Simrad MX612 Junction Box

Simrad MX612 Junction Box (MX612JB) – Commercial Marine Distribution Unit

The Simrad MX612 Junction Box (MPN: 000-10916-001) serves as the central data distribution and power management interface for commercial marine navigation systems. Engineered specifically to interface with the Simrad MX610 and MX612 Control and Display Units (CDU), this unit expands serial NMEA 0183 / IEC 61162-1/2 lines to essential bridge navigation apparatus—including ECDIS, RADAR, AIS transponders, Voyage Data Recorders (VDR), and autopilot steering systems.

Equipped with 12 total serial NMEA 0183 ports, dedicated smart-antenna interfaces with DC power feeding, isolated alarm relays, and an integrated NMEA 2000 (CAN bus) network backbone driver, the MX612JB consolidates high-baud serial inputs and outputs into a single, serviceable, bulkhead-mounted marine enclosure.

Model Details

• Manufacturer: Simrad Commercial / Navico
• Model Name: MX612 Junction Box (MX612JB)
• Manufacturer Part Number (MPN): 000-10916-001
• System Integration: Core hub for Simrad GN70, MX610, and MX612 IMO Navigation Systems

Technical Specifications

Applications

• Commercial Wheelhouse Integration: Primary distribution hub linking IMO-approved GPS/DGPS positioning to ECDIS workstations, ARPA radars, and Class A AIS units.
• Dual Antenna & Heading Sensor Redundancy: Splitting serial navigation and heading data between primary and secondary ECDIS suites.
• Voyage Data Recorder (VDR) Interfacing: Providing dedicated isolated NMEA sentences (GGA, GLL, VTG, RMC, ZDA, HDT) to VDR/SVDR telemetry nodes.
• Autopilot Steering Loops: Interfacing high-refresh rate sentences (10 Hz/20 Hz) from GPS compasses directly to steering control units (Simrad AP70/80).
• Offshore Survey & Workboats: Providing multi-drop position synchronization across dynamic positioning (DP) reference monitors, acoustic transceivers, and bathymetric sonar displays.

Our Engineer Expert’s Installation Guide

1) Grounding and Common Mode Shielding

Pro Tip: Never connect both ends of a serial cable drain wire to chassis ground. Ground the shield drain wire only at the MX612 junction box earth grounding stud. Terminating shields at both the sensor head and the J-box creates ground loops, introducing signal degradation on long bridge cable runs.

2) Port Allocation Rules for MX Antennas

When installing smart GPS sensors (such as the MX521A/B or MX575C/D), Ports 3 and 4 are mandatory. Port 3 provides bi-directional differential data and sensor control, while Port 4 handles dedicated auxiliary telemetry. Ensure you configure the display head’s port setup match—if you run an MX521B at 19,200 baud, make sure Port 3 on the CDU is explicitly assigned at that baud rate rather than standard 4,800 bps.

3) NMEA 2000 Bus Termination Check

The MX612JB features an integrated internal bus terminator switch.

• If the MX612JB is installed at the physical end of the NMEA 2000 CAN trunk line, toggle the internal terminator switch to ON (120 Ω).
• If you run a continuous drop line through a central tee or external drop tap, toggle the internal termination switch to OFF to avoid pulling line resistance down to 60 Ω or 40 Ω, which drops CAN transceiver packets.

4) Differential Pair Polarity (Listener vs. Talker)

Standard IEC 61162 designations use:

• Tx_A = Talker Out (+) / Non-inverting
• Tx_B = Talker Out (-) / Inverting
• Rx_A = Listener In (+)
• Rx_B = Listener In (-)

Frequently Asked Questions

What is the primary function of the Simrad MX612 Junction Box?

The Simrad MX612 Junction Box is an industrial data and power interface unit that connects Simrad MX612, MX610, and GN70 navigation control heads with smart antennas and peripheral bridge equipment. It splits and distributes NMEA 0183 and NMEA 2000 navigation sentences across 12 serial ports to systems such as ECDIS, RADAR, AIS, and VDR.

What is the difference between the MX610JB and MX612JB junction boxes?

The MX610JB features 6 NMEA 0183 serial ports, whereas the MX612JB includes 12 NMEA 0183 serial ports. The MX612JB is intended for complex commercial vessels requiring wider data distribution across multiple bridge consoles and repeaters without requiring additional third-party serial buffers.

Can the MX612JB power smart antennas directly?

Yes. Ports 3 and 4 of the MX612JB are specifically wired with dedicated DC supply rails to power Simrad smart sensors, including the MX521A, MX521B, and MX575D, directly through the interface cabling.

What should I check if a listener device is not receiving NMEA data from the MX612?

First, verify that the baud rate of the specific MX612 port matches the receiving equipment (e.g., standard 4,800 bps vs. 38,400 bps high-speed). Next, verify line polarity between Tx_A (+) and Tx_B (-). Swapping polarity is safe on differential circuits and often resolves connectivity issues with non-standard legacy listeners.

Does the MX612 Junction Box meet IMO requirements for commercial vessels?

Yes. When installed alongside the Simrad MX612 Control and Display Unit and an approved smart antenna (such as the MX521B), the MX612JB forms part of an IMO type-approved, Wheelmark MED-certified navigation system for SOLAS-compliant vessels.