By means of small magnetic field ac susceptibility measurement at 10 kHz we found that the real and imaginary parts of ceramic $YBa_2Cu_3O_ x$ susceptibility in presence of the external low frequency field close to 0.1 Hz exhibit frequency dependence. The wide maximum of hysteresis losses and {color{black} the exponential dependence} of the {color{black} effectiveness of flux penetration} with increasing of external field frequency were obtained. We observed a nonlinear dynamic magnetic response in presence dc field and we suggest that this behavior is due to the dynamic and static Josephson vortex-vortex interaction.
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