Further dramatic manifestations of the frequency shift caused by the dipolar field were also observed. One such example is shown in Fig. , where the induction signal has a quasi rectangular profile that lasts several tens of ms, quite remote from the typical (or approximately) hyperbolic secant maser pulse envelope. These signals exhibited time-varying frequency, giving rise to a squared chirped maser pulse, and a simultaneous slight decaying intensity preceding an abrupt return to zero of the signal amplitude. A time-frequency analysis of this FID based on the short-time Fourier transform depicted in Fig. shows the frequency change with time during the pulse. The frequency shift between the beginning and the end of the pulse was about 7500 Hz. The combined resonance and intensity changes are characteristic of the presence of the DDF, and such induction signals are yet a surprising manifestation of nonlinear dynamics of the magnetization in the simultaneous presence of a strong dipolar field and an efficient radiation feedback.