The EPR from the DPPG was investigated on a spectrometer with different angles between a constant polarization field and an adjustable RF pump field at a frequency of 20 MHz in a continuous mode and a receiver tuned to the second harmonic frequency of the EPR signal. A technique for processing and more accurate measurement of the parameters of the EPR lines and the Bloch – Siegert shift is proposed. The conditions for maximizing the signal of even EPR harmonics are obtained depending on the angle of inclination of the HF field to the constant field. On the basis of experimental data and numerical solutions of the Bloch system of differential equations, the effect of asymmetry and a change in the sign of the second harmonic of the EPR line when the direction of the constant field is reversed is discovered and explained. An additional effect of displacement of the resonance line was discovered due to the inhomogeneous polarization of this line during scanning of the polarizing field. The effect of the appearance of the observed and possible resonant EPR harmonics is explained by the frequency modulation of the resonance conditions by both the perpendicular and parallel components of the RF pump field. It is concluded that the Bloch equations describe well in quality and satisfactory in accuracy all the observed parameters of EPR lines, such as intensity, width, shape, and their shifts. It is also shown that these equations describe the experiment on Bloch-Siegert shifts at least five times more accurately than the data of competing theories. A detailed description of the spectrometer is given and a computer program for the numerical calculation of the EPR spectra is presented.