NMEA Combiner /
This Brookhouse multiplexer model has been designed specifically to combine data from an AIS receiver with data from standard low-speed NMEA sources, such as marine instruments and a GPS, to a single data-stream. This single data stream can be fed into a computer or chart plotter via RS232, USB, or via an external blue tooth transmitter.
The standard baudrate of AIS receivers and transponders is 38400 bps (bits per second), whilst standard NMEA talkers transmit at 4800 bps. Brookhouse multiplexer model AIS accepts standard NMEA input at 4800 bps from 3 input ports and a fourth port is dedicated for connection of an AIS receiver at 38400 bps.
The multiplexer transmits the combined data at 38400 bps via RS232 or an optional USB port and has a 4800 bps NMEA output port for connection of an auto-pilot, a DSC radio or other NMEA compatible devices that require input at 4800 bps. A maximum of 4 NMEA listeners can be connected to this port.
Please note that there is a special model Brookhouse NMEA multiplexer AIS-C, which has been specifically designed for use with Raymarine C-series and E-series chart plotters. The functionality is almost identical to model AIS.
The Brookhouse AIS multiplexer has 4 opto-isolated NMEA input ports, one 4800 bps NMEA (RS422) output port, one 38400 bps RS232 output , one 38400 bps RS232 input, optional USB.
For a long time standard Brookhouse NMEA multiplexers have been favorites for connecting multiple NMEA compatible instruments, including AIS, to computers or chart plotters. Based on the experience with typical installations, this new model AIS NMEA multiplexer was developed to take seamless integration a step further.
No other multiplexer or interface available today offers the same degree of integration of computers, chart plotters and marine instruments.
NMEA baudrate conversion
Before multiplexer model AIS became available, the standard Brookhouse multiplexer was already widely used for combining high speed AIS and other (standard 4800 bps) NMEA instrument data. By setting the configurable standard mux' 5th input port to 38400, this port can be used for AIS. The multiplexer's combined output data stream is transmited to the computer or chart plotter at 38400 bps.
However, setting the baud rate of a computer or chart plotter port to 38400 bps to make it suitable for AIS or combined AIS and other NMEA input, affects both the transmitted and received data. Therefore, if the same port is used for NMEA output, the baudrate is too high for feeding standard NMEA listeners. For example, if the navigation software is set up to control an auto-pilot (track mode) to steer to a waypoint or along a route, 38400 bps output from the same port cannot be used for this purpose, because auto pilots do not accept this high baudrate.
The new Brookhouse multiplexer model AIS overcomes this problem by converting the baudrate of the computer's or chart plotter's output back to 4800. The resulting datastream is then output by the multiplexer from a standard RS422 NMEA output port to feed multiple NMEA listeners at 4800 bps.
The baudrate conversion is a separate, independent function of the multiplexer and does not affect the combined output data stream in any way.
Configurable 4800 bps NMEA output
The above explains how the baudrate of the combined output data stream of multiplexer model AIS is 38400 and that return data from the computer or chart plotter is converted back to 4800. However, it is often important to be able to output data from one or more of the standard NMEA inputs at 4800 bps as well. Three configurable modes are available:
The above is described in detail, with diagrams, on the page "baudrate conversion" under Multiplexer features. Mode 2 is also described under "data stream switching".
On vessels with equipment installed over longer periods of time or after (partial) refits, often the problem of NMEA compatibility is encountered.
A practical example: A new repeater instrument is added to an installation with older, but still perfectly l working instruments. The new repeater expects input of NMEA version 3.01, but the instruments produce NMEA v 2.1. Consequently, old cannot “talk” to new and the only solution seems upgrading the old instruments at considerable cost.
A Brookhouse multiplexer makes this unnecessary. All Brookhouse NMEA multiplexers offer a unique feature that allows conversion of NMEA data to adapt different versions to be made compatible with each other. NMEA data flowing through the multiplexer can be modified, using simple instructions that can be entered by the user. Redundant NMEA data can be filtered out, if necessary, to create a clean, efficient data-stream. It is even possible to apply offsets to certain NMEA data (e.g. wind instr. or depth sounder). Details are available in the Brookhouse document ”NMEA data manipulation and filtering” A number of scripts for often required NMEA conversions and adaptions are available from Brookhouse at no charge.
Other features and optional extras.
All standard features described under "Multiplexer features" are included for model AIS and all optional extras are available.
There are many applications for Brookhouse multiplexer model AIS. Integration of the new NSE series Simrad chart plotters with is one example. Click here for a data sheet: NSE integration.
Note: Seatalk is a trade-mark of RayMarine.