FFT in oscilloscope measuring Frequency spectrum

Thread Starter

Electronic_Maniac

Joined Oct 26, 2017
252
I am using a Keysight InfiniiVision MSOX3054T Scope having Bandwidth of 500MHz and Sampling rate of 5Gsa/s.

I am learning to use the FFT Option in the scope.

Below is the waveform I captured of my QSPI Clock signal (48MHz)


My questions :

  1. What is the threshold and the excursion levels (marked in red) mean? How to play around this value?
  2. And how is the -4.97dBV calculated (again marked in red)? Can someone show the calculation for the -4.97dBV value?



1576582773499.png
 

tautech

Joined Oct 8, 2019
63
The Threshold and Excursion settings are only relevant for Search of frequency peaks.
You need to slow the timebase and then adjust the Hz/div in FFT mode for more meaningful results.
Amplitude levels are dependent on signal source impedance and connection type.

If you have a sig gen or AWG use that to help get your head around FFT.
 
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