How to create FFT from XY Envlope

[Slizeer]

How can I create FFT from XY Envelope? I must create Time Signal with Y, dt and t0, but I don't know how.

Can anyone hlep me? 

[johnsold]

If you use the FFT VI from the Signal Processing >> Transforms palette, you do not need the waveform datatype.  If you want to use one of the other transform VI, you can use Build Waveform from the Waveform palette.

Lynn

[altenbach]

You already have a time signal with all these parameters, the brown wire on the left. After FFT you no longer have t0 and dt, but f0 and df.

Your question is not clear at all. Can you explain what you actually want?

[Slizeer]

I want to get FFT from Envelope signal (last graph - pink colour) not from Mathan Waveform. Envelope's data type is cluster of 2 elements. To perform FFT analysis I need Waveform DBL data type. How can I get this?

[JJava]

1-D FFT is performed on an 1 dimensional signal array, which means that you can simply perfrom FFT on Y.

Y has 83 sample points acording to your vi, and you will get a FFT result with 83 elements.

Hope this will help 🙂

[Slizeer]

I need to get receive something like this:

[altenbach]

Whatever your showing us on this picture cannot be a FFT of the envelope signal in your example program. Most of the fft will be in the first few bins.

[Slizeer]

This is only a example picture. Can anyone say me, how can I get FFT envelope and receive something like on picture above?

[johnsold]

The VI I posted above takes the FFT of the envelope signal in XY Graph 2 and plots it on XY Graph 3.  As altenbach said, almost all the energy is the the lowest 4 bins.

If the result is not what you want, maybe you are asking the wrong question.  It is not clear what the FFT of the envelope represents.  If the envelope represents a periodic keying of the higher frequency carrier wave, you need more data so that you can see what the keying frequency is.  What you have shown could be one complete cycle or 0.001% of a cycle, or something completely unrepresentative of the real periodic signal.

Lynn

[Slizeer]

Thanks for Your answer.

Clipboard01. jpg shows the sequence of tasks that I perform. My_file.vi shows my current achievements. I don't know why the timeline has all values equal 3.40356 E 9 and why the FFT doesn't show the main harmonics.
And apologize for my English ...