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signal represents a threat an audio signal is sent to the
RW control panel and an audio alarm is sounded in the
pilots helmet. The audio alarm frequency represents
the relative strength of the intercepted radar signals.
Also during radar signal threats, the RW display missile
alert (MA) lamp is illuminated. The MA lamp
flashes to represent the relative strength of the intercepted
radar signals. The operating controls and indicators
of the RW control panel (fig 4-20) are described
in table 4-23.
4-71
CAUTION
TM 1-1520-238-10
Table 4--23. AN/APR-39(V)1 Radar Warning System (CRT) Control/Indicator Functions
Control/
Indicator Position Function
PWR ON Turns set on. Fully operational after l-minute warmup.
OFF Turns set off.
DSCRM Selects mode of operation.
ON Activates discriminator circuit.
OFF Deactivates discriminator circuit.
SELF-TEST When pressed, initiates self-test check (except for antenna and receiver).
AUDIO Adjusts volume to the intercommunications system.
4.37.1 AN/APR-39(V)1 Operating Procedures. The 2. BRIL and filter controls - Adjust as desired.
procedure for turning on and off the RW equipment is
as follows:
To prevent damage to the receiver detector
crystals, assure that the radar
warning set antennas are at least 60
meters from active ground radar antennas
or 6 meters from active airborne
radar antennas. Allow an extra
margin for new, unusual, or high
power emitters.
1. Equipment on. PWR switch - ON. Allow
3. AUDIO control - Adjust volume as desired.
4. DSCRM switch - Set for mission requirement.
5. Equipment off. PWR switch - OFF.
4.37.2 AN/APR-39(V)1 Radar Warning Display Controls.
The operating controls of the RW display, located
on the right side of the pilot instrument panel (fig
2-9 and 4-21), are described in table 4-24. The display
shows a line-of-bearing radial stroke for each processed
l-minute for warm-up. signal.
Table 4-24. AN/APR-39(V) 1 Radar Warning Display Control/Indicator Functions
Control/Indicator Function
BRIL Control Adjust CRT display brightness.
MA Indicator Missile Alert. Flashes on and off to indicate time correlation between missile guidance
and associated tracking radar.
Filter Control Varies density of red polarized CRT faceplate filter (used for day or night operation) by
moving tang right or left.
4-72
TM 1-1520-238-10
4.37.3 AN/APR-39(V)1 Operation Modes. The RW
set may be operated in either the discriminator off or
discriminator on mode. The RW set receives 28 vdc
from the emergency dc bus through the RDR WARN
circuit breaker on the pilot overhead circuit breaker
panel. The RW set is not monitored by FD/LS.
NOTE
Display strobe lengths indicate only relative
signal amplitude. Since many variables
can affect the atmospheric attenuation
of the signals, strobe length should
not be considered as a direct interpretation
of the distance to the emitter.
a. Discriminator Off Mode. When operating in
the discriminator off mode, the DSCRM switch is
placed OFF. In this mode all high band received signals
with amplitude greater than a predetermined threshold
level are displayed on the CRT and an audio signal,
representative of the combined amplitudes and pulse
repetition frequencies (PRF), is present at the headset.
The displays indicate the total radar environment in
which the helicopter is operating. Each radial strobe on
the CRT is a line of bearing to an active emitter. When
a SAM radar complex becomes a threat to the helicopter
(low band signals correlated with high band signals),
the alarm audio is superimposed on the PRF audio
signal and the MA light and associated strobe start
flashing. Lengths of strobes and audio levels depend on
the relative strength of the intercepted signals. A typical
display when operating in the discriminator off
mode is shown in figure 4-21.
N O T E
In this mode, received low band signals
which are not correlated with a high band
intercept will cause the MA light to flash
and an alarm audio will sound.
b. Discriminator On Mode. When operating in
the discriminator on mode, the DSCRM switch is set to
ON. In this mode, signals are processed to determine
their conformance to certain threat associated criteria
as follows:
(1) The signal level must be greater than the
minimum threshold level.
(2) Pulse width must be less than the maximum
pulse width.
Figure 4-21. Radar Warning Discriminator Off
Mode Display
(3) PRF must be greater than the minimum
pulses per second.
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