Considerations on the read out of low frequency NMR for 3He

For studies of the superfmid phases of 3He the technique low of frequency (500 kHz) NMR is widely used. One way to read out the NMR signal is with the continuous wave experiment. In this experiment the NMR signal is proportional with the quality factor of a tank circuit. However direct connection with a coax cable will, because of its resistivity and parasitic capacitance load the tank circuit and by that lower the quality factor In this paper two passive methods, which minimize the loading to read out the NMR signal are described and simulated. The first method reads the NMR signal over the parasitic capacitance of the coax cable, which is put in series with the tank circuit. The second method makes use of a pick up coil, which is weakly coupled to the coil of the tank circuit Both methods can preserve a high quality factor, and are optimized for best SNR