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The light rail programme: Broadcasting Radio 2 from a tram

To celebrate 40 years of underground trains in Antwerp, VRT broadcast live from a tram

On 25 March, the VRT’s Radio 2 Antwerpen celebrated 40 years of Antwerp’s pre-metro network with a live broadcast on an early tram travelling from the left bank of the Scheldt river to Sportpaleis station. The event also served as an introduction by public transport company De Lijn to free wi-fi on its trams and buses.

Radio 2 Antwerpen engineer Ward Weis, an aficionado of audio over IP (AoIP) and Luci technology, developed the idea to broadcast from a moving tram. “We talked to De Lijn’s corporate and events division to see how the technical facilities were on the tram, as we needed an absolutely clean line for our UDP and RTP streaming protocols,” explains Weis (pictured below right). “The big difference to HTTP or audio streaming is that, in this case, the signal is routed to the studio but there’s no handshaking between transmitter and receiver. Codecs have correction and buffering features but not ad lib, so a 100 per cent clean line was crucial.”

After testing the tram’s 3G/4G modem, Weis found the connection quite stable in the tunnels thanks to De Lijn’s wi-fi network ring. “In the open air, where the connection switched over multiple transmitters, the quality was less stable, so we opted to do all live presentation and interviews in the tunnels,” he says.

To secure the 220V mains supply on the (600V/24V) tram, Weis took a APC UPS power supply along, offering three hours of autonomy.

The first part of the broadcast was effected in the left-bank tram station, with interviews and mini-concerts. The VRT’s new satellite Mini Cooper van was right alongside the tram for broadcast back-up; Weis also used the Cooper’s power supply.

At 7.30am, Radio 2 presenter Els Broekmans steered the tram into the city’s subway network. On the tram, interviews were conducted with a Sennheiser MD21 Sennheiser wireless condenser mic with EM3031 and SR3054 receivers/transmitters.

“The core of the driving radio set-up was a RME UCX USB audio interface that included a no-latency console, two microphone inputs, line I/O and up to 32 channels,” continues Weis. “I used the RME’s DSP for high pass and slight compression for the voices. We hooked it up to the Luci Studio 3.5 software for AoIP transmission to the main studio.”

A double Luci connectivity (HE-AAC 56kbps mono) consisted of Luci-1 – a microphone signal (with presentation and interviews) routed to the on-air studio, returning with programme feed, headphone and talkback – and Luci-2, which offered a clean feed with the actual broadcast and the ‘national audio sources’ like news and commercials for the audio system on the tram.

The broadcast kicked off the festivities for the 40th anniversary of the introduction of underground trams in Antwerp.