Absolute calibration of microwave loss in ESR spectrometers

Studies of field‐dependent microwave losses are useful for the detection and characterization of superconducting materials. The measurements are made in a conventional ESR spectrometer, but until now the data interpretation has been mainly qualitative. A calibration procedure using just a frequency counter, DC voltmeter, and ball bearing is decribed. This allows a quantitative determination of magnetic losses to ∼ 5% accuracy without the need to determine the cavity Q, power level, or field strength.