  Parametric transducers, such as superconducting rf cavities, can boost the
bandwidth and sensitivity of the next generation resonant antennas, thanks to a
readily available technology. We have developed a fully coupled dynamic model
of the system "antenna--transducer" and worked out some estimates of
signal--to--noise ratio and the stability conditions in various experimental
configurations. We also show the design and the prototype of a rf cavity which,
together with a suitable read--out electronic, will be used as a test bench for
the parametric transducer.
