Table of Contents
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Link Quality
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Appendix Overview
This appendix describes Vislink's Link Quality indicator, and how
it helps you maintain good quality video and audio.
The topics covered in this chapter are listed below.
Topic
Analog vs. Digital Systems
Understanding Link Quality
Description
The LQ Scale
LQ and Signal Quality
Factors
GI
BW
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Link Quality
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Analog vs. Digital Systems
One of the key differences between analog and digital
transmission is the behavior of the receiving system as the
quality of the received signal degrades.
Analog Systems In traditional analog transmissions, each link
in the signal path adds a small amount of noise and distortion.
This noise and distortion accumulates as the signal progresses
toward its destination. By the time the signal reaches the final
receiver, the distortion and noise can be quite noticeable.
These sources of distortion and noise also typically change over
time with changes in atmospheric conditions, movement of the
transmitter or receiver, etc. Overall signal quality therefore varies
over time as well.
In this analog system, when the signal begins to degrade it
begins almost immediately to degrade the quality of the
demodulated video and audio. This provides an 'early warning'
that conditions are worsening, allowing the operator to make
adjustments to restore signal quality before video is lost.
Digital Systems In a digital transmission, the original data is
reconstituted at each link. This eliminates many of the noise and
distortion problems found with analog transmission.
Thus in a digital system, when the signal quality begins to
degrade it initially has no effect on the video and audio. Powerful
error-correction algorithms repair the signal before it is passed to
the MPEG decoder. The operator continues to observe clean
video and audio, and does not realize the signal quality is
deteriorating.
As the signal quality continues to degrade, the number of errors
finally exceeds what the algorithms are able to correct. Then
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Table of Contents
Troubleshooting
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