Broadcast RF have been supplying RF facilities and wireless cameras to marathon events all over the world for years now, but we were commissioned for the first time this year to provide the complete RF facility for BBC Sport to cover their home marathon in London.
The London Marathon is recognised as one of the top five international marathons in the world, and holds the Guinness world record as the largest annual fund raising event in the world
Live TV coverage of the London Marathon is a complex affair. The 26 mile route has 6 OB locations along its length, which individually link back to the master OB at the finish, but cabled cameras at each of these OB’s can still only cover a fraction of the course. A high reliance is therefore placed on mobile cameras, on motor bikes, which can follow the runners along the whole 26 mile course. Complementing the bike cameras are a couple of helicopter cameras, also covering the whole course. Most of the OB locations also deploy a hand-held radio-camera, able to get close to the masses of runners and provide opportunities for interviews with the “fun-runners”.
Broadcast RF were employed to provide the links for all the above cameras with the mobile and airborne cameras being linked directly into the master OB. Because of the high reliance placed on these cameras a robust engineering solution was required to ensure continuous coverage of the various races.
The Wheelchair athlete’s race starts at 0900 followed by the Elite Women’s race at 0915 and the Elite Men at 1000. With the elite runners crossing the finish line at around 1210 there is over 3 hours of live elite race coverage, predominantly provided by the mobile and airborne cameras. Then there are the “fun runners” ranging from serious club athletes, through celebrities, to charity fund-raising once-a-year runners, who continue cross the finish line for many hours after the elite runners, all adding to the magnificent spectacle that is the London Marathon.
Broadcast RF employed a bespoke engineering system to provide the mobile camera coverage with each of the 5 camera bikes and the 2 helicopter cameras being linked up to a fixed wing aircraft circling the route at 20,000ft altitude. The pictures from these cameras were multiplexed into 2 downlinks from the aircraft, received on a tall hoist in the finish OB TV compound, located alongside The Mall, and delivered straight to the master OB from the RF control point.
The aircraft is fitted with GPS steered receive antennas, one for each camera bike and a steered downlink antenna thus ensuring the best possible signal quality whatever the relative positions of bikes, aircraft and downlink receive site. Each bike is fitted with a GPS transponder and the data is relayed, via the aircraft, to the master receive site. Each mobile source can then be plotted on a map overlay to provide detailed positional information and the GPS data is used to steer, automatically, the antennas in the plane and the downlink receive antennas at the master receive site.
The latest generation of Vislink 2GHz transmitter, the L1700, were deployed in each of the bikes. These have the advantage of providing MPEG4 H.264 video encoding, providing excellent picture quality over a limited link bandwidth as well as deep time interleaving, a system of error correction designed to cope seamlessly with interruptions to the link path as will inevitably occur with this type of event coverage. The L1700 is also smaller and less power hungry than its predecessor, thus making it ideal for mobile cameras where space and power are always important considerations.
Broadcast RF manufactured bespoke panniers for each motor bike to house the technical equipment and to provide a quick and reliable mounting option on the selection of bikes provided by Williams Moto, with whom we have a long and successful partnership in providing mobile bike cameras.
The transmission system parameters are carefully selected to provide the optimum picture quality and reliability whilst keeping the required frequency bandwidth used and the overall latency (picture delay) to acceptable minimums.
Frequency spectrum is a valuable resource, in short supply for RF hungry events such as Marathon coverage. Careful planning is undertaken by the Broadcast RF Project Manager to ensure the most suitable deployment of frequencies, and frequency bands, to ensure a successful operation. This inevitably requires the acquisition of extra channels, not normally available to Broadcasters, to fulfil the requirements of this complex event. Planning therefore commences several months before the event and is continuously updated to reflect the changes in production requirements as the transmission date approaches.
Keeping with one RF equipment manufacturer, for all the links required for this event, ensures compatibility between the various transmitters and receivers deployed and the versatility of Vislink equipment is of paramount importance in this respect. The Variable Bandwidth LMS-T modulation system available in the Vislink transmitters employed for the aircraft downlinks means that just two wideband downlinks can be employed, each carrying four mobile camera pictures without compromising picture quality. In addition, because high reliance is placed on the GPS tracking and antenna steering systems, the links also carry the GPS data, backed up by separate UHF data links to provide a reliable diversity GPS system.
The advantages of using a fixed wing aircraft as a relay platform for the RF links are many;
The aircraft has a flying duration in excess of that required for the event coverage, unlike a helicopter relay solution which would require refuelling stops.
The altitude of the aircraft means it can maintain a line-of-sight link path to a single receive point on a hoist, rather than requiring a taller building roof to be made available with the additional complexity and expense of linking the received signals back to the master OB that this would entail.
For this reason the helicopter links are also relayed via the aircraft, ensuring consistent pictures from these airborne cameras without requiring the additional complication of a remote receive site.
The aircraft has more room for RF engineers and monitoring and control equipment than the helicopter alternative, increasing the reliability of the overall RF system.
Broadcast RF also used the aircraft to relay, not only the GPS data but also, the production and engineering talkback communications systems required to keep the mobile camera operators in touch with the OB Director and the engineering crews in touch with the master RF control point.
In addition to the complex provision of these mobile camera pictures the majority of the OB’s along the marathon route also deploy a conventional hand-held RF camera which is often required to operate in more than one position in the area covered by that OB. The diversity reception facility offered by the Vislink receivers deployed by Broadcast RF makes for a straightforward engineering solution. The additional frequency requirements of these radio-cameras have to be integrated in the overall plan, placing more demands on available spectrum.
Full coverage of the 2014 London Marathon was a first for Broadcast RF but the event TV Broadcast went extremely smoothly with a very relaxed atmosphere in the master OB control room. This is a testimony to the detailed planning and attention to the exacting engineering requirements that is the trademark of the Broadcast RF team.