Repeaters close gaps in the coverage area of the digital radio DAB (Digital Audio Broadcasting). The DAB repeater systems receive weak signals, amplify and retransmit them straight into the underserved areas. They are typically used for tunnels, valleys, underground stations, or similar. After developing a prototype VHF repeater we provided L-band repeaters for various DAB pilot projects. These devices repeat the entire DAB L-band from 1452 to 1492 MHz and possibly unwanted signals, too. To avoid interference between adjacent DAB channels or other services, a new generation of repeaters is necessary. The new repeater amplifies only the wanted 1.5 MHz wide DAB channel and retransmits it. Adjacent channels are suppressed sufficiently.
A high quality SAW filter at an intermediate frequency provides the good adjacent channel suppression. The synthesizer is adjustable over the whole 40 MHz wide DAB band. The repeater gain is controlled digitally. Its control loop ensures a good overall system linearity and low system noise figure. A microcontroller performs the task of system control and monitoring. The main parameters can be set and queried at the repeater directly. Additionally the repeater is configurable by a PC via a RS232 interface. Alternatively a full remote control and monitoring can be realized with a (wireless) modem.
