FFT tips
■
You can only display FFT waveforms for 1000, 2000 and 20K record length
waveforms.
■
Use the Vertical Position knob of the source channel to change the vertical
position of the FFT waveform.
■
Use the Vertical Scale knob of the source channel to change the vertical size
of the FFT waveform.
■
Use cursors to measure frequencies and relative signal levels.
■
Input signals that have a DC component or offset can cause incorrect FFT
waveform component magnitude values. To minimize the DC component,
use AC Coupling on the input signal.
■
To reduce random noise and aliased components See FFT and display
waveform aliasing on page 119. in repetitive or single-shot events, set the
oscilloscope acquisition mode to average over 16 or more samples. Average
mode attenuates signals not synchronized with the trigger.
■
Do not use the Average acquisition mode if the source signal contains
frequencies of interest that are not synchronized with the trigger rate.
■
For transient (impulse, one-shot) signals, set the oscilloscope trigger
conditions so that the transient pulse waveform is centered in the waveform
record.
About FFT windows
The FFT algorithm applies a ‘window’ process to the source waveform record to
‘shape’ the record so that the start and stop values for the FFT waveform are
close to the same amplitude. Starting and stopping the waveform at close to the
same amplitude reduces adding artificial waveform that are not present in the
actual signal. Using a window on the source signal results in an FFT waveform
that more accurately represents the source signal frequency components.
Analyzing a waveform
116 TBS2000B Series Oscilloscopes User Manual
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