TM 1-1510-218-10 3A-7 (2)   Manual Frequency Selector Switch (Tenths).  Selects tenths digit of frequency (0 through 9) in MHz. (3)   Manual Frequency Selector Switch (Units).    Selects  unit  digit  of  frequency  (0  and  9)  in MHz. (4)   CHAN Indicator. Displays preset channels. (5)   Manual Frequency Selector Switch (Tenths).  Selects tenths digit of frequency (0 through 9) in MHz. (6)   Preset Channel Selector Switch.  Selects one of 20 preset channel frequencies. (7)   Manual Frequency Selector Switch (Hundredths  and  Thousandths).    Selects  hundredths and thousandths digits of frequency (00, 25, 50, or 75) in MHz. (8)   MANUAL   /   PRESET   /   GUARD   Mode Selector    Switch.        Selects    method    of    frequency selection. (a)  MANUAL.          Enables     the     manual selection of any one of 7,000 frequencies is manually selected using the five frequency selector switches. (b)  PRESET.        Frequency    is    selected using  the  preset  Channel  selector  switch  for  selecting any one of 20 preset channels. (c)  GUARD.        The    main    receiver    and transmitter automatically tuned to the guard frequency and the guard receiver is disabled. (9)   SQUELCH   OFF   /   ON   Switch.      Turns main receiver squelch circuit of main receiver on or off. (10)   VOL Control.  Adjusts volume. (11)   TONE   Push   Button.        When    pressed, transmits a 1,020 Hz tone on the selected frequency. (12)   Function     Switch.          Selects     operating function. (a)  OFF.  Shuts down equipment. (b)  MAIN.    Selects  normal  transmission with reception on main receiver. (c)  BOTH. Selects main receiver, transmitter and guard receiver. (d)  ADF.  Not used. c.   Normal Operation. (1)   Turn On Procedure. NOTE It   is   presumed   aircraft   power   is   on   and normally    used    avionic    circuit    breakers remain depressed. 1.   AVIONICS  MASTER  POWER  switch – ON. 2.   Function switch  –  MAIN or  BOTH, as required. 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  communications will both be received. (2)   Receiver Operating Procedure. 1.   Transmitter   selector   switch   –  No.  3 position. 2.   UHF audio monitor switch  – ON, No. 3 position. 3.   VOL control – Mid position. (3)   To Use Preset Frequency. 1.   Mode selector switch – PRESET. 2.   Preset  channel  selector  switch   –  As desired. (4)   To Use Non-Preset Frequency. NOTE The PRESET channel selector and manual frequency  selectors  are  inoperative  when the   mode   selector   switch   is   set   to   the GUARD position. 1.   Mode selector switch – MANUAL. 2.   Five    manual    frequency    selectors   – Rotate    each    knob    to    set    desired frequency digits.