In this paper we report multi-frequency measurements of pulse broadening times ( \tau _ { d } ) for nine medium dispersion measure ( DM \approx 150 - 400 pc cm ^ { -3 } ) pulsars observed over a wide frequency range .
The low frequency data at 243 , 325 and 610 MHz are new observations done with the Giant Metrewave Radio Telescope ( GMRT ) .
The frequency dependence of \tau _ { d } for all but one ( PSR B1933+16 ) of our sources is consistent with the Kolmogorov spectrum of electron density fluctuations in a turbulent medium .
PSR B1933+16 , however , shows a very flat spectrum as previously observed for high DM pulsars .
Our observations combined with earlier published results enable us to study the spectral index of \tau _ { d } over the whole observed DM range .
While the spectral properties are generally consistent with a Kolmogorov spectrum , pulsars seen along line-of-sights towards the inner Galaxy or complex regions often show deviations from this expected behaviour .