PSD to Time History and back to PSD?

[JXBWk]

To all

In need of some expert input. I am trying (haven’t started yet so no 1st –go mcad sheet attached yet- It will come soon!) to do the following (all standard stuff for anyone into signal processing)
1. From a PSD create a time history
2. Superimposed some other time profiles to the time history created in #1
3. Create a PSD (via FFT ) of the new time signal

Thanks

[Edit] attached mcad 15 file

[Fred_Kohlhepp]

Getting from time history to FFT (fast Fourier transform) and back is simple; Mathcad has four functions and their inverses to accomplish that (my favorite used to be CFFT.)

But the power spectral density is gotten by squaring the amplitudes of the Fourier transform.  This operation causes the phase information in the transform to be lost.  So you can go from time history to PSD, but the information required to reconstruct the time history from the PSD isn't available.