with a basic  understanding of how they operate. But first,  we  need  to  discuss  FLTSATCOM  Shorebased Terminals. FLTSATCOM  SHOREBASED  TERMINALS SATCOM installations at shore terminals operate from   existing   naval   communications   centers   and certain   command   operations   centers.   Four   Naval Computer   and   Telecommunications   Area   Master Stations  (NCTAMS)  have  primary  responsibility  for naval communications via satellite. They are: NCTAMS  LANT,  Norfolk,  Virginia NCTAMS  MED,  Naples,  Italy NCTAMS  WESTPAC,  Finegayan,  Guam NCTAMS  EASTPAC,  Wahiawa,  Hawaii The   Naval   Computer   and   Telecommunications Station   (NCTS),   San   Diego,   California,   as   part   of TADIXS,   provides   connectivity   between   NCTAMS EASTPAC  and  NCTAMS  LANT. Ten NCTSs are used to retransmit Fleet Broadcast message traffic via hf links. In addition, an rf terminal at   Yokosuka,   Japan,   transmits   SSIXS   and   Secure Voice   communications   to   the   western   Pacific   and Indian   Oceans.   Also,   there   is   landline   connection between  Japan  and  NCTAMS  WESTPAC  to  support TADIXS  and  OTCIXS  transmissions. Within these facilities, each subsystem consists of two parts: the baseband equipment (used to collect and control  the  transmitted  or  received  communications) and  the  rf  terminal  (used  by  the  baseband  system  to transmit   and   receive   via   satellite   link).   Some subsystems   have   the   baseband   equipment   and   rf terminals in the same building, while others have the baseband   equipment   installed   at   a   remote   facility located   some   distance   from   the   rf   terminal.   Most subsystems  use  a  common  rf  terminal.  However,  the Fleet   Broadcast   has   an   rf   terminal   specifically designed for that subsystem. FLEET  SATELLITE  BROADCAST SUBSYSTEM The   Fleet   Satellite   Broadcast   Subsystem provides  the  capability  to  transmit  Fleet  Broadcast message   traffic   in   a   high-level   jamming   en- vironment.   The   subsystem   has   15   subchannels   of encrypted  message  traffic  at  an  input  data  rate  of  75 bps   per   channel.   These   subchannels   are   time- division  multiplexed  and  are  transmitted  in  a  one- way  rf  transmission  at  1200  bps.  The  shore  terminal transmits  this  data  on  a  direct-sequence,  spread- spectrum  shf  signal  to  the  satellite,  where  the  signal is   translated   to   uhf   and   down-linked   to   the subscriber.  Figure  3-2  shows  a  block  diagram  of  the Fleet   Satellite   Broadcast   Subsystem. The   High-Speed   Fleet   Broadcast   (HSFB)  is  a planned   upgrade   to   the   Fleet   Satellite   Broadcast Subsystem.  This  upgrade  will  improve  broadcast transmission speed, information through-put (capabil- ity of equipment to process or transmit data during a specific period of time), and flexibility. Message Traffic Input The  Fleet  Satellite  Broadcast  message  traffic  is queued   and/or   channel   selected   by   two   processor- controlled   message   switching   systems   before transmission.  These  systems  are  the  Naval  Com- munications   Processing   and   Routing   System (NAVCOMPARS)   for   general   service   message traffic, and  STREAMLINER  for  special  intelligence message   traffic.   Fleet   weather   data   from   Naval Oceanographic  Command  Centers  is  also  transmitted on nonprocessor controlled channels. Rf Transmission The FLTSATCOM satellites have two rf channels allocated for Fleet Satellite Broadcast message traffic. The primary channel is configured for an shf uplink to the satellite and for translation within the satellite for transmission  as  uhf  in  the  downlink.  The  second  rf channel is designed for backup use only. Since   two   channels   are   available,   and   several different  modulation  techniques  are  used  for  the uplink, there are seven different modes in which the rf link can be transmitted. In  modes  1  through  6,  the  shf  transmissions  are made   by   the   Satellite   Communications   Terminal AN/FSC-79.   Mode   7   operates   the   rf   uplink   and downlink  at  ultra-high  frequencies  and  uses  the  uhf transceiver   AN/WSC-5(V). Reception Subscribers   receive   the   uhf   downlink   signal through   the   AN/SSR-1   receiver   system,   which demodulates  and  demultiplexes  the  signal.  The demuxed   signal   is   decrypted   and   read   into   the 3-4