Plotting double-sided graph for FFT.

[davizpoh@yahoo.com.sg]

    Hi everyone,

I have searched through the NI discussion forum and have read through the tutorial article "Using FFT & Power spectra in Labview".
Have found it quite useful, but just cannot find most of all the functions given in the example block diagrams (eg. in figure 8).

I have attached a sample VI (LV 7.1) which I wish  to display the doubled-sided spectrum in the graph.

Really appreciate is someone can help me with this.


Regards,
Daviz

[johnsold]

Daviz,

I don't think the double sided data is available on this express VI. If you open the front panel and convert it to a standard VI,then you can dig down into the diagram. When I did that I found that the two-sided FFT is performed 8 levels of subVIs down into your program. To get a double sided result you would need to modify everything in that hierarchy.

It would probably be much simpler to start over. Just go to the Functions Palette >> Signal Processing >> Transforms >> FFT.vi and build your own from there. If you need windowing functions they are also availble.

Express VIs are nice for doing the things they are set up to do, but if you want soemthing different, it is usually easier to build it from the elementary functions than to try to adapt the express VIs.

Lynn