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Earth Stations and Network Technology
In a broadcast center, the routing and switching function is central to the
operation of the distribution network; hence, its design and installation are critical
to success. The function requires a large capacity in terms of the number of simulta-
neous video/audio channels (numbering in the hundreds). Both computer and
human control are involved: the computers are programmed ahead of time with
the requirements of the network, and humans are always present to observe that
the system is working correctly. Numerous backup modes are provided, including
dual feeding of the same (important) video channels, and human intervention may
be needed at any time to ensure that the right programs are being transferred to
the right channels. More recently, computer automation has been added to reduce
the amount of manual labor involved and to improve the overall reliability of
switching operation. Mistakes at this level can be detrimental to the quality of
service and, ultimately, the revenue derived from programming and advertising.
9.7.2.3
Program Acquisition and Playback
Whether we are talking about a basic video uplink or a comprehensive broadcast
center, there is always a need to obtain the programming input from multiple
sources. Program acquisition in this context means that the video signal is originat-
ing outside the station from one or more remote sources. An uplink that serves a
TV network acquires its programming from the originating studio through a terres-
trial link. As discussed earlier in this chapter, tail links use either line-of-sight
microwave communication or fiber optic cable. Fiber optic cable transmission
usually is preferred because of the wider bandwidths for either analog or digital
video formats and because of the absence of signal fading (except, of course, for
a backhoe fade). If we are talking about receiving from other satellites, there must
be sufficient TVRO antennas to provide the desired access. For that reason, a large
uplink station, such as that shown in Figure 9.24, includes a considerable quantity
of transmit and receive antennas.
The other potential source of programming is from video files, which are either
developed at the site or delivered to it (a process called ‘‘bicycling’’). Files on digital
tape, hard drives and DVDs are received, cataloged, and stored on servers for
subsequent playback. The advantage of video server technology is that it precludes
mistakes in setting up the transmission and allows content to be selected for
particular transmissions (e.g., the insertion of promotions and advertising targeted
to a particular audience).
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