65.8. Recommendations

Consider the following hints and recommendations when setting up and performing your own ping test:

  • Disable automatic time stepping (AUTOTS,OFF) when generating the data for the *FFT command, as the data must use time steps of constant size.

  • When performing a mode-superposition transient analysis, results are saved every fourth time step by default; therefore, be sure to account for the default save behavior when interpreting the *FFT results. If necessary, you can either change how frequently the results are saved (OUTRES) or modify the vector array size accordingly.

  • For transient data, set *FFT to return partial results (ResultFormat = PART). (Full results return a mirror of the data which should be ignored when interpreting results.)

  • *FFT does not directly account for time data. To determine the associated frequency, divide the number of cycles by the time duration of the signal.[3]


[3] Because index number 1 (Bin 1) is 0 Hz, the actual number of cycles = index number - 1. To calculate frequency after obtaining the *FFT results, subtract 1 from each index number before dividing by the signal duration.