Questions about example FFT

[Rafi2003]

Hi,

I"m working on a project of analyzing analog signals (from VB6) and I'm trying to understand the FFT example.

1.  How does the zooming works on the graph.  I wasn't able to see it.....not in the program and not in the properties of the graph.

2.  I expected to see a frequency on the X-axes and what I see is the number of samples.  Can anybody explain it?

3.  My present objective is to plot the signal on a frequency domain graph where the X-axes is frequency and the Y-axes is db.

Thank you very much

Rafi

[Snowman 6008]

For zooming  drag over the portion of the graph you wish to zoom into. If you take a look into the method help for the .fft it specifically talks about all of the outputs and give a link to another document that discusses the Fast Fourier Transform itself.
 

If you are looking to plot power versus frequency I recommend checking out the example located at 

 C:\Documents and Settings\All Users\Documents\National Instruments\MStudioVS6\VB\Samples\Analysis\Spectrum\Power Spectrum

[Rafi2003]

I Richard,

I was looking at this exact example and apparently this is what I was looking for.

However, I have few more questions:

1.  How to set the Y-Axes to show db

2.  How to calculate the energy of the 1st harmonic, 2nd harmonic,  3rd harmonic

Thanks for your support

[Snowman 6008]

Since in this example we're getting back the spectrum you can pull out the y values and take a logarithm on them. I'm familiar with Measurement Studio, but not familiar with a "1st harmonic" calculation in reference to a fast fourier transforms.