Tektronix TPS2000 Series User Manual page 79

H If the trigger frequency is faster than the display information, you
may have aliasing or a waveform that crosses the trigger level
multiple times. Examining the waveform allows you to identify
whether the shape of the signal is going to allow a single trigger
crossing per cycle at the selected trigger level. If multiple
triggers are likely to occur, select a trigger level that will
generate only a single trigger per cycle. If the trigger frequency is
still faster than the display indicates, you may have aliasing.
If the trigger frequency is slower, this test is not useful.
H If the signal you are viewing is also the trigger source, use the
graticule or the cursors to estimate the frequency of the displayed
waveform. Compare this to the Trigger Frequency readout in the
lower right corner of the screen. If they differ by a large amount,
you may have aliasing.
The next table lists the time base settings that you can use to avoid
aliasing at various frequencies and the respective sample rate. At the
fastest SEC/DIV setting, aliasing is not likely to occur due to the
bandwidth limitations of the oscilloscope input amplifiers.
TPS2000 Series Digital Oscilloscope User Manual
Understanding Oscilloscope Functions
3- 11