Abstract: A method and apparatus for analyzing a sample comprising gyromagnetic species in which the sample, is placed in a uniform DC polarizing magnetic field and irradiated by an AC magnetic field, at an angle to the DC field, while the DC field is modulated by square wave signal whereby the resultant resonance signal comprises a frequency modulated spectrum centered around the resonance frequency and having sideband components separated by the frequency of the square wave signal and the amplitudes of which are proportional to the difference of two resonance intensities switched by the two extreme intensity values of the DC field. Upon detection of the sidebands by an RF receiver, DC levels, proportional to the intensity of the detected sidebands, are provided, permitting display of the resonance line shape on an oscilloscope.