An amplifier unit to be placed in an antenna mast and belonging to a two-way radio system. The amplifier unit comprises two front stages for implementing diversity, each front stage comprising a receiving branch with an amplifier and a transmitting branch including a transmit bandpass filter. In both front stages the output of the receiving branch and the input of the transmitting branch are coupled together and further to a base station (BT1, BT2) by an intermediate cable. There is at least one pair of antenna radiators. One radiator of the pair is coupled to the input of the receiving branch of the first front stage and the output of the transmitting branch of the second front stage, and the other radiator to the input of the receiving branch of the second front stage and the output of the transmitting branch of the first front stage. Then, the feedback path of the signal amplified in the receiving branch circulates for the part of both front stages via both radiators and the airspace. Because of isolation between the radiators, the attenuation of the feedback path increases, in which case the transmit bandpass filters can be made smaller and cheaper.