A method uses an electromagnetic navigation system, including a number of field transmitters and at least one receiver. The method includes receiving a field signal from the at least one receiver, and the field signal includes a number of different frequencies corresponding to each of the field transmitters. The received field signal is multiplied by a synchronization signal using a frequency-division multiplexing scheme, and the received field signal is integrated over a predetermined sampling interval and converted into an integrated signal having only a desired signal based on the synchronization signal. The integrated signal is outputted for subsequent processing of the electromagnetic navigation system.