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PC On Board
 Pc as a Chartplotter

A Chartplotter is a device used in marine navigation that integrates GPS data with an electronic navigational chart (ENC). The chartplotter displays the ENC along with the position, heading and speed of the ship, and may display additional information from radar, automatic information systems (AIS) or other sensors. As appropriate to particular marine applications, chartplotters may also display data from other sensors, such as echolocators/sonar.

Electronic chartplotters always require a computer, or sometimes multiple computers. It is a feature of the implementation, and sometimes of regulatory requirements, whether the computer is a general-purpose one that can run other applications, or must be dedicated to the chartplotter application. Especially when the chartplotter generates three-dimensional displays, as used for fishing, considerable processing power and video memory can be needed.

Recreational marine chartplotters are used for displaying chart data. Normally a chartplotter is also fed GPS input to compute an accurate position of the vessel. These marine electronics devices are continuously evolving with larger screens, increased processing power, and multi-function capabilities that allow them to display data from a connected radar, fish finder, weather receiver, or be coupled to another marine chartplotter via a marine network. Reviews and reports on a number of modern chartplotters can be found at Marine Electronics Reviews

Electronic Charts

An individual electronic chart, or, more commonly, a database of charts, is the heart of a chartplotter. The chartplotter system can be no more accurate than its charts. While there are different formats for electronic charts, there are even more important quality and legal aspects.

Without charts that are accredited by appropriate governmental organizations, a chartplotter is an example of an Electronic Charting System (ECS). When the charts meet the technical requirements of the International Maritime Organization (IMO) and national hydrographic bodies, the chartplotter can qualify as an Electronic Chart Display and Information System(ECDIS). ECDIS legally can be substituted for paper charts while navigating in active waterways, but vessels are required to maintain paper charts if their chartplotter does not use ECDIS.

ECDIS will use IMO-standardized formats, but some chartplotters require specific data formats. A charter may use one or both types of ENC:

  • Raster Charts: The chart plotter displays a "picture" of a paper chart or map which is referenced to geographic coordinates. A GPS position can be displayed upon the raster chart, but accuracy depends upon many factors including the type of projection (eg. conic or mercator) used in the original chart, and the reference system used (eg. NAD-27 or WGS-84).
  • Vector Charts: The chart plotter constructs a facsimile of a chart using raw data from a data base. The major advantages are a reduction in the amount of data to be stored, and the ability of the chart plotter to identify certain features (such as water depth) and act upon them (eg. do not allow the ship to run aground)
Electronic chart data
Vector charts

Vector charts are the chart databases for ECDIS, with standardized content, structure and format, issued for use with ECDIS on the authority of government authorized hydrographic offices. ENCs are vector charts that also conform to International Hydrographic Organization (IHO) specifications stated in Special Publication S-57.[2]

ENCs contain all the chart information necessary for safe navigation, and may contain supplementary information in addition to that contained in the paper chart (e.g., Sailing Directions). These supplementary information may be considered necessary for safe navigation and can be displayed together as a seamless chart. ENCs are intelligent, in that systems using them can be programmed to give warning of impending danger in relation to the vessel's position and movement.

Electronic Navigational Charts (ENC). ENCs are vector charts that conform to IHO specifications, as contained in Publication S-57. They are compiled from a database of individual items ('objects') of digitised chart data which can be displayed as a seamless chart. When used in an ECDIS or some ECS, the data can be reassembled to display either an entire chart image or a user-selected combination of chart data. ENCs are "intelligent" in that systems using them can be programmed to give warning of impending danger in relation to charted information and the vessel's position and movement.
Raster charts

Raster navigational charts are raster charts that conform to IHO specifications and are produced by converting paper charts to digital image by scanner. The image is similar to digital camera pictures, which could be zoomed in for more detailed information as it does in ENCs. IHO Special Publication S-61 provides guidelines for the production of raster data. IMO Resolution MSC.86(70) permits ECDIS equipment to operate in a Raster Chart Display System (RCDS) mode in the absence of ENC

Raster Nautical Charts(RNC). RNCs are raster charts that conform to IHO specifications and are produced by digitally scanning and geo-referencing the image of a paper chart. In other words, every pixel that makes up the image is associated with the geographical position that it represents. The image may be either the finished chart itself or the stable colour bases used in the multi-colour printing process. The resulting digital file may then be displayed in an electronic navigation system where the vessel's position, generally derived from electronic position fixing systems, can be shown. Since the displayed chart data are merely a digital photocopy of the original paper chart, the image has no direct "intelligence" and the chart data cannot be interrogated or analysed to trigger alarms or warnings. However, because the image is georeferenced, a mariner can still indicate positions on the chart at which a warning will be activated. IHO Special Publication S-61 "Raster Nautical Chart Product Specification" provides guidelines for the production of raster data. IMO resolution MSC.86(70) permits ECDIS equipment to operate in a Raster Chart Display System (RCDS) mode in those areas where Electronic Navigational Charts are no yet available. The RCDS mode of operation is described in Appendix 7 of the IMO Performance Standards for ECDIS
Nautical Symbols
Much of the information contained on charts is shown by symbols. These symbols are not shown to scale, but they indicate the correct position of the feature to which they refer.The standard symbols and abbreviations used on charts published by the United States of America are shown in Chart No. 1, Nautical Chart Symbols and Abbreviations. Click to the image on the left to enlarge.

Electronic chart symbols are, within programming and display limits, much the same as printed ones. The less expensive electronic charts have less extensive symbol libraries, and the screen’s resolution may affect the presentation detail.


The scale of a nautical chart is the ratio of a given distance on the nautical chart to the actual distance which it represents on the earth. It may be expressed in various ways. The most common are:

  1. A simple ratio or fraction, known as the representative fraction. For example, 1:80,000 or 1/80,000 means that one unit (such as a meter) on the chart represents 80,000 of the same unit on the surface of the earth. This scale is sometimes called the natural or fractional scale.
  2. A statement that a given distance on the earth equals a given measure on the chart, or vice versa. For example, “30 miles to the inch” means that 1 inch on the chart represents 30 miles of the earth’s surface. Similarly, “2 inches to a mile” indicates that 2 inches on the chart represent 1 mile on the earth. This is sometimes called the numerical scale.
  3. A line or bar called a graphic scale may be drawn at a convenient place on the chart and subdivided into nautical miles, meters, etc. All charts vary somewhat in scale from point to point, and in some projections the scale is not the same in all directions about a single point. A single subdivided line or bar for use over an entire chart is shown only when the chart is of such scale and projection that the scale varies a negligible amount over the chart, usually one of about 1:75,000 or larger. Since 1 minute of latitude is very nearly equal to 1 nautical mile, the latitude scale serves as an approximate graphic scale. On most nautical charts the east and west borders are subdivided to facilitate distance measurements.

On a Mercator chart the scale varies with the latitude. This is noticeable on a chart covering a relatively large distance in a north-south direction. On such a chart the border scale near the latitude in question should be used for measuring distances.

Of the various methods of indicating scale, the graphical method is normally available in some form on the chart. In addition, the scale is customarily stated on charts on which the scale does not change appreciably over the chart. The ways of expressing the scale of a chart are readily interchangeable. For instance, in a nautical mile there are about 72,913.39 inches. If the natural scale of a chart is 1:80,000, one inch of the chart represents 80,000 inches of the earth, or a little more than a mile. To find the exact amount, divide the scale by the number of inches in a mile, or 80,000/72,913.39 = 1.097. Thus, a scale of 1:80,000 is the same as a scale of 1.097 (or approximately 1.1) miles to an inch. Stated another way, there are: 72,913.39/80,000 = 0.911 (approximately 0.9) inch to a mile. Similarly, if the scale is 60 nautical miles to an inch, the representative fraction is 1:(60 x 72,913.39) = 1:4,374,803.

A chart covering a relatively large area is called a small-scale chart and one covering a relatively small area is called a large-scale chart. Since the terms are relative, there is no sharp division between the two. Thus, a chart of scale 1:100,000 is large scale when compared with a chart of 1:1,000,000 but small scale when compared with one of 1:25,000.

As scale decreases, the amount of detail which can be shown decreases also. Cartographers selectively decrease the detail in a process called generalization when producing small scale charts using large scale charts as sources. The amount of detail shown depends on several factors, among them the coverage of the area at larger scales and the intended use of the chart.

 PC Conection
NMEA 0183 
NMEA 0183, ou simplesmente NMEA, é um conjunto de especificações de dados e elétricas para comunicação de dispositivos eletrônicos de navegação tais como Anemômetros, ecolocalizadores, girocompassos, piloto automático, receptores GPS e muitos outros tipos de instrumentos

The NMEA 0183 standard uses a simple ASCII, serial communications protocol that defines how data is transmitted in a "sentence" from one "talker" to multiple "listeners" at a time. Through the use of intermediate expanders, a talker can have a unidirectional conversation with a nearly unlimited number of listeners, and using multiplexers, multiple sensors can talk to a single computer port. Third-party switches are available that can establish a primary and secondary talker, with automatic failover if the primary fails.

At the application layer, the standard also defines the contents of each sentence (message) type so that all listeners can parse messages accurately.

Serial configuration (data link layer)

Baud rate 4800
Data bits 8
Parity None
Stop bits 1
Handshake None

AIS units use a default baud rate of 38400.

NMEA-0183 and GPS Information/

Connecting NMEA equipment

Interconnecting NMEA instruments can be a real hassle if one is not familiar with the different types of connections. The NMEA-0183 standard specifies the talker ports (outputs) and listener ports (inputs) to be differential. This means that the data is transported by means of voltage levels over two wires, separated from ground. Roughly, the voltage levels swing between 0 and 5 Volt, and both wires are in opposite phase. When one is at 5V, the other is 0V and vice versa. Such a system has two major advantages:

  1. It is less susceptible for interference since an induced voltage has the same polarity on both wires and therefore not changing the ratio between the voltages on both wires. A differential listener only detects the voltage difference between both wires and not the absolute value so interference has no influence on this.
  2. A differential system produces less interference on HF systems. When a current flows through a wire, a magnetic field is generated around that wire. This magnetic field can induce currents in other wires, like the power or antenna wiring to a HF or VHF radio. This results in interference. In a differential system, both wires carry the same signal (=current) but in opposite phase. The magnetic fields around both wires are also in opposite phase and therefore canceling each other.

The NMEA world could be a perfect world if every manufacturer would adhere to the standard. You could simply connect the 'A' terminal on a talker to the 'A terminal of a listener and do the same with the 'B' terminal, as depicted in figure


fig.1 Differential                                           fig.2 Single-ended

However, manufacturers like to save money where they can, and many of them found that they could do so by leaving out proper drivers and even the optocoupler that is required for the mandatory galvanic isolation. So many equipment has single-ended inputs and outputs, where the signal is transported over a single wire while the common ground connection serves as the signal return path, as shown in figure 2. It might seem similar to the setup in figure 1, but the main difference is that the ground connection also carries the supply current of the equipment, together with all power spikes and surges that occur in an electrical system.

From a pure wiring viewpoint, a single ended setup is still easy to connect. But in the real world, we have both differential and single-ended equipment. This results in four possible connections:

  1. Differential -> differential (fig.1 & 3)
  2. Single-ended -> single-ended (fig.2)
  3. Single-ended -> differential (fig.4)
  4. Differential -> single-ended (fig.5)

The following examples will show how to make different types of connections. In each example, a single-ended or differential talker or listener is connected to our multiplexer, which features differential NMEA inputs and outputs.

Differential -> differential

This setup is very straightforward. The talkers' A and B terminals are simply connected to the corresponding A and B terminals of a listener port on the multiplexer

The same method is used to connect the multiplexers' talker port to an instrument

Single-ended -> differential

The output of a single-ended instrument can be connected to the A terminal of a listener port. To close the circuit, the B terminal of the listener port is connected to the instrument ground. Do not connect the B terminal to a power ground close to the multiplexer but feed a ground wire to the instrument and connect it there to the instrument ground. This prevents any supply currents to disturb the data. No ground loops are created since the listener ports of the multiplexer are galvanically isolated and thus floating from ground

Fig.4: Single-ended -> differential

Differential -> single-ended

When connecting a differential talker to a single-ended listener, only the A terminal of the talker is connected to the input of the listener. The B terminal of the talker is left open. The return path of the signal is the common ground of the talker and the listener. Since there is no galvanic isolation on a talker port and certainly not on a single-ended input, it is best to keep the ground wires as short as possible and preferably on a single bus to minimize the chance of interference.
Note: Never connect the B terminal of a talker to ground! A B terminal on a talker is also supplying signal, which would be short-circuited to ground

Fig.5: Differential -> single-ended

Multiple listeners

When multiple listeners of different nature (single-ended vs. differential) are to be connected to a talker port, the same connection rules apply. In the example in figure 6, two differential and one single-ended listener are connected to the differential output of a multiplexer.

Fig.6: Multiple listeners



Connecting to a PC

NMEA 0183 instruments have serial ports. With a suitable cable they can generally by plugged into the PC's RS232 serial connector. Software like Windmill can then collect and interpret the data being sent from the instrument to the PC. Some manufacturers may use non-standard cables and plugs. It is often easiest, therefore, to buy the cable from your instrument supplier but you can make or modify your own. The NMEA signal or output line needs to be connected to the RS232 receiver or input line (line 2 on a 9-pin plug). The NMEA ground or earth needs to be connected to the RS232 ground or earth (5 on a 9-pin plug). Issue 42 of Monitor gave details on RS232 connections.

The NMEA 0183 Interface Standard specifies the communication settings as
Baud Rate: 4800
Data Bits: 8
Parity: None
Stop Bits: 1 (or more)
These should work for all instruments but, depending on your device, you may be able to use a higher baud rate.

You will need to tell the data acquisition software about the communication settings your instrument is using.

 NMEA-0183 Multiplexers

NMEA and Multiplexers

The NMEA standard, a communication standard defined by the NMEA organization, defines a communication protocol called NMEA-0183, that enables navigation instruments to exchange data with each other.

A compass can, for example, send a bearing to a radar to enable a north-up display. And a GPS can send cross-track information to an autopilot in order to steer a programmed course.

Talkers and Listeners

Communication with the NMEA-0183 protocol involves at least one instrument that sends data and another that receives data. By convention, an instrument that sends data is called a talker, while an instrument that receives data is called a listener. Fig.1 shows such a system.

A compass can, for example, send a bearing to a radar to enable a north-up display. And a GPS can send cross-track information to an autopilot in order to steer a programmed course.

With the NMEA-0183 protocol, information is passed in sentences that are made up of readable characters. The contents of a sentence is well defined by the standard and always starts with a '$' or a '!' character and always ends with a special code, called a LF (Line Feed). Thus, a listener always knows when and sentence starts and ends. The NMEA standard also specifies that a talker may send one ore more sentences any time it wishes, but preferably not more that once per second. An exception to this rule are gyro- and fluxgate compasses, which often transmit 10 sentences per second or more.

The NMEA standard specifies that a talker should have enough driving capability to drive up to four listeners. This means that you should be able to connect up to four instruments that receive data from one other instrument, as shown in fig.2. This is very easy to achieve, just like one person telling a story to an audience of up to four people. The only requirement for the talker is to talk loud enough.


The situation gets complicated when several talkers have to send data to one listener. A typical example is where a GPS and a wind meter have to send data to an autopilot. Computer navigation is another example where several talkers (sailing instruments) must talk to one listener (the computer)(fig.3). The NMEA standard has no provision for these situations, so without special equipment, this is impossible. The outputs of the talkers will effectively short-circuit each other and the sentences they transmit will be corrupted since any talker can start sending at any time. The result will be like four persons telling a different story to one listener at the same time.

The Multiplexer

An NMEA multiplexer, also called combiner, solves the problem by offering an intermediate storage of sentences. Every talker in the system in fig.4 is connected to its own NMEA input on the multiplexer. The multiplexer reads complete sentences from every connected listener and stores them in a buffer. There is a buffer for every input, large enough to contain several sentences. Subsequently, the multiplexer checks every buffer in a round-robin fashion for the presence of sentences. Each time, one sentence is taken from a buffer and sent to the NMEA output of the multiplexer.

Fig. shows a multiplexer in a typical installation, where the NMEA data from four instruments is combined into one stream. This stream is sent to the connected computer over an RS-232 or USB interface, to be used for electronic navigation. Also connected is an autopilot which receives NMEA data from the instruments or the computer or both, depending on the configuration of the multiplexer.


The MiniPlex-AIS is dedicated to be used with Raymarine® C- and E-Series displays. It enables the use of an AIS receiver, a Smart Heading Sensor and other NMEA compatible instruments at the same time.


Supply voltage: 8-30VDC, secured against reversed polarity.
Current consumption: 40mA (70mA max. with fully loaded talker ports)
Inputs: 4 x NMEA-183/RS-422, galvanically isolated. 3 x 4800 baud, 1 x 38400 baud.
1 x RS-232 at 38400 baud
Outputs: 1 x RS-232 at 38400 baud
1 x NMEA-183/RS-422 at 38400 baud
1 x NMEA-183/RS-422 at 4800 baud
Buffers: 5 buffers of 800 characters (4 x NMEA, 1 x RS-232)
Compliance: EN/IEC 60945 and EN/IEC 61162-1
Dimensions: 138 x 62 x 30mm
The MiniPlex-AIS is an NMEA multiplexer dedicated to be used with Raymarine® C/E-Series displays. It enables the use of an AIS receiver*, a Smart Heading Sensor and other NMEA compatible instruments at the same time.

The MiniPlex-AIS has 4 galvanically isolated NMEA inputs, 2 NMEA outputs and one RS-232 interface.

Three inputs operate at the standard NMEA communication speed of 4800 baud and one input operates at 38400 baud, as used by AIS receivers. One NMEA output also operates at 38400 baud, to be connected to the NMEA input of a Raymarine® C/E-Series display.

How to Combine NMEA and SeaTalk

One of the simplest ways to put SeaTalk data onto your NMEA network is to use the Brookhouse Multiplexer (MUX). I am designing a network aboard s/v C# and had the following requirements:

  1. PUT DSC information onto the NMEA bus and SeaTalk bus from a Standard Horizon Radio
  2. Receive GPS information into the Standard Horizon Radio from the NMEA bus
  3. Transfer routes and waypoints from software to the Raymarine C-80 over the network
  4. Control the Raymarine ST4000+ Autopilot from nav software or the C-80 (Have one or the other be the source of the route talking)
  5. Put AIS from an SR161 information onto the network at 38000 and have it available on the C-80 as well as nav software
  6. Have a redundant NMEA GPS wired to a NMEA in (already have a Raymarine SeaTalk GPS)
  7. Have all SeaTalk data available to nav software when the C-80 is disconnected

After a quick note to Bookhouse with these requirements, they replied indicating all of this would be possible and provided the graphic below -

Integrated Raymarine C and E Series to NMEA Network

How SeaTalk works


SeaTalk uses three wires, connected in parallel to all devices on the bus:
  1.  +12V    Supply, red
  2.  GND    Supply, grey
  3.  Data     Serial Data, yellow: +12V=Idle/Mark=1, 0V=Space/Data=0, 4800 Baud, pullup circuit in each device, talker pulls down to 0V (wired OR). For connection to a RS232 receiver voltage levels must be inverted.

Serial Data Transmission

11 bits are transmitted for each character:
  • 1  Start bit (0V)
  • 8  Data Bits (least significant bit transmitted first)
  • 1  Command bit, set on the first character of each datagram. Reflected in the parity bit of most UARTs. Not compatible with NMEA0183 but well suited for the multiprocessor communications mode of 8051-family microcontrollers (bit SM2 in SCON set).
  • 1  Stop bit (+12V)
  • Composition of Messages

    Each datagram contains between 3 and 18 characters:
    1. Type of command (the only byte with the command-bit set)
    2. Attribute Character, specifying the total length of the datagram in the least significant nibble:
            Most  significant 4 bits: 0 or part of a data value
            Least significant 4 bits: Number of additional data bytes = n  =>
            Total length of datagram = 3 + n  characters
    3. First, mandatory data byte
    4. - 18.  optional, additional data bytes

    The Seatalk Option for Brookhouse NMEA Multiplexers

    Seatalk is the proprietry protocol used by RayMarine for communication between ST Marine Instruments. Brookhouse NMEA Multiplexers support this protocol, as a low-cost optional extra. If the Seatalk option is purchased when you order your Brookhouse Multiplexer, channel 1 can be configured (by the user) for connection of either an NMEA-talker or Raymarine Seatalk intruments. If set up for Seatalk, data is extracted from the Seatalk bus and converted to NMEA sentences before being output via the multiplexer's RS232 output-port. This function is often referred to as a "Seatalk-NMEA bridge". A single cable connects the NMEA Multiplexer with the Seatalk instruments. This single connection gives access to the data, produced by all Seatalk instruments on the Seatalk bus. On the remaining three Mux channels, other NMEA talkers can be connected.

    The Brookhouse NMEA Multiplexer with Seatalk option provides 3 functions in one:

    • NMEA Multiplexer.
    • Seatalk-NMEA "bridge" (protocol converter). Seatalk-USB bridge if USB option is installed.
    • Seatalk & NMEA combiner.  

    A typical situation is the following:

    A yacht is equipped with Seatalk Wind Instruments, Depth Sounder and Log/Speed Instrument. The GPS is of a different make and provides NMEA output. Installation of an on-board laptop computer is planned and to make best use of all instrument and GPS data in the Laptop software (navigation s/w, optimum track calc, etc.), there is a requirement to combine and input instrument and GPS data in the computer in NMEA format. If a separate Seatalk-NMEA bridge would be used, an NMEA Multiplexer would still be required to combine the NMEA output of the bridge with NMEA data from the GPS. If the Brookhouse NMEA Multiplexer with Seatalk option is installed, no further electronics are necessary, which results in substantial cost savings.  

    If the Seatalk option is purchased for the Brookhouse NMEA Multiplexer with compact user-programmable Repeater display, 5 functions become available:

    • NMEA Multiplexer.
    • NMEA Repeater Display  (Selected data)
    • Seatalk - NMEA "bridge" (Seatalk converter, selected data). Seatalk-USB bridge if USB option is installed.
    • Seatalk - NMEA combiner
    • Seatalk Repeater Display (selected data).

    All data from result-sentences of the Seatalk-NMEA conversion can be displayed on the LCD. The user can select the display by pressing the selection pushbutton. Any of the displays can be set as the power-up default, simply by depressing and holding the selection-pushbutton until the word "Set" appears. For example, if a ST50 depth-sounder instrument has been installed and the navigator wants the "depth in feet" (or metres) displayed  at all times, this data can be selected as the power-up default.

    Seatalk Connections

     There are several easy ways of connecting the Brookhouse Multiplexer to the Seatalk instruments. As all data is present on all Seatalk connectors on the instruments and on all interconnecting Seatalk cables, the signal can be picked up from any convenient point. Seatalk instruments always have two Seatalk connectors, to enable them to be "chained". The instruments at both ends of the Seatalk chain therefore have an unused connector. One of those connectors can be used to link the Seatalk bus to the NMEA Multiplexer (channel 1, Seatalk option enabled). A standard Seatalk cable with the required length can be purchased from the local RayMarine dealer for this purpose. These cables come with plugs at both ends. One plug has to be cut off so that the individual wires can be  inserted and fixed in the screw-terminals on the Brookhouse multiplexer.

    The connection can also be made without the special cable, by cutting an existing Seatalk cable that connects 2 instruments and by making a simple splice.  The following Seatalk data is extracted from the Seatalk bus and converted to NMEA by the Brookhouse Mux Seatalk option:


    Connection diagrams

    Please note that the text and diagrams below apply to the standard Brookhouse NMEA multiplexer. The diagrams are a number of years old and many of the options available now are not mentioned. However, the information has proven to be valuable for a general understanding of NMEA multiplexers, so we have kept it on the website.

    The following diagrams show integrated instrument/computer installations, whereby the NMEA Multiplexer plays a crucial role. In all cases the objective is the same: to combine all instrument data in one data stream which is then sent to a computer, a chart plotter, to a repeater instrument, auto pilot etc.

    There are many applications for the multiplexer, in the text below we will concentrate on combining data to be used by a (laptop) computer. 
    Seatalk bridge
    PC-SeaTalk-NMEA Interface Box
  • Conversion of NMEA 0183 data formats to SeaTalk
  • Conversion of SeaTalk to NMEA 0183 format
  • Operation of the Raymarine Main Alarm when an alarm condition exists on the SeaTalk bus
  • RS232 terminals to send NMEA data to a personal computer (echoes NMEA out)


    For the navigator of a cruising yacht, the GPS connection to the computer is the most important because positional data is required for the navigation/chart plotting software, but the various software packages offer an ever increasing number of features, which also require other instrument data. For example, it is very useful  for the navigator to be able to read out the actual water-depth and wind direction at the current position of the vesssel as plotted in the in the electronic chart. Many navigation programs can display a window with all instrument data in analog and/or digital format, even with graphs. Wind strength graphs can play an important role in decision making. Also, automated log systems can make log-entries at certain time-intervals,  which include magnetic heading, wind speed and direction. To make optimal use of what the on- board computer has to offer, all the available NMEA data has to be fed into the computer via a NMEA multiplexer.

    For the race-tactition other programs help determine the best course/tack. Again, all instrument data has to be available as input to this software to enable it to perform its calculations.  Therefore, after the decision has been taken to build an integrated computer/instruments system, it is important to hook up the instruments and computer in such a way, that the set goals can be achieved. If the basis of the system is not properly designed, it will not work, not even with the best software.

    An important point when planning how to interconnect instruments and computer, is whether an autopilot will be part of the integrated system and which features of the auto-pilot will be used. Most auto-pilots can be used in three ways:

    1. To steer a set course. The navigator  works out a course, the boat is manually steered on that course and the helmsman presses the “auto” button of the auto-pilot. The auto pilot will maintain that course from this point onwards. It is the simplest use of the AP and no other instrument data is required.
    2. In “track mode”. The boat is steered along a track to a waypoint. The advantage is that the boat is not only steered in the right direction, but it is also steered exactly along the line (track) that the navigator has plotted to the waypoint in the (electronic) chart, i.e. by following the track, fixed obstacles such as shallows are avoided. This is ideal for navigation in bad visability or at night and as the track is “over the ground”  the autopilot automatically compensates for drift and current. In most cases the autopilot does a better job than a helmsman.
    3. In “wind vane mode”. The boat is steered at a set angle with the wind direction. This mode is useful to maintain the sailtrim, but if the wind direction changes, the course changes. Most auto-pilots will give an audible warning if the change is more than a set maximum.

    To be able to work in track mode (2), the auto-pilot needs special NMEA sentences with data such as the bearing and range between origin and destination, the bearing and range from present position to destination and cross track error (NMEA APB). A GPS can produce this data, but it is necessary to load the waypoint(s) in the GPS and to set the GPS to navigation mode. In an integrated system whereby the navigation is done on the computer, waypoints are set with the mouse, directly in the electronic chart. This much user-friendlier, faster and less error-prone method is one of the advantages of using a computer. The GPS is only used for providing the computer with latitude and longitude of the position. Therefore, instead of connecting the auto-pilot to the GPS NMEA output, it is hooked up directly to the computer and the navigation software generates the NMEA sentences for auto-pilot control.  When selecting the navigation software, it is important to check if auto-pilot control is supported if this is required.

    If wind-vane mode is required (3), the autopilot needs NMEA data from the wind-instrument. However, if it is connected to the computer for track-mode, no direct NMEA connection with the wind-instrument is possible at the same time. Therefore, the navigation software has to be able to pass the NMEA sentences it receives from the windinstrument on to the output port, where the autopilot is connected to. Naturally, the wind-instrument data has to be available in the computer in the first place. In the setup section for most navigation software, the user can specify which NMEA sentences should be sent to the output port. Sometimes this is referred to as “NMEA pass-through”.

    In most cases the output port for the auto-pilot will be the same as the port where the NMEA multiplexer is connected to. The auto-pilot will most likely require a transmission speed of 4800BPS (NMEA standard). As transmission and reception speed for PC ports have to be the same, this dictates that the computer input port and therefore also the output of the NMEA Multiplexer has to be set to 4800bps as well.

    This shows a relatively simple system with individual NMEA outputs of  the instruments. The instruments may be of different manufacture. The speed instrument is directly hooked up to the wind instrument for true wind direction and speed calculation. All instruments and a GPS are connected to opto-isolated input ports of the NMEA multiplexer. The combined NMEA data is sent to the computer via RS232 or USB and/or to a chart plotter or other NMEA listeners via RS422.

    This diagram shows a basic instrument network. Instrument manufacturers often have their own protocols for connecting instruments to eachother, but usually an NMEA output is provided for connection to the “outside world”. This NMEA talker port outputs sentences for data from all instruments in the network. The GPS is not part of the instrument network and therefore an NMEA multiplexer is necessary to combine the data from the separate NMEA data sources

    The instruments in this example are Raymarine Seatalk instruments. Seatalk is the name of the proprietry Raymarine protocol that links the instruments. No NMEA output is provided. However, the Brookhouse NMEA multiplexer with Seatalk option can accept the Seatalk bus signal on input channel 1.  The multiplexer converts the Seatalk data of all connected Seatalk instruments and Seatalk GPS to standard NMEA sentences and outputs these sentences combined with the NMEA data from the GPS and other “NMEA talkers” via the RS232 port or USB to the computer and via RS422 for other NMEA listeners. This is an efficient and cost-effective solution because the multiplexer provides both the combiner function and the Seatalk-NMEA conversion.

    Here, an autopilot is added to the configuration of diagram 2. As discussed in the intruduction of this chapter, it is advantageous to control the autopilot directly by the navigation software.  Computer output is sent to the multiplexer via RS232 or USB and enters the multiplexer via a 5th input port. Therefore, the standard Brookhouse multiplexer is in fact a 5-channel multiplexer. The auto pilot is connected to the multiplexer’s NMEA OUT (RS422) port.  Please note that in this case the multiplexer’s output baudrate has to be set to 4800 bps, because most auto pilots will only support this standard NMEA baudrate. There are now also Brookhouse multiplexer models available with baudrate conversion, that allow connection of a standard 4800 bps “listeners”, whilst the output baudrate to the computer or chartplotter is higher.

    The combined data stream sent to the auto pilot contains GPS data plus computer output. Therefore, both the GPS and the computer (or chartplotter) can control the auto pilot, without physically switching.

    Many autopilots also have a NMEA-out (talker) port. NMEA data such as magnetic heading (from the fluxgate compass) is output via this port. In this diagram the autopilot NMEA output is fed back into the NMEA multiplexer, so that the magnetic heading is available to the navigation or other software running in the computer

    In this diagram both the instruments and the autopilot are Raymarine Seatalk. The Raymarine autopilots that support track-mode also have an NMEA IN (listener) port, so that the NMEA sentences for autopilot control from non-Seatalk devices can be accepted. As in diagram 4, the navigation software running on the computer or the GPS controls the autopilot. The autopilot is also connected to the other instruments via Seatalk and therefore the data from the wind instrument is already available to the autopilot for wind steering mode. The autopilot also has a NMEA output. The primary function of this output is to send out heading data from the fluxgate compass. In the diagram, this is linked to NMEA multiplexer Ch3 with the dotted line. The reason is, that this NMEA connection is not always necessary, as the NMEA multiplexer also translates the heading data it detects on the Seatalk bus to NMEA and the computer does not need the same data twice.

    Note: Although the autopilot is connected to the Seatalk bus and also has a NMEA output port, this does not mean that the other instrument data is available as NMEA sentences via this port. Only heading data is sent and Seatalk-NMEA conversion in the multiplexer is still required

    In diagram 6 the connection of a radar is shown, in combination with an autopilot. It is assumed that this radar unit is capable of displaying navigation data such as L/L, bearing and range to waypoint (BWC sentence), heading and speed. Provided the required data is available, some radars are capable of plotting the current active waypoint on the screen. This is an vey useful feature for navigation in bad visability. Either the computer or the GPS can be used for auto pilot control without physically switching. The full combined data stream is sent to both the autopilot and the radar NMEA IN ports from the multiplexer’s NMEA OUT port (RS422). The radar can therefore display waypoint data originating from either the computer or the GPS. A maximum of 5 NMEA listeners can be connected in parallel to the RS422 output port.

    Note 1:

    If the instrument system includes a universal NMEA repeater instrument, that is capable of displaying bearing & distance to waypoint and cross-track plus other NMEA data, this instrument can be connected in parallel with auto pilot and/or radar to the mux RS422 port.

     Note 3:

    In the diagrams, the Brookhouse NMEA Multiplexer model  without the LCD display is depicted. The model with compact LCD provides exactly the same functionality, with the additional advantage that the data that passes through the multiplexer can also be displayed, independently from the computer.

    Note 4:

    VHF or SSB radio connections are not shown in any of the diagrams. If the VHF or SSB radio supports DSC, a GPS can be connected to automatically transmit the position of the vessel in distress. In any of the diagrams shown above, the GPS signal can be split to go to both the NMEA multiplexer and the radio

    USB to NMEA 0183
    • Create a safe serial port connection to an NMEA 0183 system that may be on a different power circuit.
  • Connect two PCs together that are on different power circuits
  • Provide a fully compliant NMEA 0183 port from a USB port
  • Receive low level differential signals that are too small to be received directly by a PC serial port
  •  USB to Serial Gateway 1 RS422 (connection diagram)
    Connect your data network to your PC USB port with full electrical isolation...
    The Actisense™ USG-1 interface is an easy, safe and low-cost method of connecting a marine NMEA 0183 system to a USB equipped PC. Whilst protecting the most vital and expensive devices in the NMEA 0183 system, it also creates a virtual serial port that allows connection to an NMEA 0183 (RS422) marine bus link.

    Total galvanic isolation is assured using an ISO-Drive output and the use of the trusted Actisense OPTO isolated input circuitry.

    The ISO-Drive output offers total galvanic isolation from the input and can "float" safely up to 1500 VDC from ground. Its sophisticated circuitry is 100% compatible with the NMEA 0183 RS422, industrial RS485 and single-ended PC RS232 "COM" ports.

    The USG-1 provides comprehensive isolation of the expensive PC hardware when connecting to an NMEA 0183 (RS422) bus that may have picked up potentially hazardous voltages around the electrically noisy environment of a vessel or factory, and makes installation simple due to the isolation of the PC ground from the NMEA 0183 data network ground, often the biggest cause of data errors and one of the biggest safety hazards in any electronic installation.

    No external power supply is required as the cable takes all necessary power from the USB port. Simple installation using plug & play USB drivers supplied on CD allows the PC to start sending and receiving data to the NMEA 0183 data network within minutes of installation
    NMEA 2000

    NMEA 2000 is a combined electrical and data specification for a marine data network for communication between marine electronic devices such as depth finders, nautical chart plotters, navigation instruments, engines, tank level sensors, and GPS receivers. It has been defined by, and is controlled by, the US based National Marine Electronics Association (NMEA).

    NMEA 2000 connects devices using Controller Area Network (CAN) technology originally developed for the auto industry. NMEA 2000 is based on the SAE J1939 high-level protocol, but defines its own messages. NMEA 2000 devices and J1939 devices can be made to co-exist on the same physical network.

    NMEA 2000 (IEC 61162-3) can be considered a successor to the NMEA 0183 (IEC 61162-1) serial data bus standard. It has a significantly higher data rate (250k bits/second vs. 4800 bits/second for NMEA 0183). It uses a compact binary message format as opposed to the ASCII serial communications protocol used by NMEA 0183. Another improvement is that NMEA 2000 supports a disciplined multiple-talker, multiple-listener data network whereas NMEA 0183 requires a single-talker, multiple-listener (simplex) serial communications protocol.

     File:NMEA2000 Modified motor yacht.jpg

     In telecommunications, RS-232 (Recommended Standard 232) is a standard for serial binary data signals connecting between a DTE (Data Terminal Equipment) and a DCE (Data Circuit-terminating Equipment). It is commonly used in computer serial ports. A similar ITU-T standard is V.24.

    The following table lists commonly-used RS-232 signals and pin assignments


    Signal Origin DB-25 DE-9
    EIA/TIA 561 Yost
    Name Abbrevation DTE DCE
    Common Ground G 7 5 4 4,5
    Protective Ground PG 1 - -
    Transmitted Data TxD 2 3 6 3
    Received Data RxD 3 2 5 6
    Data Terminal Ready DTR 20 4 3 2
    Data Set Ready DSR 6 6 1 7
    Request To Send RTS 4 7 8 1
    Clear To Send CTS 5 8 7 8
    Carrier Detect DCD 8 1 2 7
    Ring Indicator RI 22 9 1 -




    Commonly-used signals are:

    Transmitted Data (TxD) 
    Data sent from DTE to DCE.
    Received Data (RxD) 
    Data sent from DCE to DTE.
    Request To Send (RTS) 
    Asserted (set to logic 0, positive voltage) by DTE to prepare DCE to receive data. This may require action on the part of the DCE, e.g. transmitting a carrier or reversing the direction of a half-duplex channel. For the modern usage of "RTS/CTS handshaking," see the section of that name.
    Ready To Receive (RTR) 
    Asserted by DTE to indicate to DCE that DTE is ready to receive data. If in use, this signal appears on the pin that would otherwise be used for Request To Send, and the DCE assumes that RTS is always asserted; see RTS/CTS handshaking for details.
    Clear To Send (CTS) 
    Asserted by DCE to acknowledge RTS and allow DTE to transmit. This signaling was originally used with half-duplex modems and by slave terminals on multidrop lines: The DTE would raise RTS to indicate that it had data to send, and the modem would raise CTS to indicate that transmission was possible. For the modern usage of "RTS/CTS handshaking," see the section of that name.
    Data Terminal Ready (DTR) 
    Asserted by DTE to indicate that it is ready to be connected. If the DCE is a modem, this may "wake up" the modem, bringing it out of a power saving mode. This behaviour is seen quite often in modern PSTN and GSM modems. When this signal is de-asserted, the modem may return to its standby mode, immediately hanging up any calls in progress.
    Data Set Ready (DSR) 
    Asserted by DCE to indicate the DCE is powered on and is ready to receive commands or data for transmission from the DTE. For example, if the DCE is a modem, DSR is asserted as soon as the modem is ready to receive dialing or other commands; DSR is not dependent on the connection to the remote DCE (see Data Carrier Detect for that function). If the DCE is not a modem (e.g. a null modem cable or other equipment), this signal should be permanently asserted (set to 0), possibly by a jumper to another signal.
    Data Carrier Detect (DCD) 
    Asserted by DCE when a connection has been established with remote equipment.
    Ring Indicator (RI) 
    Asserted by DCE when it detects a ring signal from the telephone line.
    Null modem
    Null modem is a communication method to connect two DTEs (computer, terminal, printer etc.) directly using a RS-232 serial cable. The RS-232 standard is asymmetrical as to the definitions of the two ends of the communications link so it assumes that one end is a DTE and the other is a DCE e.g. a modem. With a null modem connection the transmit and receive lines are crosslinked. Depending on the purpose, sometimes also one or more handshake lines are crosslinked. Several wiring layouts are in use because the null modem connection is not covered by a standard.
    Null modem cable pin mapping
    Signal Name DB-25 Pin DE-9 Pin DE-9 Pin DB-25 Pin
    FG (Frame Ground) 1 - X - 1 FG
    TD (Transmit Data) 2 3 - 2 3 RD
    RD (Receive Data) 3 2 - 3 2 TD
    RTS (Request To Send) 4 7 - 8 5 CTS
    CTS (Clear To Send) 5 8 - 7 4 RTS
    SG (Signal Ground) 7 5 - 5 7 SG
    DSR (Data Set Ready) 6 6 - 4 20 DTR
    CD (Carrier Detect) 8 1 - 4 20 DTR
    DTR (Data Terminal Ready) 20 4 - 1 8 CD
    DTR (Data Terminal Ready) 20 4 - 6 6 DSR
     Installation is very simple. From each NMEA device 2 wires have to be connected (+ and -). The documentation of the instruments will describe this. If the output port is  connected to a computer, the + and - have to be connected to pins 2 and 5 of a standard female 9-pin connector.

    PC Serial Port Connections to NMEA

    The following diagram shows the pin connections for 25-pin and 9-pin PC serial ports to NMEA.


    Universal Serial Bus
    USB is intended to replace many varieties of serial and parallel ports. USB can connect computer peripherals such as mice, keyboards, PDAs, gamepads and joysticks, scanners, digital cameras, printers, personal media players, flash drives, and external hard drives. For many of those devices, USB has become the standard connection method. USB was designed for personal computers, but it has become commonplace on other devices such as PDAs and video game consoles, and as a power cord between a device and an AC adapter plugged into a wall plug for charging. As of 2008, there are about 2 billion USB devices sold per year, and about 6 billion total sold to date

    USB supports following signaling rates:

    • A low speed rate of 1.5 Mbit/s is defined by USB 1.0. It is very similar to "full speed" operation except each bit takes 8 times as long to transmit. It is intended primarily to save cost in low-bandwidth human interface devices (HID) such as keyboards, mice, and joysticks.
    • The full speed rate of 12 Mbit/s is the basic USB data rate defined by USB 1.1. All USB hubs support full speed.
    • A hi-speed (USB 2.0) rate of 480 Mbit/s was introduced in 2001. All hi-speed devices are capable of falling back to full-speed operation if necessary; they are backward compatible. Connectors are identical.
    • A SuperSpeed (USB 3.0) rate of 5.0 Gbit/s. The USB 3.0 specification was released by Intel and partners in August 2008, according to early reports from CNET news. The first USB 3 controller chips were sampled by NEC May 2009 [9] and products using the 3.0 specification are expected to arrive beginning in Q3 2009 and 2010.[10] USB 3.0 connectors are generally backwards compatible, but include new wiring and full duplex operation. There is some incompatibility with older connectors
    Connector types
    There are several types of USB connectors, including some that have been added while the specification progressed. The original USB specification detailed Standard-A and Standard-B plugs and receptacles. The first engineering change notice to the USB 2.0 specification added Mini-B plugs and receptacles.

    The maximum length of a standard USB cable (for USB 2.0 or earlier) is 5.0 metres (16.4 ft). The primary reason for this limit is the maximum allowed round-trip delay of about 1,500 ns. If USB host commands are unanswered by the USB device within the allowed time, the host considers the command lost. When adding USB device response time, delays from the maximum number of hubs added to the delays from connecting cables, the maximum acceptable delay per cable amounts to be 26 ns.The USB 2.0 specification requires cable delay to be less than 5.2 ns per meter (192,000 km/s, which is close to the maximum achievable speed for standard copper cable).This allows for a 5 meter cable. The USB 3.0 standard does not directly specify a maximum cable length, requiring only that all cables meet an electrical specification. For copper wire cabling, some calculations have suggested that a maximum length of perhaps 3m. No fiber optic cable designs are known to be under development, but they would be likely to have a much longer maximum allowable length, and more complex construction.

    USB 1.x/2.0 cable wiring

    Pin Name Cable color Description








    Data −




    Data +






    USB 1.x/2.0 Miniplug/Microplug

    1 VCC Red +5 V
    2 D− White Data −
    3 D+ Green Data +
    4 ID none permits distinction of

    Micro-A- and Micro-B-Plug

    Type A: connected to Ground

    Type B: not connected

    5 GND Black Signal Ground
     PS/2 pinout
    5      6
    3      4
      1  2
    1. KBDAT (data)
    2. not used
    3. GND (Ground)
    4. VCC (+5V Common-collector voltage)
    5. KBDCLK (Clock signal)
    6. not used

    Ethernet is a family of frame-based computer networking technologies for local area networks (LANs). The name comes from the physical concept of the ether. It defines a number of wiring and signaling standards for the Physical Layer of the OSI networking model, through means of network access at the Media Access Control (MAC) /Data Link Layer, and a common addressing format.

    Ethernet is standardized as IEEE 802.3. The combination of the twisted pair versions of Ethernet for connecting end systems to the network, along with the fiber optic versions for site backbones, is the most widespread wired LAN technology. It has been in use from around 1980 to the present, largely replacing competing LAN standards such as token ring, FDDI, and ARCNET.

    Registered jack

    A registered jack (RJ) is a standardized physical network interface — both jack construction and wiring pattern — for connecting telecommunications, or data equipment (commonly, a telephone jack) or computer networking equipment to a service provided by a local exchange carrier, a long distance carrier, or a data network in the case of the RJ45 connector. The standard designs for these connectors and their wiring are named RJ11, RJ14, RJ45, etc. These interface standards are most commonly used in North America, though some interfaces are used world-wide

    The physical connectors that registered jacks use are of the modular connector type, except RJ21X which is a 25-pair Amphenol connector. For example, RJ11 uses a 6 position 4 conductor (6P4C) modular plug and jack.

    RJ11, RJ14, RJ25

    RJ11 is a physical interface often used for terminating telephone wires. It is probably the most familiar of the registered jacks, being used for single line POTS telephone jacks in most homes across the world.

    RJ14 is similar, but for two lines, and RJ25 is for three lines. RJ61 is a similar registered jack for four lines. The telephone line cord and its plug are more often a true RJ11 with only two conductors.

    position RJ25 pin RJ14 pin RJ11 pin Pair T/R ± Cat 5e/6 colors Colors Old colors German
    1 1 3 T + Pair 3 Wire 1 Cat 5e/6 white/green Pair 4 Wire 1 white/green Pair 4 Wire 1 orange Pair 3 wire 1 pink
    2 2 1 2 T + Pair 2 Wire 1 Cat 5e/6 white/orange Pair 2 Wire 1 white/orange Pair 2 Wire 1 Old black Pair 2 ext. bell green
    3 3 2 1 1 R Pair 3 Wire 2 Cat 5e/6 blue Pair 1 Wire 2 blue/white Pair 1 Wire 2 Old red Pair 1 wire A white
    4 4 3 2 1 T + Pair 1 Wire 1 Cat 5e/6 white/blue Pair 1 Wire 1 white/blue Pair 1 Wire 1 Old green Pair 1 wire B brown
    5 5 4 2 R Pair 3 Wire 1 Cat 5e orange Pair 2 Wire 2 orange/white Pair 2 Wire 2 Old yellow Pair 2 ground yellow
    6 6 3 R Pair 1 Wire 1 Cat 5e green Pair 3 Wire 2 green/white Pair 3 Wire 2 blue Pair 3 wire 2 gray


    RJ45 (8P8C) is the more regularly used to connect ethernet adaptros. The connectors are typically used to terminate twisted pair cable.

    RJ-45 conductor data cable contains 4 pairs of wires each consists of a solid colored wire and a strip of the same colorThere are two wiring standards for RJ45: T-568A and T-568-B.

    180px-Uncrimped_rj-45_connector_close-up.jpg    8 pin RJ45 male connector layout

    Straight-through Cable

    If you wish to create a straight-through cable you will have to choose between T-568A or T-568B and have it on both ends of the cable. The straight-through cable is used to connect data terminating equipment(DTE) to Data Communication Equipment(DCE) for example:

    • Computer to switch
    • Computer to hub
    • Computer to router

    Cross-over cable

    If you wish to create a cross-over cable you will have to implement T-568B on one side and T-568A on the other side. We want to use this kind of cable to connect DCE to DCE or DTE TO DTE for example:

    • computer to computer
    • Router to Router
    • Hub to Hub
    • Switch to Switch
    How to Make a Network Cable
    The steps below are general Ethernet Category 5 (commonly known as Cat 5) cable construction guidelines. For our example, we will be making a Category 5e patch cable, but the same general method will work for making any category of network cables.
    Pc as a Radio
     PC control wideband receiver!

    Icom PCR1000

    The PCR-1000 is a wideband radio receiver that is controlled from the PC. In fact it can only be controlled from a PC. The PCR 100 is similar but lacks SSB reception.

    ICOM state this: -

    • Wideband Coverage:100 kHz - 1.3 GHz*
    • All Mode: AM, FM, WFM, SSB, CW
    • Tunable Bandpass Filters for VHF/UHF bands
    • Unlimited Number of Memory Channels
    • Digital Auto Frequency Control (AFC) Circuit to compensate for frequency drift in FM mode
    • Auto Mode Function: you input a frequency, the IC-PCR1000 selects the correct mode
    • Real-Time Bandscope
    • IF Shift
    • Voice Scan Control (VSC) Function
    • High Performance PLL Circuit
    • S-Meter Squelch
    • Large Selection of Tuning Steps Available
    • Noise Blanker
    • A Variety of Scans
    • Tone Squelch
    • Optional UT-106 DSP
    • RF Attenuator (20 dB)
    • Automatic Gain Control (AGC) Function for SSB, CW and AM Modes
    • External Speaker Level Converter

    When using the USB serial adapter cable, USB serial port can be used. It is necessary to USB driver installation. The driver is supplied with the USB serial adapter cable.

    TNC connection

    The IC-PCR1000 can receive 9600 bps packet communication (AFSK). Connect the TNC (Terminal Node Controller) as follows.




     Pc as a Satelite Receiver



     Using a PC as a Satellite receiver and PVR

    Satellite DVB cards work similar in a way to TV Tuners with the exception that Satellite DVB cards work solely on Satellite reception. As the broadcast remains in digital all the way to the PC unlike with analogue TV tuners, both the picture and recording quality remains the same as what is broadcast from the source.

    The most popular satellite PCI based DVB card is the Skystar2. With this card and suitable drivers and software, this can pick up a wide range of content as well as handle various symbol rates, audio & video encoding and send out Diseq 1.0 & 1.2 signals for motorised and multi dish setups. Note that the Skystar2 does not provide support for a Common Interface.

    Some of the more advanced satellite DVB cards offer Common Interface support where the user can plug in a CAM and thus tune premium or subscription content on their PC.

    The minimum PC requirements for viewing satellite content is a 900MHz Pentium III or AMD with at least a 2x AGP graphics card (4x recommended).

    The APT-06 was especially designed to receive Polar Orbiter Weather Satellites in the  VHF frequency range. It feeds the received image data into the sound input of a PC or laptop computer for further processing so that an automatically operating weather satellite image reception station can be set up. Besides automatic operation, the APT-06 also offers manual control capability, which is helpful especially during setup and for experiments. Furthermore the APT-06 package comprises the Windows software program APT-CONTROL, which can be operated in a separate window besides the image decoding program. It allows detailed frequency- and other remote control functions on the APT-06.


    The days of guessing the weather by looking at the clouds overhead have just ended. Now you can look at the clouds from above! This project will allow you to receive pictures from satellites 600 km overhead. A typical NOAA satellite can cover nearly 1/16 of the earth in a single pass! In New York, we are able to clearly capture images from mid-Hudson bay (where there was still ice in late spring), all the way down past Cuba, as well as spanning from Wisconsin to far out in the Atlantic Ocean. The clarity of the image was enough to see the individual Finger Lakes (in New York), and shadows on the underside of thunderstorms.

    This receiver kit allows you to receive weather satellite transmissions on the VHF band, where most of the polar-orbiting satellites are located. You will recognize these transmissions on the news when you see the time lapse of the clouds darting across the countryside. The weather man in this case has taken multiple images on the computer, aligned and pieced them together, and then run through one image after the other. It is possible to do this same thing with this kit and the proper software.

    The way in which a weather satellite works is fairly simple. Just think of your office fax machine as an example. The satellites circle the Earth going north to south back to north again almost directly over the poles, which is why they call it a polar orbit. This means that the satellite will cover every location on the Earth at least twice per day. With a good antenna, and partly because of overlap of consecutive orbits, you can conceivably receive the same satellite up to six times a day! Notice though that the image received from polar orbits will be upside down on every other pass.

    The satellite retrieves the data in a linear fashion, one line at a time using a

    scanning radiometer
    . The scanning radiometer transmits the equivalent of a single television horizontal line as the satellite circles the earth. The system uses a series of optics and a motor driven rotating mirror system to receive a very narrow line of the image of the Earth. Each line is received at a right angle to the satellite’s orbital track, so as the satellite circles the earth, a line is received from west to east or east to west depending on the orbit of the satellite. The total image is received from north to south or south to north depending on the orbit also, and this motion is what relays the equivalent of the vertical scan in a television. You can continue receiving this satellite as long as it is within the line of sight.

    Since all of the receivable satellites are similar, we will describe the ones you will most commonly receive. The NOAA/TIROS satellites, during the first half of the transmission, send visible light data to the receiver at the same time they are taking in the view. Meanwhile during the same part of the scan, they are recording the infrared view. During the second half of the scan, while the sensors are facing away from the earth, it sends the infrared data. The user then sees the data as two images side by side, on the left the visible light data is seen, and on the right, infrared data is seen. In between the images are synchronization pulses that help computers to align the individual lines precisely.

    These particular satellites continuously transmit an FM signal modulated with a 2400Hz tone. This tone is very precise in frequency so the image seen is aligned properly. The 2400Hz tone is AM modulated with the intensity of the current view of the earth. The brighter or colder the point on the earth, the higher in amplitude the 2400Hz signal is.

    The receiver demodulates the FM signal and retrieves the 2400Hz tone. The detector board in the computer will then find the peak amplitude of each wave of the 2400Hz tone, and each peak, upper and lower now represents a single pixel on the screen. For the NOAA/TIROS satellites, each horizontal line represents 2400 pixels, since the incoming frequency is 2400Hz, and the scanning radiometer rotates twice per second. The full 12 minute pass of a NOAA satellite requires approximately 3.5 MB (3.5 million 8 bit pixels) of storage! This is much more data (pixels) than can be seen on a super VGA screen at any one time. NOTE TO NEWCOMERS: If you are a first time kit builder you may find this manual easier to understand than you may have expected. Each part in the kit is checked off as you go, while a detailed description of each part is given. If you follow each step in the manual in order, and practice good soldering and kit building skills, the kit is next to fail-safe. If a problem does occur, the manual will lead you through step by step in the troubleshooting guide until you find the problem and are able to correct it.

    Building a Weather Satellite Station

     The Introduction provides information about:
    System 1

    First setup

    Our apartment was in the center of Stockholm. The antenna was mounted on our balcony and connected by a cable running through the window to a laptop running on our kitchen table!

    Unfortunately, the "field of view" to the sky was very limited by the buildings surrounding our courtyard. Combined with the bad weather of winter and the short days, the images from home were dark and short (see one above).

    However, this first setup was still a lot of fun, especially when I first managed to hear the 'tick-tock' sound of the NOAA satellite AM signal.

    When the same system was set up at the institute with the antenna on top of the building we obtained much better pictures. (See example above.)

    Setup: a basic system as show above consists of the following:

    • Antenna - for the apartment we used a discone, which is useful for a wide range of signals but crossed dipole or QFH (quadrifilar helix) are normally recommended for APT reception. These cost as low as $50-100 range.
    • Receiver - a typical consumer shortwave scanner will not work well for APT satellite reception. The IF (Intermediate Frequency) bandwidth is either too wide or too narrow. (Ideally, it is 42Khz.) So we purchased an Icom IC-PCR1000 [Update Nov.1.08: Icom now offers the PCR1500 in place of the PCR1000.] receiver that is controlled from a PC via a serial port connection. Its IF bandwidth can be set as desired from the control program.
    • PC with sound card - the PC controls the receiver and uses the sound card to decode the image signal from the receiver's audio output.
    • Software:
      • Radio control - the PCR1000 comes with a control program but we more often used RadioCom 3.0 (now available in version 5.0), which has many features useful for all kinds of shortwave scanning. (RadioCom screen image)
      • Image decoder - the audio from the receiver must be decoded to obtain the weather sat image. We used the freeware WXSAT progam in this setup. It can run directly from the sound card or from a WAV file. (WXSAT screen image)
      • Satellite tracker - the NOAA polar satellites crosses overhead about twice during the day. (Areas, like Sweden, near the poles can see them more often.) Currently two of the NOAA satellites are active (NOAA-14 & NOAA-15). So one must know when the pass will occur and how high in the sky it will be above the horizon. Therefore, a tracking program is needed. There are a number of such programs, both freeware and for purchase, with a varying range of features. Here we used the WinOrbit freeware program. .(WinOrbit screen image)
                                                      System 2

                                                      The second setup was basically the same as the first but switched Henry's receiver with the Icom. The frequency selection was done on the box rather than from the computer. This setup was used only at the institute with the antenna on the roof.

                                                      This receiver was optimally built for APT reception and we got our first really nice image with it. (The System 1 images actually came after the one above.)

                                                      System 3

                                                      First setup
                                                      System 3 still used the PCR1000 receiver and the same antenna. However, we replaced the decoding by sound card with a commercial interface box and its software from Timestep in Great Britain [Update Nov.1.08: Timestep has updated some of the following hardware/software.] :
                                                      • PROsat LC Interface - this box receives the audio output from the receiver and decodes the image.
                                                      • Software:
                                                        • PROsat for Windows - this program environment talks to the LC interface. It combines the image decoding and handling with a satellite tracker. The satellite tracking program runs as a child window within PROsat and will monitor when a selected satellite will comes in range. (PROsat screen image)
                                                        • Receiver control - the receiver still needed a separate control program such as the Icom program or RadioCom 3.0.

                                                      System 4

                                                      First setup

                                                      This receiver can scan several frequencies to look not only for the NOAA satellite transmissions but also those from the Russian METEOR, OKEAN and SICH satellites. (Sweden is close enough to Russia to pick up the signals when the latter two satellites download their data.)

                                                      [Update Nov.1.08: Timestep has updated some of the following hardware/software.]

                                                      • PROscan APT Receiver - designed specifically for APT reception, this unit can scan for transmissions from more than one satellite.
                                                      • Preamplifier - this device is added at the antenna to boost and filter the output of the signal before it propagates through 30 meters or so of cables. It helps to improve the signal to noise ratio and get sharper pictures.
                                                      • PROsat LC Interface - same as in System 3
                                                      • Software:
                                                        • PROsat for Windows - the same program environment as in System 3 can also control the PROscan receiver. One can arrange a scheduling feature such that images from selected satellites, and only when above a minumum elevation, are recorded and saved to disk automatially.

                                                      The APT visible image data is in grey scale, not color. That is, a numerical value is assigned to a pixel (the smallest image element) according to it's brightness.

                                                      However, it's found that similar features tend to have similar grey values: dark areas correspond to water, medium grey to land, and light to clouds. Thus, you can assign blue, green, white to these respective areas and get a colorful image that more or less looks plausible.

                                                      More sophisticated algorithms include the IR image data to provide additional clues to what color to assign a particular area.

                                                      However, it should be clear that there is a large degree of "art" to making these color images.

                                                      For example, different "color palattes", i.e. what color is applied to what grey level, will produce significant differences in the images. Also, typically, one will apply various filters to the images to sharpen them and reduce the background noise. In what sequence the filters and colors are carried out can result in big variations.

                                                      Note that in the above image, the green areas correspond fairly well with the land areas. However, just below Great Britain we see that France has melted out into the ocean. The grey scale of a mix of clouds and water were just not sharp enough to avoid this mixup.

                                                      System 5

                                                      Our fifth system became a full weather satellite ground station system (see below) with the addition of the capability to receive geostationary satellite images. The higher frequency transmissions required a parabolic dish and an additional receiver

                                                      We chose to look at the images transmitted in the WEFAX format by the European Metosat weather satellites (WEFAX is also sent the NOAA GEOS satellites.) This is a format that is roughly similar to the FAX format.

                                                      A 1691MHz signal carrys images in the visible and infrared and for different regions of the hemisphere seen by the satellite.

                                                      The image transmissions of a given region are repeated periodically, as often as every 30minutes, so that an animation of the weather for that region can be accumulated over several hours.

                                                      A 90cm dish antenna with a low noise preamplifier mounted directly on the dish was used to pick up the signals.

                                                      The Timestep WEFAX receiver takes the 1691MHz input signal and outputs an audio signal to the PROsat interface box.

                                                      The PROsat program can thus obtain images from both the polar orbiters and GEO sats. The program includes various tools for handling the GEO images and for building animations

                                                      Weather Satellite Receiver

                                                      The Weather Satellite Receiver with its QFH antenna works with special software installed on your PC to form an ideal weather monitoring station.You can use it to receive data from the NOAA series of orbiting satellites. The satellites that are currently active are NOAA12, 15,17 and NOAA18, these satellites are operated by the U.S Governments National Oceanic and Atmospheric Administration.

                                                      There are other satellites operated by Russia and the Ukraine that could also be received.


                                                      Special requirements for the weather satellite antenna

                                                      Since the satellite signals come from all directions, we need an antenna that will pick up signals from all around. Here, “all around" means the entire hemisphere of the sky (with respect to our current location). Conventional antennas with their directional characteristics tend to be very poor for receiving satellites in polar orbits. Satellites in polar orbits transmit radio waves with circular polarization. The receiving antenna must have the same polarization. A distant satellite situated over the Mediterranean, Spain or Scandinavia (with respect to Germany) will have a relatively flat angle of incidence and will be received primarily with linear polarization. As the satellite gets closer, the elevation angle will increase and the polarization will become increasing circular

                                                       A QuadriFilar Helix (QFH) antenna is well suited to receiving such signals.


                                                      Configuration example for a weather satellite receiver station for polar orbiter (NOAA) satellites.  To avoid interference, the antenna should be mounted in some distance from the computer.

                                                      Power comes either from the supplied power-adaptor or any other 12-V DC source (only about 150 mA).   DC for the antenna KX-137 is automatically supplied throught the coaxial antenna cable from the WRX-137 receiver. Frequency selection is either manual or automatic, controlled from the PC software

                                                      Portable Weather Satellite Receiver System WRAASE

                                                      Configuration example of a portable satellite receiver station for NOAA polar orbiter satellites. The tiny MX-137 with its removable and flexible antenna sticks outperforms many other, much bigger antenna constructions.

                                                      Yacht-Set for polar orbiter satellites (NOAA), consisting of:

                                                      • Receiver APT-06 with 12 V DC power input,
                                                      • Image reception software (feeds PC sound input)
                                                      • Active antenna  MX-137,
                                                      • 230V AC power adaptor
                                                      • Sound-data cable, serial data cable.
                                                      • 20m antenna cable, complete with plugs


                                                      Ultra wideband coverage

                                                      The IC-PCR1500 is a PC control receiver and all functions are controllable from your PC. Explore radio signals from all over the world from 0.01 to 3299.999MHz*

                                                      WXtoImg Software
                                                      The world's best weather satellite (WXsat) signal to image decoder.

                                                      Simply connect a 137-138MHz FM communications receiver, scanner, or weather satellite receiver to your soundcard and get stunning colour images directly from weather satellites. The only other item you'll need is an antenna for receiving the circularly polarised signals
                                                      WXtoImg is a fully automated APT and WEFAX weather satellite (wxsat) decoder. The software supports recording, decoding, editing, and viewing on all versions of Windows, Linux, and Mac OS X. WXtoImg supports real-time decoding, map overlays, advanced colour enhancements, 3-D images, animations, multi-pass images, projection transformation (e.g. Mercator), text overlays, automated web page creation, temperature display, GPS interfacing, and computer control for many weather satellite receivers, communications receivers, and scanners.
                                                      Active VHF-ANTENNA for on-board reception of polar  orbiter weather satellites
                                                      Portable VHF-Satellite Antenna, with built-in low-noise preamplifier and Hi-Q-filter 137-138 MHz. Small size, light weight, flexible elements, especially designed for on-board use.
                                                      MX-137 Weather Satellite Antenna
                                                      For on-board operation regular full-size satellite antennas are in most cases too large and too weather-sensitive. The MX-137, however, being especially designed for this, has only about half the size with its flexible and very sturdy elements. Due to a built-in very low-noise preamplifier, a high-Q-filter and a well designed matching circuit, reception performance and stability is  nearly equal, sometimes even better than with regular full-size antennas.  DC-power for the preamp is fed through the coaxial from the receiver (WRX-137 or APT-06).  All sensitive components are contained in a  water- and UV-resistant sturdy box, the mast mount is stainless steel only and the connector is a watertight N-type

                                                      Weather  Satellite Antenna WRAASE MX-137

                                                      • Maximum size between the ends of the elements:  48cm
                                                      • Size antenna-box: 13,5cm x 7,5cm x 10,5cm
                                                      • Weight with mastmount: 0,6kg
                                                      • Internal low-noise preamplifier 17 dB gain 
                                                      • Internal Hi-Q-Filter, suppresses unwanted strong signals from the neighborhood.
                                                      ANTENA HELIX CUADRIFILAR
                                                      Antena de alta performance de VHF con alimentación coaxil.
                                                      AluminoT6064 de alta resistencia, pintura epoxi UV.
                                                      Opcional, Preamplificar de antena incorporado.
                                                      Resistente al agua
                                                      Tipo de antena Heliax cuadrifilar ½ lambda
                                                      Polarización Circular derecha
                                                      Ganancia 4db
                                                      Frecuencia 137-138 Mhz
                                                      ROE Mejor 1.5:1
                                                      Diámetro 350mm
                                                      Peso aprox. 1,5 Kg
                                                        Pc as NAVTEX Receiver
                                                        What is Navtex?

                                                        NAVTEX is a system for the broadcast and automatic reception of maritime safety information by means of a narrow-band direct-printing telegraphy. NAVTEX provides shipping with navigational and meteorological warnings and urgent information through automatic printouts from a dedicated receiver.

                                                        NAVTEX is a component of the IMO/IHO Worldwide Navigational Warning Service (WWNWS) defined by IMO Assembly resolution A.706(17). It has also been included as an element of the Global Maritime Distress and Safety System (GMDSS). Since 1 August 1993, NAVTEX receiving capability has become part of the mandatory equipment which is required to be carried in certain vessels under the provisions of the International Convention for the Safety of Life at Sea (SOLAS).

                                                        How does it Work?

                                                        NAVTEX transmissions are sent via a single frequency from localized stations situated worldwide. The power of each transmission is regulated so as to avoid the possibility of interference between transmitters. Users can set their NAVTEX receivers to receive
                                                        specific message types and reject others. Messages such as navigational and meteorological warnings and search and rescue information are non-rejectable to ensure that ships equipped with NAVTEX always receive the most vital information. Users can choose to receive information from the single transmitter that serves the sea area around their position, or from a number of transmitters. If you would like to know more about how NAVTEX messages are created and transmitted you may find this pictorial representation helpful.
                                                        NAVTEX Coverage

                                                        NAVTEX messages are transmitted worldwide from local stations, the number of stations grows month by month. We have produced a
                                                        NAVTEX Database which provides details about all known NAVTEX stations, details include name, position, range, and operational status.
                                                        PC/USB Navtex receiver!

                                                        For those of you cruising coastally this new NAVTEX receiver that needs nothing other than a USB slot in your PC may be pretty exciting for your weather needs. No price listed. Any of our Euro cruisers like GIU know how much these cost or have an info on these guys?? Needs no antenna and powered by your PC


                                                        The PC Navtex Pro is a two channel navtex receiver designed to operate on your personal computer. It will receive navtex message even without your PC connected. Navtex messages are stored in a vast internal memory for you to dowload when you get on board. Down loading is quick and the software provided allows you to select the messages you want.

                                                        Leave the unit on 24/7 then, when you get on board, just plug in your PC and immediately download the latest weather forecast from your local station, or any other message stored in the PC Navtex Pro's memory.

                                                        • 518 and 490kHz message reception.
                                                        • Supply voltage nominal 12v DC consumption.
                                                        • Connects to standard Nasa Navtex antenna (supplied)
                                                        • Supply voltage 10 to 16 volts DC
                                                        • Supply current 20mA
                                                        • Dimensions 115 x 100 x 30mm
                                                        • Antenna 195mm long (complete with 7 metre cable) 
                                                        Nasa Navtex Pro Engine - Navtex for PC
                                                            Pc as AIS Receiver
                                                          AIS reception with a PC
                                                          PC with soundcard
                                                          • A receiver with a discriminator output or 9600 bps packet radio output
                                                          • An audio cable between your receiver and PC
                                                          • A PC with soundcard, runningthe appropriate software:
                                                            - Shipplotter, a complete solution. Or
                                                            - AISMon with navigation software like SeaClear or
                                                              WinGPS. This requires somewhat more computer
                                                              knowledge to configure.
                                                          Be advised that your receiver should not be scanning when you want to receive AIS, since it would miss AIS transmissions (hence ships) while scanning other frequencies.

                                                          If you use a marine VHF, it should be on channel 87 or 88 constantly. Since it can't be used for normal traffic while monitoring AIS, it is advisable to use a (cheap) scanner or a second marine VHF for AIS.

                                                          PC with serial port

                                                          AIS reception with a PC
                                                          • A dedicated AIS receiver, like the NASA AIS Engine or the SR161/SR162. These receivers contain a microprocessor that translates the raw AIS signal into NMEA sentences
                                                          • A PC with a serial port, running navigation software to process the NMEA sentences, or an AIS plotter
                                                          This (more expensive) option is out of scope for this website, which focuses on using a (cheap) scanner or marine VHF.

                                                          AIS is a transponder system for ships intending to increase the safety at sea. It operates in the VHF band. The two frequencies used are 161.975 and 162.025 MHz.

                                                          An AIS transmitter regularly transmits the ship's position, heading, speed and MMSI (the unique maritime identification number). This data is received by ships in the vicinity. The data can be plotted automatically on a digital map or radar screen. 

                                                          Every 2 - 10 seconds, a ship equipped with AIS e.g. transmits the following data:

                                                          • MMSI number
                                                          • Navigation status, e.g. 'at anchor' or 'under way'
                                                          • Ground speed, from 0 to 102 kts in steps of 0,1 kt
                                                          • Rate of turn, 0 to 720 degrees per minute
                                                          • Position
                                                          • Heading and Course over Ground
                                                          • Time stamp
                                                          Furthermore, every six minutes the following information is transmitted:
                                                          • MMSI number
                                                          • Callsign
                                                          • Ship's name
                                                          • Type of ship or cargo
                                                          • Dimensions of the ship
                                                          • Draught, 0.1 to 25.5 m
                                                          • Destination
                                                          • Estimated time of arrival (ETA) at destination (captain's discretion)
                                                           NASA AIS Engine

                                                          NASA AIS Engine

                                                          All vessels over 300 tons and all passenger vessels are obliged to carry an AIS transponder. The Nasa AIS engine receives these transmissions an converts them to NMEA format for use with PC chart plotting programs and dedicated chartplotters.

                                                          The unit is supplied with a 12 volt power cable and a 9 pin serial computer cable. For convenience the engine can also recive NMEA information from a GPS receiver (at 4800 baud) which it then sends on to the display with the AIS data (at 38,400 baud).

                                                          If you Laptop does not have a RS232 Serial port, a USB to Serial adaptor will be required. - See related products.

                                                          Supplied with SeaClear II PC Plotter CD Software

                                                          The AIS Engine requires NMEA input from a GPS and a marine VHF antenna (not supplied). The antenna can be either a dedicated antenna or the output from an antenna splitter such as the EasyAIS splitter.

                                                          The AIS Engine is not watertight so it must be mounted in a position, which is dry at all times.

                                                          As few display units will have a socket for both a GPS receiver and an AIS Engine so provision has been made in the Engine to reply the GPS position.

                                                          SeaClear software is freeware and is given freely with the AIS Engine. It is a PC based chart plotter for Windows 2000/XP/NT/95/98/ME. With a GPS connected it displays the current position, speed, heading and other data on the screen. The chart is repositioned and new charts are loaded automatically as needed. Tracks may be saved to file for later reviewing and log book entries can be manually and automatically entered. Unlimited number of routes and waypoints can be created and used to assist the navigation. The screen area for charts is maximized with most functions accessed with the right mouse button. Zooming is provided with support for IntelliMouse wheel. SeaClear is created for nautical navigation but can probably be used for other navigation needs.

                                                          Version 2 includes improved connector layout for easier installation and indicator LED's for easy diagnostics.
                                                          • Operating frequencies - 162.025 and 161.975 mHz (2 Channel)
                                                          • Supply voltage - 10 to 16 volts DC
                                                          • Supply current - 43mA
                                                          • Messages relayed - 1, 2, 3, 4, 5, 11 and 21
                                                          • Antenna input - 50 ohm BNC
                                                          • Data converter - 9 pin "D" type
                                                          • Mounting - via two moulded flanges
                                                          • Dimensions - 115 x 100 x 30mm
                                                          • Output format - NMEA 2000/0183 (38400 Baud) VDM encapsulation string conforming to ITU-1371
                                                          • Required Input - NMEA RMC from GPS
                                                           Nasa AIS engine install
                                                          AIS (Automatic Identification Systems) are radio signals sent out by vessels indicating position, speed, heading, destination etc. The signals from these transponders can be picked up by an AIS receiver and the information overlayed on a chart plotter. The NASA AIS Engine is a "black box" unit, which receives these VHF signals and converts them to NMEA messages which can be read by a suitable chart plotter. Version 2 receives the Class A signals which all commercial vessels over 300 tonnes (and a lot of smaller ones) broadcast, and Class B which is for leisure boats 

                                                          What You Need

                                                          You need the AIS Engine, a standard VHF aerial, a BNC plug and this web site to explain what to do, because you won't find the NASA instruction manual, sorry - scrap of paper, much use. For some reason the AIS engine has a BNC socket instead of a standard VHF aerial socket so you will need a suitable 50 Ohm plug - a few pence from Maplins or a lot more from a chandlers. Any VHF aerial will do, although I chose to match my existing VHF radio aerial so I have a flashy pair.


                                                          This is the easy bit. Find somewhere hidden, like behind the dash, and screw the unit to a bulkhead with two screws. Fit the BNC plug to the VHF cable and connect it to the unit. Add power (fused), and plug in the data cable. If your chart plotter has a socket to match the cable you are laughing, otherwise you will need to cut the cable and make your own connections.

                                                          Connecting Up

                                                          I connected the AIS engine to a Garmin GPSMAP 4008, which provides a number of NMEA ports for data in and out. Other chartplotters will have similar configurations. You will need to connect the AIS data cable screen wire to the negative of your boat wiring loom. The black wire is connected to the + wire of one of the NMEA Data In Ports of the chart plotter. The - wire of the NMEA Data In Port is also connected to the negative of your boat wiring loom. That is all you have to do - solder and heat-shrink tube is the recommended method.The AIS engine has two LEDs, one for power and one for data. If red is on and green is flickering, you know that bit is working fine


                                                          Again, easy when you know how. All you need to do on the Garmin unit is to tell it that the NMEA port you chose for the AIS signal is High Speed, then everything else is automatic. This vital snippet of information is well hidden in the Garmin manual so it had me struggling for a long time.


                                                          On the Garmin unit everything is automatic. By selecting "Other Boats" in the Information page, you see a list of vessels transmitting AIS signals, and you can select any of them for more data. More useful however is the chart image itself. The vessels are now shown in their actual positions, with a heading line and a label. You can set an alert so you are warned if a vessel is within a pre-set danger zone and a potential hazard. The most valuable element is the MMSI number, which is displayed on the Alert and on the vessel data. This means you can call the ship's bridge directly if you need to alert them to your existence. The last image on the right shows the display as I am following the 110metre tanker Shinousse which is heading away from me at 12 knots - all this is shown on screen.

                                                           Garmin GPS with Nasa AIS screen
                                                          internet on Board
                                                           Banda Larga Móvel
                                                          Os equipamentos de Banda Larga Móvel permitem o acesso à Internet, de forma simples e rápida, em qualquer computador em qualquer lugar!
                                                          A rede 3G Banda Larga da  permite aceder à Internet a velocidades até 3,6 Mbps ou 7,2 Mbps nas principais cidades do país. Na maioria das restantes localidades as velocidades vão até 1,8 Mbps. Garantimos sempre o acesso à rede de maior velocidade disponível

                                                          Vodafone Wi-Fi é um serviço de comunicação de dados através de radiofrequências, baseado na tecnologia Wireless LAN, utilizada para acessos de Banda Larga à Internet.

                                                          Pode utilizar este serviço nos vários pontos de acesso (hotspots) disponíveis em todo o País
                                                          Satellite Phone & Internet 
                                                          Inmarsat is a global satellite communications system offering highly reliable mobile phone, fax, and data communications.  Its new Broadband Global Area Network (BGAN) uses incredibly small terminals -- weighing as little as 2.2 lbs!  Now you can carry the same internet and voice services you have come to expect when you are at home or at the office -- almost anywhere on earth


                                                          Inmarsat Global Area Network (GAN) and Inmarsat Mini-M
                                                          GAN offers voice, 64 kbps ISDN, 3.1 Khz audio ISDN, and other services.   Inmarsat Mini-M offers voice, fax, and 2.4 kbps data.  The coverage area for these services is shown below as indicated by the light blue shaded "spot beam" coverage areas.   Inmarsat M offers voice, fax, and data in the "global beam" coverage areas indicated by the large oblate pink, red, yellow and blue circles.  A variety of terminals have been manufactured for land portable, vehicular, and marine applications.  Generally this equipment in no longer manufactured because it has been replaced by newer Inmarsat BGAN or FLEET equipment.  Outfitter Satellite occasionally has used Inmarsat M4 (GAN), Inmarsat Mini-M, and Inmarsat M equipment for sale