Frequency dependence of the dispersion measure and superdispersion delay of radiowave pulses of pulsars

We call an attention to the fact of a systematic, increase of the values of pulsar dispersion measures (DM) at frequencies below 100 MHz is discussed. The analysis of this increase detected the extra dispersion time delay of pulses of all pulsars under consideration: PRS 0329+54, 0823+26, 0834+06, 0950+08, 1133+16, 1929+10 and 2016+28. Following Shitov (1983) interpretation of an extra disperson time delay as a twist of the pulsar magnetic field line it is shown that a twist angle is nearly proportional to the pulsar rotation rate and radius of an emitting region power four. The extra dispersion time delay may cause the difference of the DM values, measured in different frequencies intervals. To avoid this effect to measure DM in the frequency interval between 100 and 1000 MHz may be recomended