Flattop
Use for amplitude accuracy.
Window Characteristics
The window characteristics are shown below.
Window
Highest
Side Lobe
(dB)
3 dB
Bandwidth
(bins)
6 dB
Bandwidth
(bins)
Scallop
Loss
(dB)
Rectangular
−
13
0.89 1.21 3.92
Hanning
−
32
1.44 2.00 1.42
Flattop
−
70
3.38 4.17 0.005
Highest Side Lobe
The minimum attenuation in the stop band. It indicates the level
of leakage present in the filter; that is, how high the skirts are in relation to the main
peak.
3 dB bandwidth
The width of the peak at a level 3 dB down. A narrow 3 dB
bandwidth helps in separating frequency peaks that are close together.
6 dB Bandwidth
The width of the peak at a level 6 dB down.
Bins
The distance between frequency points. One bin equals the resolution.
Scallop Loss
The attenuation of the peak half way between bins. The scallop loss
determines the amplitude accuracy of a window. It measures the attenuation of a
signal that falls between frequency bins versus one that is exactly on a frequency bin.
FFT Measurements
FFT Freq Frequency of a peak TMin Frequency at minimum point
FFT Mag Magnitude of a peak VMax Maximum amplitude
FFT
∆
Freq
∆
Magnitude between peaks
VMin Minimum amplitude
FFT
∆
Mag
∆
Frequency between peaks
Vp-p
∆
Magnitude, Max–Min
TMax Frequency at maximum point Vtim Magnitude at a frequency (HP-IB only)
FFT Update Time
Points Update Time Points Update Time
64 10 ms 2048 140 ms
128 15 ms 4096 290 ms
256 20 ms 8192 600 ms
512 35 ms 16384 1.25 s
1024 70 ms 32768 2.60 s
The update time includes acquisition, window calculation, FFT calculation,
and the display of the FFT. The conditions are: 125 MHz span, real time,
triggered mode, channels off, measurements and markers off, other functions
off, and interpolation off.
Specifications and Characteristics
Characteristics
16–7
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