A Simple Method of Measuring the Noise Figure of the NMR Spectometer

Abstract

Sensitivity is one of the fundamental parameters of the Nuclear Magnetic Resonance experiment. It depends particularly on the coil and impedance matching of the resonance circuit of the probe to the input amplifier. However, sensitivity is also influenced by the noise of the receiver of the spectrometer, and the insertion loss of the matching and switching circuits as well as of passive fillers inserted in front of the input preamplifier manifests itself markedly. In this paper, a simple method of measuring the noise figure feasible in the NMR laboratory is described. Using non-standard probes and coils, the measurement of the noise figure enables one to estimate to what degree the detection system itself participates in the signal/noise ratio deterioration. The method can be used also for measurements of other radio-frequency signal processing systems.