  Context. We analyse the line and continuum spectra of the symbiotic system CH
Cygni. Aims. To show that the colliding-wind model is valid to explain this
symbiotic star at different phases. Methods. Peculiar observed features such as
flickering, radio variation, X-ray emission, as well as the distribution of the
nebulae and shells throughout the system are investigated by modelling the
spectra at different epochs. The models account consistently for shock and
photoionization and are constrained by absolute fluxes. Results. We find that
the reverse shock between the stars leads to the broad lines observed during
the active phases, as well as to radio and hard X-ray emission, while the
expanding shock is invoked to explain the data during the transition phases.
