TM   55-1520-240-T 18-4.3 HF  LIAISON  FACILITY  OPERATIONAL  CHECK  (CONTINUED) 18-4.3 TASK RESULT 12.  Turn  HF  Control  (4)  Function  Switch  (7)  to T/R,  Mode  Switch  (11)  to  MAN,  Channel/Net Selector  (14)  to  1,  and  press  the  Edit  line- select  switch  (3).  Using  the  cursor  keys  (23), move  cursor  to  beginning  of  RCV  field  and use  the  Value  switches  (12)  to  enter frequency  of  2.5  MHz,  AM  mode.  Press  RTN line-select  switch  (3). 13.  While  still  tuned  to  2.5MHz,  AM,  set SQUELCH to minimum by depressing SQL pushbuttons  (16).  Adjust  VOL  control  (15)  to a  comfortable  listening  level.  Note  pitch  of audio  tone  received.  Then  change  to  USB then  to  LSB  mode.  Also,  vary  squelch  setting by  depressing  SQL  pushbuttons  (16)  to  verify audio can be muted and unmuted. This  tests  reception  of  a  distant  station  which broadcasts  time  and  frequency  primary  standards. If  reception  is  not  clear,  go  to  task  18-4.10. If  the  pitch  of  the  audio  tone  received  changes significantly,  go  to  next  task.  If  squelch  does  not vary  while  depressing  SQL  pushbuttons  (16)  or audio cannot be muted or unmuted, replace HF Control  C-12436/URC. 14.  Repeat  steps  12  and  13  for  the  following frequencies:  3.334,  5.0,  7.335,  10.0,  15.0 and  20.0  MHz. 15. Using either a preset or manually entered authorized  test  frequency  establish communications  with  a  known  properly functioning  ground  station  (NOTE:  If  ground station  is  on  the  same  field,  set  the  output power  to  LOW  so  communications  will  not  be distorted). NOTE Ensure Keys and Data are loaded into ARC-220  (steps  10  and  11)  before performing  step  16. 16.  Set  HF  Control  (4)  Function  Switch  (7)  to  T/R, and  Mode  Switch  (11)  to  ALE.  Establish communication  with  a  known  properly functioning  ground  station  with  a  compatible ALE  fill.  Set  Channel/Net  selector  (14)  of aircraft  radio  to  call  address  of  ground  station. Place a call from aircraft HF radio to ground station.  After  a  link  Is  established  and  a  call made  to  the  ground  station,  allow  the  link  to be  broken  by  not  using  the  radio  for  a  period of  time  (normally  around  30  seconds,  but  the exact  time  Is  programmed  in  the  fill).  Set  the Channel/Net  selector  of  ground  station  to called  address  of  the  aircraft  radio  under  test and place a call to aircraft radio. Results should be the same as steps 12 and 13. Ensure selected channel is heard loud and clear without  undesirable  chirps,  squeals,  or  hums,  thru both  aircraft  and  ground  station  radios.  If  not refer  to  task  18-4.10. The  radio  the  call  is  being  generated  from  should display CALLING on HF Control Display line 3. After  an  appropriate  delay  a  short  gong  tone  is heard in the headset and LINKED is displayed on display  line  3.  If  CALL  FAIL  is  displayed  on display  line  3,  go  to  task  18-4.11. Communication  can  begin  after  link  is  established. Headset  audio  is  muted  until  a  link  is  established. If  headset  audio  is  not  muted  or  communications cannot  be  established  or  is  not  clear,  go  to  task 18-4.10.  After  a  period  of  inactivity  the  link should  be  broken.  If  link  does  not  break,  replace HF  Receiver-Transmitter  RT-1749/URC.  The  radio receiving  an  ALE  call,  will  have  INCOMING  CALL displayed  on  HF  Control  display  line  3  and  the address  fields  will  change  to  the  caller’s. TASK RESULT ALE  address.  When  a  link  is  established,  a  short gong tone is heard in the headset and LINKED is displayed  on  display  line  3.  Communication should  then  be  generated  by  the  calling  station. If  reception  is  not  clear,  go  to  task  18-4.10. NOTE Ensure Keys and Data are loaded into ARC-220  (steps  10  and  11)  before performing  step  17. 17.  Set  HF  Control  (4)  Function  Switch  (7)  to  T/R, and  Mode  Switch  (7)  to  ECCM.  Establish communication   with   a   known   functional ground  station  with  a  compatible  ECCM  fill. Set  Channel/Net  selector  (14)  of  aircraft  radio to  ECCM  net  of  ground  station.  Place  a  call from  aircraft  HF  radio  to  ground  station.  After a link is established and a call made to the ground  station,  allow  the  link  to  be  broken  by not  using  the  radio  for  a  period  of  time (normally  around  30  seconds,  the  exact  time is  programmed  in  the  fill).  Set  the  Channel/Net selector  of  ground  station  to  ECCM  net  of  the aircraft  radio  under  test  and  place  a  call  to aircraft  radio. NOTE Perform  the  following  step  after  all  checks are  complete  and  just  before  shutdown. 18.  Gently  pull  and  turn  HF  Control  (4)  Function Switch  (7)  to  ZERO  position. If the HF Control displays UNTUNED or UNSYNCH  after  an  ECCM  net  is  chosen,  either press  TUNE  line-select  switch  or  microphone  PTT switch.  HF  Control  (4)  will  display  TUNING followed  by  SYNCHING  while  the  process  is occurring.  When  SYNCHING  is  no  longer displayed,  the  system  is  ready  for  ECCM operation.  If  system  cannot  be  tuned  or  synched, go  to  task  18-4.12.  The  radio  from  which  a  call is  initiated  the  following  will  occur:  preamble tones  will  be  heard,  wait  until  they  cease  before communicating;  when  link  is  established  a  short gong  tone  sounds  in  headset,  LINKED  is  displayed and  headset  audio  is  restored.  If  this  calling sequence  does  not  occur,  go  to  tasks  18-4.13 and  18- .14.  If  after  a  period  of  inactivity  the  link is  not  broken,  go  to  task  18-15.  When  a  call  is being received RCVING PREAMBLE is displayed before  communications  from  the  calling  station  is heard.  If  RCVING  PREAMBLE  is  not  displayed  go to  task  18-4.16.  If  communications  is  not received  from  calling  station,  go  to  task  18-4.10. All  preprogrammed  information,  including  datafill and  keyfill  data,  will  be  erased.  The  HF  Control (4)  will  display  ZEROIZED.  If  ZEROIZED  is  not displayed,  go  to  task  18-4.17. GO  TO  THE  NEXT  PAGE 18-104    Change 21