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An aerial view


Integrated antennas enable the virtual office on trains. By Robin George.

With wireless services about to become broadly available, train passengers will expect to use their PDAs, notebooks and other devices to make calls from the train and have access to internet, email and infotainment applications. Demand from busy executives for a ‘virtual office’ is encouraging train operators to provide this access as a useful value added service or as a potential revenue stream.
Being an almost perfect Faraday cage, railway carriages will attenuate or block radio signals from the outside world and vice versa. So there is little chance for any mobile communications operator to provide a high quality service inside a train without the use of radio repeaters. This is especially true for modern trains using metallic windows for climate control.
The configuration shown in figure 1 comprises a set of three repeaters: GSM 900, GSM1800 and UMTS. The repeaters and the combiner network are hosted within special equipment rooms inside the carriages. The antenna connects to the output of the repeater combiner network – in this case, a triplexer that handles GSM900, GSM1800 and UMTS. Radio signals are picked up outside the carriage by the antenna, reamplified within the repeaters and transmitted either to a leaky feeder or to directional antennas which provide seamless coverage inside the carriage.

Author
Graham Pitcher

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