  We report on the development of a numerical code to calculate the
angle-dependent synchrotron + synchrotron self-Compton radiation from
relativistic jet sources with partially ordered magnetic fields and anisotropic
particle distributions. Using a multi-zone radiation transfer approach, we can
simulate magnetic-field configurations ranging from perfectly ordered
(unidirectional) to randomly oriented (tangled). We demonstrate that
synchrotron self-Compton model fits to the spectral energy distributions (SEDs)
of extragalactic jet sources may be possible with a wide range of
magnetic-field values, depending on their orientation with respect to the jet
axis and the observer. This is illustrated with the example of a spectral fit
to the SED of Mrk~421 from multi-wavelength observations in 2006, where
acceptable fits are possible with magnetic-field values varying within a range
of an order of magnitude for different degrees of B-field alignment and
orientation.
