In the framework of one-dimensional non-stationary nonlinear Schrödinger equation, linebreak magnetostatic wave self-modulation was numerically studied under excitation of periodic signal, producing magnetostatic waves amplitude at the input transducer in the form φ =φ_0(1+MsinΩt). It was shown, that for φ_0, greater than the modulation instability threshold, the magnetostatic waves envelope dynamics strongly depends both on the modulation depth M and on the relation between self-modulation frequency F of magnetostatic waves and external force frequency W. As а result, one can found the effects of forced synchronization for regular and chaotic self-modulation regimes, of beating on the frequencies of self-modulation and external force, and of transformation of magnetostatic waves envelope to multiple-soliton trains with the period of external force. For fixed values of the frequency and depth of external modulation, the nature of magnetostatic waves envelope dynamics at the «observation» point depends on the distance of this point from the input antenna.