GB1433397A - Receiver circuits for nuclear magnetic resonance analysers - Google Patents

Abstract

1433397 Filter circuits NIPPON ELECTRIC VARIAN Ltd 24 Sept 1973 [30 Sept 1972] 44641/73 Heading H3U [Also in Division G1] The signal pick-up coil of an NMR spectrometer is connected to a crystal resonator so as to be resonant at two frequencies, the crystal being such that at the higher of the two frequencies it acts as a capacitor and at the lower of the two it acts as an inductor. The two frequencies may be from a nucleus being investigated (e.g. 60 MHz) and a <SP>2</SP>H nucleus for field locking (e.g. 9 MHz). The narrow bandwidth of Ae crystal allows the fundamental frequency of the RF magnetic excitation to be eliminated. The impedance of the crystal is shown in Fig. 4; the higher frequency must lie above f p , the crystals parallel resonant frequency, and the lower frequency must lie between f p and f o , the series resonant frequency of the crystal. Fig. 3 shows an embodiment in which the pickup coil 20 forms a resonant circuit with crystal 43 and capacitors 41, 42. The two resonant frequencies are passed to transistor 50 and separated by inductors and capacitors in the collector circuit to give outputs F 1 , F 2 . Equivalent circuits at these two frequencies are given, Figs. 5, 6 (not shown). In another embodiment, Figs. 9-11 (not shown), the two frequencies at extracted at opposite sides of the crystal and are separately amplified.