A company is undertaking an upgrade project for the TETRA digital trunked communication system across the entire subway line in a first-tier city, requiring full wireless signal coverage in tunnels and stations, without interference.

Challenges

· The metro environment has limited space, and a multi-band (380-400MHz) shared antenna feeder system requires high-isolation combiners to prevent intermodulation interference between different channels.

· Circulators with load-protected power amplifier modules are required at the output of base stations and repeater stations to prevent power reflection and damage from interference.

· Devices are required to have earthquake resistance, moisture-proofing, and wide-temperature operation capabilities.

Solutions

Noxinbo provided customized cavity combiners and high-power circulator components:

· Combiner: 3-port combination, with insertion loss ≤1.2dB, port-to-port isolation ≥70dB, and PIM better than -150dBc.

· Circulator: using ring isolation components, average power 200W, with built-in load and coupled detection port; VSWR detection port can trigger alarms.

· All devices are certified according to IEC61373 impact and vibration standards and have IP54 protection.

Results

· Communication coverage across all 23 stations and inter-station tunnels is stable, with a call success rate increased to 99.95%.

· The metro project passed acceptance in one go and was subsequently replicated in other city metro lines.

· Noxinbo became the customer's "Rail Transit RF Device Technology Innovation Award Supplier.