Abstract
A digital system for a programmable frequency synthesiser is described. It performs a staircase frequency sweep with a step of 1 Hz and digitally programmed bidirectional square-wave frequency modulation in an NQR spectrometer with a frequency-locked super-regenerative oscillator. The system is particularly convenient when using digital averaging techniques. NQR spectra parameters are not influenced by frequency modulation even when extremely large frequency modulation deviations are used. Parameters such as the sweep rate and the amplitude of frequency modulation deviation are stable, accurately fixed and independent of the running frequency. NQR spectra of 35Cl in p-dichlorobenzene and 65Cu in Cu2O were plotted against frequency by an X-Y recorder.