A device and a method at a mobile communication system which provide a flexible and realistic way of emulating the time dispersive qualities and the broadband frequency correlation qualities of a radio channel. The device includes two or more flexible delay modules, and each module is arranged to emulate a tap and a continuously varying tap attenuation can be attained to describe the variation of the radio channel over the time. The modules may be realized in SAW-technology, and continuously varying tap attenuation may be achieved by the utilization of PIN-diode attenuators.