Receiver gain function: the actual NMR receiver gain.

The observed NMR signal size depends on the receiver gain parameter. We propose a receiver gain function to characterize how much the raw FID is amplified by the receiver as a function of the receiver gain setting. Although the receiver is linear for a fixed gain setting, the actual gain of the receiver may differ from what the gain setting suggests. Nevertheless, for a given receiver, we demonstrate that the receiver gain function can be calibrated. Such a calibration enables accurate comparison of separately acquired NMR signals in quantitative analysis, which frequently requires different receiver gain settings to avoid receiver saturation or achieve optimum sensitivity. The application of receiver gain function, along with the definition of receiving efficiency, allows easy concentration determination by a single internal or external concentration reference.