SDI Eye and Jitter Measurements
How-to Guide
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www.tektronix.com/wfm2300
7
Cable Stress Loop
To assist in checking the performance of a cable link the Cable Stress Loop can be used within the
WFM2300. This adds a simulated 20 meter length of 1694A cable between the I/O loop and can be
used in two ways
.
Figure 4.
Monitored signal stress loop.
A monitored signal can be input to the stress loop as shown in Figure 4 and the additional simulated
length of cable is added to the signal before it is input into SDI A. Monitoring the video session display
allows the user to check that the signal is still error free with the additional length of cable. If the signal
is producing CRC errors every second or every minute then the signal is marginal and the user needs to
investigate further using the eye and jitter displays to determine the problem. The cable type may need
to be changed or a re-clocking Distribution Amplifier (DA) may have to be inserted in the link to
guarantee performance of the signal.
NOTE:
The Video Session display will shows CRC errors that are occurring within the transmission path.
In some cases these errors may not be visible on the internal picture display or on a large picture
monitor, since they may be one pixel sparkle effects (black, or white pixel errors) as the error rate
increases. This sparkle effect will become more pronounced, until lines or parts of the line start to
drop out. Finally, there is no picture at all or the devices freezes on the last frame before loss of the
signal.
