Tektronix WFM2300 How-to Manual

How-to-Guide

SDI Eye and Jitter Measurements

WFM2300 Portable Waveform Monitor

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SDI Eye and Jitter Measurements How-to Guide

Table of Contents

Introduction ………………………………………………………………………… 3

Troubleshooting the SDI Signal Path …………………………….……………. 3

How to Configure Video Session Display ……………………….……………. 4

How to Configure SDI Status Display ……………………….………………… 5

Cable Stress Loop ……………………………………………….……………….. 7

How to Configure SDI Stress Loop Amplitude …………….………………… 9

How to Configure Eye Measurements ……………………….………………… 10

Enabling Pseudo Color Display …………………………….…………………... 12

Measuring Jitter within an SDI Signal …………………….…………………… 14

Enabling Infinite Persistence Mode …………………….……………………… 18

Conclusion ………………………………………………….……………………… 20

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SDI Eye and Jitter Measurements How-to Guide

Serial Digital Interface (SDI) Physical Layer Monitoring

Reliable transmission of the SDI signal from point A to point B is dependent on a variety of factors such as:

 Amplitude of the Signal

 Overshoot

 Undershoot

 Jitter

 Rise and Fall Time of the Transitions

These parameters are affected by the cable length, that over longer runs of cable will introduce amplitude
and frequency losses to the signal resulting in longer rise and fall times of the signal. Overshoot and
undershoot are typically a result of incorrectly terminated devices or panels which introduce reflections into
the signal. Additionally deformation of the cable can also introduce reflections into the signal along with cable
loss. Active devices may introduce jitter into the signal as the signal is processed or genlocked to a
reference signal. The first stage of troubleshooting a physical layer issue is to verify the link by using CRC
(Cyclic Redundancy Code) words to verify the link is error free. The Video Session display will shows
statistics of the CRC Errors.

Troubleshooting the SDI Signal Path

 Error Free signal path, check for CRC (HD or 3G) or EDH (Error Detection Handling) if present

within SD-SDI signals. Use the video session of the WFM2300 to determine this.

 Determine if the signal path has a safety margin by adding an additional length of cable or using

a stressing signal. Does the addition of the cable length or stress cause CRC issues or loss of
the signal? The cable simulator of the WFM2300 adds 20m of Belden 1694A cable along with
the ability to add an interfering signal or use the internal test signal generator with the
pathological test signal to stress the signal path.

 Estimate the cable length of the signal path to determine if the receiving device is operating

within its specification, using the SDI Status displays of the WFM2300.

 Check at various points along the transmission path to characterize the SDI signal.

 Use the Eye displays of the WFM2300 to characterize the health and possible artifacts present

within the SDI signal along the signal path.

 Use the Jitter thermometer within the eye, jitter and SDI status display of the WFM2300 to

determine the timing and alignment jitter present within the signal.

 Use the Jitter display in two-field sweep to characterize the jitter within the signal and use the

high pass filters to determine the amount of jitter present within each frequency band.

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SDI Eye and Jitter Measurements How-to Guide

How to Configure Video Session Display

1. Select one of the tiles (1, 2, 3 or 4) using the Display Select and press the STATUS button.

2. Push and Hold the STATUS button to display the Status menu.

3. Using the general knob or up/down arrow keys navigate to and select Display Type as shown in
Figure 1.

4. Press SEL to enter the submenu and navigate to Video Session to show a summary of video
parameters of the current video signal as shown in Figure 1.

Figure 1. Video Session Display.

For HD-SDI, Dual Link and 3G-SDI signals there is a CRC calculated every line with a value produce
one for Y Luma and one for C Chroma samples. This is shown in the lower statistics information of
Figure 1.

 If the signal attached to the WFM2300 is error free then the Status will show OK in green.
 If a CRC error occurs then this will show in the Video Session display in red and a count of the

number of values that have occurred during the session will be displayed.

In order to determine the error rate of CRC errored seconds, the user may need to monitor the signal
path for several minutes or hours. Within the Status menu for the Video Session display the user can
reset the duration of the session and the statistics will be reset too.

See Figure 1. Video Session menu All Sessions Reset)

NOTE:

For standard definition (SD-SDI) signals there is no embedded CRC check and instead an Error
Detection Handling ancillary packet must be inserted by the device in order to provide CRC check of
the signal.

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SDI Eye and Jitter Measurements How-to Guide

If you see errors every minute or every second then this is an indication that the signal is getting close to the
digital cliff and there is a problem in recovering the clock and data of the signal within the receiver. Not all
receivers are identical and this can affect the devices ability to recover the clock and data.

The WFM2300 has been designed with a robust equalizer and receiver to allow the user to determine signal
issues. Some devices may fail before the WFM2300 and so it is important to check the manufacture’s
specification for cable length distance and type of cable. The SDI status display provides an estimated cable
length measurement based on selection of specific cable types.

NOTE:

Most manufacturers specify the performance of their equipment to a specific cable type typically Belden
8281 or Belden 1694A and it is recommend to select this cable type when estimating the cable length of
the device, even though the cable being used may not be this type of cable.

How to Configure SDI Status Display

1. Select one of the tiles (1, 2, 3 or 4) and press the STATUS button.

2. Push and Hold the STATUS button to enable the menu.

3. Using the up and down arrows to navigate to Display Type and press right arrow to select the
sub menu as shown in Figure 2.

4. Select SDI Status display to show a summary of physical layer parameters of the current video
signal as shown in Figure 3.

Figure 2. SDI Status Display Type menu.

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SDI Eye and Jitter Measurements How-to Guide

NO

Figure 3. SDI Status Display showing physical layer measurement summary.

The SDI Status provides a summary of the physical layer measurements of the SDI input. Jitter and Cable
Loss Thermometer shows the value represented as a horizontal bar graph. The 0-170% scale is divided into
threshold regions, from 0 to 70% value is represented by the green area, the level 70-100% by a yellow area
and 100-170% by a red area. The measured value is also shown within the display.

 Jitter – Measured Jitter using selected High Pass Filter
 Cable Loss – Shows the signal loss in dB at the frequency specified
 Approx Cable – Shows the approximate cable length, assuming a continuous run of the specified

cable type selected by the user.

 Source Level – Shows the calculated launch amplitude of the signal source, assuming a continuous

run of cable.

 Cable Type – Shows the cable type used to make physical layer measurements and is user selectable

within CONFIG Physical Layer Settings Cable Type.

 Eye Amplitude – Shows the amplitude of the eye waveform
 Eye Risetime – Shows the rise time of the eye waveform
 Eye Falltime – Shows the fall time of the eye waveform
 Eye Rise-Fall – Shows the delta of the rise and fall time of the eye waveform
 Eye Rise Overshoot – Shows the percentage of the rise time overshoot of the eye waveform
 Eye Fall Overshoot – Shows the percentage of the fall time overshoot of the eye waveform
 The user can set the threshold for the jitter meter within the configuration menu

CONFIG Physical Layer Settings SMPTE XXX Thresholds Jitter Level

NOTE:

Physical layer measurements can only be performed on Channel A input, so ensure that Input A is
selected on the front panel.

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SDI Eye and Jitter Measurements How-to Guide

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.

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