Investigation of radio pulsar emission features using power spectra

Since 2013 round-the-clock monitoring of the sky is carried out simultaneously in 96 space beams using the high-sensitivity radio telescope of LPA (Large Phased Array) at the frequency 110.25 MHz. These observations are made under the program of the interplanetary plasma investigation. The same data is used for the search for pulsars by means of the power spectra. For the increase of the pulsar search sensitivity the summation to 500-600 of power spectra corresponding to the different days of the observations is made. In the integrated spectra of the known pulsars, besides expected improvement of a signal-to-noise ($S/N$) ratio for the frequency harmonics, were showed some features which are explored in the paper. We present 27 strongest pulsars which are in the field of declinations $21\degr - 42\degr$ at which the connection of observable details in the integrated power spectra with the presence of pulsar periods of the second ($P_2$) and third ($P_3$) class has been discovered. The empirical relations for the calculation of these periods are obtained. The value $P_2$ is estimated for 26 pulsars, and for 15 sources it is made for the first time. The value $P_3$ is estimated for 13 pulsars, from them for 5 sources they are given for the first time.