Noise characteristics of a 750-MHz electronically tunable resonator for electron paramagnetic resonance spectroscopy

This paper describes an experimental investigation of the noise characteristics of a 750-MHz electronically tunable resonator for electron paramagnetic resonance (EPR) spectroscopy. The RF noise of the tunable resonator and its influence on the baseline noise of an EPR spectrum were systematically measured, considering both the noise of varactor diodes used in the impedance matching network of the resonator and noise from the ambient environment. The influence of magnetic field modulation and its amplitude on the baseline noise of the EPR spectrum was also measured. The tunable resonator itself increased the noise level of the spectral baseline of a home-built 750-MHz continuous-wave (CW) EPR spectrometer. A significant decrease in the noise level of the EPR spectral baseline was demonstrated by replacing the varactor diodes in the matching network by a trimmer capacitor, which led to a 6.1-fold improvement in EPR spectrum signal-to-noise ratio.