  We have developed a set of experimental techniques with levitation to
investigate the macroscopic magnetic properties of bulk HTS: (i) resonance
oscillation technique; (ii) high speed magnetic rotor technique; (iii) the
method of viscous motion of a permanent magnet through a HTS aperture under a
steady force. Early, we used these techniques to investigate the magnetic flux
dynamics in granular HTS. Now, we have extended and modified these techniques
to study the large grain melt-textured HTS. With resonance oscillations
technique we obtain the energy losses vs ac magnetic field amplitude at HTS
surface and can derive the values of critical current density with high
accuracy. We extract information about distribution of critical current in a
thin undersurface layer and, in this way, check the HTS degradation processes.
The treatment of the HTS surface that has influence on the surface pinning was
investigated with this technique.
