Communication cables for Sydney's rail link

Radiocommunication underground has always been a difficult and specialised branch of technology. Mines and underground railways where conditions can be dark and cramped have always been in particular need of reliable contact with the surface.

Today's radio systems have reached a development point where they can provide good communications from underground to the surface as well as to other points below the surface. A radio system is now being installed in one of the latest railway projects in Australia - the two tunnels that are being built to extend Sydney's rail network.

Radiating cables will be used for radiocommunications in the twin tunnels now being built as part of the Epping to Chatswood rail link.

Radio Frequency Systems is supplying the cables which are a combination of Radiaflex RLVL Vario and its RTLK series. These will support an in-tunnel train and emergency radio system.

The line, formerly called the Parramatta Rail Link, is the largest publicly-funded infrastructure project under way in NSW. Two separate tunnels each 7.2 m in diameter are being constructed with cross passages spaced about 200 m apart to ensure passenger safety in an emergency. Three crossover passages will allow trains to change between tunnels.

When it opens in 2008, the line will be integrated into the existing CityRail network and will create capacity for an additional 12,000 passengers a day.

Domenic Lobriza, RFS technical sales manager, said that a key challenge in the project was addressing points of the tunnels where access and manoeuvrability were limited.

"This meant we needed to design the cable lengths to specifically meet those installation limitations," he said.

"Drum sizes and cable lengths were tailored to ensure the installation was practical and achievable in such spaces," he added.

The two cable types were needed to reach the desired in-tunnel coverage. The Vario has been included in the customised hybrid system to give good performance over the longer stretches of the tunnels. Providing broadband coverage for longer transmission lengths without using amplifiers, this cable gives graded coupling loss with nearly constant system loss. The two longest cable runs are 1750 and 1875 m.

Each tunnel will be equipped with a radio system designed to support the Government Radio Network (GRN), police and MetroNet (train radio) services.