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.