Velleman PCSU1000 DSO - Manual (Page 11)

Menu Options 10
© 2005 ... Velleman
Print
Prints the image in color.
You can edit the image caption.
Print Setup
Selects a printer and sets printer options before printing. The available options depend on the
printer you select.
Exit
Terminates the program.
Calibrate & Exit
Makes the oscilloscope calibration, saves the calibration values to the WinDSO.INI file and
terminates the program. This option should be used when the new oscilloscope has been on for
about 1h.
This option performs following operations:
1. The fine adjustment of the trace Y-position (offset) on different Volt/Div and Time/Div scales.
2. Sets the trace labels (on the left side of the screen) to correspond the trace GND level.
3. Sets the triggering level mark to correspond the triggering level.
2.2 Edit Menu
Copy
Copies the image to the Windows' clipboard.
Paste
Pastes the image residing in Windows' clipboard to the screen.
2.3 Options Menu
FFT Window
Set the window function used to taper the original signal before calculating the FFT..
Spectrum analyzer supports six different FFT windows
1. Rectangular
2. Bartlett
3. Hamming
4. Hanning
5. Blackman
6. Flat top
The Hamming window is set as default at the startup
Background information
It is common practice to taper the original signal before calculating the FFT (Fast Fourier
Transformation). This reduces any discontinuities at the edges of the signal. This is done by
multiplying the signal with a suitable window function. By choosing a tapered window it is possible to
achieve a good compromise between main lobe width and sidelobe levels of a spectral line. The
undesirable spectral leakage can be reduced using a tapered window, at the expense of some
broadening around individual spectral lines. Many different windows have been designed for this
purpose.
The choice of a suitable one depends on the nature of the signal or data, and on the type of
information to be extracted from its spectrum. In general, a good FFT window has a narrow main
spectral lobe to prevent local spreading of the spectrum, and low sidelobe levels to reduce 'distant'
spectral leakage. In some cases it may be best to leave the data alone -- in effect, to use a
rectangular window. For example, if a signal has close spaced components of roughly the same
amplitude, the rectangular window will probably offer the best chance of resolving them. Conversely,