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1.2.3
Video Switching Subracks
All of the available video sources (cameras etc.) are distributed across one or more
video switching subracks, to construct the required video switching matrix. Depending
on the system's requirements (the number of video inputs and outputs), the video
switching subracks come in several fixed sizes to best suit individual applications.
By installing a video-switching module (RD85) into every slot of the video switching
subrack (again, depending on the size of the subrack), a full 32 by 32 video-switching
matrix can be achieved. Where a larger switching matrix is required, combiner subracks
are used.
At this point, two new concepts will be introduced for use in a large switching matrix.
They are:
•
Cascading
•
Combining
Cascading
There are at least two video switching subracks present. The outputs of the first subrack
are connected to the cascade inputs of the second subrack. By doing so, the second
video switching subrack can access, in addition to its own video inputs, the other video
inputs on the first subrack.
This application is very useful for a simple video system having up to 96 video inputs.
Please refer to section 3.2 Cascading, for a more detailed description.
Combining
Two different types of video switching subracks are used:
•
Preselection subracks, and
•
Combiner subracks.
The pre-selection subracks referred to in Combining, are identical to the subracks in
Cascading. They would be the normal video switching subracks that have been referred
to previously.
The combiner subracks are specially designed to multiplex the video outputs from the
pre-selection subracks. Unlike the pre-selection subracks, video inputs to the combiner
subracks are not distributed across the channels. The video inputs are only available to
the very slot that they are physically connected to.
Video inputs are fed into the pre-selection subracks. As the name implies, the video
inputs are pre-selected by these subracks before going to the combiner subracks. The
outputs from the combiner subracks would then go to video output devices, like
monitors.
This application is very practical for a video system consisting of hundreds of video
inputs to maintain the high quality of the video signal.
Section 3.3 Combining, describes and illustrates the concept of combining in more
detail.
Rev. B
1-3
HMXMC001013
31-Mar-06
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