Advantages of digital phase-sensitive detection for upgrading an obsolete CW EPR spectrometer

The replacement of the commonly used analog phase-sensitive detection (PSD) by digital PSD for demodulation of electron paramagnetic resonance (EPR) signals is suggested for upgrading of an out-of-date EPR spectrometer. Connection of the microwave bridge output to a fast analog-digital converter (ADC) eliminates some of the spectrometer’s components: the electronics responsible for analog PSD, ADC for sampling of demodulated signals, and a computer, as well as the usage of some of the spectrometer’s settings. The spectrometer is reduced to a magnet, microwave bridge, and personal computer containing an ADC board. EPR signals digitized for a set of magnetic field positions form a two-dimensional array which is stored in a personal computer. Demodulation and filtering are done numerically to produce a conventional EPR spectrum. In comparison with analog PSD, this numerical approach does not eliminate the out-of-phase component of the signal and the signals at the higher harmonics of the modulation frequency. The details of modernizing the Bruker ER200E SRC EPR spectrometer are discussed to demonstrate these and other advantages of digital demodulation.