Severn Tunnel

Project Description

 ADComms was contracted by Network Rail Telecom to work with them and Mobile Network Operator, EE, to modify the existing Severn Tunnel radio infrastructure by designing and installing a Neutral Host Distributed Antenna System. The objective was to provide radio coverage with the lowest Radio Frequency (RF) loss that can reasonably be achieved, within the technical and financial constraints, across the multiple frequency bands currently used by the four UK Mobile Network Operators.

Work Streams

  • Termination of new low PIM-rated radiating cable connectors throughout the entire length of the existing radiating cable (including shaft No2)
  • Installation of six new MBF-40 dual band 800/1800MHz repeaters within the Severn Tunnel
  • Installation of six new RF Combiners
  • Replacement of existing low-level coax cables from existing repeaters to the new combiners within the tunnel
  • Installation of 12-coax feeder earth kits within the tunnel rated appropriately for the impending electrification of the route
  • Installation of new Wideband portal antennas and new RF Combiner
  • Installation and Commission of a new System Control capability within the radio room, complete with new Uninterrupted Power Supply, combiner and new feeder cables

Description of Works Carried Out

The project involved complex technical work and testing in a difficult railway environment, carrying out all works in a limited time window. ADComms modified the existing critical railway services, carrying out testing at the end of each shift to ensure correct operation, before returning the railway to service in good time for trains to continue running the next morning. ADComms understood and recognised the constraints of the existing infrastructure and delivered a practical, value-engineered solution that avoided the replacement of 8km of existing leaky feeder cable. ADComms introduced new repeaters at multiple locations in the tunnel, applying intelligent product selection and use of Passive Intermodulation (PIM) testing. This approach added additional cellular frequencies into the existing tunnel cable system in the most cost-effective and practical way. Throughout the project, ADComms took on responsibility for planning possessions to enable surveys and installation works, and acted as engineering supervisor, when required.


The programme supports the Department for Transport, and some franchise obligations, to provide guaranteed mobile and Wi‐Fi connectivity to rail passengers, and to support the Emergency Services Network connectivity challenges across the rail network. Before the project, no mobile or Wi-Fi connectivity was available in the Severn Tunnel. The completed multi-phase project addressed this issue and now provides robust mobile and Wi-Fi signals throughout the tunnel.

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