  The electronic model of Van der Pol oscillator with piecewise linear
V-I--characteristics of nonlinear element is proposed. It is carried out the
experimental investigations of behaviour of the Van der Pol oscillator under
external periodic force. The parameter plane "the amplitude of external force
-- the frequency of external force" for the dynamical regimes of the oscillator
is experimentally plotted. It is shown in experiments and numerical simulations
that transition to chaos in the oscillator takes place through the period
doubling cascade. It is revealed that the internal structure of the
synchronization tongues has the characteristic view as for the crossroad area.
