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An extensive TV distribution system based on Cabletime's popular MediaStar Pro, has been installed at Sky News London, serving 336 screens in the broadcaster's busy news room.

When British Sky Broadcasting decided to find a comprehensive means of delivering TV signals from a wide variety of sources to the Sky Newsroom, it presented something of a challenge to specialist integrator IVC, not least of which was a requirement to 'update' for the digital age.

Streamlining the complicated

Crucially, the team at Sky News needed access to a large number of channels that could be fed to standard television displays or LCD screens. As well as requiring viewing facilities of services from local studios and editing suites, the team also wanted to access services from off air satellite receivers. They commissioned IVC, which specialises in design, project management and installation of communications systems, to come up with a solution.

In addition to the breadth of channels needed, Sky News also wanted the facility to restrict and monitor usage of the services to groups or geographic locations within its West London building. And because of its existing structured cabling, the company also wanted to use twisted pair cabling for TV distribution, if possible. A further complication was that the services were in a combination of differing formats, with the majority of the local feeds being in serial digital format whilst all the "off air" receiver outputs were analogue.

A number of solutions were considered for the project, including network streaming and dual cable coaxial distribution. The first of these solutions was rejected on the basis of cost and the difficulties of unproven technology being implemented on such a large scale. The second was eventually rejected as it would have involved custom built equipment, which would have brought many additional problems including long lead time and difficulties with future expansion.

A proven solution

Finally, IVC recommended a solution based on Cabletime's Mediastar Pro. This system is designed specifically for audio and video delivery over structured cabling, it's fully scalable and has a powerful feature set and comprehensive software management. IVC has worked with Cabletime for many years, and was able to design and build the system for Sky News from off-the-shelf, proven technology, with only the control handsets being specially built for the project. As the system required all feeds to be analogue, a number of Axon frames were provided by Sky to convert the SDI video to PAL I analogue format and strip off the embedded audio signals.

In order to cater for the very large number of services, the dual coaxial-fed version of the Mediastar system was installed and a headend was built to provide an initial 112 channels split across the two coaxial trunks. The modulation equipment installed was Kathrein UFO compact, using dual frequency modulators that allowed a flexible system with minimal spares holding. The normal problem with using frequency agile equipment to provide very large numbers of channels tends to be accumulation of wideband noise, so IVC designed a custom passive cluster filter combiner system to effectively eliminate this problem. The final outputs were then amplified via groups of wideband amplifiers and passive wideband combiners, to eliminate single failure points. On commissioning test it was found that the noise and distortion figures on the output of the system were so low as to be virtually immeasurable, even using laboratory grade test instruments. The solution surpassed all expectations.

Joining forces

The coaxial outputs from each trunk were then distributed to a number of Mediastar hubs. From the hub outputs the signals were distributed to the users via a dedicated structured cable network. At the user destinations, Mediastar Micro settop box receivers provided the video and audio outputs for the screens. The settop boxes were line powered from the hubs, eliminating the need for excessive power supplies at the screen location. In order to have a large number of units operating in close proximity without the danger of interaction from conflicting IR handsets, each box was provided with a cabled handset. The handsets were designed by IVC in conjunction with Cabletime, working closely with Sky throughout. These have now been added to the main Mediastar product line, further enhancing flexibility.

Total control, clear guidance

The whole system runs under the control of a central PC controller running Mediasoft controller and administrator software. This provides total control of the system, from the naming and identification of services on the network, to allocation of user groups, viewing rights and actual monitoring of usage. The system is set up in such a way that even a total controller failure would not affect system users. All this functionality and considerably more are provided as standard with the Mediastar system.

With the very large number of channels, it was vital to provide a channel guide system that would give users all the information they needed to locate channels on the system. In order to achieve this, SIPI, another feature of the Mediastar operating system was utilised. The controller PC was connected via a network switch to an additional five compact computers. Each of the computers ran a custom written application to extract the latest channel identification information from the central controller and display it as a text page. Using this method ensured that the system would work in the same manner as an electronic program guide, with any changes being automatic and unseen by the users. This also meant that the same information never had to be duplicated on different systems.