  We study the transmission of a disordered waveguide subjected to a finite
bias field. The statisticaldistribution of transmission is analytically shown
to take a universal form. It depends on a singleparameter, the system length
expressed in a rescaled metrics, which encapsulates all the microscopicfeatures
of the medium and the bias field. Excellent agreement with numerics is found
for variousmodels of disorder and bias field. For white-noise disorder and a
linear bias field, we demonstratethe algebraic nature of the decay of the
transmission with distance, irrespective of the value ofthe bias field. It
contrasts with the expansion of a wave packet, which features a
delocalizationtransition for large bias field. The difference is attributed to
the different boundary conditionsfor the transmission and expansion schemes.
The observability of these effects in conductancemeasurements for electrons or
ultracold atoms is discussed, taking into account key features, suchas
finite-range disorder correlations, nonlinear bias fields, and finite
temperatures.
