Abstract: A digital frequency source designed for a 300 MHz nuclear magnetic resonance spectrometer is described. Controlled by MCU or by PC, the frequency source is capable of generating a frequency- and phase-continuous tunable signal with output frequency ranging from 5 MHz to 125 MHz and 280 MHz to 301 MHz. Practical implementation of the frequency source to a 300 MHz NMR spectrometer is described, and its performance was tested with solid state NMR experiments. It is demonstrated that the frequency source results in radiofrequency output with low phase noise, high stability and high purity.

Key words: NMR, frequency source, DDS, analog frequency doubler, phase noise