FFT Spectrum Analyzer

[Argon]

Hello everyone, I hope you can help me with a project I am working on. This is what I need to do:

Design a “Spectrum Analyzer” using the Fast Fourier Transform (FFT) method. The number of FFT points (N) should be one of the variables on the front panel.

I have been able to obtain the power spectrum by using the "Spectral" Express VI, the "FFT Power Spectrum" VI, and "FFT Power Spectrum Density" VI. All three work fine. The only problem is that I need to be able to CHANGE the number of FFT points (i.e. 64, 128, 256, 1024, etc.) on the front panel and NONE of the VIs mentioned before let me do this. I have tried using the FFT.vi which has an input called "FFT Size" but when I compare the output of this VI with the output obtained using any of the first three VIs, they are completely different. Please help me!!!

[Kallis]

Argon,

If Fs is your sampling rate and N is the number of samples that you gave to the FFT Power spectrum. vi, the the output will have N/2 points and resolution will be Fs/N.

So if you want the VI to give 64 points, then give 128 samples only to the VI. In this case your resolution will be Fs/128.

Now, if you want to do a 64 point FFT, then you need to give 64 samples to the vi and your resolution will be Fs/64 and the output of FFT vi will have 32 points.

See the attached example.

[Argon]

Thank you so much for your help!!!

[Dost]

I have data  sampled at 1000 hz.I have about 2400 data points .I want to do FFt on this data ,. by theory i know that it will give me 500 frequecy window having 1200 dat apoints. I used express VI of spectral measurement  it gives me  frquency till 250 hz having interval of 25 hz. what should i do to  properly do FFT. Any comments.

Dost