Teledyne T3DSO1000, Руководство пользователя, Страница: 140 / 227

122 User Manual
To display an FFT waveform:
1. Press the Math button on the front panel to open the MATH function menu.
2. Press the Operation softkey and then turn the Universal Knob to select FFT . The
resulting math waveform is displayed in white and labeled with “M”.
3. Press the Source softkey, and then turn the Universal Knob to select the source to
do an FFT operation. Analog channels can be used as the source.
4. Press the Window softkey, and then turn the Universal Knob to select an appropriate
window.
Spectral leakage can be considerably decreased when a window function is used. The
oscilloscope provides five windows (Rectangle, Blackman, Hanning, Hamming and
Flattop) which have different characteristics and are applicable to measure different
waveforms. You need to select the window function according to different waveforms
and their characteristics. Please read the table below carefully to make an appropriate
option choice according to the input signal.
Window Applications and Characteristics
Rectangle
This is normally used when the signal is transient (completely
contained in the time-domain window) or known to have a fundamental
frequency component that is an integer multiple of the fundamental
frequency of the window. Signals other than these types will show varying
amounts of spectral leakage and scallop loss, which can be corrected by
selecting another type of window
Hanning
Reduced leakage and improve amplitude accuracy.
Frequency resolution is also reduced.
Hamming Reduce leakage and improve amplitude accuracy.
Frequency resolution is also reduced.
Flat Top This window provides excellent amplitude accuracy with moderate
reduction of leakage, but with reduced frequency resolution.
Blackman Leakage is reduced to a minimum, but with reduced frequency
resolution.
5. Press the Center softkey, and then turn the Universal Knob to select the desired
center frequency.
6. Press the Hz/div softkey, and then turn the Universal Knob to select the desired
resolution frequency.
7. Press the Scale softkey, and then turn the Universal Knob to select the desired
vertical FFT scale
8. Press the Ref Level softkey, and then turn the Universal Knob to select the desired
vertical FFT offset.
9. Press the Unit/Load softkey to enter Unit/Load menu. Press Unit softkey to select the
unit of vertical axis. The units of the vertical axis can be dBVrms, dBm or Vrms which
use a logarithmic scale or a linear scale to display vertical amplitude respectively. If
you need to display the FFT frequency spectrum in a relatively larger dynamic range,
dBVrms is recommended. Press Ext Load softkey, and then turn the Universal Knob
to select the external load value.