TM 55-1510-219-10 3-12.    VOICE    SECURITY    SYSTEM    TSEC/KY-28 (PROVISIONS ONLY). NOTE Voice   security   system   TSEC/KY- 58   may   be   installed   in   lieu   of voice   security   system   TSEC/KY- 28.        Complete    provisions    are provided  to  install  either  the  KY- 28   or   the   KY-58   voice   security system on the pedestal extension (fig.  2-10). a.    Description.    The  KY-28  voice  security  system provides secure (ciphered) two-way voice communications  for  the  pilot  and  copilot  in  conjunction with the UHF and VHF/AM/FM command sets, and the backup VOW set.  System circuits are protected by the VHF, VHF/AM/FM, RADIO RELAY, and BU VOW circuit breakers on the overhead circuit breaker panel (fig.  2- 26).      Figure   3-6   illustrates   the   KY-28   voice   security (CIPHONY) control indicator. b.  Controls and Indicators. (1)  Voice security control/indicator.  (fig. 3-6). CONTROL FUNCTION INDICATOR POWER ON Turns set on or off. switch NOTE The POWER ON switch must be in ON    position    for    FM    liaison    or secure mission operations in either the plain or cipher mode. POWER ON Illuminates when POWER ON indicator switch is placed in ON (up) position. PLAIN indicator Illuminates when PLAIN/ CIPHER switch is in PLAIN po- sition. PLAIN/CIPHER switch PLAIN Enables unciphered communica- tions on FM liaison set. CIPHER Enables  ciphered  communica- tions on FM liaison set. RE-X/REG switch RE-X Enables  re-transmission  of ci- phered communications at a dis- tant location. REG Enables normal cipher or plain communications. ZEROIZE switch Normally OFF.  Place in ON po- sition during emergency situa- tions to neutralize and make in- operative the associated cipher equipment. CIPHER Illuminates when PLAIN/ indicator CIPHER  switch is in CIPHER position. c.  VHF/AM/FM Set and Voice Security Operation. (1)  Turn-on. 1.  POWER ON switch (fig.  3-6) - ON. NOTE The POWER ON switch must be in ON    position,    regardless    of    the mode  of  the  operation,  whenever the  voice  security  (CIPHONY)  KY- 28 is installed in the aircraft. (2)  Receive. 1.      SQUELCH         control      (VHF/AM/   FM panel) - As required. 2.    Transmitter-interphone      selector  (audio panel, fig.  3-1) - #2 position.  or Audio monitor control #2 - ON. 3.  Mode   selector   (VHF/AM/FM panel) - TR. 4.      Frequency      selectors      (VHF/AM/FM panel)  -  As  required.    PLAIN/CIPHER switch     (voice     security     panel)     -     As required. (3)  Transmit (PLAIN). 1.        Transmit/interphone    selector    (audio panel) - No.  2 position. 2.    PLAIN/CIPHER    switch    (Voice  security panel) - PLAIN. 3.  Microphone switch - Press. (4)  Transmit (CIPHER). 1.        Transmit/interphone    selector    (audio panel) - No.  2 position. 2.    PLAIN/CIPHER    switch    (Voice  security panel)  -CIPHER.    Indicator  will  be  on while switch is in CIPHER position.) 3-12