  In the framework of test-particle and cosmic-ray modified hydrodynamics, we
calculate synchrotron emission radial profiles in young ejecta-dominated
supernova remnants (SNRs) evolving in an ambient medium which is uniform in
density and magnetic field. We find that, even without any magnetic field
amplification by Raleigh-Taylor instabilities, the radio synchrotron emission
peaks at the contact discontinuity because the magnetic field is compressed and
is larger there than at the forward shock. The X-ray synchrotron emission
sharply drops behind the forward shock as the highest energy electrons suffer
severe radiative losses.
