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We have carried out nuclear magnetic resonance experiments in microtesla range.The free induction signal was recorded using a high Tc dc-superconducting quahtum interference device.The measurement was performed in a home-made magnetic shield room.Resonance spectra of 1H from a sample of 15 ml tap water was obtained in the field range from 7—70 μT,corresponding to resonance frequency of 300—3000 Hz,The signal to noise ratio in a single-shot measurement is around 4,which could be increased to about 40 after 100 times averaging.The effect of residual magnetic field in the shield room, prepolarization time and data acquisition time was investigated.
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