TM 1-1510-218-10 3A-15 5.   Microphone switch – Press to transmit. NOTE The presence of sidetone during transmission   is   an   indication   of   proper operation.    The    lack    of    sidetone    is    an indication of failure. 6.   If  squelch  operation  is  desired,  rotate squelch  control  fully  clockwise.    With no     signal     present,     rotate     squelch control     counterclockwise     until     the background   noise   is   reduced   to   a comfortably  audible  level  or  until  the control is fully counterclockwise.  After a short delay, the receiver will mute. NOTE If   background   noise   was   reduced   to   a comfortable   level   before   the   audio   was muted,    the    radio    is    equipped    with    a combination  RF  gain/squelch  feature  and control  should  be  left at setting desired in the  above  step.    If  control  was  rotated  to the  full  counterclockwise  position  with  no reduction in background noise, your system  incorporates  the  standard  squelch version and you must perform the following step. 7.   Rotate   squelch   knob   clockwise   one step  at  a  time  until  background  noise is  heard,  and  squelch  is  broken.   Set squelch control one position counterclockwise.  After a short delay, the receiver will mute. 8.   If  a  new  frequency  is  desired,  repeat steps 2 through 7. d.  Operator Maintenance. Do  not  touch  antenna  or  antenna  feedline when   radio   is   transmitting.      Painful   RF burns  and  possibly  death  may  result  from high RF voltages.  (1)   Fault  Clearing.    After  the  tune  cycle  has been     completed,     the     normal     tune     tone     should disappear.    Should  it  fail  to  disappear,  an  interrupted tone,   beeping,   will   occur   approximately   8   seconds after   the   tune   cycle   was   initiated.      This   beeping indicates a fault condition.  To clear the fault, initiate a new tune cycle by either turning the mode selector to OFF  and  back  to  the  operating  mode,  or  turning  any frequency    selector    away    from    and    back    to    the operating frequency.  The tune tone should be present for approximately 3 to 6 seconds, and then disappear.   If   the   beeping   recurs,   try   the   clearing   procedure   a second time.  If a fault is still indicated, a unit failure is probable. (2)   RF  Test.   To  isolate  a  malfunction  to  a faulty unit or cable, perform the following procedure. 1.   Set squelch control fully clockwise and tune to WWV. Check receive operation. Select USB,  20.701.0 MHz,  and  check  for  a  1-kHz tone.  Select LSB, 20.699.0 MHz, and check  for  a  1-kHz  tone.    Select  CW, 20.698.0  MHz,  and  check  for  a  1-kHz tone in receiver. 2.   RF  TEST Lamp  –  Check,  system  not keyed.  Set the mode switch to the  RF TEST position. a.   If   the   RF   TEST   lamp   does   not illuminate, the lamp is defective or the receiver-exciter is faulty. b.   If   the   RF   TEST   lamp   blinks   for more  than  1 minute,  the  receiver- exciter is faulty. c.   If   the   RF   TEST  lamp  illuminates immediately     or     after     an     initial period   of   blinking,  the   RF   TEST lamp and fault circuits are operational. 3.   Set the mode switch to the   RF TEST position.  Change frequency selection to  any  frequency  and  key  the  system momentarily.    Observe  the   RF  TEST lamp  during  the  tune  cycle  while  the tune   tone   is   audible.      Normal   tune time is 3 to 8 seconds. 4.   System    Does    Not    Complete    Tune Cycle.    If  no  tune  tone  is  heard  after initial    keying,    the    fault    is    in    the receiver-exciter,   the   PTT  key  to  the receiver-exciter is faulty, or the exciter tune  line  between  the  receiver-exciter and pa-coupler is faulty. WARNING