The QJ71BR11 is Mitsubishi Electric’s MELSECNET/H coaxial bus network module for the MELSEC-Q programmable controller series, providing 10 Mbps token-passing inter-PLC communication over coaxial cable for distributed MELSEC-Q control architectures — the established predecessor to CC-Link IE Controller Network in Mitsubishi’s PLC communication hierarchy, widely installed across manufacturing facilities globally and still actively supported for existing MELSECNET/H installations. As the coaxial bus variant of the MELSECNET/H module family, the QJ71BR11 operates on a bus topology (rather than the ring topology of the optical QJ71LP21-25 variant), connecting up to 32 stations on a single coaxial segment via BNC connectors and standard 75 Ω coaxial cable. Atlantech Drives holds stock of the QJ71BR11. Contact us for fast worldwide delivery and competitive pricing.
What Is the QJ71BR11?
The QJ71BR11 is a MELSEC-Q series intelligent communication module implementing the MELSECNET/H protocol over coaxial bus medium, enabling cyclic data sharing between MELSEC-Q controllers in a distributed multi-PLC system. In a MELSECNET/H network, each station shares a cyclic data area consisting of link relays (B devices) and link registers (W devices) with all other stations — any station can read any other station’s link data without point-to-point communication programming, simplifying the inter-controller data exchange in complex multi-PLC installations. The QJ71BR11 operates as either a network master station (managing token passing and cyclic refresh) or a local station (participating as a peer), with the operating mode configured via GX Works2 network parameters. Up to 32 stations can share a single MELSECNET/H coaxial bus network, with a total cyclic data capacity of 16,384 link relays and 16,384 link registers. The coaxial bus topology of the QJ71BR11 differs from the optical ring topology of the QJ71LP21-25 — coaxial bus systems use a linear bus configuration with termination resistors at both ends, while the optical version uses a ring where each station connects to both its upstream and downstream neighbours.
Key Technical Specifications
- Model: QJ71BR11
- Protocol: MELSECNET/H
- Transmission Speed: 10 Mbps
- Transmission Medium: Coaxial cable (75 Ω, BNC connector)
- Maximum Stations per Network: 32
- Maximum Cable Length: 500 m per segment (with up to 3 repeaters for extended distance)
- Topology: Bus (linear, with BNC T-connectors at each station)
- Cyclic Data: Link Relays (B): 16,384 points; Link Registers (W): 16,384 points
- Transient Data: Supported
- Current Consumption (5 VDC internal bus): 0.55 A
- Operating Temperature: 0°C to 55°C
- Compatible CPUs: All MELSEC-Q Universal model and H-model CPUs
- Weight: Approx. 0.22 kg
Replacement & Upgrade Notes
The QJ71BR11 is increasingly specified as a replacement module for existing MELSECNET/H coaxial bus installations where the original module has failed or reached end of service life, rather than for new system designs — new distributed PLC communication architectures standardise on CC-Link IE Controller Network (QJ71GP21S-SX or QJ71GP21-SX) which provides 100 times the bandwidth at 1 Gbps versus 10 Mbps, supports up to 120 stations versus 32, and uses the more reliable and widely available fibre optic medium versus aging coaxial cable infrastructure. When replacing a failed QJ71BR11 in an operational system, verify the replacement module’s firmware version matches the existing network configuration — MELSECNET/H firmware versions affect the supported B/W data range and network parameter compatibility, and a firmware mismatch between the replacement module and the existing network parameters can prevent the replacement module from joining the network. For facilities planning a long-term migration from MELSECNET/H to CC-Link IE Controller Network, Mitsubishi recommends a phased approach: replace individual QJ71BR11 modules with QJ71GP21S-SX modules one station at a time using MELSECNET/H-to-CC-Link IE routing via a gateway CPU, maintaining operational continuity throughout the migration rather than requiring a complete system cutover.
Troubleshooting Guide
The most common fault in MELSECNET/H coaxial bus systems using the QJ71BR11 is bus communication failure caused by coaxial cable infrastructure degradation rather than module failure. Before replacing a QJ71BR11 suspected of causing network errors, inspect the coaxial cable termination at both ends of the bus — missing or incorrect termination resistors (75 Ω required) cause signal reflections that prevent token passing and generate intermittent communication errors across all stations. Verify termination by measuring the bus impedance with a cable tester or multimeter: with both termination resistors correctly installed, the bus impedance measured at any BNC T-connector should read approximately 37.5 Ω (two 75 Ω resistors in parallel). Check each BNC T-connector for corrosion, loose center pin contact, and damaged outer shield connection — corroded BNC connectors are the most common physical cause of MELSECNET/H coaxial bus failures in systems more than 10 years old. If the QJ71BR11’s ERR LED is illuminated, check the module’s error code in buffer memory address Un\G0 via GX Works2’s buffer memory monitor — error codes above 0x0100 indicate network configuration errors (verify station count and network parameters match the physical hardware), while codes below 0x0100 indicate module hardware faults requiring module replacement.
Frequently Asked Questions
Q: Can the QJ71BR11 coaxial module communicate with QJ71LP21-25 optical ring modules on the same MELSECNET/H network?
A: No. The QJ71BR11 coaxial bus modules and QJ71LP21-25 optical ring modules use incompatible physical media and network topologies and cannot be mixed on the same MELSECNET/H network segment. Coaxial bus and optical ring networks are entirely separate physical networks. If both coaxial and optical MELSECNET/H segments exist in the same facility, inter-network data routing must be implemented via a gateway CPU connected to both networks simultaneously.
Q: What is the maximum distance a single QJ71BR11 coaxial bus network can span?
A: A single coaxial bus segment with the QJ71BR11 supports a maximum cable length of 500 m. With MELSECNET/H coaxial repeaters (QJ72BR15), up to three additional 500 m segments can be added, extending the total network span to 2,000 m. Each repeater regenerates the bus signal, allowing the network to span larger facilities while maintaining signal integrity across the full distance.
Q: Does the QJ71BR11 require any special GX Works2 license or add-on software for network configuration?
A: No special license is required. MELSECNET/H network configuration for the QJ71BR11 is performed using the standard GX Works2 network parameter editor, which is included in the base GX Works2 installation. The network parameters define the station type (master or local), station number, cyclic data send range, and link scan mode, all accessible without additional software modules.
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