Frequently Asked Questions


Q: Can I only use a NMEA multiplexer with a computer?

A: No, not at all. There are many applications for NMEA multiplexers without a computer. Example: to combine output from a GPS and a wind instrument as input for an auto pilot.

Q: Why cannot I connect instruments, a VHF radio etc. directly, in parallel, by combining the NMEA OUT wires?

A: This will never work. The output of instruments connected this way would "collide" and garbled data would be the result. The general rule is: Inputs (listeners) can be combined (max 4) to receive the same data from one output (talker) port, but talkers can never be connected in parallel to a single input (listener) port. This can only be achieved with a multiplexer/combiner.

Q: How do I know if I need a multiplexer?

A: There can be many reasons for installing a multiplexer. The most basic application is combining data from up to 4 NMEA "talkers" to a single data stream to feed into an NMEA "listener" that only has a single input port. However, Brookhouse multiplexers have many additional functions and a Brookhouse multiplexer is often installed to resolve a specific problem. Example: to convert NMEA sentences so that an old auto pilot still works with a new chartplotter.  

Q: Do I need much knowledge of marine electronics to install a multiplexer?

A: No, only a basic knowledge of  DC electric systems on boats is required. Detailed installation instructions are supplied with each multiplexer. Many Brookhouse multiplexers are owner-installed.

Q: Is a multiplexer necessary if I want to connect instruments to a chart plotter?

A: In many cases the answer is yes. If the instruments have NMEA output and the chartplotter has a single NMEA input port, a multiplexer is necessary to combine the instrument output to a single data stream for input by the chart plotter.

Q: If my instruments are connected via a network such as Raymarine Seatalk or Simrad Simnet, do I still need a multiplexer?

A: Even if the basic instruments such as depth, speed/log, wind instrument are connected via a proprietry network, a multiplexer is often required for connecting additional equipment, such as a DSC VHF radio, an AIS receiver or transponder, an electronic compass, a backup GPS etc.  Most AIS receivers and transponders only support NMEA 0183. The same applies for many popular DSC VHF radios. 

Multiplexer models AIS and AISC

Q: I have connected a GPS to one of the standard NMEA inputs of the multiplexer, but the NMEA OUT 4800 port does not output GPS data.

A: The 4800 baud NMEA OUT port of multiplexer models AIS and AISC is the baudrate conversion output port. With the factory settings this port only outputs  data received from the 38400 baudrate conversion input port. Data from the standard inputs can be included selectively, but a setup is necessary. Use menu option 6 or 7 with the appropriate channel block mask. We strongly recommend you read the document "Baudrate conversion options" carefully before using these special options.


More Q & A's will be added soon