Patent ID: 8441260

Claim:
A transmit-receive switching circuit for use in an NMR spectrometer, the switching circuit being cooled during use to reduce thermal noise, the switching circuit comprising: a first terminal to which high-power RF pulses for observation are applied; a second terminal connected with an NMR detector for applying the RF pulses to a sample and for detecting an NMR signal from the sample; a third terminal for outputting the NMR signal to an external reception circuit; crossed-diodes permitting the RF pulses applied from the first terminal to be supplied to the second terminal; a transmission line permitting the NMR signal applied from the second terminal to be transmitted to the third terminal; plural stages of phase shifters inserted in the transmission line and connected in series with each other, the phase shifters acting to shift the RF pulses in phase by an angle given by (90°+180°×n) (where n is 0 or a natural number); and shunts connected between respective ones of the output ends of the plural stages of phase shifters and earth ground; wherein when the RF pulses for observation are applied to the first terminal, the crossed-diodes and the shunts are brought into conduction to supply the RF pulses from the first terminal to the NMR detector via the second terminal; and wherein when the NMR signal is entered from the second terminal after application of the RF pulses, the crossed-diodes and the shunts are cut off to supply the NMR signal from the second terminal to the third terminal.