TM  55-1510-221-10 from  voice  security  unit  should no longer be heard). NOTE No  traffic  will  be  passed  if  the  interrupted tone  is  still  heard  after  pressing  and releasing the microphone switch. 5. Microphone switch- Press (do not talk).  Wait  until  beep  is  heard, then speak into microphone. (5.)  Shutdown  procedure: 1. Mode selector   (VHF/AM/FM panel) - OFF. 2. POWER  ON  switch  (Voice  secur- ity panel) - OFF. 3-13.  VOICE  SECURITY  SYSTEM  TSEC/KY-58 (PROVISIONS  ONLY). a. Description.  The TSEC/KY-58 voice secur- ity system provides secure (ciphered) two-way voice communications  for  the  pilot  and  copilot  in  con- junction with the UHF and VHF AM-FM command sets, and the voice order wire set. The control indi- cator is located in the forward avionics rack behind the pilot. System circuits are protected by the VHF, VHF AM-FM and BU VOW circuit breakers on the overhead circuit breaker panel (fig. 2-26). b. Controls/Indicators and Functions. off. (1.)  POWER  ON  switch.  Turns  set  on  or NOTE The power switch must be in ON position for  FM  or  secure  mission  operations  in either the plain or cipher mode. (2.)  POWER  ON  indicator.  Illuminates when POWER ON switch is placed in ON (up) posi- tion. (3.)  PLAIN  indicator.  Illuminates   when PLAIN-CIPHER switch is in PLAIN position. (4.)  PLAIN-CIPHER.  Selects  unciphered or ciphered communications on FM set. (a.)  PLAIN.  Enables  unciphered communications on FM set. (b.) CIPHER.  Enables  ciphered  com- munications on FM set. (5.)  RE-X-REG.  Two-position   switch. (a.)  RE-X.  Enables   re-transmission of  ciphered  communications  at  a  distant  location. (b.)  REG.  Enables  normal  cipher  or plain communications. (6.)  ZEROIZE  switch.  Normally  OFF. Place in ON position during emergency situations to neutralize   and   make   inoperative   the   associated cipher equipment. (7.)  CIPHER  indicator.  Illuminates   when PLAIN-CIPHER switch is in CIPHER position. c. VHF AM-FM Set and Voice Security Oper- ation. (1.)  Turn-on  procedure:  Power  switch (voice security panel, fig. 3-6) - ON. NOTE The  power  switch  must  be  in  ON  posi- tion, regardless of the mode of the opera- tion, whenever the voice security (CIPHONY) KY-58 is installed in the air- craft. (2.)  Receive  operating  procedure: 1. 2. 3. 4. 5. Squelch   control   (VHF   AM-FM panel, fig. 3-5) - As required. Transmitter-interphone selector switch  (audio  control  panel,  fig. 3-1)  -  No.2  position,  or  radio monitor  control  No.2  -ON. Mode  selector  switch  (VHF AM-FM  control  panel,  fig.  3-5)  - TR. Frequency selectors (VHF AM-FM  control  panel)  -  As required. Plain-cipher  switch  (voice  security control panel) - As required. (3.)   Transmitter operating procedure (PLAIN): 1. Transmitter-interphone selector switch  (audio  control  panel,  fig. 3-1) - No.2 position. 2.  Plain-cipher  switch  (Voice  secur- ity control panel) -PLAIN. 3.  Microphone  switch  -  Press. 3-14