  Recently detected coherent low-frequency radio emission from M dwarf systems
shares phenomenological similarities with emission produced by magnetospheric
processes from the gas giant planets of our Solar System. Such beamed
electron-cyclotron maser emission can be driven by a star-planet interaction or
a breakdown in co-rotation between a rotating plasma disk and a stellar
magnetosphere. Both models suggest that the radio emission could be periodic.
Here we present the longest low-frequency interferometric monitoring campaign
of an M dwarf system, composed of twenty-one $\approx$8 hour epochs taken in
two series of observing blocks separated by a year. We achieved a total
on-source time of 6.5 days. We show that the M dwarf binary CR Draconis has a
low-frequency 3$\sigma$ detection rate of 90$^{+5}_{-8}$% when a noise floor of
$\approx$0.1 mJy is reached, with a median flux density of 0.92 mJy, consistent
circularly polarised handedness, and a median circularly polarised fraction of
66%. We resolve three bright radio bursts in dynamic spectra, revealing the
brightest is elliptically polarised, confined to 4 MHz of bandwidth centred on
170 MHz, and reaches a flux density of 205 mJy. The burst structure is mottled,
indicating it consists of unresolved sub-bursts. Such a structure shares a
striking resemblance with the low-frequency emission from Jupiter. We suggest
the near-constant detection of high brightness temperature,
highly-circularly-polarised radiation that has a consistent circular
polarisation handedness implies the emission is produced via the
electron-cyclotron maser instability. Optical photometric data reveal the
system has a rotation period of 1.984$\pm$0.003 days. We observe no periodicity
in the radio data, but the sampling of our radio observations produces a window
function that would hide the near two-day signal.
