The distribution of coefficient values for a single FFT is exponential if the original data contain no periodic signal. This distribution can be plotted and inspected. Significant coefficients will appear beyond the high-value end of the normal distributions. The width of the histogram bins can be adjusted (before running fft) to get a nice looking plot.
To plot the power density distribution created by fft.
xt> fft.histogram_bi=0.5 # if necessary, adjust number for an aesthetic plot xt> ftpplot input table file: rp90_ftpThe plot will appear on the screen. To make hard copy, type = with cursor within plot. To return to text window type q.