TM 55-1510-219-10
(6)
Shutdown. VOL knobs (NAV panel) OFF.
3-24. MARKER BEACON.
a.
Description. A marker beacon receiver module
located inside the No. 1 VOR receiver, detects a
marker beacon signal as the aircraft passes over a
marker beacon transmitting antenna. The detected
signal is selectively filtered to activate the appropriate
marker beacon lamp on the instrument panel. In
addition, the detected signal is coupled to the aircraft
audio system to annunciate marker beacon passage.
The marker beacon receiver operates on a fixed
frequency of 75 Mhz. Volume and sensitivity of the
system are adjusted on the radio control panel (fig. 3-2)
located on the pedestal extension (fig. 2-11).
b.
Controls and Indicators.
CONTROL
FUNCTION
MKR BCN HI-
Controls sensitivity of marker
LO switch
beacon receiver.
MKR BCN VOL
Adjusts volume of marker bea-
control
con audio.
(1)
Marker beacon indicators (fig. 2-28).
INDICATOR
FUNCTION
"A" indicators
Illuminate when aircraft passes
(white)
over an inner marker beacon.
"O" indicators
Illuminate when aircraft passes
(blue)
over an outer marker beacon.
"M" indicators
Illuminate when aircraft passes
(amber)
over an middle marker beacon.
c.
Operation.
1. Marker
beacon
indicator
lights
(instrument panel) -Confirm beacon
indication.
2. Marker beacon HI-LO switch (radio
control panel) -As required.
3. Select NAV A on audio control
panel to monitor marker beacon
audio.
3-25. AUTOMATIC DIRECTION FINDER (DF-203).
a.
Description. The Automatic Direction Finder
(ADF) is a radio navigation system which provides a
visible and audible indication of aircraft bearing relative
to a selected ground radio station. It may also be used
to home on a selected station, find
aircraft position, or monitor conventional low 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 kilohertz.. Bearing indications are displayed
visually on the RMI's and aural signals are applied to the
audio control panels. Refer to Audio Control Panels (fig.
3-1) for controls used to monitor ADF audio signals.
The ADF 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 fin; 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
the 1-ampere ADF, the 5-ampere RADIO RELAY, and
the 35ampere AVIONICS BUS #2 circuit breakers on
the overhead circuit breaker panel (fig. 2-26).
NOTE
Keying the HF radio set while
operating the ADF set will cause a
momentarily
unreliable
ADF
signal.
b.
Controls and Indicators.
(1)
ADF control panel (fig. 3-16).
CONTROL/
FUNCTION
INDICATOR
LOOP control
Operative only when the func-
tion switch is in the LOOP or
ADF position. Center position
removes rotation signals from
the loop antenna and the ADF
pointer on the RMI's. First posi-
tion L (left) or R (right) of center
applies slow speed rotation sig-
nals to loop antenna and ADF
pointer on RMI's for 360-degree
rotation left or right. Second po-
sition L(left) or R (right) of cen-
ter applies fast speed rotation
signals to loop antenna and ADF
pointer on RMI's for 360-degree
rotation left or right. Center po-
sition holds antenna position.
BFO/OFF
At BFO (on) setting, permits
fine tuning with Beat Frequency
Oscillator (BFO). Also provides
audio
tone
when
receiving
un-
modulated CW. OFF turns BFO
off.
3-29
