We present a systematic study of the intermediate frequency (IF) bandwidth of hot-electron bolometer mixers made from YBa2Cu3O7-x high-temperature superconductive thin films fabricated on substrates with high thermal conductivity (MgO and sapphire). At a local oscillator frequency of 100 GHz, a strong dependence of the IF bandwidth on the bias point and temperature has been experimentally found. Moreover, an unexpected IF bandwidth variation has been detected in a broad range of operating frequencies (1–480 GHz). Besides conventional bolometric mixing mechanisms associated with thermalization of electrons and phonons, the contribution of direct interaction between radiation and magnetic vortices in the YBa2Cu3O7-x film may be responsible for the observed effects. © 2001 American Institute of Physics.