The present disclosure relates to a navigation system for placing a medical device into a patient. The system may include an external unit configured to be disposed on a chest of the patient, the external unit having: a radiating element configured to produce a first radio frequency (“RF”) signal; and a plurality of three-axis sensors configured to receive a second RF signal. The system may also include a medical device such as a catheter. The catheter may have: a first antenna configured to receive the first RF signal and produce an alternating current; a rectifier configured to convert the alternating current into a direct current; a frequency generator configured to produce a second RF signal that is received by the plurality of three-axis sensors. The RF signals received by the plurality of three-axis sensors may be used to determine a position of the catheter relative to the external unit.