Norway’s Tunnel Vision

How digital radio makes driving safer in Norway
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The image (above) shows the�L�rdal tunnel in Norway,which is 24.5 km long, among the longest in the world. Via: Flickr/xdmag.

When Norway switches off its national FM transmission network next year in favor of DAB+, motorists may notice something curious. As they drive through one of the many road tunnels in Norway, their radio will no longer cut out: and might even help them on their way.�

Gunnar Garfors, who works at public service broadcaster NRK, highlights that Norway has over 500 tunnels which are longer than 500 meters (a third of a mile). 180 of those tunnels carry a re-broadcast of just one radio station on FM � NRK P1. Some also carry the commercial broadcaster P4.

However, with the DAB+ switchover, the Norwegian Road Authority plans to increase the amount of stations carried and the coverage. All tunnels longer than 500 meters that are used by over 5,000 cars a day will need to be covered with DAB+ � and will offer all available radio stations.

Each of these tunnel DAB+ translators will be remotely controllable to switch away from regular programming and broadcast emergency information for drivers if required.

One of the companies working with the Norwegian Road Authority isPaneda, a company based in a small Norwegian village that�s six hours' drive north of Bergen � through at least 12 road tunnels.

Oddvar Fl�lo, Paneda's CTO, highlights that the solution to cover the tunnels is considerably more complex than a simple analog broadcast translator.

Each tunnel translator can be switched to broadcast emergency information, so it needs to continually analyze the current multiplex configuration, which can change multiple times a day.�The challenge," Fl�lo explained,�is that when messages need to be broadcast, they must take place in a seamless manner to prevent the DAB receiver from losing synchronization.�In effect, the DAB break-in product that Paneda has built is a complete DAB+ radio station and multiplexer.

The emergency information can be controlled at an individual tunnel level.�Paneda has developed our own monitoring and management software of our tunnel installations,�Fl�lo told me.�The installation is connected to the internet using mobile data. It can be reached from any place on earth.�

�We use a DAB receiving antenna outside each tunnel. This signal goes via a coax cable to a DAB block selective amplifier with a gain of about 95dB. Typical power level of the antenna is from -75 to -20 dBm. Output from the amplifier is adjusted to 0dBm, sent through a special relay, amplified to typically +24dBm, and fed to a leaky cable which is mounted in the roof of the tunnel. That way, the DAB signal which is distributed in the tunnel will be � from the car radio point of view � the same SFN network as outside the tunnel, and the power level from the antenna connected to the car radio will be a minimum of -82dBm. That means no interference at the entrance and exit.�

EU Directive 2004/54/EC requires radio translators for all road tunnels of over 1km in length (0.6 miles), a legal requirement which Norway is exceeding. Paneda is now looking to help other countries, like Switzerland and Austria, to achieve DAB+ coverage in tunnels for motorists.

Most eligible Norwegian tunnels will offer DAB+ coverage by the end of 2016. For a map of all Norwegian tunnels with DAB+ coverage, and their switch-on dates, visit the Norwegian-language site�http://radio.no/dekning/�� click �se kart� (either one), and then choose �tunneler.�

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