  We present quasi-simultaneous, multi-frequency VLA observations at 4.8, 8.4,
and 22.5 GHz, of a sample of 13 Wolf Rayet (WR) stars, aimed at disentangling
the nature of their radio emission and the possible detection of a non-thermal
behavior in close binary systems. We detected 12 stars from our sample, for
which we derived spectral information and estimated their mass loss rates. From
our data, we identified four thermal sources (WR 89, 113, 138, and 141), and
three sources with a composite spectrum (similar contribution of thermal and
non-thermal emission; WR 8, 98, and 156). On the other hand, from the
comparison with previous observations, we confirm the non-thermal spectrum of
one (WR 105), and also found evidence of a composite spectrum for WR 79a, 98a,
104, and 133. Finally, we discuss the possible scenarios to explain the nature
of the emission for the observed objects.
