Hello,

We've a Lecroy Waverunner 204Xi. Recently, I performed the FFT (using scope FFT function) of a measured signal. However, I found out, when I calculated the FFT of the measured signal in MATLAB, the results are different from that obtained from the scope. I'm quite sure the algorithm used in my MATLAB code is correct because I have copied it from MATLAB help file, and it has been validated using a simple sinewave example. I think I don't fully understand the FFT, and probably the way the scope calculates the FFT is different. I need some guidances here to clear all my doubts, and I've a few questions documented in a PDF file. Besides, the raw data (recorded by the scope) as well as m-files to do all the calculations, are provided in 'Lecroy.zip'.

 

Hello,

We've a Lecroy Waverunner 204Xi. Recently, I performed the FFT (using scope FFT function) of a measured signal. However, I found out, when I calculated the FFT of the measured signal in MATLAB, the results are different from that obtained from the scope. I'm quite sure the algorithm used in my MATLAB code is correct because I have copied it from MATLAB help file, and it has been validated using a simple sinewave example. I think I don't fully understand the FFT, and probably the way the scope calculates the FFT is different. I need some guidances here to clear all my doubts, and I've a few questions documented in a PDF file. Besides, the raw data (recorded by the scope) as well as m-files to do all the calculations, are provided in 'Lecroy.zip'.

Greetings:

I'm not familiar with that particular scope, but I've used LeCroys extensively. Have you checked which windowing function you're using? I think you can choose different windowing functions, which can have a major effect on the FFT.

Just a thought.

eric

 

Hi,

I selected "Rectangular" windowing function in the scope. By the way, you can have more details (e.g. scope settings, m-files, results, etc.) in the attachment in my first post. Kindly download it and I'm welcome any advices and comments.

Thank you very much

Warmest regards.

Greetings:

I'm not familiar with that particular scope, but I've used LeCroys extensively. Have you checked which windowing function you're using? I think you can choose different windowing functions, which can have a major effect on the FFT.

Just a thought.

eric