Tektronix TDS 200-Series, Руководство пользователя

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Basic Concepts
18
TDS 200-Series Digital Oscilloscope User Manual
The oscilloscope shows the time per division in the scale readout.
Since all active waveforms use the same time base, the oscilloscope
only displays one value for all the active channels, except when you
use a Window Zone.
Aliasing. Aliasing occurs when the oscilloscope does not sample the
signal fast enough to construct an accurate waveform record. When
aliasing happens, you see a waveform with a frequency lower than
the actual waveform being input or a waveform that is not stable
even though the oscilloscope triggered.
Actual high-frequency
waveform
Apparent low-frequency
waveform due to aliasing
Sampled points
One way to check for aliasing is to slowly change the horizontal
scale with the SEC/DIV knob. If the shape of the waveform changes
drastically, you may have aliasing.
To represent a signal accurately and avoid aliasing, you must sample
the signal more than twice as fast as the highest frequency compo-
nent. For example, a signal with frequency components of 5 MHz
would need to be sampled at 10 Megasamples per second or faster.