  Observations have revealed strong evidence for powerful jets in the Low/Hard
states of black hole candidate X-ray binaries. Correlations, both temporal and
spectral, between the radio -- infrared and X-ray bands suggest that jet
synchrotron as well as inverse Compton emission could also be significantly
contributing at higher frequencies. We show here that, for reasonable
assumptions about the jet physical parameters, the broadband spectrum from
radio through X-rays can be almost entirely fit by synchrotron emission. We
explore a relatively simple model for a relativistic, adiabatically expanding
jet combined with a truncated thermal disk conjoined by an ADAF, in the context
of the recently discovered black hole binary XTE J1118+480. In particular, the
X-ray power-law emission can be explained as optically thin synchrotron
emission from a shock acceleration region in the innermost part of the jet,
with a cutoff determined by cooling losses. For synchrotron cooling-limited
particle acceleration, the spectral cutoff is a function only of dimensionless
plasma parameters and thus should be around a ``canonical'' value for sources
with similar plasma properties. It is therefore possible that non-thermal jet
emission is important for XTE J1118+480 and possibly other X-ray binaries in
the Low/Hard state.
