Specifications

General Operation
VTM Series Installation and Operation Handbook
3-23
Figure 3-18. Eye Pattern Graticule at Zoom 800 mV
Eye Pattern Observation
The waveform displayed can show both amplitude variations and timing variations.
The combination of these “closes” the decision window for determining whether a bit
received is “1” or “0”. Common errors including overshoot, bandwidth limitations,
and ringing are easily observed with the Eye Pattern display and provide indications of
the general quality of the transmission channel and source.
Eye Pattern Rise Time
Rise times of the waveform can be calculated by measuring the 20% to 80% rise time
points with the time cursors.
Jitter Meter and Eye Pattern Correlation
The jitter meter located just above the Eye pattern display is intended to display the
maximum value of jitter over time. The correlation of values derived by using
measurement cursors versus the jitter meter could differ unless the eye pattern is
displayed using the maximum persistence setting. A normal persistence setting will
make it more difficult to view pixels near the widest sample points, which forces the
placement of the measurement cursors to a lower (narrower) jitter value. Jitter can
only be selected when the Eye Pattern is enabled.
Horizontal Magnification and Zoom in Eye Pattern Mode
Gain is used to set the range of amplification in the video signal. The standard gain in
the video signal is x1. The VTM Series can be used to set the gain amplification in the
video signal using the Gain group of buttons. The gain setting appears in the upper-left
portion of the waveform pane, as shown in Figure 3-12.
Press the MAG button to step through the available Horizontal Magnifications
of x1, x5, and x10: 1 nS, .20 nS, and .10 nS for SD or 250 pS, 50 pS, and 25
pS for HD. The type of magnification along with the format displayed
determines how many “Eyes” are displayed. Table 3-12 describes the Horizontal
Magnification Conditions.