The Consequences of Setting the Receiver Gain Too High

The receiver gain of an NMR spectrometer is much like the volume control on a radio. When it is set too high there will be distortion in the NMR signal. The FID will be clipped near the beginning of the signal. The Fourier transform of this distorted signal is a distorted NMR spectrum. The figure below shows what this distortion looks like.

Many spectrometers will calculate the receiver gain automatically however you should be aware that this automatic calculation is not always perfect and that the receiver gain may have to be set manually. On a Varian spectrometer the receiver gain is the "gain" parameter. On a Bruker spectrometer the parameter is "rg". In both cases higher numbers mean a higher receiver gain.

University of Ottawa NMR Facility Blog