IQ signal FFT

[pgo48]

H, I'm trying to display the FFT of a data file. This data file contains real and imaginary values from a quadrature demodulator.

I seperate the re and im data and then combine it with a re/im -> complex box. Then I use a build waveform box to provide the dt information, and then to a "FFT spectrum (real-imag)" box. I take the complex modulus and feed it to a graph - but what i get looks completely wrong!

I have no idea what I'm doing wong - I use exactly the same approach in matlab and this works fine. In other posts about this I keep seeing a pd "fhttp://www.masimo.com/pdf/whitepaper/LAB3412A.pdf Murilo Oliveira National Intruments Brazil" mentioned but the link is broken.....  

can anyone help?

[johnsold]

It is pretty hard to tell what the problem might be from a description like "...looks completely wrong!"

1. Please post your VI.

2. Please post the data.

3. Please tell us why you think it looks wrong.  In particular indicate what the spectrum should look like.

4. Why not use FFT Spectrum (Mag-Phase)?

Lynn