  Flattenings of nonthermal radiation spectra observed from knots and interknot
locations of the jets of 3C273 and M87 in UV and X-ray bands are discussed
within modern models of magnetic field generation in the relativistic jets.
Specifically, we explicitly take into account the effect of the small-scale
random magnetic field, probably present in such jets, which gives rise to
emission of Diffusive Synchrotron Radiation, whose spectrum deviates
substantially from the standard synchrotron spectrum, especially at high
frequencies. The calculated spectra agree well with the observed ones if the
energy densities contained in small-scale and large-scale magnetic fields are
comparable. The implications of this finding for magnetic field generation,
particle acceleration, and jet composition are discussed.
