A frequency translating bi-directional amplifier (10) for extending radio coverage for digital mobile radio communication devices (200) on a trunked network using a digital modulation scheme, comprising: a field programmable gate array (FPGA) with local controller (CPU) and firmware (22) configured to analyse control channel messages of a downlink control channel and modify the control channel messages of the downlink control channel that contain traffic channel information; and an antenna (12) to transmit the modified control channel messages to the digital mobile radio communication devices (200) in order to change an operating frequency of the digital mobile radio communication devices (200) to use a predetermined set of frequencies that are repeatable by the bi-directional amplifier (10); wherein the operating frequency between the digital mobile radio communication devices (200) and the bi-directional amplifier (10) is different to an operating frequency between a donor base station (300) and the bi-directional amplifier (10).