High-Resolution NMR Spectrometer with the Radio Frequency Controlled by the Magnetic Field

Abstract

A practical spectrometer for the observation of high‐resolution proton magnetic resonance spectra at 30 Mc is described. Field modulation is imposed in such a way that ``sideband'' responses are observed, and this enables lock‐in detection to be used, giving increased stability to the baseline of the records. Spectra are displayed by slowly sweeping the modulation frequency and thus are calibrated directly in frequency. The radio‐frequency source is a proton controlled super‐regenerative oscillator, whose frequency follows variations of the electromagnet field. This reduces the effects of field drift and instability, allowing relatively slow scanning speeds to be used in recording the spectra.