NOTE If  function  selector  is  at  MAIN  setting, only  the  normal  UHF  communications will  be  received.  If  selector  is  at  BOTH position,  emergency  communications  on the  guard  channel  and  normal  UHF  com- munications will both be received. (2.)  Receiver  operating  procedure: 1. UHF audio monitor switch (No.3, audio  control  panel)  -ON,  or transmitter-interphone selector switch  (audio  control  panel)  - No.3 position. 2.   Volume   control   (UHF   control panel) - Mid position. (3.) To use preset frequency (UHF control panel): 1. 2. (4.)  To control  panel): 1. 2. Mode  selector  switch  -  PRESET position. Preset  channel  selector  switch  - Rotate  to  desired  channel. use  non-preset  frequency  (UHF Mode selector switch - MANUAL position. Manual  frequency  selectors  (5)  - Rotate  each  knob  to  set  desired frequency  digits. NOTE The PRESET channel selector and man- ual  frequency  selectors  are  inoperative when the mode selector switch is set to the GUARD position. 3.  Volume  -  Adjust. NOTE To adjust volume when audio is not being received,  turn  squelch  switch  OFF,  adjust volume for comfortable noise level, then turn  squelch  switch  ON. 4. Squelch  -  As  desired. (5.)  Transmitter  operating  procedure: 1.  Transmitter-interphone  selector (audio  panel  control  panel,  fig. 3-1) - No.3 position. TM 55-1510-221-10 2. UHF control panel (fig. 3-3) - Set required  frequency  using  either PRESET CHAN control or MAN- UAL frequency select controls. 3.  Microphone  jack  selector  switch (instrument  panel,  fig.2-29)  -  As desired. 4.  Microphone  switch  -  Depress  to transmit. (6.)  Shutdown  procedure:  Function  selec- tor switch (UHF control panel, fig. 3-3) -OFF. d. UHF Command Set Voice Security Opera- tion (KY-28). NOTE Disregard  operating  procedures  involving the  voice  security  control-indicator  if  unit is  not  installed. (I.)  Turn-on  procedure: 1. Power   switch   (Voice   Security panel, fig 3-6) - ON. 2.  Function  switch  (UHF  control panel) - BOTH. (2.)  Receiver  operating  procedure: 1. Mode  selector  switch  (UHF  con- trol panel, fig. 3-3) - As required. 2.  Transmitter-interphone  selector switch  (audio  control  panel,  fig. 3-1)  -   No.3   position,   or   No.3 radio monitor control - On. 3.  Set  required  frequency  using  pre- set channel control or manual fre- quency  selector. 4.  Volume  control  -  Adjust. NOTE To adjust volume when radio signals are not  being  received,  turn  squelch  switch OFF,  adjust  volume  for  comfortable  noise level,  then  turn  squelch  disable  switch ON. 5. Squelch  switch  -  As  required. (3.)  Transmitter operating procedure (PLAIN): 1.  Transmitter-interphone selector switch  (audio  control  panel)  - No.3 position. 3-7