Nyquist Fold-backs and the Mode of Data Acquisition

Some older Bruker NMR spectrometers allow the collection of the two quadrature channels of the FID either simultaneously (where complex pairs of points are collected at the same time) or sequentially (where a real data point is collected then an imaginary point etc...). In the case of simultaneous acquisition, a Nyquist fold-back will fold in at the far side of the spectrum, whereas for sequential data acquisition, it will fold in at the near side of the spectrum. This is illustrated in the figure below. The data were collected without digital filtering.

Thank you to Dr. Michael Lumsden, the NMR Facility Manager at Dalhousie University for suggesting this entry.