[en] An investigation was made of the effects of modulation frequency and rf ENDOR power on the single and double quantum ENDOR spectral lines of ⁵³Cr³⁺ ions in single crystals and powders of CsAl sulfate alum. Measurements were made of the linewidths and intensities in the single crystals and of the linewidths in the powders. It was found in the single crystals that a factor of 2/1 exists for the ratio of single/double quantum linewidths at the limit of zero ENDOR power and modulation frequency. Interpretation of the line intensity results with the results of lineshape theory indicates that the ENDOR lines are of Lorentzian form, at least for low values of ENDOR power. (auth)