T3DSO2000A Manual. Page 126
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:
•
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 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, the
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, the FFT sample rate = sample rate in
time domain / D.
For example, in the case of sample rate in the time domain is 1 GSa/s and the
number of samples is 10 Mpts, the FFT first decimates the samples by 4, to 2.5
Mpts, and then takes the first 2 Mpts to calculate the spectrum. In this example,
FFT sample rate = 1 GSa/s ÷ 4 = 250 MSa/s.
•
FFT points (Curr): The current FFT points, which is an integer power of 2, up to 2
points (2097152, to be exact).
•
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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