Wouldn't it be great to be able to locate each digital studio-transmitter (STL) link right next to the broadcaster's facilities? In a perfect world, of course it would be, but unfortunately the reality is that terrestrial broadcast transmitters to the air are often located miles away from the place where the content is created.
Fortunately, fiber optic transmission systems offer the key to achieving high-quality broadcasts no matter the distance. With just a single-mode fiber, even broadcasters whose towers are miles away, can perceive as if the transmitter were in the next room.
The argument of having routes to the transmitters, supported in optical fiber for a digital STL, is the same as for the case of transport of other broadband signals. Fiber optics obviate the problems of copper-based systems, such as bandwidth limitations, degradation over time, and vulnerability to RF interference and electromagnetic interference, to name just a few.
Telecast's fiber systems have helped broadcasters successfully overcome their limitations of copper in transmission routes for more than a decade. First with Module 292 of the Viper I platform, and now with Module 5292 of the Viper II platform, Telecast provides broadcasters with unrivaled flexibility in the design of a specific system, according to the exact requirements of their STLs.
To achieve greater transmission efficiency, current CWDM (Coarse Wave Division Multiplexing) optical techniques allow broadcasters to carry additional signals in both directions and still use a single fiber. Digital, analog and control signals can be sent from the studio to the transmitter, while monitoring sources, control signals and even signals from microwave and satellite receivers can also be included.
Using CWDM technology in an STL station, up to 16 individual signals can be easily and economically multiplexed into a single optical fiber. L-band signals sent from the transmitter location and back to master control can also be routed, in the same way. Most Telecast systems include a locking switch, which can be used on the door of the transmitter booth to serve as an intrusion alarm. The same locking switch can be used to turn the equipment on or off remotely.
One of the first applications of HD digital STLs was installed for WTAE in Pittsburgh, Pennsylvania. Using a fully redundant system, including modules for 270 Mbps SDI video as well as NTSC analog video and analog audio and intercom, the WTAE station compressed its HDTV signals using an MPEG-2 ATSC encoder into a signal that meets SMPTE 310M specifications of 19.39 Mbps. This signal can then be easily handled by a 270 Mbps module provided for the transport of return signals to the transmitter. The modularity of the Viper I platform allowed to configure a solution tailored to the client, handling all the signals, intercoms and data required.
NESN (New England Sports Network), in Boston, covers more than 30 kilometers of fiber with its STL from the baseball park on Fenway to the transmitter site in Needham, Massachusetts. Using the Viper II platform, the network has been configured as a fully redundant system, incorporating uncompressed HD video with embedded audio. The installed fiber, supplied by local telecommunications carrier RCN, is one of the most extensive STL links for uncompressed HD in the United States.
While this example from Boston has illustrated all the technical benefits of fiber, a physical fiber optic cable is naturally required to connect the studio to the transmitter. This can be as simple as laying the fiber over the network itself. However, in the case of some remote sites, it is possible to partner with another alternative service provider, such as regional independent communications companies or with the local subscription television provider company. Another potential partner for the purpose of creating the cable path may be a local or regional utility provider.
As more and more networks migrate to digital broadcasting, the use of fiber optic-based systems will continue to expand. Optical fibers offer the appeal of high capacity, combined with the long-distance feature when faced with the bandwidth requirements of digital audio and video, which make these systems a natural solution for digital STLs.
