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Inside a Radio Outside Broadcast Truck

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James Smith | 16:00 UK time, Tuesday, 12 October 2010

On 28th September, Audio & Music Director Tim Davie officially launched the new fleet of Outside Broadcast Trucks, at the BBC Media Village in W12. You can read Tim's thoughts on the new BBC Radio blog.

These six, brand new trucks are for use across BBC National Radio. They are equipped to mix audio at Outside Broadcasts like the main stage at Glastonbury or the Proms season, as well as programmes like Any Questions for Radio 4 and bands for Friday Night is Music Night on Radio 2.

There are three types of vehicle delivered as part of this project:

"Music" vehicles which are articulated trailers designed to work on complex music shows like the main stage at a festival or Last Night of the Proms - two of these have been delivered.

"General Purpose" vehicles: these can carry out a majority of work from a simple show all the way upto a second stage at a festival - four of these have been delivered.

"Production Vans": these are unequipped mobile spaces that can be used as a production office, studio, mixing area or anything else required! Two of these vehicles are due to be delivered in November 2010.

The general purpose vehicles are fixed-chassis, 30ft trucks equipped with a Stagetec Aurus 40-fader control surface, a Stagetec Nexus core and four remote stage boxes with 16 mic channels each, two of those with video MADI and GPIO capability, each connected by military-grade fibre optics to the truck. The vehicles are also fitted with numerous different record and replay format devices, including multitrack. The mixing console sits on a sliding support structure to allow access to the rear of the console for maintenance, or to maximise the space available in the working area for non critical mixing work as well as ensuring the desk can be used in the optimum mixing position as well.

SSL C200 mixing console in Sound 2, Radio Outside Broadcast vehicle.

SSL C200 mixing console in Sound 2, BBC Radio Outside Broadcast vehicle. Photo by Sue Foll.

The two music trucks are 40ft trailers, one with a 48-fader Stagetec Aurus control surface and one with an SSL C200 mixing console, both are also fitted with a Stagetec Nexus core and two stage boxes with 64 channels of mic inputs each. These vehicles are capable of mixing the most complex music events, so they have extensive outboard processing equipment fitted as well and have space for editing or to have portable equipment rigged as required.

The general purpose and music vehicles have extensive acoustic treatment, both in terms of sound isolation from outside and internal treatment to ensure a good listening space. This is so that a vehicle can be used to create an accurate mix in a noisy environment such as close proximity to a stage at a music festival. The air conditioning has an innovative duct design to ensure that ambient noise within the mixing space is very low enabling critical listening to occur away from a studio base.

Access to vehicle roofs has always been a hazardous and risky activity. The design of the new vehicles has paid special attention to making access to the roof of the vehicle as safe as possible. The design incorporates a fixed ladder at the rear of the vehicle stored in a vertical position. When deployed it hinges out from the roof to provide a ladder at an incline, rather than a vertical ladder commonly seen on OB vehicles. Two remotely operated roof rails swing into a vertical position providing hand rails which enable a safe transition from the ladder onto the roof. The roof rails surround almost the entire perimeter of the roof, creating an enclosed area from which the rest of the roof rails can safely be deployed

External lighting is provided by five LED clusters, part of the vehicle's rigging light system. Storage on the roof is available for two and three metre scaffold poles (two of each) for the rigging of aerials and the base mounts for these are placed within the roof rail structure, thus avoiding the need to swing large scaffold poles over the side of the vehicle. A small weather proof box can store a scaffold clamp, spanners, Allen keys and other accessories for use on the roof.

From the roof, there is also access to the ten metre mast fitted to the front of the vehicle. The mast controller is plugged into a box close to the mast housing the pressure gauge and a warning lamp to warn operators of pressure within the mast. On top of the cab roof (GP vehicles), a upward facing spot light is fitted to illuminate the space above the mast and any obstacles that may interfere with the mast operation. An additional LED lamp on the front roof rail will illuminate the mast area in the event that operations have to be undertaken at night.

The general purpose vehicles have been designed to be fully operational when powered from just two 13 Amp sockets (inputs on vehicle are 16A sockets), which is often required when working at old churches and village halls. The electrical system within the vehicle is split into two technical, two general and a one utilities distribution systems. In addition to the two day to day input sockets on the vehicle, there is an additional 'night supply' input socket. This allows for a separate supply to be fed into the vehicle when the vehicle is not in use. A selector switch within the vehicle enables a portion of the Utilities distribution to be powered from the 'night supply' allowing facilities such as lighting, battery chargers, the smoke alarm and some ancillary sockets to be powered. The music vehicles require about 40 Amps to operate all systems, this is provided via a 63 Amp socket.

Both types of vehicle are fitted with uninterruptible power supplies on the technical distribution to enable the vehicles to continue broadcasting in the event of a power failure, this lasts for at least 30 minutes but initial tests have shown that the system performance is closer to an hour of availability. The UPS charging system on the general purpose vehicles has an intelligent current demand control system - it ensures that the overall current usage doesn't exceed the 26 amp maximum, it does this by varying the charging current for the UPS batteries dependant on the other usage within the vehicle (e.g. air conditioning and heating).

The two production vans are based on a Iveco van chassis and have no broadcast equipment permanently installed, but do have mains distribution, Analogue audio, AES and video tie lines as well as air conditioning and some acoustic treatment. The vehicles are close to being finished and are due in service by the end of 2010.

These vehicles replace an existing fleet that has served the BBC very well for a number of years. In fact more years than you might think - the average age of the existing vehicles is twenty two years old with one having given 28 years sterling service.

Broadcasting has moved on during the life of these vehicles, especially around the type of content we now acquire and methods used. The old vehicles were designed to use line send amplifiers over Post Office (later BT) circuits to get the programmes back to Broadcasting House, now a number of methods are used from ISDN's to VSAT and IP Codecs over the web. As a consequence the new fleet has provision for these methods built into the design as well as facilities to capture content for BBCi - there is space inside the vehicles for BBCi production staff to work alongside their audio colleagues as well as additional internal networking and digital audio connectivity to simplify rigging and operational practices.

James Smith is Portfolio Manager, Development and Delivery, BBC Future Media and Technology

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