DI-770 Oscilloscope provides five virtual instruments in one

DI-770 and WINDAQ/Scope Manual
The original signal is sampled at a sample time t. The critical frequency (Nyquist frequency) is (1/2t) Hz.
Windowing
FFT treats the FFT-block like it is one period of a periodic signal. If the sampled signal is not periodic, harmonic distortion
can arise, since the periodic waveform, 'created by the FFT', can have sharp discontinuities. See also the following
illustration. These discontinuities are also called calculation errors.
This means that because of the calculation errors extra frequency components are generated around the true frequency.
Because of this 'smearing' the amplitude of the true frequency decreases, since the area under the curve
remains the same.
The smearing, caused by the calculation errors, can be decreased by placing a window on the FFT-block samples, in
such a way that the ends of the FFT-block are smoothly tapered to zero and discontinuities do not occur when the FFT
treats the windowed block as one period of a periodic signal. Each sample of the FFT-block is therefore multiplied by
a factor, whose size is dependent on the position of the sample in the FFT-block.
The software supports six different windows:
rectangular (all data is not changed)
Hanning (sinusoidal)
Hamming (sinusoidal)
Bartlett (sinusoidal)
Blackman (triangular)
Parzen (triangular)
Displaying channels
The spectrum analyzer has several modes to display the two channels. To select the measure mode, enter the Measure
menu and select:
Ch1 measure and display only channel 1
Ch2 measure and display only channel 2
Ch1 and Ch2
measure channel 1 and channel 2 simultaneously and display the values of both channels
When only one channel is measured, the controls of the other channel are disabled or removed from the display.
The Spectrum Analyzer
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