that co-located satellites do not



interfere with each other. Inclined orbits are termed geosyncronous rather than geostationary. The difference is illustrated below:

N

S

GeosynchronuosSatellite

GeostationaryOrbit

GeostationarySatellite

GeosynchronuosOrbit

All satellites as they move in orbit, trace a Figure of eight around their nominal celestial position. The satellite operators try to minimise the size of the pattern in geostationary satellites, by using station keeping manoeuvres. The Figure of eight pattern is produced by the gravitational pull of the Sun and Moon, the solar wind and the shape of the Earth. A view of the satellite orbit, exaggerated for clarity is illustrated below:

Normal Orbit

Inclined Orbit

2 degreespacing

EastWest North

South

Inclined satellites suffer from the problem that, as the satellites moves in orbit, the footprint also moves on the Earth’s surface. To counteract this effect, the satellite physically tilts the antenna, thus resetting the footprint. The tilt is often referred to as the Comsat Manoeuvre, after the company that developed the idea.

All communications satellites carry one or more types of beam antennas: global, hemispheric, zone and spot. Each beam pattern is tailored to a specific



application. The beam pattern determines the power that any location on the Earth ‘sees’ from the satellite, and also how far a vessel can move from the footprint centre, while still receiving adequate power to provide communications services.

3.1.7 Control System Operation

3.1.7.1 Operation

The following Sections explain the components, which are combined to produce the Spacetrack stabilisation system.

3.1.7.1.1 Sensors

The system uses a combination of velocity sensors, ADTs and inclinometers to provide the stabilisation process. Each sensor is used in different methods, depending on the system mode of operation. The sensor functions are:

• Velocity Sensors – The velocity sensors produce a voltage proportional to the angular rate of rotation of the sensor. The sensors are based on piezo-electric prisms, which distort during rotation, due to the effect of gravity. The prism distortion produces a voltage, due to the piezo effect, which is measured as a direct function of rotation.

• Inclinometers – The inclinometers are used to measure the tilt of the sensor, referenced to the local horizon. The sensor is based on a cell containing an electrolytic fluid. As the cell is tilted, plates measure the change in capacitance, which is converted to a dc voltage and used as a measure of the sensor tilt.

• ADTs – The ADTs, (Angular Displacement Transducers), are high quality potentiometers. The ADTs are fixed to each axis of the system to provide pointing information relative to the base of the Spacetrack terminal.

3.1.7.1.2 Normal and Instrument Angles.

In operation, the system works with two frames of reference. The normal frame of reference is derived, by integrating the velocity output, produced by the velocity sensors to produce an inertial position. This position is used in track and lock mode, and is called the normal angles.

The second frame of reference is derived, by combining the inclinometer output with the ADT readings, to produce a pointing angle referenced to the local horizon. This angle is used to acquire the satellite, and is called the instrument angle.

3.1.7.1.3 Sensor Processing.

The process that is executed by the control system is intricate, and involves complex digital signal processing routines. The control system has two process functions, which may be adjusted to tailor the control system to the mechanical assembly. These are the torque loop and the velocity sensor input loop. All the



sensors are digital filtered before use by the control system, with characteristics that are designed for each particular sensor.

3.1.7.1.3.1 The Torque Loop.

The torque loop is used to adjust the output characteristics of the demand signal to the motors. Adjusting the torque loop will affect how fast or how slow the system will respond to an event in all modes. There are two variables, which may be altered in the torque loop, these are the filter length and the filter cut off frequency.

The filter length sets the phase delay introduced by the filter, while the cut off frequency adjust the amplitude response for the filter as plotted against frequency. In normal operation the cut off frequency is set to a value which is suitable for the terminal inertia. The phase delay may then be used to tune out any resonant modes, which may be exhibited by the mechanical structure.

3.1.7.1.3.2 The Velocity Loop.

The velocity loop is used to adjust the input characteristics of the tracking position loop. Adjusting the velocity loop will directly effect the tracking response of the system. There are two variables, which may be altered in the velocity loop, these are the filter length and the filter cut off frequency.

The filter length sets the phase delay introduced by the filter, while the cut off frequency adjusts the amplitude response for the filter as plotted against frequency. In normal operation, the velocity filter is disabled, this allows the system to operate with true phase and amplitude information.

3.1.7.1.4 Motors

The system uses high power, low speed dc torque motors to position the antenna. The motors are driven by a high frequency pulse width modulation signal, the average of which is directly proportional to the torque produced by the motor. The torque applied to the motors, is the output of the torque filter loop, and is proportional to the velocity required to position the antenna correctly. If there is no error term present in the system, the motors will be free floating; torque is only applied to correct position errors.

3.1.7.1.5 Inertia

The inertia parameters are a measure of the weight of the antenna. The inertia parameters are used as a scaling factor, which determines how much torque to apply to the motors to produce a set velocity, in essence the inertia settings are gain parameters. The moment of Inertia of a mass is defined as:

2RadiusMassInertia ×=

The effect of the square term, is that mass, which is further away from the gimbal centre has the greatest contribution to the torque required to move the antenna. In simple terms a small weight at the end of an arm is equivalent to a large



weight close the gimbal centre. The gimbal centre is important, because if the dish and arms structure is perfectly balanced, the centre of gravity is located exactly where the three axis cross. This means the inertia seen by the motors is measured from this point.

The inertia setting differs, depending primarily upon the dish size and to a lesser effect upon the transceiver equipment. The inertia settings may be derived via three methods, the standard method is that the control system estimates the inertia based on a table of preferred values and other settings such as filter characteristics. The control system may also calculate the inertia during the balance routine, or the user may enter a value for each axis. Setting the inertia manually is not recommended, without in depth knowledge of the tracking system.

To set the inertia manually, the easiest method is to observe the box pattern the antenna traces, when the system has been configured for standard track size and speed settings. See Section 3.1.7.3.2.3 for a list of the standard settings. The box pattern produced for different inertia settings is show below.

Inertia set too low,or track speed too high

Inertia and track speedcorrectly set Inertia set too high

The above method may only be used when the host vessel is not moving. The box pattern may be easily observed using a laser pointer.

An alternative method is to use a spectrum analyser, which has been configured for zero span, centred upon the tracking frequency. The desired response should be 0.5dB of tracking ripple using the standard track parameters.

3.1.7.1.6 System modes

The control system has several modes of operation. These are:

• INITIALISE - This mode is automatically entered when the control program starts. During initialise mode the system estimates the dc offset of the velocity sensors, and allows all the system sensors to reach operating temperature. The control system will remain in initialise mode for 30 seconds, then automatically enter FIND mode. However, if the system parameters are incorrect and the calculated satellite position is not visible, the system will enter MANUAL mode and display a hidden alarm, on completion of INITIALISE mode.



• MANUAL - In manual mode, the antenna can be driven to any position using the cursor keys. The system will not track in this mode.

• FIND - In find mode the antenna moves to point at the calculated position for the satellite. The position is calculated from the vessel position and the satellite longitude information provided. Once the antenna is in position, it will enter SEARCH Mode. The initial co-ordinates may also be specified by the operator.

• SEARCH - Once FIND mode has roughly positioned the antenna, the system will be pointing at the approximate position in the sky where the satellite can be found. The system will now start an expanding spiral search of the sky in that area. When the AGC signal rises above the THRESHOLD value, the system will enter LOCK mode. If the system does not find an AGC signal above the THRESHOLD value within a set time, it will re-centre the scan and begin the sequence again.

• LOCK - Once SEARCH mode has located the satellite, the system will lock onto the position which provides the strongest signal. If the AGC signal drops below the THRESHOLD value, the system will revert to SEARCH mode.

• TRACK - Once LOCK mode has been successfully completed, the system will enter TRACK mode and track the satellite for as long as the AGC signal stays above the THRESHOLD value. If the AGC signal drops below the THRESHOLD value, the system will revert to LOCK mode.

• UNWRAP - This mode is only available on systems without sliprings. In unwrap mode, the system rotates 360° in the direction required to unwrap the cables running through the centre of the pedestal. If the antenna elevation is above 30°, the elevation will drop to 30° as it turns. Once this manoeuvre has completed, the system will enter FIND mode.

• DIAGNOSTICS – DIAGNOSTIC mode is used to calibrate the system and also to detect and solve any problems that may exist within the system. In DIAGNOSTIC mode the user has full control over the motors, while the sensor readings are displayed along with statistics, detailing the sensor behaviour.

• MONITOR – MONITOR mode provides the same functions as DIAGNOSTIC mode except that direct control of the terminal is not possible. MONITOR mode works in conjunction with the previous mode to display the sensor and motor demands, while the system is operating. MONITOR mode is useful for monitoring the system for subtle faults.

The normal sequence of operation is: Initialise, Find, Search, Lock then Track. The system will repeat the find and search sequence indefinitely until the correct satellite is found. If the system locks onto the incorrect satellite, the modem carrier detect function will reset the system mode back to find mode. This is attributed to the unlikely hood, of two identical carriers, at the same frequency, on adjacent satellites.



3.1.7.2 Satellite Acquisition.

To acquire and track the satellite, the system must have some means of determining when, and how accurately, the antenna is pointed at the satellite. This feedback signal is derived form the signal level received by the down conversion equipment.

3.1.7.2.1 Tracking Sources.

The system has several different sources of tracking information, these are:

• External Interface: The external interface may be used to interface the Spacetrack systems to down conversion trains which have no standard IF frequencies or to systems such as D.A.M.A. which provide a peaking signal. The external interface may also be used with some modems, although this depends very much on the processing delay of the modem. In general an EbNo indication signal has too long a processing delay to be useful, although in some cases the Spacetrack receiver delay variable may be adjusted to take the modem processing delay into account. The systems ability to track using a modem feedback signal must be considered on an individual basis.

• Narrowband Receiver: The narrowband receiver is designed to track either a beacon signal or a modulated data carrier, at a 70MHz IF scheme. The transfer characteristics of the internal narrowband receiver is listed in Appendix C.

• Wideband Receiver: The wideband receiver is designed to track a whole transponder, at a 70MHz IF scheme. The wideband receiver is useful for tracking densely populated transponders, which allow the average transponder level to be used, rather than the power in an individual carrier. This has the advantage that the inbound carrier does not rely on the Earth station that is providing the tracking beacon or carrier. The wideband may also be used in conjunction with the L Band down converter to provide satellite TV tracking. The transfer characteristics of the wideband receiver are listed in Appendix C.

• L Band Down Converter: The L Band down converter is not a detector, but a frequency translator, that shifts an L Band signal to a 70MHz IF scheme. The L Band down converter is usually used with the wide band detector and a TV LNB. The down converter does not require a dc block.

If the external interface is activated, the system may require to be configured to match the processing delay of the AGC source. The receiver delay is important if the AGC source is a modem; this is due to the fact that most modems output an indication of the EbNo level, rather than an indication of the absolute received signal level. The modem introduces considerable delay when calculating the EbNo Figure. To overcome this problem, the Spacetrack can compensate for the modem delay, using the receiver delay parameter. The receiver delay parameter is dimensioned in seconds, and allows the control system to match the angle, that the maximum signal level was observed at, to the processing delay.



Note: Not all modems are suitable for using as a tracking source, and must be evaluated on an individual model basis. The user must also be aware when setting the delay parameters, that there is a ghost setting, with which the system will operate, but with impaired tracking. This value is equal to the time required to complete two sides of the box, and may be deduced from the track size and speed parameters. Only users with an in-depth knowledge of the tracking system should utilise the receiver delay parameter.

The internal detectors require a delay setting of zero to operate correctly.

3.1.7.2.2 Input Attenuation and Acquisition Threshold.

With all tracking sources, the levels must be carefully matched to allow the system to distinguish between background noise and the satellite signature. The level at which the system determines the presence of a satellite is called the threshold. The threshold may be illustrated graphically below:

Threshold

Pedestal

Threshold

Pedestal

Carriers

Antenna not pointed at the satellite Antenna pointed at the satellite

When the antenna is not pointed at the satellite there is no power above the threshold level, while on satellite, the carriers protrude above the threshold. The pedestal is background noise, which is amplified across the frequency range of the amplifier.

The system has two methods of positioning the on and off satellite levels, these are adjusting the threshold or adjusting the detector input attenuation.

3.1.7.2.2.1 Setting the Attenuation and Threshold Manually.

When the levels are set manually, the user selects an input attenuation, which provides suitable on and off satellite AGC readings. This attenuation then stays fixed, while the threshold is set to indicate the on and off transition point.

3.1.7.2.3 Acquisition Angles.

The system may be configured to acquire the satellite in two different methods. The standard method is that the system calculates the bearing to the satellite using the host vessel’s latitude and longitude and the satellite longitude. Alternatively the user may disable the automatic angle calculation and set the acquisition angle manually.

If the system is set to calculate the acquire angles, and polar tracking is enabled, the calculation is performed continuously, while the polar angle is adjusted to peak the polarisation. With this method, the azimuth and elevation angles are derived from the strongest satellite position, while the polar angle is calculated.



The acquisition angles are specified relative to true North. The control software compensates for the vessel’s heading when positioning the antenna.

3.1.7.2.3.1 Modem CD.

The modem CD indicator is used to indicate to the system, that the correct satellite has been located. This is often necessary due to the closely located orbits of co-located satellites. It is extremely unlikely to have two identical carriers located at the same frequency on two co-located satellites, therefore if the modem locks up, then it is a good indication of acquisition success. The output is usually derived from the modem’s demodulator locked indicator.

The user may set a demodulator lock period and a glitch period. The demodulator lock period, is the length of time the modem requires to synchronise with the far end modem. The modem demodulator locked output will not indicate a modem lock until the training sequence is complete, thus the Spacetrack must delay any decision, as to whether the correct satellite has been acquired until this time period has elapsed. The time required for the modem to lock may be derived from the manufacturer’s data, or measured directly, with a safety margin.

The glitch period is designed to defeat contact bounce and modem glitches. This period should be set for about one second, the Spacetrack will not respond to a modem lock fail signal, if the lock indicator was previously high, until the glitch period has elapsed.



The connections for a selection of modems is listed below:

Modem Interface Panel CN8

Type Connector Ground Connection

Modem CD Connection

ComTech CDM-500 Alarms

Pin 7 Pin 8

EF SDM309 Fault J7 Pin 8 Pin 9

Fairchild SM2800 Fault J6 Pin 15 Pin 16




Paradise Datacom P230 Alarms Pin 3 Pin 10

Paradise Datacom P400 Alarms Pin 2 Pin 3

3.1.7.3 Satellite Tracking.

The system tracks the satellite using a step tracking algorithm. The step track method is also sometimes called Staircase Tracking. The algorithm involves moving the antenna and measuring whether the signal level decreases or increases. The antenna is continually moved by fractions of a degree, monitoring for the strongest signal level. The staircase algorithm may be shown graphically as:

SignalStrength

Carrier

Step Tracking Algorithm



The step tracking algorithm is implemented by using a box method, where the antenna is moved left in azimuth, up in elevation, right in azimuth and finally down in elevation. This movement produces a box around the boresight position. On each side of the box, the system measures the received signal strength, looking for the peak signal on each axis. The peak signal from azimuth and elevation is then set as the boresight vector. Every consecutive box is centred on the boresight produced by the previous box. The system thus continually optimises the boresight angle with each complete box motion, and tracks the satellite as the motion of the vessel disturbs the antenna from the boresight angle.

3.1.7.3.1 Polar Tracking.

The Spacetrack system may be configured to optimise the polarisation angle automatically. There are two main methods of communicating with the satellite, these are circular polarisation and linear polarisation. The linear polarisation method is also split into horizontal and vertical polarisation.

The polarisation describes the relationship between the electrical and magnetic fields as they travel through space. The different polarisations are used to provide frequency re-use and so maximise the available bandwidth available to the satellite operator and user.

3.1.7.3.1.1 Linear Polar Tracking

The Spacetrack system is only required to optimise the polarisation angle for linear polarised communication schemes. The polarisation correction is designed to compensate for the incident beam mismatch angle, caused by the difference in vessel and satellite longitude; and due to the polarisation skew caused by inclined satellites. The Spacetrack can compensate the polarisation angle using a combination of the polarisation axis and an active feed if fitted.

Using the polarisation axis to compensate for the polar angle is not recommended due to the limited range of motion available to the polarisation axis, which may also be required to compensate for the host vessel’s motion.

An active feed is a feed and an OMT arrangement, which are fitted on a plate which can rotate when driven by a motor. The system can use the active feed to rotate the OMT physically and thus compensate for any polarisation correction required. The active feed method is recommended for vessels, which travel large distances and require polarisation compensation.

3.1.7.3.1.2 Circular Polar Tracking

If the Spacetrack system is configured as a circularly polarised system, the polar axis is held at zero degrees and any active feed is not used.

3.1.7.3.2 Scan Parameters.

The scan parameters are used by the control software to generate the box scan pattern. The system uses the same box pattern for search, lock and track operations. The dimensions and velocity of the box pattern may be adjusted for each mode.



3.1.7.3.2.1 Search Parameters.

The search parameters are used exclusively in search mode. The scan size determines the largest box dimension that the system will use to locate the satellite. During SEARCH mode, the system initially starts scanning for the satellite using the lock parameter box dimension, which is increased until the box is the same size as the search box. If the satellite has not been located before the box dimensions equal the search size, the box size collapses back to the lock size, and the process repeats.

The scan size should be dimensioned slightly less than the co-satellite orbit separation. This parameter is usually set to 2°.

The scan speed may be set to a velocity that allows the satellite to be located quickly, the default setting is 0.4°s-1.

3.1.7.3.2.2 Lock Parameters.

The lock parameters are used to initially locate the satellite boresight, and to allow the system to characterise the sensors, before the more exacting track mode is engaged.

The lock parameters are used exclusively in lock mode. The system will calculate parameters automatically based on the system configuration. The user may also enter parameters manually, although this is not recommended. The lock size and speed are mainly dependent upon the frequency band and the dish size. The following table illustrates sample recommended values.

• C Band Systems:

Dish Size (m) Lock Size (°) Lock Speed (°s-1)

1.2 0.84 0.43

1.8 0.56 0.37

2.4 0.42 0.30

3.0 0.34 0.23

3.75 0.27 0.15



• Ku Band Systems:

Dish Size (m) Lock Size (°) Lock Speed (°s-1)

1.2 0.36 0.43

1.8 0.24 0.37

2.4 0.18 0.30

3.0 0.14 0.23

3.75 0.12 0.15

3.1.7.3.2.3 Track Parameters.

The track parameters are used to position the antenna pointing directly at the satellite boresight. The track parameters are used exclusively in track mode. The system will calculate the parameters automatically, based on the system configuration. The user may also enter parameters manually, although this is not recommended. The track size and speed are mainly dependent upon the frequency band and the dish size. The system inertia also has a direct effect on the tracking performance, see Section 3.1.7.1.5 for details on setting the inertia. The following table illustrates sample recommended values.

• C Band Systems:

Dish Size (m) Track Size (°) Track Speed (°s-1)

1.2 0.49 0.49

1.8 0.32 0.42

2.4 0.24 0.35

3.0 0.19 0.28

3.75 0.16 0.20



• Ku Band Systems:

Dish Size (m) Track Size (°) Track Speed (°s-1)

1.2 0.24 0.49

1.8 0.16 0.42

2.4 0.12 0.35

3.0 0.10 0.28

3.75 0.08 0.20

The system tracking may also be optimised by observing the tracking response using a spectrum analyser, zero-spanned on the tracking frequency. The system should exhibit 0.5dB tracking ripple in moderate weather. The oscillogram below shows a typical tracking trace obtained from a construction barge operating in the North sea.

To set-up a spectrum analyser to display a zero spanned carrier, it is necessary to reduce the span and re-centre the carrier in several stages. This is due to frequency drift in the satellite, the down conversion equipment and in the spectrum analyser. The oscillogram over page was produced with the following spectrum analyser settings:

• Span – 0Hz

• Sweep – 30 seconds

• RBW – 30KHz

• VBW – 30Hz

• Video Averaging - Off



3.1.7.4 Active Weights.

The Spacetrack system derives the majority of the stabilisation action from the inherent inertia of the system. The main forces, which degrade the stabilisation process, are physical imbalance and friction. The degradation produced by friction is controlled by the manufacturing process, while the imbalance force is entirely dependant on the set-up of the terminal.

It therefore follows that, any device, which can eliminate human influence and error from the process, is extremely desirable. The Spacetrack system may be equipped with active weights to provide an automatic balancing function. Active weights are located in all three planes of rotation.



Front to BackActive Weight

Left to RightActive Weight

Top to BottomActive Weight

Active Weight Arrangement.

3.1.7.4.1 Active Weights.

Active weights balance the terminal using the electronics are located in the ADU module and the control logic is performed in the software control loop. Since the active weights are controlled directly by the control software, they are used to balance the system during the balance routine, to produce a universal balance. During operation the system integrates the output torque and moves the active weights to point balance the system. A universal balance is a balance that allows the terminal to float at any angle; whilst with a point balance, the system will sit at one angle only, usually the operating angle.



3.1.7.5 System Log.

The system log is used to store events that the control system regards as important and may warrant user attention. The log may contain information relating to mode changes, errors, automated messages and monitor messages. The types of messages are detailed below:

• Mode Changes – The system records each mode change, to allow the user to examine the link performance and the system’s operation.

• Errors – If the control system detects an error, the error is logged to allow a non-transient record and to allow the system’s history to be examined.

• Automated Messages – Automated messages occur when the system initialises, or during other tasks which require user feedback, such as Balance mode.

• Monitor Messages – Monitor messages are generated by the system supervisor module. The system supervisor module monitors all the systems parameters, scanning for error conditions such as faulty sensors or invalid values. This function is useful to provide early detection of faulty sensors, before the sensor fails completely.

The log holds 180 entries. When the log is full, any additional messages will be discarded. The log may be accessed from the front panel or via the M&C console. See Appendix F for a listing and description of the log messages.

3.1.7.6 Auxiliary Communication Port.

The auxiliary communications port is a spare serial port, which may be used to interface the BDU module to any additional offshore equipment. The equipment may then be accessed through the M&C console, as if a local connection were present, this enables remote access to the attached equipment.

The auxiliary communications port may be attached to any modem, multiplexer or RF equipment, which has an M&C interface. The auxiliary communications port may also be extended through a code switch to allow access to more than one device.

The auxiliary communications port may be configured to match the link parameters of the target equipment. There may exist a difference in data rates between the M&C console and the auxiliary serial port. The BDU module has internal buffers to compensate for the difference in data rates. The internal buffers will only compensate if the data throughput is low. If the throughput is sustained, buffer overruns will occur and data will be lost. The receive data buffer length is 2K bytes, while the transmit data buffer length is 80 bytes.

To access the auxiliary serial port, the interface must first be opened. While the port is open, it is not possible to access any other Spacetrack M&C functions; Spacetrack M&C functions are only available when the auxiliary port is closed. See Figure 22 for connection details.



3.2 ASSEMBLY AND INSTALLATION

The Spacetrack platform and radome will generally be delivered fully assembled, but the following Sections summarise how to assemble the Spacetrack platform and radome, assuming they arrive unassembled. If the system does arrive fully assembled double check that there are no parts missing and that no damage has occurred in transit.

Before the assembly is considered complete, fill out the checklist mentioned in Section 3.2.7 to make sure that nothing has been omitted. Section 3.2.8 gives a similar checklist for use when demobilising a Stabilised Platform, which has been in operation on a vessel.

3.2.1 Site Survey

Before sending the Spacetrack equipment to the vessel, a site survey should be done. The following should be kept in mind when selecting a physical location on the deck for the radome equipment:

• Visibility: The Spacetrack needs a clear line of sight to the satellite for most vessel headings.

• Vibration: High vibrations can impair performance. Choose a location as far from vibrating equipment as possible.

• Cable Runs: The installation is easier if the Radome is situated close to the Radio Room

• Antennas: Do not site in direct line with radar energy or near high power short wave transmitting antennas.

• Heat Emissions: Ensure site is well away from sources of heat, e.g. engine exhausts and gas flares.

3.2.2 Assembling The Platform

During assembly of the Stabilised Platform, the following points should be kept in mind:

• Stainless steel hardware should be used, to avoid corrosion in the marine environment

• Lockwashers, locknuts, or Loctite should be used on all threaded fasteners because of the high vibration level common on vessels.

• Particular care should be taken not to damage the ADU Module. Always check the module indicators for shock and moisture ingress. Reject if the maximum shock has been exceeded.

The system may require assembly. Check the following points, carrying out any tasks that are required:

1) Lift the unit onto the baseplate using the eyebolts supplied.



2) If the system baseplate has three rubber vibration mounts fitted, use the three longer bolts to bolt through them taking care to fit the three large washers on the underside of the mount and the three shorter bolts to screw into the tapped base via the spacer provided. If the system baseplate has no rubber vibration mounts fitted, the system should be bolted directly to the baseplate using the six bolts supplied.

3) Fit the antenna to the mounting frame.

4) Install the ADU Module, taking care to orient the box correctly. The correct orientation is shown on the face of the module.

5) Install all other platform equipment, such as the Antenna Feed, LNA, and RF unit.

6) Install all Spacetrack cables following Figures 6 & 7. Ensure that all components and cables are securely strapped down, or it will not be possible to balance the platform. Ensure cables from the gimbal support tower to the antenna support arms have enough length and flexibility to ensure that the antenna can move freely in all directions.

7) Take care in controlling the motion of the platform while adding weights to balance the antenna, watch for an indication that the platform is nearly balanced. Complete the balancing process, by following the instructions in Section 3.3.5.

8) Assemble the radome on to the baseplate, around the system. There are four eye bolts which will be provided, use these in place of four normal bolts when bolting the radome to the baseplate. They are used for the attachment of bungee cords when lifting or transporting the system fully assembled.

9) Use the four bungee cords supplied to attach the antenna and rear cross member to the four eye bolts in the radome floor.

3.2.3 Deck Installation

The Spacetrack pedestal, which holds the dome above the deck, should be securely welded to the deck of the vessel. Ensure the pedestal is correctly aligned with the heading of the vessel. See the plan view of the Spacetrack platform in Figure 1. With the system fully assembled on the radome pedestal, the antenna should be in this position relative to the baseplate when pointing in the direction of the heading of the vessel.

Note: The access hatch is located between the pedestal and the aft of the vessel.

Particular care must be taken when lifting the system. To avoid endangering personnel or damage to the system, the following precautions must be adhered to.

It is important to recognise that a fully assembled Spacetrack platform has a high centre of gravity. During lifting, take care to keep the system balanced. Use only the DMS eight legged lifting strops provided.



Under No Circumstances should spreader bars be used. Only trained banksmen should give lifting instructions to the Crane Operator.

Before attaching the strops, ensure the eye bolts around the circumference of the baseplate are screwed in and are vertical (so they will not twist when the upward force from the strops is applied). Lay out the strops on the ground and ensure there are no twists or knots in their length. The crane should lift up the strops, and lower them over the radome, until there is enough length for the strops to be attached to the eye bolts. Attach each strop leg to an eye bolt, ensuring the following:

• shackles are tightened securely • the legs are not intertwined above the radome

Once the slack has been taken up in the strop, ensure that:

• the strops lie flat against the radome, with no twisting • the strops go up over the radome vertically. Straighten any strops that are at a

slant. Lift the system onto its pedestal ensuring the dome is pointing in the correct direction and the locating pegs are fully in place.

3.2.4 Assembling the BDU

The Spacetrack 4000 Interface and BDU module should be installed in a 19” rack, along with any other associated communications equipment. The BDU module requires slides or supports along the length of the module to support the rear of the module when mounted. Electrical connections to the BDU are described in Section 3.2.5.

The BDU module will arrive with the control software pre-installed and will automatically execute on power up.

3.2.5 Electrical Connections

Figure 11 is a wiring diagram showing how the Spacetrack pedestal should be connected to the BDU and the modem. Figure 7B shows where the mains should be connected to. The following points are important:

1. Generally, in the Radome, AC power is required to be connected to the two junction boxes located in the radome, (see Figure 1). UPS power is connected to the junction box which powers the ADU Module and RF equipment. Raw mains is connected to the other junction box, this powers auxiliary equipment such as lighting.

2. The UPS can be located inside the Radio Room, so that it can provide power both to the communications equipment in the indoor unit, and to the above deck equipment. There is also the advantage that power to the radome can be switched off from indoors.



3. Check the ADU Module is set for the appropriate mains voltage.

Figure 8 is a diagram showing how the BDU Interface should be connected. A cable loom will be provided to connect the BDU module to the Interface Panel. Figure 23 shows the additional connections for an optional GPS receiver input. Figure 9 shows the additional connections for an optional heading input.

Ensure all cables are identified and installed neatly.

3.2.6 Eclipsing Headings Chart

In some installations, there will be certain headings of the vessel, which will make it impossible for the antenna to lock onto the satellite, because of physical structures on the vessel eclipsing the signal. It is good practise to calculate ahead of time, which headings will be troublesome, and warn the radio operator accordingly.

Figure 15 is an example of an Eclipsing Headings Chart, such as you might provide the radio operator, and Figure 16 is a copy of a blank chart. For each installation, take a photocopy of the blank chart found in Appendix A, fill in the headings that apply, and leave it with the radio operator.

3.2.7 Installation Checklist

When the assembly and installation are complete, photocopy the Installation Checklist found in Appendix B, complete all Sections, and include it in the unit documentation package.

3.2.8 Demobilisation

If it is necessary to remove a Spacetrack Pedestal from a vessel photocopy the Demobilisation Checklist found in Appendix B, complete all Sections, and include it in the unit documentation package.

Note: Lifting instructions provided in Section 3.2.3 equally apply when demobilising a system, and must be adhered to.

3.3 INITIALISATION

Once the Stabilised Platform has been installed, and connected to the vessels compass and GPS, it is necessary to configure various parts of the system to match the specific vessel conditions. Sections 3.3.1 through 3.3.11 below, describe the various initialisation and calibration procedures. The procedures should be completed, in the order described.

Ensure that you are familiar with the Spacetrack 4000 equipment (see Section 1) and the console software (see Section 4), before commencing the initialisation procedure. The Operators Manual also provides a basic guide to the operation of the system.



When you have completed the initialisation tasks, use the checklist mentioned in Section 3.3.11 to ensure that none of the tasks have been missed.

3.3.1 Initialising The System

Although the system can be initialised with the monitor and control terminal located in the radio room, it is easier if a console terminal is in the dome during initial setup.

1) Remove the mains input lead at the ADU Module interconnection plate and at the BDU module.

2) Switch on the power at the Uninterruptable Power Supply (UPS), and measure the mains voltage. Confirm that the ADU module is configured to operate at this voltage. The ADU module has a data plate next to the J3, the mains connector (see Figure 4), which specifies the operating voltage that the module is set for.

3) Switch off the UPS.

4) Connect the console terminal to the above deck interface panel, and ensure the terminal emulation software is active.

5) Re-connect the mains input lead first to the ADU Module and then to the BDU Module.

6) Switch on the UPS.

7) Log into the monitor and control port, the default password is FACTORYkSETUP.

8) Once the BDU module has established a connection to the ADU Module, select the diagnostic option from the mode menu. Keystroke sequence M65.

9) Systems Without Sliprings Only: check the coarse azimuth limit switch. See Section 3.3.2.1

10)Adjust the coarse azimuth ADT. (See Section 3.3.2.2)

11)Systems Without Sliprings Only check the mechanical stop. See Section 3.3.3

12)Check the potentiometers for each gimbal motor have not moved in transit and are set correctly . (See Section 3.3.4.)

13)Check the system is balanced. (See Section 3.3.5.)

14)Reboot the control module, Keystroke sequence M67Y.

15)Wait for the Control System to enter initialise mode, and select the real-time display, Keystroke sequence M71. Step 16 should be carried out during INITIALISE Mode. The Control Program will remain in initialise mode for 30 seconds.

16)Confirm the antenna moves to an elevation of approximately 30 degrees, polarisation 0 degrees and the fine azimuth remains in centre of gimbal support and stays in this position.



17)Wait for the INITIALISE mode to expire and change to manual mode. Keystroke sequence kM64.

18)Move the antenna to several positions using the cursor keys. Check the antenna follows the cursor commands in all directions. Ensure the coarse azimuth motor also functions in both directions, by rotating the fine azimuth axis by hand, until the coarse azimuth attempts to centre the fine azimuth axis.

19)Ensure the main system parameters match the above deck configuration. A system summary may be obtained by typing kM18, from which the correct parameters may be compared. The main system parameters are:

• Dish Size, (to change see Section 4.1.2.2.8.1).

• Tracking Source And Frequency, (to change see Section 4.1.2.2.2).

• Frequency Band (C or Ku) , (to change see Section 4.1.2.2.8.2).

• Satellite Longitude, (to change see Section 4.1.2.5.1).

• System auto configuration settings. (Keystroke sequence kM71ff. Ensure all auto configuration variables are enabled.) To change see Section 4.1.2.2.1.

See Section 4 to alter or enable any variables, which display as incorrect.

20)Set-up the RF equipment. (See Section 3.3.7)

21)Perform a lock on test. (See Section 3.3.10)

22)Perform power balancing, cross polar correction procedures as appropriate. The tests performed will vary with the satellite operator.

23)Confirm all bolts and cables are tightly secured and the system is perfectly balanced. (See Section 3.3.5)

24)Complete the Initialisation Checklist. See Section 3.3.11.

3.3.2 Setting the Coarse Azimuth

The Coarse Azimuth ADT is located in the centre, between the gimbal support struts, directly below the gimbal (see Figures 1 and 14). The Coarse Azimuth ADT must be calibrated so that the control system knows the relative direction of the gimbal support tower to the bow of the vessel. Continuous (with sliprings) systems vary from unwrap systems as described in Section 3.1.2. The calibration of the coarse azimuth differs in the following manner.

• Unwrap Systems - the coarse azimuth ADT calibration voltage is +5.0V (i.e. the ADT is set to produce +5.0V when the antenna is pointing at the bow of the vessel and the coarse azimuth is in the centre of its mechanical limits). The coarse azimuth electrical limit switch must be set, and the mechanical stop must be checked for correct operation.

• Slipring systems - the coarse azimuth ADT calibration voltage is 0.0V (i.e. the ADT is set to read 0.0V when the antenna is pointing at the bow of the vessel), there are no limit switches.



Although the calibration voltages are different, the diagnostics software will automatically adjust the calibration set point according to the terminal configuration; therefore, the ADT should always be calibrated to give a zero error reading. The system should be aligned with the vessel heading (i.e. the sides of the square plate that the pedestal stands on, are parallel with the vessel's heading). This gives an indication of the ships heading from inside the radome, when setting the coarse azimuth.

3.3.2.1 Set the coarse azimuth limit switch

This procedure does not apply to systems with sliprings

• The ADU module should be switched off

• Turn the gimbal support by hand, so it is in line with the heading of the vessel. i.e. with the antenna in the centre of the fine azimuth travel, the antenna will point exactly at the vessel’s bow. Ensure the gimbal support is in the centre of its travel between the mechanical stop.

• The micro switch trip peg should now be located 180° from the micro switch, as shown in Figure 14. If this is not the case, the coarse azimuth mounting plate must be removed. The limit switch, coarse azimuth ADT gear cog and the ADT are mounted on this plate. Line up the micro switch trip peg exactly 180° from the micro switch and replace the coarse azimuth mounting plate.

3.3.2.2 Set the coarse azimuth ADT

• The ADU module should be switched on.

• Connect the M&C console to the above deck interface panel in the radome. Set the system into diagnostics mode, Keystroke sequence kM64.

• Turn the gimbal support by hand, so that it is in line with the heading of the vessel. i.e. with the antenna in the centre of the fine azimuth travel, the antenna points directly at the heading of the vessel.

• If the system has no sliprings, ensure the gimbal support is in the centre of its travel between the mechanical stops.

• Loosen the three screws locking the ADT in position just enough to allow the ADT to turn by hand.

• Check the angle reading for the Coarse Az in the Error column on the console. This displays the difference between the signal received and the calibration reference point, the value should be set to zero.

• Tighten the transducer in place and recheck the error reading is zero.

• Reboot the control module. , Keystroke sequence kM67Y. If the fine azimuth pot has been calibrated, confirm, during INITIATIALISE Mode, on the console display that the azimuth of the antenna is the same as the vessel heading. If the fine azimuth has not been calibrated, confirm this is true after calibrating the fine azimuth.



3.3.3 Mechanical Unwrap Limit

This procedure does not apply to systems with sliprings

Warning! The mechanical unwrap limit mechanism should never be altered unless the adjustment is required. Incorrectly moving the mechanism will cause the coarse azimuth drive to stop before the electrical limit switch trips, causing damage to the system.

• Ensure the coarse azimuth limit switch, and the coarse azimuth ADT calibration has been checked first.

• The system should now be correctly calibrated to check the mechanical unwrap limit.

• Check the mechanical unwrap limit is set correctly by turning the gimbal support in both directions until the gimbal support is prevented from turning by the mechanical stop. The gimbal support should turn the same amount in both directions from the ADT calibration reference position.

• It is extremely important to ensure the mechanical stop occurs after the electrical limit switch has tripped.

• If this is not the case, the mechanism needs to be moved to the correct position.

• Finally, recheck that the mechanical stop occurs after the electrical limit switch has tripped.

3.3.4 Setting the Gimbal Motor Potentiometers

Each of the gimbal axes has a potentiometer coupled to its shaft. These give an indication of the angular displacement of the antenna frame.

The ADTs are all set in the following manner

• Connect the M&C console to the above deck interface panel in the radome. Set the system into diagnostics mode, Keystroke sequence kM64.

• Move the platform to the reference position, for the potentiometer to be calibrated. Fine azimuth - centre of travel between the gimbal support. Elevation - orthogonal to the pedestal. Polarisation - orthogonal to the pedestal.

• Check the angle reading for the potentiometer to be calibrated, in the Error column on the console. This displays the difference between the signal received and the calibration reference point.

• If the error is not zero, proceed with the following.

1. Loosen the screws for each of the three cleats, holding the potentiometer in position, by just enough so the pot will turn by hand.

2. With the antenna in its reference position given above, turn the potentiometer until the error shown in the diagnostics display is 0.



3. Fix the potentiometer in position by tightening the cleats, to firmly grip the potentiometer.

4. Recheck the Error reading

3.3.5 Balancing the platform.

3.3.5.1 Platform Balance.

It is vital that the system is properly balanced - i.e. with the motors off, the system should sit stationary at any angle. A poorly balanced system will cause more stress on the motors, and impaired tracking ability.

For balancing, there are a number of weights, on the antenna support and side rails, that can be moved or changed. Mounted on each side rail is a weight that slides away or towards the antenna; and a weight that slides up, or down. On the antenna support, there is a weight on a U-bracket, which slides right or left. The position of the balance weights is illustrated in Figure 1.

The aim of balancing is to move the centre of gravity of the arms / antenna arrangement to the centre of the gimbal. It can be simplified by splitting the system into the three orthogonal axes and visualising each as a seesaw arrangement.

• Horizontal - moves the centre of gravity behind, or in front of the gimbal centre.

• Polar - moves the centre of gravity to the right, or to the left side of the gimbal centre.

• Vertical - moves the centre of gravity above, or below the gimbal centre.

Balancing each of the axes is described below. The procedure may require several iterations before the system is accurately balanced. This may be tested by moving the platform to any position. After releasing the platform, the dish should stay at the desired angle or rotate very slowly from its position. Check this in several positions.

Before starting the balancing procedure, ensure that:

• The system is in diagnostic mode, Keystroke sequence kM64.

• The cables are not restricting or impeding movement

• The platform does not rest against its mechanical stops. The platform must be free floating while the following procedure is carried out.

a) Horizontal balance of the platform:

• With the antenna pointing horizontally, watch the direction the elevation rotates when released.

• If the antenna elevation rotates downward, the centre of gravity is forward of the gimbal centre, towards the antenna, and needs to be moved back. Move the front to back weight towards the rear. If required, add weight to the rear or remove weight from the front.



• If the antenna elevation rotates upward, the centre of gravity is at the rear, behind the gimbal, and needs to be moved forwards. Move the front to back weight towards the antenna. If required, add weight to the front or remove weight from the rear.

• When moving or changing the weights, bear in mind the effect this will have on the other axes. Try to ensure the weights, when moved from one side of the structure to the other, are the same distance from the gimbal centre to prevent changing the polar balance.

b) Polar balance of the platform

• With the antenna pointing horizontally, watch the direction the polarisation rotates when released.

• If the antenna rotates to the right side, the centre of gravity is to the right of the gimbal. Move the left to right weight to the left. If required, add weight to the left side or remove weight from the right side.

• If the antenna rotates to the left side, the centre of gravity is to the left of the gimbal. Move the left to right weight to the right. If required, add weight to the right side or remove weight from the left side.

• When moving or changing the weights, bear in mind the effect this will have on the other axes. Try to ensure that the weights, when moved from one side of the structure to the other, are the same distance from the gimbal centre to prevent changing the horizontal balance.

c) Vertical balance of the platform:

• With the antenna pointing vertically upwards, watch the direction the elevation rotates when released.

• If the antenna moves further back, with the rear cross rail striking the pedestal, the centre of gravity is towards the top of the antenna. Move the top to bottom weight towards the bottom of the antenna. If required, add weight to the bottom of the antenna or remove weight from the top of the antenna.

• If the antenna moves the other direction towards a normally horizontally pointing position, the centre of gravity is towards the bottom of the antenna. Move the top to bottom weight upwards towards the top of the antenna. If required, add weight to the top of the antenna or remove weight from the bottom of the antenna.

• When moving or changing the weights, bear in mind the effect this will have on the other axes. Try to ensure the weights, when moved are the same distance from the centre of the gimbal.

Remember that the addition or moving of any equipment cables supported by the gimbal will require the system to be re-balanced.

If the system appears to change balance often, check for anything on the system, which may be loose or could move.

The system should be balanced with the minimum of weight required. Simply adding weights at each stage will not result in a viable tracking system, try to



optimise the weight distribution at each stage, rather than continuously adding weight.

3.3.5.2 Gimbal Balance.

If the elevation axis will balance perfectly at both the horizontal and vertical positions, but not at the 45 degrees position; then it is possible that the gimbal balance is not correct. On the gimbal cage, there are two weights, which are positioned to counterbalance the azimuth motor. These weights may be used to achieve a perfect balance at all angles. When the system is balanced at the horizontal and vertical positions, adjust the gimbal weights until a balance is achieved at 45 degrees. The process of balancing, at all three angles may be required to be repeated, until a universal balance is achieved.

3.3.6 Setting the Inertias

The inertias must be set correctly, badly set inertias will impair tracking ability.

It may be visually observed when the inertias are set correctly. During track mode, the aim is to ensure that the box shape that the antenna moves through is a perfect square. If the box is circularly distorted, then the inertias are set too low, or the tracking speed is too high. If there is an overshoot at the corners of the box, then the inertias are set too high.

Observing the tracking pattern using the received tracking signal on a zero spanned spectrum analyser is also a good method of optimising the inertias in the field. See Section 3.1.7.1.5 for more details.

3.3.7 Setting Up The RF Equipment

As each terminal is designed for specific customer requirements, the RF equipment will vary depending on the installation. See the RF equipment manuals for details of set-up.

The following general points should be noted though.

• Ensure the transmit RF waveguide is securely connected all the way from the RF transceiver to the feed.

• The RF equipment transmits microwave radiation. Do not work in the dome while the system is transmitting.

• Check the focal length of the antenna. The focal length depends on the size of the dish and may be confirmed with Data Marine Systems technical support, telephone 44 (0)1224 773727.

• If any of the RF equipment or cables on the stabilised platform requires moving, including rotation of the feed, the system must be re-balanced. see Section 3.3.5.

• The RF equipment must be programmed, with the correct receive parameters before the system will operate.



• Do not switch the transmit carrier on, until it is confirmed that the system is tracking the correct satellite, and the satellite operator has granted permission to radiate. The modem transmit should be set, to switch on only when the modem detects, and locks onto, a receive carrier.

3.3.8 Set-up The Tracking Receiver

If the receiver is external to the BDU, follow the manufacturers instructions for details on any set up required. A 0V to +10V dc signal will be required. If the internal receiver is to be utilised, the user may choose from either the integral wideband or narrowband. Generally, the wideband detector is used for heavily populated transponders, or when there are no beacon signals available. The narrowband detector is used for either tracking the receive carrier, or a dedicated tracking beacon. Both types require a set up routine.

• Frequency - The frequency of operation of the Narrowband Receiver is set using either the front panel or the M&C console. The frequency used may be that of the received data carrier (usually the same as the modem receive frequency), or a beacon signal. To set the tracking frequency using the M&C console, type kM1111, and enter the desired frequency. The selected frequency band must match the cabled connections at the back of the BDU module.

Attenuation – The following procedure should be followed to set the correct attenuation level.

• With the antenna off satellite, adjust the attenuation until the AGC signal is just above zero.

• With the system in Manual Mode, point the antenna at the satellite, using the cursor keys wyxz. View the received signal strength in the real-time display, Keystroke sequence kM71.

• If the signal rises above 80%, adjust the attenuation so the maximum signal strength is around 80%. The attenuation may be adjusted with the following Keystroke sequence, narrowband detector, kM1112, or wideband detector, kM1122.The system will not track if the signal strength is at full scale (100%). By biasing, the maximum signal strength at no more than 80%, allows some leeway for an increase in signal strength.

• The attenuation may require adjusting once the system is in Track Mode, as the system will often find the satellite boresight more accurately.

3.3.9 Setting the Signal Threshold

The Threshold value is used by the control system to determine which AGC values indicates a satellite signal, and which indicates background noise. If, for example, the threshold is set to 20%, then the system will go into LOCK Mode as soon as the AGC value becomes greater than 20%. This would be a problem if the radio equipment outputs an AGC Value of 50% when the antenna is pointed away from the satellite, therefore it is important to use the correct threshold value.



In normal operation, the threshold remains fixed, while the user adjusts the input attenuation to provide the correct receive level. The following procedure should only be followed if the system is set to track from the external interface or if the user wishes to set the threshold manually. Note that setting a incorrect threshold value may cause the system automatic acquire feature to function incorrectly.

• Before setting the Threshold, test the system as follows:

• With the system in Manual Mode, point the antenna at the satellite, and watch the AGC value in the real-time display. Record the AGC value that is indicated when the antenna is pointing at the satellite.

• Move the antenna off satellite, and record the AGC value when the signal is completely lost.

• When you have recorded both these values, set the threshold as follows:

1. Select a point higher than the "lost" value but well below the "found" value. If, for example, the "lost" value is 5% and the "found" value is 20%, then a Threshold of 10% would be a good setting. This value may need adjusting once the system is in track mode, as the system will often find the peak satellite signal more accurately.

2. Alter the attenuation setting by typing, kM33. Enter the desired threshold and press f.

Be aware that additional equipment loading the IF signal will affect the signal level

3.3.10 Lock-On Test

The best way to confirm that all the stored initialisation values are correct, is to reboot the control module, Key stroke sequence kM67Y, and confirm that the system automatically re-acquires the signal.

Monitor the system, for a period of time, as it tracks the satellite. The AGC signal reading should remain reasonably constant.

3.3.11 Initialisation Checklist

When the system initialisation is complete, photocopy the Initialisation Checklist in Appendix B, complete it, and include it in the unit documentation package.

3.4 TROUBLESHOOTING

Should a fault occur in the system, this Section may be used as a guide to locating the likely cause of the fault, and provide guidance on how to rectify the problem.

If the system is not operating correctly, first check for any error messages that may be displayed by the control program. Section 3.4.1 lists the most common error messages that may occur, along with a brief explanation of what the error means. Some plausible explanations are also offered. A full listing of all log messages is listed in Appendix F. Section 3.4.2 gives some suggestions for



locating a fault, should no error messages be displayed. Finally, Section 3.4.3 describes how to check individual system components, if any part of the system is suspected faulty.

The system will aid the fault detection process by continuously monitoring all operating conditions and sensors. Any unusual events, which may indicate an error or a faulty sensor, are logged in the system log. In this manner prior warning may be obtained if a sensor is developing a fault. The full list of monitor messages is contained in Appendix F.

3.4.1 Error Messages

The system displays active errors on a special display screen on both the M&C console, and on the BDU module LCD display. The system log, stores any previous errors that may have occurred, along with a time stamp indicating when the error occurred. The log may be accessed from either the module front panel or from the console interface.

The console error display may be accessed with the following key sequence kM72.

The BDU module error display may be accessed with the following key sequence Main 5 . If there are no active errors, the error display option will not be available.

The following is a list of the most common error messages that may appear. The message that appears for each display type is shown next to the symbol for the display method.

Spacetrack Antenna Controller

0 1 2 3

654

7 8 9

+ -/

M a i nNoPrev

YesEnter

Aux

Track

Manual Indicates errors shown on the BDU module.

Indicates errors shown on the M&C console.

• BDU to ADU Link Error Spacetrack Antenna Controller

0 1 2 3

6547 8 9

+ -/

M a i nNoPrev

YesEnter

Aux

Track

Manual ADU

ADU module data not present.

This message appears when the BDU is no longer receiving messages from the ADU. This may be caused by a faulty link (see Section 3.4.3.1) or no power to the ADU module (see Section 3.4.3.8).

• Azimuth Motor Error Spacetrack Antenna Controller

0 1 2 3

654

7 8 9

+ -/

M a i nNoPrev

YesEnter

Aux

Track

Manual MTR A

Azimuth Motor error.

Indicates that the fine azimuth gimbal motor is not in its expected position. This may be due to the motor not moving (short circuit, open circuit or faulty motor - see Section 3.4.3.2), the motor may not have the torque required to



keep up with the movement required (see Section 3.4.3.2), or a faulty potentiometer (see Section 3.4.3.4). This message may also be cause by a poor balance.

• Elevation Motor Error Spacetrack Antenna Controller

0 1 2 3

6547 8 9

+ -/

M a i nNoPrev

YesEnter

Aux

Track

Manual MTR E

Elevation Motor error.

Indicates that the elevation gimbal motor is not in its expected position. This may be due to the motor not moving (short circuit, open circuit or faulty motor - see Section 3.4.3.2), the motor may not have the torque required to keep up with the movement required (see Section 3.4.3.2), or a faulty potentiometer (see Section 3.4.3.4). This message may also be cause by a poor balance.

• Polarisation Motor Error Spacetrack Antenna Controller

0 1 2 3

6547 8 9

+ -/

M a i nNoPrev

YesEnter

Aux

Track

Manual MTR P

Polarisation Motor error.

Indicates that the polarisation gimbal motor is not in its expected position. This may be due to the motor not moving (short circuit, open circuit or faulty motor - see Section 3.4.3.2), the motor may not have the torque required to keep up with the movement required (see Section 3.4.3.2), or a faulty potentiometer (see Section 3.4.3.4). This message may also be cause by a poor balance.

• Coarse Azimuth Motor Error Spacetrack Antenna Controller

0 1 2 3

654

7 8 9

+ -/

M a i nNoPrev

YesEnter

Aux

Track

Manual MTR C

Coarse Azimuth Motor error.

Indicates that the coarse azimuth motor is not in its expected position. This may be due to the motor not moving (short circuit, open circuit or faulty motor - see Section 3.4.3.3), or a faulty ADT(see Section 3.4.3.5).

• Step by Step Heading Information not present. Spacetrack Antenna Controller

0 1 2 3

654

7 8 9

+ -/

M a i nNoPrev

YesEnter

Aux

Track

Manual CMPS

Compass heading information not present.

Indicates an invalid code has been received from the step by step interface. This may be due to a faulty link, a faulty gyro, or the gyro may not be switched on. See Figure 9 for details on the step by step compass connection to the BDU Interface Panel.

• NMEA Heading Information not present. Spacetrack Antenna Controller

0 1 2 3

654

7 8 9

+ -/

M a i nNoPrev

YesEnter

Aux

Track

Manual CMPS

NMEA heading information not present.



Indicates that the system has not received a heading update in the required time period. This may be due to a faulty compass, or a faulty connection to the BDU Interface Panel. An enabled NMEA source, which does not output any excepted messages, may also cause this error, (non supported NMEA messages are ignored). See Appendix D for supported messages, and Figure 9 for wiring details.

• GPS Position Information not present. Spacetrack Antenna Controller

0 1 2 3

6547 8 9

+ -/

M a i nNoPrev

YesEnter

Aux

Track

Manual GPS

GPS location information not present.

No valid data has been received from the GPS in the required time. This may be due to a faulty connection between the GPS receiver and the BDU interface panel, or a faulty GPS. The message may also be caused by a GPS receiver, which does not have a current position fix, in which case most GPS receivers null the output data string. See Figure 23 for details on the GPS connection to the BDU Interface. Appendix D lists the accepted NMEA data formats.

• The Satellite is not visible. Spacetrack Antenna Controller

0 1 2 3

654

7 8 9

+ -/

M a i nNoPrev

YesEnter

Aux

Track

Manual HDN

Satellite is not visible.

The calculated satellite position is below the horizon. Recheck the parameters for vessel position and the satellite longitude are correct. See Section 4.1.2.6 for details on changing parameters. A non obtainable polarisation angle may also cause a hidden alarm, if the system is configured for linear polarisation.

• The System is unwrapping. Spacetrack Antenna Controller

0 1 2 3

654

7 8 9

+ -/

M a i nNoPrev

YesEnter

Aux

Track

Manual UNWP

Unwrap warning angle reached.

This message applies to unwrap system only and indicates that an unwrap is in progress or is imminent.

The system log may also contain error messages, which are not listed above, these messages are listed and explained in detail in Appendix F.

3.4.2 Fault Finding

If no errors are reported, the faults that may occur will generally fall into one of three areas, as shown below. Should any component in the system appear faulty, use Section 3.4.3 to help pinpoint the exact cause.

The system does not change into TRACK mode after the mode is changed to FIND.



• Try to find the satellite in MANUAL mode. This should help narrow down the exact cause of the problem.

• Check that the antenna is moving as expected. If not, read the Check Parameters and Check Sensors Sections below.

• Does the AGC value varying as expected ?. If not, read the Check AGC Section below

• If the satellite can be found in MANUAL Mode, was the system searching in the correct area of the sky in SEARCH Mode? If not, read the Check Parameters and the Check Sensors Sections below.

• Does the system stay pointed at the satellite when left for an extended period of time, (approximately five minutes), ?. The system is capable of maintaining, in manual mode, a communications link for long periods of time, if the vessel motion is not excessive. This usually indicates that the stabilisation is functioning correctly and the fault does not lie with the above deck platform sensors or module.

• Check AGC.

• If the AGC does not rise significantly above zero, check the following

⇒ Check the RF unit is powered up. The RF unit power lead should connect to the Mains Out Connector on the ADU Module. See Figure 6.

⇒ Check the receive IF signal is connected to the tracking receiver.

⇒ Check the receiver is set up correctly. See Section 3.3.8 for details on setting up an internal or external receiver.

⇒ Check the wiring to the RF unit. Refer to the manufacturers manual for details.

⇒ Check the RF unit is set up correctly. Refer to the manufacturers manual for details.

• Check that the antenna is not obstructed. Check that nothing is permanently or temporarily blocking the signal.

• If the internal narrowband tracking receiver is selected, double check that the tracking frequency is correct. See Section 3.3.8 for details.

• Double check the allocated receive frequency with the aid of a spectrum analyser if possible.

• Check the RF unit is correctly configured. Refer to the manufacturers manual for details.

• Check with the service provider that the Earth station outbound carrier is present.



• Check Parameters. See Section 4.1 for details on changing parameters.

• Check the THRESHOLD parameter is set correctly. See Section 3.3.9

• Check the SEARCH SIZE and SEARCH SPEED parameters are set correctly. See Section 3.1.7.3.2.1 for details.

• Check the LOCK SIZE and LOCK SPEED parameters are set correctly. See Section 3.1.7.3.2.2 for details.

• Check the vessel's latitude, longitude and heading are correct. See Section 4.1.2.8.2 for details. If the vessel does not have a NMEA source of latitude and longitude, these parameters must be entered every time the vessel moves location. See Section 4.1.2.6 for details.

• Check the satellite longitude is correctly set.

• Check that the vessel has not sailed out of the satellite footprint and also that there is sufficient coverage available.

• Check that the vessel has not sailed into an area where the antenna polarisation is incorrect.

• Check Sensors

• Check the gimbal motor potentiometers. See Section 3.4.3.4

• Check the coarse azimuth ADT. See Section 3.4.3.5.

• Check, the three velocity sensors. See Section 3.4.3.6

• Check the inclinometers. See Section 3.4.3.7

The system changes to TRACK mode after FIND, but tracks badly (modem drops in and out, AGC signal varies by a large amount, or the EbNo fluctuates) or drops out of TRACK mode.

• Check AGC

• Check that the THRESHOLD value is not set too high. See Section 3.3.9 for details on setting the THRESHOLD value.

• Check that the tracking receiver has been set up correctly. See Section 3.3.8 for details of internal receivers. Refer to manufacturers manual for any external receivers.

• Check Balance

• Check that the system is balanced correctly. See Section 3.3.5 and Appendix G for details. Incorrectly balanced systems account for the majority of tracking problems.

• Check Parameters

• Check the Inertia values. Check the antenna is tracing a clean edged square box during its scan. See Section 3.3.6 for details.



• Check that the TRACK SPEED and TRACK SIZE parameters are set correctly. See Section 3.1.7.3.2.3 for details.

• If the vessel is moving, check that its location and heading are correctly displayed. If a compass or GPS is connected to the system, check the correct interface has been selected. See Section 4.1.2.2.4 for details on setting these parameters.

• Check Sensors.

• Check the gimbal motor potentiometers. See Section 3.4.3.4.

• Check the coarse azimuth ADT. See Section 3.4.3.5.

• Check the three velocity sensors. See Section 3.4.3.6.

• Check the inclinometer readings. See Section 3.4.3.7

• Check the gimbal motors temperature. See Section 3.4.3.2

• Check the antenna has a clear view of the satellite (i.e. nothing is temporarily blocking the antenna).

The system changes to TRACK mode and tracks, but the modem does not indicate lock.

• Check that the modem is wired correctly. See Figure 11 for details of the transmit and receive IF signal wiring for the modem.

• Check the modem is configured correctly. Refer to manufacturers manual and the satellite operator for details.

• Check the AGC level

• If the AGC value on the BDU display is 100%, check the following

⇒ Check the attenuation setting of the receiver. See Section 3.1.7.2.2.

• Does the AGC level fall when off satellite? If not, check the following

⇒ Is the receiver set up correctly. see Section 3.1.7.2.1.

• Check the AGC threshold. Has the threshold been set too low ? See Section 3.3.9 for details.

• Check the system has acquired the correct satellite, or is the system tracking something other than a satellite ?, (the sun, during sun spot season !) Confirm this by trying to acquire the satellite in Manual Mode.

The displayed heading does not follow the vessel heading correctly.

• Step by Step Output Compass.

1. Ensure the heading source is configured for a step by step compass. See Section 4.1.2.2.4.1.2.



2. The system heading does not match the vessel heading. The step by step heading source is not absolute, it only indicates a change in heading from the previous heading. Reset the system heading to the same reading as the vessel heading, and observe the heading for a period of time to ensure the headings do not diverge.

3. The system does not display gyro errors but the heading diverges from the correct heading. This is usually solved by swapping step A and step B, at the BDU interface panel.

4. The system displays gyro errors and the heading tracks the vessel heading but with a varying offset. The step by step compass outputs a gray code sequence, this means that only certain code sequences are valid. The invalid codes are all outputs high or all outputs low. Check the interface does not output this sequence.

5. Heading does not change. Some repeater outputs do not step all the way down to zero volts, for example the output levels may be +12V low and +70V high. To overcome this problem insert a zener diode, equal to the offset (i.e. 12V in the example), in series with the common connection. The diode should drop the zener breakdown voltage across itself, if the zener only drops 0.7V, reverse the diode. The power rating of the diode should be sufficient to ensure the body of the diode does not get too hot.

6. Measure the voltage at the step by step terminal connector CN4. If all the steps measure 0V with respect to the common connection, check the repeater fuses and the cable between the repeater and the interface panel.

• NMEA Output Compass.

1. Ensure the heading source is configured for a NMEA output compass. See Section 4.1.2.2.4.1.5 and 4.1.2.2.4.1.6.

2. The system heading does not change. This indicates that the system is not receiving any messages that contain heading information. Check the output NMEA message formats with those accepted, which are listed in Appendix D.

3. The system heading does not change. Check the cabling between the repeater and the BDU interface panel.

4. The system heading does not change. Check the output data rate, stop, parity bits and physical interface format, (RS232 or RS422), matches the configuration in the BDU module, see Section 4.1.2.2.4.1.7.

5. The system heading does not change. Verify the compass data stream output using a console configured to the correct communication format, paralleled with the CN5 connections.

6. Check that the compass is not sending magnetic and true heading messages simultaneously. Since the magnetic heading rarely



matches the true heading this can cause the heading to vary between two different angles.

The displayed location does not follow the vessel location correctly.

• NMEA Output GPS.

1. Ensure the position source is configured for a NMEA GPS. See Section 4.1.2.2.4.2.1 and 4.1.2.2.4.2.2.

2. The system position does not change. This indicates that the system is not receiving any messages that contain position information. Check the output NMEA message formats with those accepted, which are listed in Appendix D.

3. The system position does not change. Check the cabling between the repeater and the BDU interface panel.

4. The system position does not change. Check the output data rate, stop, parity bits and physical interface format, (RS232 or RS422), match the configuration in the BDU module, see Section 4.1.2.2.4.2.3.

5. The system position does not change. Verify the GPS data stream output using a console, configured to the correct communication format, paralleled with the CN5 connections.

6. The system position does not change. Verify the GPS receiver has a valid fix. Some receivers invalidate the message content if they loose contact with the required number of satellites.

3.4.3 Checking Individual System Components

3.4.3.1 ADU/BDU Comms Link

The link from the BDU Interface panel connector CN2 to the ADU interface panel connector CN2 consists of two, optically isolated, twisted pairs, as described below.

ADU A and ADU B lines transmit information from the BDU to the ADU at 38400 baud using the RS422 physical protocol. Approximately 50 packets of information are sent per second. Each packet is checked for errors using a Cyclic Redundancy Check (CRC). If these connections are faulty, the ADU module will not receive any information, or discard any information that fails the CRC. If no error free information is received, the ADU will shut down the power to all the motors. The sensor information will continue to be sent by the ADU module to the BDU module. If the ADU to BDU link is intact the BDU module will flag this error as an ADU low receive rate or an ADU link fault.

ADU Y and ADU Z lines transmit information from the ADU to the BDU at 38400 baud using the RS422 physical protocol. Approximately 100 packets of information are sent per second. Each packet is checked for errors using a Cyclic Redundancy Check (CRC). If these connections are faulty, the BDU module will not receive any information, or discard any information that fails the



CRC. If no error free information is received, the control system will display an ADU error, usually accompanied by motor errors.

The link is optically isolated, no ground is required.

Check the following to confirm the communications link is at fault.

• Check the BDU module is powered up.

• Check the ADU Module power is on, see Section 3.4.3.8 for checking the ADU Module power.

• Select diagnostics mode via the M&C console, keystroke sequence kM64, see Section 4.1.2.7.5 for a detailed description of diagnostic mode. Briefly, Diagnostic mode shows information on the data being sent between the above and below deck modules. This information is especially useful if the problem is not affecting all of the received packets.

• Check the data link from the BDU module to the ADU module is correct. The packets count displayed should be larger then 45.

• Check the data link from the ADU module to the BDU module is correct. The packets count displayed should be larger then 90.

• Check the voltage levels at the BDU interface panel and also at the ADU interface panel. See Appendix E for a list of connector pin outs and their expected voltage levels. Recheck these voltages with the ADU attached to the BDU and also with the BDU disconnected from the ADU.

See Section 3.5 for replacing any components that may appear faulty

3.4.3.2 Gimbal Motor

Before assuming a gimbal motor is faulty, a number of checks should be carried out to ensure that the motor is receiving the correct power.

It is unlikely that a motor would fail and very unlikely that more than one motor would fail at the same time. If there appears to be problems with more than one motor, suspect the pedestal wiring, the ADU module or an ADU / BDU communications link problem.

• Check the motor is connected correctly. See Figure 6 for details of how the motors are wired.

• Check there is a voltage present at the connector to the motor. The signal present, is a PWM signal at 20kHz, and will only be a constant dc signal at +100% or -100% demand. If the motor wiring has been checked, remove the appropriate motor connector. Measure the motor supply voltage at the connector with the negative meter probe to the negative output and the positive meter probe to the positive output, (see Appendix E for pinout details). Change the motor demand via the diagnostics software (see Section 4.1.2.7.5.3.3). Although the signal is pulse width modulated, a dc voltage meter will average this signal and indicate the voltage changing from +VBUS at +100% demand, to 0V at



zero demand, and to the negative of +VBUS at -100% demand. Incorrect voltages indicate a problem with the motor amplifier in the ADU module. Replace the ADU module as detailed in Section 3.5.7. Sophisticated meters may also be able to measure frequency, in which case the meter should indicate a frequency greater than 20KHz. Please note that this usually represents the upper limit of most meters, therefore the reading may not be totally accurate.

• Check the operation of the motor using the diagnostics program. If the motor appears to function using the diagnostics program, but not in the control program, check the motor pot calibration. See Section 3.4.3.4.

• Check the temperature of the motor. If it is too hot to touch for any length of time, check the system balance (see Section 3.3.5). Check that the gimbal moves freely, over the entire axis range of motion. Pay special attention for changes in friction, or mechanical kicks, as the axis is rotated.

• Check the wiring from P2 on the ADU module to the appropriate motor, for evidence of damage. See Figure 6 for wiring details.

• If after all the above checks, the motor appears faulty, follow the instructions in Section 3.5.6 for replacing the motor.

3.4.3.3 Coarse Azimuth Motor

Check the gimbal motors are functioning. If they are not, read Section 3.4.3.2.

• Check the coarse azimuth is enabled in software. See Section 4.1.2.2.9.

• Check the motor is connected correctly. See Figure 6 for details of how the coarse azimuth motor is connected.

• Unwrap systems - check if the electrical limit switch has tripped or the system is against its mechanical stop. See Figure 14 for a layout of the coarse azimuth set-up.

• Check the brakes located on the terminal body; to ensure the brake body has clearance from the slide way, and is not jamming the terminal movement.

• Check there is a voltage present at the motor. If the motor wiring has been checked, on the inclinometer termination plate, connect a multimeter positive probe to the positive output wire, and the negative probe to the negative output wire (see Appendix E for pin outs). Select diagnostic mode via the M&C console. Switch the motor on in a clockwise direction (see Section 4.1.2.7.5.3.4), the voltage reading should be +VBUS. Switch the motor on in a counter clockwise direction, the voltage should be the negative of +VBUS. Switch the motor off, the voltage should be zero. If the test fails, retry the procedure with the red motor wire disconnected. Failure again, would



indicate a problem with the motor amplifier in the ADU module; replace the ADU module as detailed in Section 3.5.7.

• Check the coarse azimuth drive is free to turn by switching off the coarse azimuth motor and turning the gimbal support tower by hand. It will be stiff, but possible to rotate.

• Check the coarse azimuth drive chain is connected.

• Check the wiring from P2 on the ADU module to the inclinometer module, for evidence of damage. See Figure 6 for wiring details.

• Check the operation of the motor using the diagnostics program. If the motor appears to function using the diagnostics program, but not in the control program, check the coarse azimuth ADT calibration. See Section 3.4.3.5.

• If after all the above checks, the motor appears faulty, follow the instructions in Section 3.5.4 for replacing the motor.

3.4.3.4 Motor Pots

If the motor potentiometers appear faulty, check the following

• Check the potentiometer calibration. See Section 3.3.4.

• Move the antenna around in all directions for a period of time and recheck the potentiometer calibration. If the ADT is not calibrated check that the fixing screws are tight, otherwise replace the potentiometer. See Section 3.5.2 for details.

• Check the wiring from P1 on the ADU module to the appropriate potentiometer, for evidence of damage. See Figure 6 for wiring details.

• Check the voltages at the potentiometer connector. See Appendix E for pin outs and voltages expected. If the voltage reference is not +10V, disconnect all connectors which output this reference until the voltage reference returns to +10V. This should isolate the sensor, which is causing the fault. If the voltage reference is still not +10V, replace the ADU module as detailed in Section 3.5.7.

• Select diagnostic mode on the BDU module (see Section 4.1.2.7.5). Check the potentiometer is giving correct readings at all angles.

• Check the potentiometer reading increases in the correct direction (see Section 3.4.4). If the readings increase in wrong direction, the potentiometer is faulty.

• Check the noise reading for the potentiometer in the diagnostics program. While the antenna is stationary, it should be no more than 1 count. The vessel must obviously be stationary to perform this test, even slight vessel motion will produce noise counts.



3.4.3.5 Coarse Azimuth ADT

If the coarse azimuth ADT appears faulty, check the following

• Check the ADT calibration. See Section 3.3.2.2.

• Move the gimbal support tower around in both directions, and recheck the potentiometer calibration. If the calibration is not correct, check the lock screws are tight, and that the coarse azimuth drive mechanics are making contact at all points, otherwise replace the ADT. See Section 3.5.3 for details.

• Check the wiring from P1 on the ADU module to the coarse azimuth ADT, for evidence of damage. See Figure 6 for wiring details.

• Check the voltages at the coarse azimuth ADT connector. See Appendix E for pin outs and the voltages expected. If any output voltage appears incorrect, remove all connectors, which use that voltage until the voltage returns to its correct value. This will isolate the sensor causing the problem. If the voltage does not return to its correct value, replace the ADU module as detailed in Section 3.5.7.

• Select diagnostics mode on the BDU module (see Section 4.1.2.7.5). Check that the ADT is giving correct readings at all angles.

• Check that the ADT reading increases in the correct direction (see Section 3.4.4).

• Check the noise reading for the ADT in the diagnostics program. The noise should not be no more than 1 count.

3.4.3.6 Velocity Sensors

If the velocity sensors are possibly causing a problem, check the following

• Ensure the ADU module is correctly oriented and securely attached.

• Select the diagnostics mode on the BDU module (see Section 4.1.2.7.5). Check the velocity sensor is returning a sensible value, and that the value deflects positive in the correct direction (see Section 3.4.4). Also check the sensor readings deflect both positive and negative for similar physical movements.

• With the gimbal stationary, check that the noise reading is less than 1 count. As the velocity sensors measure rotation relative to the local horizon, this check is obviously not possible if the vessel is moving, but the noise count may still be indicative of a problem.

• See Section 3.5.7 for details on replacing the ADU Module.

3.4.3.7 Inclinometers

If the inclinometers are suspected of causing a problem, check the following



• Check that the inclinometers are installed in the correct orientation. The writing on its face should be the correct way up for reading.

• Check that the wiring is correct. See Figure 6 for wiring details.

• Check that the voltages present at the connector. See Appendix E for pinouts, and details of what the voltages should be present.

• Select diagnostics mode on the BDU module (see Section 4.1.2.7.5) and check that the readings are correct. Check that the readings also display a noise reading of less than 1 counts when there is no motion in the system, or on the host vessel. This check is obviously not possible if the vessel is moving, but the noise count may still be helpful.

• Loosen the inclinometer fixing screws and check that physical rotation of the sensor matches the desired reading deflection as listed in Section 3.4.4.

3.4.3.8 ADU Module Power

• Check that the mains is correctly connected to the system and is switched on. Check that the mains wiring to the junction box, (see Figure 7B), and that the mains lead is connected to the ADU module, (see Figure 4).

• Check all the wiring to the ADU Module. There may be a short circuit caused by a wiring / component failure.

• ADU / BDU communications link. If the ADU is not receiving error free information from the BDU, the ADU will switch off the motor power. See Section 3.4.3.1

• If all the above checks prove acceptable, see Section 3.5.7 for details on replacing the ADU module.

3.4.3.9 BDU Module Power

• The LCD display indicates when power is applied to the module. If the display is blank, then the BDU module is faulty, or the BIOS is active. See Section 3.5.8 for details on replacing the BDU module, see Section 4.1.3 for details on the BIOS.

3.4.3.10 Internal Tracking Receiver

If the internal tracking receiver is suspected of causing a problem, check the following

• Check the receiver is set up correctly. See Section 3.3.8

• Apply an input level using a signal generator or modem, using a CW carrier, to the appropriate input. Check the AGC reading responds in sympathy to the transfer specification in Appendix E. Care should be



observed when applying the input signal, so that the applied level never exceeds, a composite or carrier level, of minus 10dBm. Exceeding this level will cause the detectors to fail and invalidate any DMS warranty. Modem outputs are usually at a relatively high level, therefore attenuation pads will normally be required.

• See Section 3.5.8 for details on replacing the BDU module.

3.4.4 Checking Sensor and Motor Polarity

In order for the system to function correctly, the sensors must return the correct polarity of voltage for the direction that the platform rotates and the motors must drive in the correct direction. This Section lists the checks required to ensure the sensor and motor polarities are correct.

Note: The directions CW (clockwise) and CCW (counter clockwise) refer to the rotation of the platform as viewed from the rear of the motor or sensor for the axis in question.

Select diagnostics mode on the BDU module and check the following. See Section 4.1.2.7.5 for details on diagnostics mode and the meaning of the abbreviated sensor names.

• Az Pot Turn platform CCW to increase displayed count

• El Pot Turn platform CCW to increase displayed count

• Pz Pot Turn platform CW to increase displayed count

• Az RS Turn platform CW to increase displayed count

• El RS Turn platform CW to increase displayed count

• Pz RS Turn platform CCW to increase displayed count

• Coarse Az Turn platform CW to increase displayed count

• Feed Turn CW to increase displayed count

• Az Motor >127 demand will turn motor CCW

• EL Motor >127 demand will turn motor CCW

• Pz Motor >127 demand will turn motor CCW

• CA Motor Positive direction will turn gimbal tower CCW

• Feed Motor Positive direction will turn motor CW



3.5 COMPONENT REPLACEMENT

This Section details how to replace various components of the Spacetrack Stabilised Antenna Platform. Ensure the component has been inspected using the checks in Section 3.4.3, before replacing any suspected faulty components.

Any faulty components should be returned to Data Marine Systems Ltd for failure analysis and logging.

3.5.1 Replacing an Inclinometer Block

To replace a faulty inclinometer block (see Figures 17 and 18), remove the mains power to the ADU.

1. Remove connector CN4 from the inclinometer block.

2. Unscrew the three terminals connecting the coarse azimuth motor.

3. Remove the four screws holding the block to the gimbal support tower.

4. Screw the replacement inclinometer block into position.

5. Reconnect the coarse azimuth motor wires, using Figure 18 as a reference.

6. Reconnect CN4, ensuring that the connector is fully screwed in.

3.5.2 Replacing a Gimbal Motor Potentiometer

1. Turn the ADU power off.

2. Unscrew the connector from the potentiometer.

3. Unscrew the three cleats that hold the pot in position and remove the pot, taking care not to lose the nylon coupling between the potentiometer and motor shaft.

4. Fit the brass coupling to the end of the replacement pot.

5. Test the pot and for fit, by holding in place, inserting the nylon coupling and screwing the pot in place using the three cleats. The nylon coupling should have a very small amount of play. No play, will cause mechanical stress, but too much play will allow the coupling to slip. On the azimuth and elevation axis, this amount of play can be altered by adjusting the pot coupling shaft. Tighten the lock nut when finished adjusting the potentiometer shaft.

6. Check the pot shaft is in line with the shaft. Any skew may cause mechanical stress.

7. Once all the components are fitted correctly, remove the pot and apply Loctite to the pot brass coupling grub screw.

8. Screw the replacement pot in place.

9. Check that the pot turns freely with the motor.

10.Screw the connector onto the potentiometer.

11.Set up the pot as described in Section 3.3.4.



12.Check the balance is still correct. See Section 3.3.5.

3.5.3 Replacing the Coarse Azimuth ADT

1. Turn the ADU power off and remove the connector on the Coarse Azimuth ADT, and remove the transducer itself, by unscrewing the three cleats that hold the ADT in place.

2. Remove the cog, or coupling, from the shaft of the faulty ADT and fit the cog, or coupling, to the replacement ADT.

3. Replace the Coarse Azimuth ADT, and tighten the cleats.

4. Replace the connector.

5. Set up the ADT as described in Section 3.3.2.2.

3.5.4 Replacing the Coarse Azimuth Motor

1. Turn off the power to the ADU module

2. Unscrew the coarse azimuth motor wires from the inclinometer block terminals (see Figure 18).

3. The motor is fixed to the system with four bolts. Loosen these bolts and remove the motor.

4. Remove the belt / chain coupling from the faulty motor and attach to the new motor.

5. Screw the new motor to the fixing point, but allow the motor to slide in the slot.

6. Replace the belt / chain over the pulley, ensuring the belt is seated in the teeth or groove of the cog correctly.

7. Tighten the coarse azimuth motor bolts.

8. Rewire the motor to the inclinometer block. See Figure 18 for wiring details

3.5.5 Replacing the Coarse Azimuth Limit Switch

Only applicable for systems with an unwrap feature

1. Before replacing the switch, turn off the power to the ADU module.

2. Remove the coarse azimuth mounting plate from the centre of the gimbal support tower.

3. Disconnect the cable from the limit switch.

4. Remove the limit switch from the mounting bracket.

5. Install the replacement limit switch.

6. Reconnect the cable to the limit switch.



7. Set up the coarse azimuth as detailed in Section 3.3.2

3.5.6 Replacing A Gimbal Motor

1. Turn off all power and secure the antenna, in a position that the motor can be worked on.

2. Remove the connector to the motor (and to the pot, if the polar motor is being removed).

3. Polar motor only: Loosen the grub screw, which clamps the motor drive shaft.

4. Unbolt the motor. The new motor may require the coupling and flange plate from the faulty motor.

5. Fit the replacement motor.

6. Replace the connector to the new motor.

7. If a polar motor is to be replaced, ensure the new motor has an ADT fitted to the rear shaft. Calibrate the new polar motor potentiometer as detailed in Section 3.3.4.

8. Check that the balance is still correct. See Section 3.3.5.

3.5.7 Replacing the ADU Module

Caution: The ADU module is heavy. Removing the ADU module will cause the system to become unbalanced. Ensure the antenna is fully secured before starting work and seek assistance, so that the module may be held in place while removing and tightening the bolts.

1. Turn off all power and secure the antenna in a position that, the module can be worked on.

2. Remove the three connectors from the module.

3. While supporting the module in place, remove the mounting bolts.

4. Inspect the replacement module before fitting. Check the module shock indicator, reject the module if the maximum shock has been exceeded. See Figure 4.

5. Check the system balance is still correct. See Section 3.3.5.

3.5.8 Replacing The BDU Module

1. Switch off the power to the BDU Module.

2. Remove the BDU module from the rack.

3. Remove all connectors and the Earth bond strap, from the rear of the BDU module.



4. Replace the faulty module with the new module.

5. Replace all connectors, taking care to screw the D type pillar bolts in firmly. Securely attach the Earth bond strap.

6. Replace the unit in the rack, and apply power.

3.5.9 Replacing the RF equipment

The RF equipment may come in a variety of different configurations. Please see the relevant RF equipment manuals for replacement procedures.

The following general points should be noted though.

• The RF equipment transmits microwave radiation. Do not work in the radome while the system is transmitting.

• Switch off the power to the ADU and to the RF transceiver, and ensure that the antenna is fully secured before starting work. Removing any equipment will cause the system to become dangerously unbalanced. Seek assistance when removing or installing a RF transceiver.

• Always rebalance the system after moving or replacing any RF equipment, mounted on the stabilised platform.

• Ensure the transmit RF co-ax or waveguide is securely connected, from the RF transceiver to the feed before powering up the new RF equipment.

• The RF equipment must be programmed with the correct receive parameters, before the system will track.

3.6 MAINTENANCE

The maintenance requirements of the Stabilised Platform are minimal, the most important items are inspection for loose bolts, and corrosion prevention. A thorough maintenance inspection should be performed yearly at a minimum.

Before performing any maintenance procedures, obtain a photocopy of the Maintenance Checklist in Appendix B, and complete the form as each task is completed. Keep the completed checklist with unit documentation.

3.6.1 Lubrication

There is no lubrication requirement for the Spacetrack system. All bearings are sealed and pre-lubricated.

Do NOT attempt to lubricate the gimbal bearings or any part of the Coarse Azimuth Drive Assembly.



3.6.2 Inspection for Loose Bolts

All bolts should be secured by Loctite or lock washers. Check for loose bolts in the locations listed on the checklist, and if necessary, add lockwashers or Loctite.

3.6.3 Corrosion Prevention

Before the Spacetrack unit leaves the factory, all metal surfaces are protected from marine corrosion, either with a marine paint system, or by the application of an anti-corrosion metal protector.

A visual inspection should be performed, to locate areas of corrosion or exposed metal. Corrosion should be removed, if possible, and exposed metal either painted, with Marine Primer, or coated with an anti-corrosion substance.

If there are indications that the equipment has been mistreated, the specific details should be recorded on the checklist.

3.6.4 ADU Module Care

Inspect the shock indicator on the ADU module. If the module has received an impact exceeding the shock rating, replace the ADU module.

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