approximately 5 seconds, the control will return to
(4) Tuning knobs. Two concentric tuning
knobs control the preset or active frequency displays.
The larger knob changes the 1,000's and 100's kHz digit.
The smaller knob changes the 10's, units, and tenths
kHz digits. Each detent of the larger knob changes the
frequency in the display in 100-kHz steps. Each detent
of the smaller knob changes the frequency in the display
in 1 kHz steps, with the exception that the first two
detent positions following a change in rotational direction
of the knob will cause a 0.5 kHz change in frequency.
Rapid rotation of the smaller knob will cause frequency
changes greater than 1-kHz as a function of rate of
rotation. Frequencies roll over at the upper and lower
limits. The two tuning knobs are independent of each
other in that the upper and lower limit rollover of the 10-
kHz digit will not cause the 100-kHz digit to change.
(5) Active switch. The active switch,
placarded ACT, enables the tuning knobs to directly tune
the ADF receiver when depressed and held for two
seconds. The bottom window will display dashes and
the upper window will continue to display the active
frequency. Pushing the ACT switch a second time will
return the control unit to the normal two-display mode.
(6) Test switch. This switch, placarded
TEST, initiates the receiver self-test diagnostic routine.
(Self-test is active only when the TEST switch is
(7) Light sensor. This built-in light sensor
automatically controls display brightness.
(8) Volume control. The volume control is
concentric with the power and mode switch.
(9) Power and mode switch. The power
and mode switch contains four detented positions
placarded OFF, ANT, ADF, and TONE. The OFF
position removes system power. Selecting ANT, ADF,
or TONE position applies power to the ADF system and
establishes the system mode of operation.
(10)Annunciators. The receiver control unit
contains a MEM (memory) and a RMT (remove)
whenever a preset frequency is being displayed in the
lower window. The RMT annunciator is not used in this
(11)Preset frequency display. The preset
(inactive) frequency and diagnostic messages are
displayed in the lower window.
Active Frequency Display
Power and Mode Switch
Annunciators (MEM )
Preset Frequency Display
Figure 3-25. ADF Control Unit