A catheter calibration system includes a calibration chamber, a receiver and a processor. The calibration chamber is configured to generate a calibration magnetic field that oscillates at a first frequency. The calibration chamber includes a cavity for inserting a distal end of a catheter having one or more magnetic-field sensors. The receiver is configured to be connected to the catheter, to receive from the catheter one or more signals, which are generated by the one or more magnetic-field sensors in response to the calibration magnetic field, and to convert the one or more signals into one or more respective intermediate frequency (IF) signals having a second frequency that is lower than the first frequency. The processor is configured to receive the one or more IF signals from the receiver and to calculate catheter navigation calibration data from the one or more IF signals.