  We report on high speed photometry of EX Dra in quiescence and in outburst.
The analysis of the lightcurves indicates that the outbursts do not start in
the outer disc regions. The disc expands during rise to maximum and shrinks
during decline and along the quiescent period. At the end of two outbursts the
system was seen to go through a phase of lower brightness, characterized by an
out-of-eclipse level ~15 per cent lower than the typical quiescent level and by
the fairly symmetric eclipse of a compact source at disc centre with little
evidence of a bright spot at disc rim. New eclipse timings were measured and a
revised ephemeris was derived. The residuals with respect to the linear
ephemeris are well described by a sinusoid of amplitude 1.2 minutes and period
\~4 years and are possibly related to a solar-like magnetic activity cycle in
the secondary star. Eclipse phases of the compact central source and of the
bright spot were used to derive the geometry of the binary. By constraining the
gas stream trajectory to pass through the observed position of the bright spot
we find q=0.72+/-0.06 and i= 85 +3/-2 degrees. The binary parameters were
estimated by combining the measured mass ratio with the assumption that the
secondary star obeys an empirical main sequence mass-radius relation. We find
M_1= 0.75+/-0.15 M_sun and M_2= 0.54+/-0.10 M_sun. The white dwarf at disc
centre is surrounded by an extended and variable atmosphere or boundary layer
of at least 3 times its radius and a temperature of T ~28000 K. The fluxes at
mid-eclipse yield an upper limit to the contribution of the secondary star and
lead to a lower limit photometric parallax distance of D= 290+/-80 pc. The
fluxes of the secondary star are well matched by those of a M0+/-2 main
sequence star.

Astrophysics