RF modulator upgrading for NMR spectrometer

Resumen

Magnetic Resonance (MR) at low fields for studying chemical compounds is a very common and an important area of research. However, the higher the intensity of the magnetic field the better the signal to noise ratio of the signal obtained from the substance under study and thus more possibilities to identify different chemical compounds. To carry out these studies an NMR spectrometer was built in Centro de Biofísica Médica, which parts were taken from other equipment and in some cases modernized such as the RF modulator, that belonged to the MRI (Magnetic Resonance Imaging) machine GIROIMAG 03. In this work it is described the upgrading and changes aspects made to the Radio Frequency (RF) modulator that allowed the spectrometer to work properly at the new field of 1,5 T. The latter changes included: change in the working frequencies of the modulator to operate well at the new frequency of 64 MHz, change of the RF switch to achieve a better attenuation of the non-desired RF signal, design and implementation of a circuit to control the RF switch and design and implementation of a new 64 MHz passband filter. The performance of the upgraded modulator was demonstrated through the measuring of the harmonic suppression, the sideband rejection and the conversion loss. Finally, the modulator incorporated to spectrometer was validated through the realization of a complete experiment that ended up with the acquisition of an MR signal.