Adjustment of Pulse Frequency

For routine PFT NMR measurements, the pulse frequency is adjusted by changing the frequency of the transmitter until the CW spectrum of a reference sample with signals at both ends of the spectral width (e.g. acetone, Fig. 1.10) is reproduced exactly by Fourier transformation of the FID signal. 

If the pulse frequency offset is chosen in the center of Larmor frequency range zl, both halves A/2 of the spectrum are sampled simultaneously and folded into each other. Folding can be corrected by a modification of the Fourier transformation software and 

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