by Jonathan M. Stern
Automatic Direction Finder
The automatic direction finder is a navigation radio used to track to and from nondirectional beacons (NDBs). NDBs operate in the low/medium frequency range between 190 and 535 KHz. Unlike VOR and ILS navigation, the ADF displays information relative to the heading of the aircraft. In other words, the ADF display has a pointer that points in the direction of the NDB. Also unlike VHF transmissions, the L/MF transmissions do not require an unobstructed line of sight between transmitter and receiver.
On the negative side, however, the NDB signals are sensitive to precipitation, thunderstorms, twilight, and certain terrain features. Their signals lack the reliability of a VOR.
ADF information is displayed on a compass card indicator. In Flight Simulator's Cessna, you must choose between the NAV 2 display and the ADF display (see Figure 11.8). To select the ADF display, hold down the Shift key and press Tab or, using the menus, click the Activate ADF Gauge in the NAV/COM/Navigation Radios menu selection. In the Lear 35, the Shift+Tab combination toggles through the NAV 1, NAV 2, and ADF displays.
Figure 11.8. The Flight Simulator ADF must be selected in lieu of the NAV 2 display.
Use and interpretation of the ADF is discussed in Chapter 18 "Instrument Approach Procedures."