User guide

This is the bit error rate threshold at which the Threshold Margin is determined.
It is also the upper threshold for the Q-factor calculations.
The BER Threshold is displayed in the BER vs. Threshold graph. There, it can
be positioned with the mouse (or your finger, if you are working directly on the
Serial BERT).
• Min BER for Q
This is the lower threshold for the Q-factor calculations.
You can select the number of Decimal Places to be displayed in the table.
Graph Tab
On the Graph tab, you can use the several options to optimize the graphical display
according to your needs.
Choose between Logarithmic and Linear to select the scale for the display's x-
axis.
The scale of the QBER vs. Threshold graph is always linear.
Ratios in the numerical results (such as SNR) can be displayed linearly or
logarithmically in dB.
To analyze the graphs at a particular point, you can use the markers. Optionally,
you can display all related values for the markers in the marker readout.
Pressing the Reset Markers button will set the markers back to the default
positions.
Linear markers are available for the BER vs. Thresholdgraph and the QBER vs.
Threshold graph. A gaussian marker is available for the dBER vs. Threshold graph.
See “Marker Definitions” on page 236 for details.
Several zoom factors are available. When you show the zoom graph, you can also
allow the zoom graph to track the mouse (or your finger, if you are working directly
on the Serial BERT).
If you want to see the points that have actually been measured, choose Show
Measured Points.
6 Advanced Analysis
276 Agilent J-BERT N4903B High-Performance Serial BERT
Table Number Format
Scale
Ratio Unit
Markers
Zoom
Show Measured Points