  We have studied the flow properties of vortices driven through easy flow
mesoscopic channels by means of the mode locking (ML) technique. We observe a
ML jump with large voltage broadening in the real part of the rf-impedance.
Upon approaching the pure dc flow by reducing the rf amplitude, the ML jump is
smeared out via a divergence of the voltage width. This indicates a large
spread in internal frequencies and lack of temporal coherence in the dc-driven
state.
