TM 55-1520-228-10
3-45. CONTROLS AND FUNCTIONS - RADIO
BEARING HEADING INDICATOR.
Refer to figure 3-10.
3-46. OPERATING PROCEDURES - RADIO
BEARING HEADING INDICATOR.
a. Gyro-magnetic Heading Display and
Synchronization.
(1) Gyro-magnetic heading dial rotates to
indicate the helicopter’s magnetic heading under the
index.
(2) Heading synchronization is accomplished
by rotating the synchronizing knob. The annunciator
indicates, by means of a dot (•) or cross (+), the direction
that the synchronizing knob should be turned to give
immediate and accurate synchronization. If a cross (+)
is showing in the annunciator, the synchronizing knob
should be turned clockwise, and if a dot (•) is showing,
the synchronizing knob should be turned counterclock-
wise. The system is synchronized when the annunciator
indicates neither a dot (•) nor a cross (+). If, shortly after
synchronizing the system, the heading dial drifts and a
dot (•) or cross (+) appears in the annunciator, then
the system was synchronized to a false null located
180 degrees from the correct heading and should be re-
synchronized to the correct helicopter heading. The hel-
icopter standby magnetic compass may be checked for
reference.
b. ADF Pointer (Bearing Pointer ).
Radio magnetic bearing information is indicated by the
ADF pointer of the indicator. The arrow end of this
pointer indicates the bearing of the radio station from the
helicopter. The ADF set furnishes the bearing infor-
mation to the pointer (VOR or ADF as selected by the
RMI BRG PTR switch located on the instrument panel
).
c. FM Homing.
(1) The steering indicator receives its input
from the number 1 FM radio homing system. By moving
to the right or left of its center indication, the indicator
shows helicopter deviation from a direct approach path
to the FM radio transmitter. The indicator moves to the
right when the homing transmitter site is to the right of
the helicopter, and to the left when the transmitter is to
the left of the helicopter.
(2) An FM signal strength indicator shows red
whenever the FM radio receiver signal is absent or is too
weak for a reliable indication. When the signal strength
is acceptable, the FM signal strength indicator shows
black
(3) The station approach indicator indicates
helicopter approach to the FM radio transmitter. The
pointer moves down as the transmitter is approached.
d. The power warning indicator comes into
view whenever electrical AC power to the gyromagnetic
compass is off, or inoperative.
3-47. CONUS NAVIGATION RECEIVER.
NOTE
Keying of the AN/ARC-115, VHF-AM
transmitter may cause the AN/ARN-123
VOR receiver to lose station lock-on.
The RMI BRG PTR on the heading radio
bearing indicator and the course pointer
on the course deviation indicator will
return to center position and the VOR
NAV warning flag will appear. The VOR
receiver will return to normal operation
when the AN/ARC-115 transmitter is
unkeyed.
3-48. DESCRIPTION - CONUS NAVIGATION
RECEIVER.
The CONUS navigation receiver AN/ARN-123(V)
receives the combined VOR (VHF omni-range) and LOC
(localizer) signals over a frequency range of 108.00 to 1
17.95 MHz, GS (glideslope) signals over a frequency
range of 329.15 to 335.00 MHz, and MB (marker
beacon) signals on 75.00 MHz from ground transmitters.
The receiver is controlled by the C-10048/ARN-123
control panel (figure 3-11) mounted on the lower right
side of the instrument panel. The signals are visually
displayed on the CDI (figure 3-12), and the marker
beacon light as required. The VOR and localizer audio
signals are received from ground transmitters through
the helicopter intercommunications system by placing
the interphone control (figure 3-2) AUX switch to ON.
The set enables the operator to determine his present
position, direction to a given point, and fly a
predetermined flight path to localizer circuitry provides a
visual display of the helicopter position relative to a
localizer course. The marker beacon circuitry provides a
visual display and aural tone to indicate helicopter
position relative to a marker ground transmitter.
3-21
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