DSC radio NMEA output conversion by
Brookhouse NMEA multiplexer.

 This feature in Brookhouse multiplexers provides a way of automatically plotting another
vessel’s position, obtained with a DSC VHF call, as a waypoint in an electronic chart.


 

In discussions about DSC, the emphasis is often placed on the ability to send an automatic distress call by a single push on a button. However, DSC offers many other advantages and useful features for ship-to-ship communication. As most VHF radios sold today support DSC, these features are becoming available on more and more boats. To be able to use them the radio owner has to obtain a special unique identification code, the MMSI (Maritime Mobile Service Identity).

The radio supplier can usually tell where to apply for an MMSI code.

With the MMSI number programmed in the VHF radio, besides digital calling for voice calls, features such as Position Request and Position Send become available.
There are many situations in which these features can be extremely useful. For example with a Position Request DSC call, which takes only a few seconds, the lat/lon of another vessel can be obtained, human error-free and fast. A great advantage in SAR operations or simply to find out where your “buddy” is to arrange a rendez-vous.

The position received in the Position Response is displayed on the LCD screen of the requesting radio and most radios output the position data via an NMEA output port.

The NMEA sentences generated for this purpose are DSC and DSE. A number of chart plotters support these sentences, but far from all. Even if these sentences are supported, the other vessel’s position cannot always be plotted in the chart. There are many popular navigation software packages that lack the support of the DSC/DSE sequence.


 
 

 
It is now possible to convert the DSC/DSE sequence to a standard WPL (waypoint) NMEA sentence with the Brookhouse multiplexer. The MMSI number of the other vessel plus the time of the position report are used as the waypoint name. The WPL sentence is supported by most chart plotters and navigation software for importing waypoints.

Chart plotters and navigation software often do not process the WPL if it occurs in the normal NMEA input stream. The software has to be set in “Waypoint Import-mode” first. If this is done the moment before the Position Request is issued from the radio, the waypoint will be received and plotted in the chart. The software or chart plotter can now return to normal operating mode and the waypoint can be made active for navigation, if required. It is all done in seconds with a few mouse-clicks.

The original DSC/DSE sequence is also transmitted by the multiplexer.
The generation of the WPL sentence is achieved by a small user-uploadable script. The firmware version installed in multiplexers shipped after Nov 9, 2007 is required. The DSC/DSE sequence is standard NMEA, but there can be small differences in the format between different VHF radios. The conversion to WPL has been tested with Standard Horizon DSC VHF radios. If you intend to use this feature with other radios, contact Brookhouse first prior to ordering.