The EPR spectrometer based on the 25 Tesla resistive magnet uses as microwave source a series of the Backward Wave Oscillators (BWO) covering the frequency range 150 – 700 GHz. The instrument design is similar to that of the transmission instrument with the 17 T magnet; the transmission geometry and the homodyne detection are used. Samples that may be powders or frozen solutions are put in 9 mm Teflon containers.
Measurements are typically done at 4.2 K. The resistive magnet has been precalibrated, but for accurate measurements usage of g standards is recommended (DPPH or phosphorus doped into silicon, for example). The main advantages of the Keck-based apparatus are the very wide field and frequency ranges allowing studies on transition metal ions exhibiting very large zero-field splitting. The magnet may be swept at a rate much higher than superconductive magnets. Jurek Krzystek performs measurements on this instrument.