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SDS6000L User Manual
int. s i g l e n t . c o m 1 9 1
A. Time-domain waveform display area
B. Spectrum (FFT) waveform display area
C. FFT parameter display area
D. Dialog box
Parameter Display Area
The FFT parameters are displayed in the upper right of the spectrum waveform display area:
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FFT sample rate (Sa):
FFT operation results present the first Nyquist zone (DC ~ Sa/2) of the
frequency spectrum. Be aware that the FFT sample rate may be inconsistent with the sample rate
in the time domain. Assuming the max points value is set to 2 Mpts:
✓ When the number of points in the time domain, N, is less than 2 Mpts, the FFT takes the
number which is an integer power of 2 closest to N. In this case, FFT sample rate = sample
rate in the time domain.
✓ When N is greater than 2 Mpts, FFT first decimates N by D and then takes the first 2 Mpts
for the calculation. In this case, FFT sample rate = sample rate in time domain/D.
For example, in the case of sample rate in the time domain is 5 GSa/s and the number of
samples is 5 Mpts, the FFT first decimates the samples by 2, to 2.5 Mpts, and then takes the
first 2 Mpts to calculate the spectrum. In this example, FFT sample rate = 5 GSa/s ÷ 2 = 2.5
GSa/s.
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FFT points (Curr):
The current FFT points, which is an integer power of 2. The SDS6000L
supports up to 8 M points (8388608, to be exact).
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Frequency interval (
â–³
f):
The frequency interval between two adjacent points in the FFT
sequence, which is proportional to the frequency resolution.
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Average count of FFT (Avg):
Displayed only when the FFT mode is set to "Average", indicating
the completed average count.
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