Noise measurement of a preamplifier with high input impedance using an NMR console

This article describes the noise measurement of a preamplifier with high input impedance designed for experiments with receive coils in nuclear magnetic resonance (NMR). The noise of the preamplifier was determined in two ways. A circuital analysis of the preamplifier provided an equation for the preamplifier noise calculation and the noise voltage was measured with an NMR console and in accordance with known theory the measured analogue noise signal was modified to a discrete noise signal. An objective function with noise parameters of the preamplifier as variables was created. The noise parameters of the preamplifier were calculated with an optimization procedure and the results of the calculation and of the measurement compared. Qualitative and quantitative agreement was good. It was proved that the noise parameters of a preamplifier for NMR experiments can be measured with an NMR console and derived theory.