  Magnetoresistance and radio frequency penetration depth techniques are used
to study grain connectivity and broadening of superconducting transition. We
study and compare these issues in clean polycrytalline samples of three
different superconducting systems e.g. MgB2, NbSe2 and Bi2Sr2Ca2Cu3O10. From
the rf response, the bulk pinning force constant is evaluated. From high field
transport measurements, H-T phase diagram is ascertained for the three systems
with varying degrees of fluctuation and connectivity.
