33 30 24 21 15 12 6 3 S W E N HDG Radio station N-S E- W 33 30 24 21 15 12 6 3 W S E N M a g n e t i c b e a r i n g t o s t a tio n R e l a t i v e b e a ri n g Magnetic heading Magnetic North Figure 11-103.  Older ADF indicators have nonrotating azimuth  cards. 0° is fixed at the top of the instrument and the pointer always  indicates the relative bearing to the ADF transmission antenna. To  fly to the station, the pilot turns the aircraft until the ADF pointer  indicates 0°.  Figure 11-104.  A movable card ADF indicator can be rotated to put  the aircraft’s heading at the top of the scale. The pointer then points  to the magnetic bearing the ADF broadcast antenna.  Pattern of sense antenna Pattern of loop Loop antenna Combined pattern of loop and sense antenna Tx Figure 11-105.  The reception fields of a loop and sense antenna  combine to create a field with a sharp null on just one side. This  removes directional ambiguity when navigating to an ADF station. 11-47 In modern ADF systems, an additional antenna is used to  remove the ambiguity concerning whether the aircraft is  heading to or from the transmitter. It is called a sense antenna.  The reception field of the sense antenna is omnidirectional.  When combined with the fields of the loop antenna, it forms  a field with a single significant null reception area on one  side. This is used for tuning and produces an indication in the  direction toward the ADF station at all times. The onboard  ADF receiver needs only to be tuned to the correct frequency  of the broadcast transmitter for the system to work. The loop  and sense antenna are normally housed in a single, low profile  antenna housing.  [Figure 11-105] As ADF technology progressed, indicators with rotatable  azimuth cards became the norm. When an ADF signal is  received, the pilot rotates the card so that the present heading  is at the top of the scale. This results in the pointer indicating  the magnetic bearing to the ADF transmitter. This is more  intuitive and consistent with other navigational practices.  [Figure 11-104]  The direction to the broadcast antenna was shown on an  azimuth scale of an ADF indicator in the flight deck. This  type of instrument is still found in use today. It has a fixed  card with 0° always at the top of a non-rotating dial. A  pointer indicates the relative bearing to the station. When  the indication is 0°, the aircraft is on course to (or from) the  station.  [Figure 11-103] 