  The presence of inhomogeneities in a spatially unresolved source is often
hard to establish. This limits the accuracy with which the source properties
can be determined. It is shown how observed features not expected for a
homogeneous model can be used to infer the properties of the inhomogeneities in
radio supernovae. Furthermore, the observed consequences of radiative cooling
can be seriously affected by inhomogeneities. It is shown that the deduced
source properties are very sensitive to the observed value of the cooling
frequency; even a lower limit is often useful to constrain its characteristics.
It is argued that the main synchrotron emission region in SN 2003L has a small
volume filling factor, possibly as low as a few per cent. On the contrary,
deviations from homogeneity are substantially smaller in SN 2002ap. The
observed properties of type Ib/c radio supernovae in general indicate the
volume filling factor to remain rather constant with time for individual
sources but those peaking later at radio frequencies have lower filling
factors. The conditions in the main synchrotron component in both SN 2003L and
SN 2002ap are consistent with equipartition of energy between relativistic
electrons and magnetic fields.
