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TM   11-5821-333-12 1-15. FH SYNC TIME. The FH sync time feature of the RT is for FH operation. It is not a substitute for a wrist watch or a clock. There are seven different clocks in the RT. There is a base clock and separate clocks for PRESET switch positions 1 through 6. When FH sync time is first loaded into the RT, either from a cold start or manually, all seven clocks are set to the  same  time.  When  an  ERF  is  received,  that  sender’s  time  is  loaded  into  the  preset  along  with  the  hopset.  It must  be  within  one  hour  of  the  base  clock. The clock of an RT operating in an FH net must match the FH sync time within +4 seconds. Regular radio traffic keeps the radio clocks synchronized. The FH sync time in any RT is updated every time a message is received. The Net Control Station (NCS) is the time standard for the net. It is important for the NCS to be an active member of the net. If you are a member of more than one net, you should communicate with the NCS of each net daily. NOTE An NCS operator may load FH sync time by using the keyboard. In this case, all clocks in the RT are reset to the base clock. If the NCS is operating in more than one net, sync time for other channels is obtained by ERF. It is not possible to reset the FH sync time for only one channel manually. This can only  be  done  using  ERF. 1-16. AUDIO SIGNAL PATHS. The radio set transmits RF signals. The RF is radiated by the aircraft communications antenna. When the headset push-to-talk (PTT) is pressed, an RF carrier in the RT is frequency modulated by audio from the headset and by a 150-Hz  squelch  tone.  An  optional  power  amplifier  may  be  connected  between  RT  and  antenna. PATHS OF AUDIO SIGNALS Radio  signals  received  at  the  antenna  enter  the  RT  at  J3.  The  optional  power  amplifier  passes  receive  signals unchanged. The RT processes the FM signal and recovers the audio signal. The recovered audio signal is then sent through system connector J1 to the aircraft intercom and headset. If a Remote Control Unit (RCU) is used, the audio goes through the VOL control in the RCU, For the RT to operate in receive, the intercom PTT line must be open (not ground). A 150-Hz squelch tone must be detected to break squelch when SQ ON (squelch on) and SC  (single  channel)  are  selected  on  the  RT  or  RCU.  All  FH  (frequency  hopping)  operation  is  in  squelch  on,  no matter  where  the  FUNCTION  switch  is  set. Radios  that  have  data  and  communications  security  (COMSEC)  capability  will  route  audio  signals  through  the KY-58  or  data  rate  adapter.  (See  paragraphs  1-18  and  1-20.) 1-11

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