Creating and Using Math Waveforms
3- 194
CSA7000B Series & TDS7000B Series Instruments User Manual
Table 3- 13: Window characteristics
Window 3dBBWinbins Scallop loss
Nearest
side lobe
Zero phase
reference
Coefficients
Rectangular
0.89 3.96 dB --13 dB 50% 1.0
Hamming
1.3 1.78 dB --43 dB 50% 0.543478, 0.456522
Hanning
1.44 1.42 dB --32 dB 50% 0.5, 0.5
Kaiser--Bessel
1.72 1.02 dB --69 dB 50% 0.40243, 0.49804, 0.09831,
0.00122
Blackman -- Harris
1.92 0.81 dB --92 dB 50% 0.35875, 0.48829, 0.14128,
0.01168
Gaussian
2.0 0.76 dB --79 dB 50% a = 3.75 (not cosine series)
Flattop2
3.8 0.0065 dB --90 dB 50% 0.213348, --0.206985,
0.139512, --0.043084,
0.003745
Tek Exponential
1.42 0.60 dB --67 dB 20% na
H 3 dB BW in B ins. This is the bandwidth of the filter response of the spectral
analyzer to a sine wave input for a given window function. It is given in
units of bins. A bin is the interval between spectral samples when the
interpolation ratio due to FFT zero fill is one. The bandwidth is measured
between the points on the lobe that are 3 dB down from the peak of the lobe.
The bandwidth in Hz may be computed by dividing the BW in bins by the
gate duration in seconds. This is also referred to as resolution
bandwidth (RBW).
H Coherent gain. The gain factor normally associated with different window
functions is correctly scaled into the magnitude spectrum output. Therefore,
the magnitudes in the output spectrum do not change as different windows
are selected.
H Scallop Loss. This is the magnitude error of an FFT when the frequency of
the observed signal is exactly half way between two frequency samples of
the spectrum when the interpolation ratio due to zero fill of the FFT is one.
The spectral analyzer FFT length is controlled so that zero fill is always in
effect. This essentially eliminates scallop loss because zero fill in the time
domain causes interpolation in the frequency domain. This results in accurate
magnitude measurements for all window functions.
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