Navigation signals emitted by a navigation transmitter (46), in a first signal path (41), have a time reference generated and, based on this time reference, navigation signals are generated which are subsequently emitted by way of a transmitting device (39, 40). In the event of interferences in the first signal path (41), a switch-over takes place to a second signal path (45) parallel to the first signal path (41). The navigation transmitter (46) receives time reference signals and/or navigation signals, and the received signals are guided by way of the second signal path (45) to the transmitting device (39, 40) and emitted.