  A joint action of depth and bandwidth depolarization in the interstellar
medium is considered using a model of N homogeneous synchrotron layers with
Faraday rotation. The bandwidth depolarization can be used in multifrequency
polarimetric observations of Galactic diffuse synchrotron radio emission to
investigate the interstellar ionized medium and magnetic field in the direction
to the Faraday-thick objects of known distances.
