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SDS5000X Series Digital Oscilloscope User Manual
161 / 236 W W W. S I G L E N T. C O M
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.
When the number of points in 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 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 time domain is 5 GSa/s and
number of samples is 5 Mpts, FFT first decimates the samples by 2, to
2.5 Mpts, and then take the first 2 Mpts to calculate the spectrum. In
this example, FFT sample rate = 5 GSa/s ÷ 2 = 2.5 GSa/s.
FFT points (Curr): The current FFT points, which is an integer power of 2.
The SDS5000X supports up to 2M (2097152) points.
Frequency interval (△f): The frequency interval between two adjacent
points in the FFT sequence, which is proportional to the frequency
resolution.
Average count of FFT (Avg): Displayed only when the FFT mode is set to
"Average", indicating the completed average count.
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