  We present high time-resolution spectroscopy of the eclipsing cataclysmic
variable SDSSJ143317.78+101123.3 obtained with QUCAM2, a high-speed/low-noise
electron-multiplying CCD camera. Littlefair et al. measured the mass of the
secondary star in SDSSJ143317.78+101123.3 using a light-curve fitting technique
and obtained a value of M2=0.060+/-0.003 Msun, making it one of the three first
bona-fide detections of a brown-dwarf mass donor in a cataclysmic variable. In
this paper we present a dynamical measurement supporting this important result.
We measured the radial-velocity semi-amplitude of the white dwarf from the
motion of the wings of the Halpha emission line and obtained a figure of
K1=34+/-4 km/s, in excellent agreement with the value of K1=35+/-2 km/s
predicted by Littlefair et al.'s model.
