Magnifying and positioning an FFT spectrum
You can magnify and use cursors to take measurements on the FFT spectrum.
The oscilloscope includes an FFT Zoom option to magnify horizontally. To
magnify vertically, you can use the vertical controls.
Horizontal zoom and
position
The FFT Zoom option lets you horizontally magnify the FFT spectrum without
changing the sample rate. Zoom factors are X1 (default), X2, X5, and X10. At
zoom factor X1, and with the waveform centered in the graticule, the left
graticule line is at 0 Hz and the right graticule line is at the Nyquist frequency.
When you change the zoom factor, the FFT spectrum is magnified about the
center graticule line. In other words, the axis of horizontal magnification is the
center graticule line.
Turn the Horizontal Position knob clockwise to move the FFT spectrum to the
right. Push the knob to position the center of the spectrum at the center of the
graticule.
Vertical zoom and position
The channel vertical knobs become vertical zoom and position controls for their
respective channels when displaying the FFT spectrum.
Turn the Vertical Position knob clockwise to move the spectrum up for the
source channel.
Measuring an FFT spectrum using cursors
You can take two measurements on FFT spectrums: magnitude (in dB), and
frequency (in Hz). Magnitude is referenced to 0 dB, where 0 dB equals 1 V
RMS
.
You can use the cursors to take measurements at any zoom factor. To do so,
follow these steps:
1. Push the Cursor button to see the cursor side menu.
2. Push Source ► FFT.
3. Push the Type option button and use the Multipurpose knob to select
Magnitude or Frequency.
4. Select Cursor 1 or Cursor 2.
5. Use the Multipurpose knob to move the selected cursor.
Use horizontal cursors to measure magnitude and vertical cursors to measure
frequency. The options display the delta between the two cursors, the value at
cursor 1 position, and the value at cursor 2 position. Delta is the absolute value
of cursor 1 minus cursor 2.
FFT
TBS1000B and TBS1000B-EDU Series Oscilloscopes User Manual 59
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