jotron RA-2500 User manual

82693_Op&Ins MAN_TR2500_D 1

82694_Op&Ins MAN_RA2500_D 2
EC Declaration of Conformity, available at www.jotron.com
Abbreviations and definitions
AIS -Automatic Identification System.
A shipborne broadcast transponder system in which ships continually transmit their position, course, speed and other
data to other nearby ships and shoreline authorities on a common VHF radio channel.
ALARM
Message by which the navigator signals the occurrence of an event. The alarm is indicated by an audible tone and/or a
message (or icon) on the display.
ALTITUDE
The height of the antenna over mean sea level.
AMBIENT
Surrounding or encompassing environment.
ANTENNA HEIGHT
The height (over the waterline) in which the antenna is installed.
ASM
AIS Service Management – Controlling entity for the whole AIS service
AUX
Auxiliary Port -A communication port on the AIS transponder, which can be used for NMEA or RTCM, input.
BAUD
Transmission rate unit of measurement for binary coded data (bit per second).
BIT
Short form of Binary Digit. The smallest element of data in a binary-coded value.
bps
Bits Per Second.
BSC
Base Station Controller
CHARACTER STRING
Continuous characters (other than spaces) in a message.
CHECKSUM
The value sent with a binary-coded message to be checked at the receiving end to verify the integrity of the message.
CLICK (KEYBOARD)
The audible tone generated when a key is activated
CLOCK
A precisely-spaced, stable train of pulses generated within an electronic system to synchronize the timing of digital
operations within the system.
CLOCK OFFSET
The differences between the times at the CDU/processor tracking a satellite, the satellite itself, and GPS system time.

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COG
See COURSE OVER GROUND
COURSE OVER GROUND
Course made good relative to the sea bed.
CURSOR
A flashing rectangle superimposed on a character position in the display window, indicating that a character may be
entered in that position, or that the existing character may be changed via the keyboard.
DEFAULT
A condition that the navigator assumes automatically if no other condition is initiated by the operator.
DGPS
See DIFFERENTIAL GPS.
DIFFERENTIAL GPS (OOPS)
A method of refining GPS position solution accuracy by modifying
the locally computed position solution with correction signals from an external reference GPS CDU (monitor).
ECDIS
Electronic Chart Display and Information System
EPFS
Electronic Position Fixing System (GPS is mostly used)
ETA
Estimated Time of Arrival. Calculated on basis of the distance to the destination and the current (or estimated) speed.
FATDMA
Fixed Access Time Division Multiple Access -Data link access protocol used by base station transponders to allocate
transmission slots on the data link. These slots are fixed and will thus not change until the base station transponder is re-
configured.
FM
Frequency Modulation -The method by which a signal offsets the frequency in order to modulate it on a data link.
position (latitude, longitude, altitude, and time). See DILUTION OF PRECISION.
GFSK
Gaussian-Filtered-Shift-Keying -A standardised method of modulating digital data prior to transmission on a data link.
GMSK
Gaussian-Minimum-Shift-Keying -GFSK using BT -products and modulation index, which optimises the modulated
signal.
GNSS
Global Navigation Satellite System -A common label for satellite navigation systems (such as GPS and GLONASS).
GLOBAL POSITIONING SYSTEM (GPS)The NAVSTAR Global Positioning System, which consists of or- biting
satellites, a network of ground control stations, and user positioning and navigation equipment. The system has 24
satellites plus 3 active spare satellites in six orbital planes about 20,200 kilometres above the earth.
GLONASS
A satellite navigation system developed and operated by Russia.

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GMT
Greenwich Mean Time. See also UNIVERSAL TIME COORDINATED.
GPS SYSTEM TIME
Time corrected to Universal Time Coordinated (UTC) and used as the time standard by the user segment of the GPS
system.
HEADING
The direction in which the vessel is pointed, expressed as angular distance from north clockwise through 360 degrees.
HEADING should not be confused with COURSE. The HEADING is constantly changing as the vessel yaws back and
forth across the course due to the effects of sea, wind, and steering error.
IALA
International Association of Marine Aids to Navigation ans Lighthouse Authorities
IEC
International Electro-technical Commission.
IEC 61162-1 Maritime navigation and radiocommunication equipment and systems – Digital interfaces Single Talker-
Multiple listeners: Closely related to NMEA0183 version 2.3, communication at 4800 baud. Definition of both
electrical and protocol to be used.
IEC 61162-2 Maritime navigation and radiocommunication equipment and systems – Digital interfaces
Single Talker- Multiple listeners, High speed transmission: Closely related to NMEA0183HS version 2.3,
communication at 34800 baud. Definition of both electrical and protocol to be used.
IEC 61993-2 Maritime navigation and radiocommunication equipment and systems – Automatic Information Systems
(AIS)
Definitions of the sentences used for AIS in addition to those mentioned in IEC 61162-1 and IEC 61162-2.
IMO
International Maritime Organisation
INTERFACE
Electronic circuits that permit the passage of data between different types of devices; For example, the speed and
heading interface circuit permits data from a speed log and compass to pass to the navigator processor.
IP
Internet Protocol (IP) is the central, unifying protocol in the TCP/IP suite. It provides the basic delivery mechanism for
packets of data sent between all systems on an internet, regardless of whether the systems are in the same room or on
opposite sides of the world. All other protocols in the TCP/IP suite depend on IP to carry out the fundamental function
of moving packets across the internet.
ITDMA
Incremental Time Division Multiple Access -Access protocol for pre-announced transmissions of temporary or non-
repeatable character. It is also used during data link network entry.
ITU
International Telecommunication Union.
LED
Light Emitting Diode.
LSS
Logical AIS Shore Station. A LSS is a software process, which transform the AIS data flow associated with one or
more PSS into different AIS-related data flow. The SW process of a logical AIS station can run on any appropriate
computer at any appropriate place.

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MMI
Man Machine Interface
NMEA
National Marine Electronics Association. The NMEA electronics interface specifications have been developed under
the auspices of the Association. The NMEA 0183 is an internationally recognized specification for interfacing marine
electronics. NMEA 0183 version 2.3 is identical to lEC 61162-1.
POLLED MODE
A transponder is in a polled mode during a request-response session only. Distinguish this from a station, which is
polled into certain slots. This station is first polled and then enters assigned mode.
POSITION UPDATE
The redefining of position by analysis of satellite orbital data as referenced to time.
PROCESSOR
The processor circuit card in the console that controls system operations and computes the positioning/navigation
solutions.
PROMPT
A message on the display instructing the operator to make a keyboard entry.
PSS
Physical AIS Shore Station. The PSS is the most basic AIS-related entry, which can exist on its own in a real physical
environment, as opposed to an AIS base station or AIS repeater station.
PULSE SPEED SENSOR
Speed log whose speed output signal is defined by a pulse mte output.
RATDMA
Random Access Time Division Multiple Access -Access protocol for transmissions which have not been pre-
announced. This is used for the first transmission during data link network entry or for messages of non-repeatable
character.
REFERENCE COMPASS
The compass against which the steering compass (see STEERING COMPASS) may be calibrated.
REFERENCE ELLIPSOID
A mathematical description of the Earth's ellipsoidal shape (see ELLIPSOID), which is the reference frame for
positioning computation.
RESET
To return stored values to either the default value or zero in memory.
RMS
See ROOT MEAN SQUARED.
ROOT MEAN SQUARED (RMS)
A statistical measure of probability, stating that an expected event
will happen 68% of the time. In terms of position update accuracy, 68 position updates out of 100 will be accurate to
within specified system accuracy.
SENSOR
A device that detects a change in a physical stimulus and turns it into a signal that can be measured.

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SET AND DRIFT
The direction and the speed of the water over ground (current).
SIGNAL- TO-NOISE RATIO (SIN)
Quantitative relationship between the useful and non-useful part of the received satellite signal. A high SIN indicates a
good receiving condition.
S/N See SIGNAL- TO-NOISE RATIO
SOFTWARE
Values programmed and preloaded into memory. The values represent a permanent set of instructions for running the
automatic functions (computations) of the navigator.
SOG
See SPEED OVER GROUND
SOTMA
Self Organised Time Division Multiple Access -An access protocol, which allows autonomous operation on a data link
while automatically resolving transmission conflicts.
SPEED OVER GROUND
Speed in relation to the seabed.
TCP
Transmission Control Protocol (TCP) provides a reliable byte-stream transfer service between two endpoints on an
internet. TCP depends on IP to move packets around the network on its behalf.
TCP/IP
A name given to the collection (or suite) of networking protocols that have been used to construct the global Internet.
The protocols are also referred to as the DoD (dee-oh-dee) or Arpanet protocol suite because their early development
was funded by the Advanced Research Projects Agency (ARPA) of the US Department of Defense (DoD).
TDMA
Time Division Multiple Access. An access scheme for multiple access to the same data link.
UDP
User Datagram Protocol provides a packetized data transfer service between endpoints on an internet. UDP depends on
IP to move packets around the network on its behalf.
UNIVERSAL TIME COORDINATED (UTC)
Greenwich mean time corrected for polar motion of the Earth and seasonal variation in the Earth's rotation.
UPDATE
See POSITION UPDATE.
UTC
See UNIVERSAL TIME COORDINATED.
VDL
VHF Data Link.
VHF
Very High Frequency -A set of frequencies in the MHz region.
VSWR
Voltage standing wave ratio

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Amendment Record
AMENDMENT
NO. INCORP.
BY DATE PAGE(S) VERSION REASON
FOR CHANGE
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2 ES 08.11.2006 58 B Kontroll med documenter.doc
3 ES 31.03.2007 Total: 59 C New company name
New logo
4 ES 04.01.2008 5-16 D Talker identifier
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The information in this book has been carefully checked and is believed to be accurate. However,
no responsibility is assumed for inaccuracies.
Jotron AS reserves the right to make changes without further notice
to any products or modules described herein to improve reliability, function or design.
Jotron AS does not assume any liability arising
out of the application or use of the described product.
SAFETY INSTRUCTIONS
1. Do not place liquid-filled containers on top of the equipment.
2. Immediately turn off the power if water or other liquid leaks into the equipment.
Continued use of the equipment can cause fire or electrical shock. Contact a Jotron AS
agent for service.
3. Immediately turn off the power if the equipment is emitting smoke or fire.
4. Do not operate the equipment with wet hands.
5. CAUTION!
This equipment contains CMOS integrated circuits. Observe handling precautions
to avoid static discharges which may damage these devices.

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LIST OF CONTENTS
1 GENERAL .............................................................................................................1-1
1.1 Features......................................................................................................................1-1
1.1.1 The main features are:.........................................................................................1-1
1.2 Receiver module description......................................................................................1-2
1.2.1 Front board..........................................................................................................1-2
1.2.2 Digital board........................................................................................................1-2
1.2.3 RF board..............................................................................................................1-2
1.2.4 Power board.........................................................................................................1-2
1.2.5 Connector board..................................................................................................1-2
1.3 System overview........................................................................................................1-3
2 SPECIFICATIONS ...............................................................................................2-1
2.1 RA-2500 environmental specifications and integrated GPS .....................................2-1
3 RA-2500 CONFIGURATION ..............................................................................3-1
3.1 Using serial interface (through “External display” port)..........................................3-1
3.2 Using Ethernet interface ............................................................................................3-2
3.3 Not all ships carry AIS...............................................................................................3-2
3.4 Use of AIS in collision avoidance .............................................................................3-2
3.5 Erroneous information...............................................................................................3-2
3.6 AIS in an Operational Environment ..........................................................................3-3
4 INSTALLATION...................................................................................................4-1
4.1 Antennas ....................................................................................................................4-1
4.1.1 GPS antenna location..........................................................................................4-1
4.1.2 VHF antenna location..........................................................................................4-1
4.1.3 GPS/VHF combined antenna..............................................................................4-2
4.2 Cabling.......................................................................................................................4-3
4.2.1 Cable installation.................................................................................................4-4
4.3 Receiver unit..............................................................................................................4-5
4.3.1 Desktop Mounting...............................................................................................4-5
4.3.2 Roof Mounting....................................................................................................4-6
4.3.3 Bracket mounting hole measurements ................................................................4-7
4.3.4 Flush Mounting ...................................................................................................4-7
4.3.5 19``Rack Tray Mounting.....................................................................................4-8
5 OPERATION .........................................................................................................5-1
5.1 Description of keys ....................................................................................................5-1
5.2 Menus.........................................................................................................................5-2
5.2.1 Menu Flowchart ..................................................................................................5-2
5.3 Connecting power......................................................................................................5-3
5.3.1 LAN configuration..............................................................................................5-3
5.4 Normal use.................................................................................................................5-5
5.4.1 Display received vessels......................................................................................5-5
5.4.2 Current Sensors / Dynamic Data menu...............................................................5-6
5.4.3 Internal GPS Menu..............................................................................................5-7

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5.4.4 Diagnostic Menu .................................................................................................5-7
5.4.5 Config Menu .......................................................................................................5-9
5.5 Description of sentence format................................................................................5-13
5.6 Input.........................................................................................................................5-14
5.6.1 Definitions.........................................................................................................5-14
5.6.2 Receiving actions ..............................................................................................5-14
5.6.3 Format BCF:......................................................................................................5-15
5.7 Output ......................................................................................................................5-16
5.7.1 Definitions.........................................................................................................5-16
5.7.2 VDM VHF Data-link Message ........................................................................5-16
5.7.3 ALR - Set alarm state........................................................................................5-17
5.7.4 TXT Text transmission.....................................................................................5-17
5.7.5 GLL Geographic position latitude/longitude ..................................................5-18
5.7.6 GGA Global positioning system (GPS) fix data..............................................5-19
6 EQUIPMENT LIST ..............................................................................................6-1
6.1 Standard supply 80500...............................................................................................6-1
6.2 Optional supply..........................................................................................................6-1
7 WIRING AND CONNECTIONS.........................................................................7-1
7.1 RA-2500 Rear Connections.......................................................................................7-1
7.2 Description of Junction Box Connector.....................................................................7-2
7.3 Description of 24VDC connection to receiver...........................................................7-3
7.4 Description of LAN connector...................................................................................7-3
8 ALARM MESSAGES ...........................................................................................8-1
8.1 Receiver malfunction.................................................................................................8-1
9 LIST OF VHF CHANNELS.................................................................................9-1
10 OUTLINE DRAWINGS .....................................................................................10-1
10.1TR-2500 AIS Transponder ......................................................................................10-1
10.2Procom CXL 2-1/l....................................................................................................10-2
10.3Procom GPS 4 Antenna...........................................................................................10-3
10.4BNC connector.........................................................................................................10-4
10.5FME Connector Female...........................................................................................10-4
10.6BNC Connector Male ..............................................................................................10-5
10.7TNC Connector Male...............................................................................................10-5
10.8N Connector Male...................................................................................................10-6
10.924VDC Power Connector ........................................................................................10-6
11 REGISTRATION FORM ...................................................................................11-1

82693_Op&Ins MAN_TR2500_D 1-1
1 GENERAL
1.1 Features
The RA-2500 is a ship borne AIS Receiver (Automatic Identification System) capable of receiving
navigation data and ship data from other ships and costal stations.
The RA-2500 system consists of a receiver, a cable and connector to PC (RS-232), a AC adaptor
and a combined VHF/GPS antenna.
1.1.1 The main features are:
Safety of navigation by automatically receiving navigational data from ships and coast stations.
●Static data:
- MMSI ( Maritime Mobile Service Identity).
- IMO number (where available).
- Call sign and name.
- Length and beam.
- Type of ship.
- Location of position-fixing antenna on the ship.
●Dynamic data:
- Ships position with accuracy indication and integrity status.
- UTC.
- Course over ground (COG).
- Speed over ground (SOG).
- Heading.
- Navigation status (manual input).
- Rate of turn (where available).
●Voyage related data
- Ships draught.
- Hazardous cargo (type).
- Destination and ETA (at masters discretion).
●LCD panel.
●GPS and VHF antenna, separate or combined, for easy installation available.
●Built-in GPS receiver for UTC synchronization and backup position fixing.

82694_Op&Ins MAN_RA2500_D 1-2
1.2 Receiver module description
The receiver consist of:
1.2.1 Front board
The Front board consist of keyboard, LCD panel and four status lights for alarm, power and RX.
The Front board communicates directly with the MMI micro controller at the Digital board.
The LCD panel displays all required information about static data, dynamic data, voyage related
data and short safety related messages. The information and messages are automatically updated
according to the necessary international standards.
1.2.2 Digital board
The Digital board consist of Timer/MMI chapter, PC module and DGPS module.
Timer/MMI chapter
The Timer MMI chapter main task is to receive DGPS information.
PC module
The PC module is the communication centre for the RA-2500: analysing data, building and
controlling data base, communication with external units and controlling RX messages into the right
time slots.
DGPS module
The DGPS board receive GPS information from the GPS network. The internal GPS is a 12 channel
all-in-view receiver with a differential capacity, and provides UTC reference for system
synchronization to eliminate synchronisation problems among multiple users. It also gives COG
and SOG when the external GPS fails.
1.2.3 RF board
The RF board consist of two TDMA receivers.
1.2.4 Power board
The Power board consist of a DC/DC converter giving the necessary internal voltages to operate the
RA-2500.
1.2.5 Connector board
The connector board is the interface between the internal modules in RA-2500 and external units.

82694_Op&Ins MAN_RA2500_D 1-3
1.3 System overview
The system is based on the IMO regulation for Universal AIS.
The system is synchronized with GPS time to avoid conflict among multiple users.
The VHF channels 87B and 88B are commonly used in addition to local AIS frequencies.
The AIS receiver receives various data as specified by IMO and ITU on the frequency manually set
up by the user.

82693_Op&Ins MAN_TR2500_D 2-1
2 SPECIFICATIONS
2.1 RA-2500 environmental specifications and integrated GPS
RA-2500 ENVIRONMENTAL SPECIFICATIONS AND INTEGRATED GPS
STANDARDS
IEC 60945 (2002), IEC 61993-2 (2001),
IEC 61162-1 (2000) –2 (1998), IEC 61108-1 (1996)
Temperature range -15°C to +55°C (operating) -40°C to +70°C (storage)
Humidity 90% at +40°C (non condensing)
Seal standard IP64
GENERAL RECEIVER
Size 244 x 108 x 146mm
Weight 2.8kg
Colour Slate Grey (RAL7015) / Black (RAL9004)
Enclosure Polycarbonate / Aluminium
Compass safety distance Standard magnetic: 0.9m Steering magnetic: 0.65m
Frequency range 156 – 162.025MHz
Data ports RS232 and RS422
Supply voltage, DC 21.6 - 31.2VDC negative ground.
Power consumption <20W
DISPLAY / KEYBOARD
Display Monochrome STN-LCD, 24 characters x 4 lines. Adjustable backlight.
Keyboard 19 keys. Adjustable backlight.
LED 4 LED for identification of: Alarm, OK, RX and TX.
INTEGRATED GPS
No. of channels 12 channels parallel
Tracking 12 channels simultaneously
Frequency L1 – 1575.42MHz
RX code C/A code
Velocity >500m/s
Acceleration Up to 5G
Accuracy Horizontal: <3m (CEP), 5m (2dRMS). 3D:<5m (SEP). DGPS:<1m
Timing < 100ns (absolute), < 40ns (1 sigma).
Acquisition/Reacquisition <23s TTFF with time, pos. and ephemeris. <45s with almanac,
time and pos. <120s cold start
DGPS interface RTCM SC-104

82694_Op&Ins MAN_RA2500_D 2-2
TR-2500 RECEIVER UNITS
RECEIVER TDMA
25kHz 12.5kHz
-107dBm (n.c.)
-101dBm (e.c.) -101dBm (n.c.)
Sensitivity -98dBm (e.c.)
20% at
Packet error rate sensitivity 20% at
sensitivity
Receive BT product 0.5.GMSK 0.3/0.5.GMSK
Co-channel rejection > -10dB > -16dB
Adjacent channel
selectivity 70dBm (n.c.) 50dBm (n.c.) 50dBm (e.c.)60dBm (e.c.)
Modulation GMSK , 9600 bits/s ±50ppm.
Frequency range 156 - 162.025MHz
Frequency error ±3ppm.
Spurious response
rejection > 70dB two channels away from frequency
Intermodulation
rejection
Blocking
/desensitisation
>=74dB at PER 20% for 1 tone – 15dBm at
FO ±5.725MHz and 2 tones of -27dBm at
+500kHz and FO +1MHz, when usable signal
has a level of -101dBm.
Large signal PER < 1% between -7dBm and -77dBm
Spurious emission
from RX < -57dBm (150kHz to 1 GHz) < -47dBm (1GHz to 2 GHz)

82693_Op&Ins MAN_TR2500_D 3-1
3 RA-2500 CONFIGURATION
Figure 3.0, Complete Tron RA-2500 system.
(Dotted lines in the figure above, means options)
3.1 Using serial interface (through “External display” port)
When using this port, the RA-2500 needs a PC to connect and control the data flow.
For connection details, see chapter-------
PC with compatible
chartin
g
software
Figure 3.1, Communication between the RA-2500 and the PC is through the RS232 interface
communicating on 38400 bits/second (baud).
RA-2500
VHF & GPS Antenna
Protection
and filters Serial interface cable

82694_Op&Ins MAN_RA2500_D 3-2
3.2 Using Ethernet interface
Using this port, the RA-2500 is connected to the Ethernet port on a PC or a network node.
See chapter 7.3 for description of LAN connector.
3.3 Not all ships carry AIS
It is important to remember that not all ships carry AIS, in particular leisure crafts, fishing boats,
warships and some costal shore stations including Vessel Traffic Service Centers.
3.4 Use of AIS in collision avoidance
As an anti-collision aid the AIS has some advantages over radar:
- Information provided in near real-time.
- Capable of instant presentation of target course alternations.
- Not subject to target swap.
- Not subject to target loss in clutter.
- Not subject to target loss due to fast maneuvers.
- Able to detect ships within VHF/FM coverage.
-
IMPORTANT
When using the AIS for anti-collision purposes it is important to remember that the AIS is an
additional source of navigation information. It does not replace other navigational systems. The AIS
may not separately always give the right picture of the traffic in your area.
3.5 Erroneous information
Erroneous information implies a risk to other ships as well as your own. Poorly configured or
calibrated sensors might lead to transmission of incorrect information. It is the users responsibility
to ensure that all information entered into the system is correct and up to date.

82694_Op&Ins MAN_RA2500_D 3-3
3.6 AIS in an Operational Environment
This illustration shows a typical AIS system where equipped ships, vessels and shore-based
systems are automatically communicating with each other.
Figure 3.6, The total UAIS system.

82693_Op&Ins MAN_TR2500_D 4-1
4 INSTALLATION
Important notice
In a radio environment, depending of frequency and antenna separation, it may be necessary
to use cavity filters to avoid transmitter noise and receiver blocking problems.
4.1 Antennas
4.1.1 GPS antenna location
Install the GPS antenna unit referring to figure 4.1.3. When selecting a mounting location for the
antenna, keep in mind the following points.
1. Select a location out of the radar beam. The radar beam will obstruct or prevent reception
of the GPS satellite signal.
2. There should be no interfering object within the line-of-sight to the satellites. Objects
within line-of-sight to a satellite, for example a mast, may block reception or prolong
acquisition time.
3. Mount the antenna unit as high as possible to keep it free of interfering objects and water
spray, which can interrupt reception of GPS satellite signal it the water freezes.
4.1.2 VHF antenna location
Location of the mandatory AIS VHF-antenna should be carefully considered. Digital
communication is more sensitive than analogue/voice communication to interference created by
reflections in obstructions like masts and booms. It may be necessary to relocate the VHF
radiotelephone antenna to minimize interference effects.
Install the VHF whip antenna referring to figure 4.1.3. Separate this antenna from other VHF
radiotelephone antennas to prevent interference to the RA-2500.
To minimise interference effects, the following guidelines apply:
1. The AIS VHF antenna should be placed in an elevated position that is as free as possible
with a minimum of 0.5 meters in the horizontal direction from constructions made of
conductive materials. The antenna should not be installed close to any large vertical
obstruction. The objective for the AIS VHF antenna is to see the horizon freely through
360 degrees.
2. The AIS VHF antenna should be installed safely away from interfering high-power
energy sources like radar and other transmitting radio antennas, preferably at least 3
meters away from and out of the transmitting beam.

82694_Op&Ins MAN_RA2500_D 4-2
3. There should not be more than one antenna on the same plane. The AIS VHF antenna
should be mounted directly above or below the ship's primary VHF radiotelephone
antenna, with no horizontal separation and with a minimum of 2.8 meters vertical
separation. If it is located on the same plane as other antennas, the distance apart should
be at least 10 meters.
4.1.3 GPS/VHF combined antenna
See figure 4.1.3. Select a location out of the radar beam. The radar beam will obstruct or prevent
reception of the GPS satellite signal.
There should be no interfering object within the line-of-sight to the satellites. Objects within line-
of-sight to a satellite, for example, a mast, may block reception or prolong acquisition time.
Mount the antenna unit as high as possible. Mounting it this way keeps it free of interfering objects
and water spray, which can interrupt reception of GPS satellite signal if the water freezes.
Horizontal separation distance:
>aa meters
VHF antenna for AIS: Other VHF antenna
or GPS antenna
Figure 4.1.3a, Example of horizontal distance between antennas