calibration of magnetometer problem

I have time series(magnetic field strength) in mV.I want to convert them to nT.The tutorial says I should perform FFT,than calibration and then inverse FFT.Calibration formula is

H=0.8V/nT*Fm*Ft*V
Fm=jf/jf+4Hz,
Ft=1591Hz/(1591Hz+jf)

Click to expand...

Can someone elaborate more on this please?

The "calibration formula" and the frequency characteristic described in the "calibration file" are considerably different.

Which is describing the magnetometer behaviour, how are both calibration data sets related?

The advantage of the calibration formula (high-pass/low-pass combination) is that it can be transformed to a digital filter that applies the calibration in time domain without taking the FFT detour.

To use the calibration file table, it must be interpolated for all frequency points. Calibration points in frequency domain are applied by performing a complex division.

I have posted
https://dsp.stackexchange.com/questions/26168/why-do-i-need-inverse-fft

with more details.

Post the relevant information here if you expect answers.

The company has supplied us with calibration file with amplitude and phase
FREQUENCY MAGNITUDE PHASE
Hz deg
Chopper On
+4.0000E-01 +2.0029E-02 +8.9240E+01
+5.5580E-01 +2.0014E-02 +8.8988E+01
+7.7230E-01 +2.0015E-02 +8.8581E+01
+1.0731E+00 +1.9983E-02 +8.8125E+01
+1.4910E+00 +1.9968E-02 +8.7434E+01
+2.0718E+00 +1.9905E-02 +8.6420E+01
+2.8787E+00 +1.9982E-02 +8.5051E+01
+4.0000E+00 +1.9870E-02 +8.3150E+01
+5.5580E+00 +1.9682E-02 +8.0568E+01
+7.7230E+00 +1.9384E-02 +7.7043E+01
+1.0731E+01 +1.9086E-02 +7.2226E+01
+1.4910E+01 +1.8299E-02 +6.5992E+01
+2.0718E+01 +1.7111E-02 +5.7990E+01
+2.8788E+01 +1.5136E-02 +4.9340E+01
+4.0000E+01 +1.2827E-02 +3.9938E+01
+5.5580E+01 +1.0216E-02 +3.0869E+01
+7.7230E+01 +7.9651E-03 +2.3202E+01
+1.0731E+02 +5.9657E-03 +1.6897E+01
+1.4910E+02 +4.3858E-03 +1.2038E+01
+2.0717E+02 +3.1915E-03 +8.2451E+00
+2.8788E+02 +2.3104E-03 +5.3458E+00
+4.0000E+02 +1.6673E-03 +3.0228E+00
+5.5580E+02 +1.2001E-03 +1.0869E+00
+7.7230E+02 +8.6420E-04 -7.2983E-01
+1.0731E+03 +6.2182E-04 -2.6219E+00
+1.4911E+03 +4.4726E-04 -4.8106E+00
+2.0718E+03 +3.2083E-04 -7.3421E+00
+2.8788E+03 +2.3068E-04 -1.0992E+01
+4.0000E+03 +1.6523E-04 -1.5672E+01
+5.5580E+03 +1.1835E-04 -2.2118E+01
+7.7230E+03 +8.3076E-05 -3.1815E+01
+1.0731E+04 +5.6489E-05 -4.4129E+01
+1.4910E+04 +3.6531E-05 -5.9932E+01
+2.0718E+04 +2.1365E-05 -7.6540E+01
+2.8788E+04 +1.2866E-05 -9.1590E+01
+4.0000E+04 +8.3595E-06 -1.1793E+02
+5.5581E+04 +4.4340E-06 -1.5828E+02
+6.0000E+04 +3.6318E-06 -1.6734E+02
How to convert this file in file with real and imaginary components(instead of amplitude and phase)?