Experimental results are cited from an investigation of the volumetric nonlinear inertial elements of n-InSb as a frequency converter in the wave bands of 4 and 2 mm. Recommendations are given on selecting a material for such a converter type and optimal operating modes. Losses in conversion of about 7 dB are reached at a wavelength of 4 mm and 8 dB at a wavelength of 2 mm.