  We show the results of our analysis of the pulse broadening phenomenon in 25
pulsars at several frequencies using the data gathered with GMRT and Effelsberg
radiotelescopes. Twenty two of these pulsars were not studied in that regard
before and our work has increased the total number of pulsars with
multi-frequency scattering measurements to almost 50, basically doubling the
amount available so far. The majority of the pulsars we observed have high to
very-high dispersion measures (DM>200) and our results confirm the suggestion
of Loehmer et al.(2001, 2004) that the scatter time spectral indices for
high-DM pulsars deviate from the value predicted by a single thin screen model
with Kolmogorov's distribution of the density fluctuations. In this paper we
discuss the possible explanations for such deviations.
