  We consider a system of identical van der Pol oscillators, globally coupled
through their velocities, and study how the presence of competitive
interactions affects its synchronisation properties. We will address the
question from two points of view. Firstly, we will investigate the role of
competitive interactions on the synchronisation among identical oscillators.
Then, we will show that the presence of an intermediate fraction of repulsive
links results in the appearance of macroscopic oscillations at that signal's
rhythm, in regions where the individual oscillator is unable to synchronise
with a weak external signal.
