A HIGHLY LINEAR PULSE-SHAPE MODULATOR FOR NMR APPLICATIONS

A single sideband modulator for NMR applications is presented. The cir cuit arrangement is based on the use of analogue multipliers AD834 (An alog Devices). A test of the performance of the circuit was carried ou t by harmonic analysis of the phase modulated output over a bandwidth centred at the carrier frequency using the NMR spectrometer itself. A frequency offset may be generated with 60 dB carrier rejection, wherea s the unwanted sideband and all the harmonics are attenuated by more t han 50 dB with a peak to peak low-frequency voltage input of 2.0 V. Th e high linearity of the modulator is illustrated by comparing experime ntal and theoretical slice profiles resulting from the use of auto-ref ocusing pulses.