Window technology in frequency domain of oscilloscope
The FFT function of oscilloscope USES window technology to reduce the influence of spectrum leakage.Before executing the DFT, the DFT frame is multiplied by a window function of the same length for each sample.Window functions are usually bell-shaped and reduce or eliminate discontinuities at both ends of the DFT frame.
The four most commonly used window functions are listed below for recommended purposes:
1) Rectangle - measures a sudden transient signal in which the signal level before and after the event is almost equal
2) Hamming – measurement of sinusoidal, periodic, or narrow-band random noise, where the signal level before and after the event is significantly different
3) Hanning - measuring amplitude accuracy (low at analytical frequency) with significantly different levels of transient or burst signals before and after an event
4）Blackman/Harris - measure frequency amplitude, measure waveform with single frequency, search for higher harmonics