  Observers at rest in two inertial reference frames are located within the
propagation space of the same electromagnetic wave. Raising receiving antennas
in a suitable way, these observers use the electromagnetic oscillations in the
wave as an electromagnetic clock. The invariance of the wave phase ensures that
the observers of the two frames detect the same phase of the oscillation when
they are located at the same point in space and consequently theirs
synchronization proceeds automatically. Because the Doppler Effect is free of
any clock synchronization, we use the formula that accounts for this effect for
deriving the basic formulas of relativistic kinematics.
