TM 55-1510-221-10
2. Marker beacon HI-LO switch (marker
beacon audio control panel, fig. 3-2) -
As required.
3. Marker
beacon
indicator
lights
(instrument panel, fig. 2-29) - Confirm
beacon indication.
3-27. AUTOMATIC DIRECTION FINDER (DF-203).
a.
Description. The Automatic Direction
Finder (ADF) (fig. 3-18), is a radio navigation sys-
tem which provides a visual indication of aircraft
bearing, relative to a selected ground radio station.
It may also be used to home to a selected station,
find aircraft position, or monitor conventional
medium frequency AM radio transmissions. The
system is designed to provide reliable reception of a
400-watt radio station at a range of 65 nautical
miles throughout a 360-degree turn of the aircraft. It
operates in a frequency range of 190 to 1750 kilo-
hertz. Bearing indications are displayed visually on
the RMI's and aural signals are applied to the audio
control panels. The ADF system consists of a
receiver, located on the forward side of the aft cabin
bulkhead inside the pressure vessel; a control unit,
located on the pedestal extension; a non-directional
sense antenna, installed in the aircraft dorsal tin; a
directional loop antenna, located on the underside
of the fuselage; and a quadrangle error corrector,
installed on the loop antenna (to compensate for the
deflection of arriving radio signals by the wings and
fuselage of the aircraft). The system is protected by
a l-ampere ADF, a 5-ampere RADIO RELAY, and
a 35-ampere AVIONICS BUS FEEDER No.2 circuit
breaker located on the overhead circuit breaker
panel (fig. 2-26).
The only warning that the crewmember
has for an unreliable ADF signal or loss
of the ADF receiver is the loss of the
ADF audio signal in the crewmember’s
headset. This signal should be monitored
during all phases of the approach in IMC
conditions.
NOTE
Keying the HF radio set while operating
the ADF radio set will cause a momentar-
ily unreliable ADF signal.
Figure 3-18. ADF Control Panel (DF-203)
3-33
