300MHz Digital NMR Frequency Source

Nuclear Magnetic Resonance (NMR) spectroscopy is the absorption of radio frequency radiation by a nucleus in a strong magnetic field. NMR is one of the most powerful tools in a synthetic or structural chemist's arsenal. The radio frequency source is an essential part in nuclear magnetic resonance spectroscopy or magnetic resonance imaging instrument. Modern NMR technique such as selective excitation, composite pulses and RF receiver require that the RF source has the characteristic of high stability, high frequency spectrum purity, high frequency resolution and low phase noise.In this paper, a kind of 300MHz frequency source is designed by means of combining DDS with analog frequency doubler. The design details and the experiment results are presented and discussed.The paper begins with a brief outline of the historical development of NMR in chapter 1. Chapter 2 illustrates the NMR basic theory and NMR spectrometer structure including the influence of RF source to the NMR spectrometer. The advantage and disadvantage of all frequency sources are compared in the third section. The fourth section introduced the design process. The design is fit for using in 300MHz NMR spectrometer due mainly to its low phase noise, high stability, high frequency and high purity output. The implementation of this frequency source to NMR is discussed. Finally the test results and 300MHz solid NMR experiment results are shown.