Noise current measurements and signal-to-noise improvement in low-temperature, low-frequency nuclear-magnetic-resonance experiments

A NMR pickup coil cooled to low temperature generates virtually no noise. Advantage can be taken of this fact in the low megahertz range by proper design and, in particular, by taking the current noise sources in of the room-temperature input circuitry carefully into account. A low-noise rf line and a method to measure very small in’s in the 10-kHz–1-MHz frequency range are described.