NMEA Multiplexer

The NDC-1 is no longer in production. Please see the current NDC-4 model.







Why would I want or need an NMEA Data Multiplexer?

The NMEA 0183 standard allows any suitably designed marine electronic device to share its gathered information with any other device on a vessel. Unfortunately, there is one very large drawback with this standard - only one device on a connected network can actually send data (a single 'talker' device), with multiple devices (determined by the current limit of the sending unit) listening to that data (multiple listeners).

If the vessel owner has an instrument that ideally requires the data output of two or more devices, for example a chart plotter, then the owner has no alternative but to settle on connecting only the most important device, usually the GPS.

What happens if the owner prefers the vessels gyro compass output to that of the GPS, or requires that the current depth be displayed on the plotted chart to help avoid the possible case of running the vessel aground on a shifting sand bank? The NMEA 0183 standard cannot supply an answer to those questions: "one transmitting / talking device only".

The Actisense NMEA Data Multiplexer's can solve all these problems and more with their simple, easy and flexible designs.

Can I use an NMEA Autoswitch with my NMEA Data Multiplexer?

Yes, is the simple answer. The Actisense NMEA Autoswitch has been specifically designed to work together with the NMEA Multiplexer / Combiner to create a complete NMEA system solution.

The normal NMEA system would have an Actisense Autoswitch connected to two (or more) GPS / Depth sounder units. The Autoswitch adds a special NMEA tag to the data that passes through it to help identify which of these GPS / Depth sounder units supplied the NMEA data.  

The autoswitched NMEA output is connected to one of the NMEA Data Multiplexer's inputs. In this way the highest priority device's NMEA data is autoswitched into the complete NMEA system and the actual device supplying the NMEA data can be determined (and displayed if required and possible) to help the user.

How can the NMEA data Multiplexer reduce the congestion on my NMEA network?

Some NMEA instruments output a large number of NMEA sentences every period (usually 1-3 seconds), some of which are of no use to the average boat owner and just clog up the NMEA network. GPS units are especially guilty of this and not all allow the user to reduce the number of unwanted sentences that are transmitted. Of those that do, the procedure can often be fiddly and time consuming.

The Actisense NDC-1 and NDC-2 can filter the incoming NMEA data to remove any sentences that are deemed unnecessary by the user. Each input port has its own 'Inclusion List' which it uses to stop any NMEA sentences that are not on the list from appearing on the combined NMEA output port. If you do not require the ability to filter out unwanted NMEA data, then please view the Actisense NDC-3.

end faq

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