  We report measurements of the microwave complex resistivity at 48 GHz in
SmBaCuO thin films. Measurements are performed with a moderate magnetic field,
$\mu_{0}H<$ 0.8T, applied along the c-axis. We find that the complex
resistivity presents clear sublinear field dependences, and that the imaginary
part is remarkably sensitive to the moderate magnetic field. Interpretation
considering an unusually strong pinning leads to very anomalous field
dependences of the single-vortex viscosity and of the pinning constant. By
contrast, allowing for a significant effect of the magnetic field on the
depletion of the condensate, the data are quantitatively described by simple
free-flux flow model, supplemented with two-fluid conductivity. In this frame,
we obtain the vortex viscosity from the data. We compare vortex viscosity in
SmBaCuO and in YBaCuO.
