NB. read in data and subtract linear background
D14=: |: mread 'your_path/14Hz.dat'
't d'=. D14
k=. i. 130
t0=: k{t         NB. take only the first 130 frequency points
d0=. k{d         NB. and the corresponding Fourier transform data
linear=: {{ 0.6 + 0.0286*(y-11.5) }}
lin=. linear t0  NB. evaluate points on the linear baseline
d1=: d0-lin      NB. Fourier data with baseline subtracted
lhs=: t0;d1      NB. we define global values "lhs"
pwh=: 14 2 0.3   NB. just an example of the 1st guess