7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. SQ control knob–Controls the amount of squelch threshold voltage in VO and AME operations. SQ OFF switch–When this switch is pressed, the squelch circuits are disabled. CPLR READY indicator–This indicator will illuminate when the associated coupler is properly tuned. CPLR FAULT indicator–This indicator will illuminate to indicate improper tuning of the associated coupler. SYS READY indicator–This indicator will illuminate when the radio set has passed the self-test routine. SYS FAULT indicator–This indicator will illuminate anytime the radio set fails self-test. RESET switch–This switch resets the SYS FAULT indicator to a GO condition after a NO-GO condition was detected XMTR OFF indicator–When 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 control–This control knob is not used in the P-3 aircraft configuration. BLANKER ON switch–This switch is not used in the P-3 aircraft configuration. COND switch–This switch selects the radio set’s condition of operation. a. OFF–This position removes primary power from the radio set. b. STBY–Applies power to the radio set’s RF Amp final stage filament, frequency standard and other critical circuits. c. HI–Energizes the radio set and sets the transmitter for high-power output. d. LO–Energizes the radio set and sets the transmitter for low-power output. e. TEST–Initializes the radio set’s self-test 18.   MODE switch–This switch selects the radio set’s mode of operation. a. b. c. d. VO–This position permits forced mode selection by the COMM system selector panel. AME–This position permits AME transmission and reception. CW–With the switch in this position, the radio set will transmit and receive continuous-wave signals. DATA, DIV, LSB–In this position, permits forced mode selection by the COMM system selector panel. CU-2070/ARC Coupler 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 antenna. Long-wire Antenna 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 fuselage. 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 mode. functions. 1-18 Figure 1-12.-CU-2070/ARC coupler.