Keysight Technologies 3458A Guide D'utilisation page 195

The Sampling Rate
The Nyquist or Sampling Theorem states:
In practice, the multimeter's sampling rate must be at least twice the highest
frequency component of the signal being measured. The sampling rate is the
reciprocal of the time interval specified by the TIMER command or the
effective_interval specified by the SWEEP command. For example, assume the
effective_interval is specified as 20 µs. The sampling rate is then 1/20 µs = 50,000
samples per second.
Figure 5-4
the dashed line, the result is an alias frequency which is much different than the
frequency of the signal being measured.
Figure 5-4 Aliasing caused by undersampling
Keysight 3458A User's Guide
If a continuous, bandwidth-limited signal contains no frequency components
higher than F, then the original signal can be recovered without distortion
(aliasing) if it is sampled at a rate that is greater than 2F samples per second.
shows a sine wave sampled at a rate slightly less than 2F. As shown by
Digitizing 5
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