SQ control knobControls the amount of
squelch threshold voltage in VO and AME
SQ OFF switchWhen this switch is pressed,
the squelch circuits are disabled.
CPLR READY indicatorThis indicator will
illuminate when the associated coupler is
CPLR FAULT indicatorThis indicator will
illuminate to indicate improper tuning of the
SYS READY indicatorThis indicator will
illuminate when the radio set has passed the
SYS FAULT indicatorThis indicator will
illuminate anytime the radio set fails self-test.
RESET switchThis switch resets the SYS
FAULT indicator to a GO condition after a
NO-GO condition was detected
XMTR OFF indicatorWhen this indicator is
illuminated the radio set cannot be used to
transmit. This indicator will come on during the
3-minute warmup period (the first 3 minutes of
initial power up), and anytime the operating
frequency is changed by more than 1 MHz.
Other than that, anytime there is a fault in the
system that affects the transmitter, this
indicator will illuminate.
VOL controlThis control knob is not used in
the P-3 aircraft configuration.
BLANKER ON switchThis switch is not used
in the P-3 aircraft configuration.
COND switchThis switch selects the radio
sets condition of operation.
a. OFFThis position removes primary power
from the radio set.
b. STBYApplies power to the radio sets RF
Amp final stage filament, frequency
standard and other critical circuits.
c. HIEnergizes the radio set and sets the
transmitter for high-power output.
d. LOEnergizes the radio set and sets the
transmitter for low-power output.
e. TESTInitializes the radio sets self-test
18. MODE switchThis switch selects the radio
sets mode of operation.
VOThis position permits forced mode
selection by the COMM system selector
AMEThis position permits AME
transmission and reception.
CWWith the switch in this position, the
radio set will transmit and receive
DATA, DIV, LSBIn this position, permits
forced mode selection by the COMM system
The CU-2070/ARC coupler (fig. 1-12) provides
impedance matching between the receiver transmitter
and the antenna. The lightning arrester provides a spark
gap to protect the radio if lightning strikes the long-wire
There are two antennas used in the P-3 aircraft for
the HF system. Both are located external of the aircraft,
and stretch from the top of the vertical stabilizer to the
fuselage. The one on the left is used by HF-1, and the
one on the right is for the HF-2 radio set. Both of the top
mounts for the antennas are the breakaway type. If either
antenna breaks in flight, the wire will depart the aircraft.
This is designed for safety reasons. Should the wire get
hung up and not depart the aircraft, structural damage
could occur from the wire whipping against the
TSEC/KY-75 Security Unit
The TSEC/KY-75 provides the encoding and
decoding of the signals when the radio set is in the cipher
Figure 1-12.-CU-2070/ARC coupler.