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  Integrating GNSS Receiver, DSC Radio, and Chart Plotter

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Author Topic:   Integrating GNSS Receiver, DSC Radio, and Chart Plotter
jimh posted 04-13-2012 09:04 AM ET (US)   Profile for jimh   Send Email to jimh  
Today a small boat will commonly have a digital selective calling (DSC) VHF Marine Band radio, a global navigation satellite system receiver (GNSSr), and a chart plotter (CP). To make optimum use of the capabilities of these devices, the three should be interconnected. The general plan for the connections is a follows:

GNSSr ---> [your boat's position data] ---> DSC transmitter

DSC receiver ---> [other boat's position data] ---> chart plotter

The first link will allow your GNSSr to sent position data to your DSC radio transmitter. This is critical for safety. All DSC trasmitters have an EMERGENCY broadcast button that sends a distress signal. The distress signal will also send you boat's position if the position information is available from your GNSSr.

The United States Coast Guard reports that only ten percent of the distress calls being sent to them via DSC include the vessel position. This means that nine out of ten boaters do not have the DSC radio properly connected to a GNSS receiver. (See for more details.)

To provide position data to a DSC radio there are two general options:

--the position data can be manually entered into the DSC radio by the operator

--the position data can be electronically entered into the DSC radio using a NMEA protocol and interface

While the manual entry of the data is possible, this method is of little practical value. The only practical method is to provide the position data to the radio electronically using a NMEA protocol and interface, and DSC radios will have a NMEA interface. The most common is a NMEA-0183 interface, but a few radios will have a NMEA-2000 interface.

The second link (mentioned above) allows the DSC radio receiver to send information it has received from other boats to your chart plotter. The most significant information will be the position of another boat that may be in distress. Most modern chart plotters can utilize position information received from a DSC radio to plot the position of another boat on your boat's chart potter. With this integration of your radio and chart plotter, you can immediately see the position of a boat in distress whose DSC emergency broadcast your have received. The information for this second link is also sent by NMEA protocol and interface. Unfortunately, many times boaters do not bother to provide for this second interface.

It is quite common on a small boat that the GNSSr and the chart plotter are contained in the same assembly. This means that the NMEA interface for the GNSSr and the chart plotter are probably provided on the same accessory wiring cable. The electrical connection for the second interface is typically nothing more than connecting a few wires in the same cables used to make the first interface. Adding the second link for the radio-to-chart-plotter will entail just a few moments of extra effort in the integration of the three devices, but it will add a very nice function to the system.

jimh posted 04-13-2012 09:33 PM ET (US)     Profile for jimh  Send Email to jimh     
If your GNSS receiver, DSC radio, and chart plotter are all NMEA-2000 devices the interconnection between them is very simple: you just connect all three to your network backbone. If your GNSS receiver, DSC radio, and chart plotter are not all NMEA-2000 device, then you will have to make specific connections between them using NMEA-0183 serial data ports and protocols.

If you need to use NMEA-0183 connections, the arrangement of the connections is going to be much more complicated than if NMEA-2000 is used. Although the NMEA-0183 defines many elements of the connections and protocols, there is not much conformity among manufacturers for the serial port configuration and the color of the wires used in the cables. I have developed a universal method for interfacing NMEA-0183 devices. See:

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