FFT of Several Sine Wave Signals

[jamison.suade]

How come I am not having a frequency corresponding to my frequency in my time domain. I used several sine waves and do FFT  to examine its response. My frequency is from 20 to 10000 Hz, with an amplitude of 1 an increment of 10. However the one Im seeing in my FFT graph shows only the spectrum up to 100Hz, where it must be at 10000Hz. Can you guys please help me.

[Zwired1]

The .001 in your FOR loop is saying that the sample frequency in each case is 1000 Hz.  The FFT will not give you frequencies > 500 Hz in this case.  Looks like you need to output a frequency array from your mathscript and use that to calculate a delta_t (1 / f ) for use in constructing the waveforms.   

[Henrik_Volkers]

As Zwierd1 mentioned, you need to wire your delta input (1e-5) also to the dt in your wrfm creating loop.

And voila!  all frequencies in your FFT are multiplied by 100 🙂