A combination of a GPS receiver (52) and a communications receiver (22) or transceiver (22, 46) which share a processor (26) in the communications receiver in order to handle normal communications traffic and to determine the position of the secondary station (SS). In order to reduce the acquisition time and current consumed by the secondary station (SS), a primary station (PS) of the communication system is also equipped with a GPS receiver (14) and digital baseband processor (15) for recovering at least the ephemeris data transmitted by orbiting GPS satellites (SAT1 to SAT4), the ephemeris data being down-loaded to the secondary station (SS) and stored in a memory (32) ready for use when a positional fix is required.