Antenna coupler and antenna LINK-11  NET  OPERATING  MODES—  The six modes of Link-11 operation are as follows: Net Synchronization Net Test Roll  Call Broadcast Short Broadcast Radio Silence The  Net  Synchronization  mode  establishes  the initial   time   base   between   the   NCS   and   all participating  units. The  Net  Test  mode  tests  the connectivity of all units in the net and the operation of the DTS. The Roll Call mode is the normal mode of Link-11  operations.    The Broadcast mode allows a single unit to transmit tactical data to all other units repeatedly. The Short Broadcast mode allows a unit to  broadcast  its  tactical  data  once  every  time  the operator  depresses  the  transmit  start  switch.  Radio Silence allows a unit to receive Link-11 data, but that unit will not transmit data. BUILDING  A  LINK-11  MESSAGE—  A Link-11 message consists of the preamble, the phase reference  frame,  and  the  information  segment.  The preamble is five frames long and contains the 605-Hz Doppler tone and the 2,915-Hz sync tone. The phase reference frame is one frame and provides a starting reference   for   the   information   segment. The information  segment  of  the  Link-11  message  contains control  codes  and  tactical  data.  Control  codes  are  the start codes, the stop codes, and the address codes. LINK-11  MESSAGE  FORMATS—  The  format of  a  Link-11  message  is  depends  on  the  mode  of operation. The   Roll   Call   mode   consists   of   the following   three   different   messages:   the   call-up (interrogation) message, the NCS report and call-up message, and the picket reply message. The call-up message consists of the preamble, the phase reference frame,  and  the  address  code  of  the  unit  being interrogated. The  NCS  report  is  made  up  of  the preamble, the phase reference frame, the start code, the tactical information, the control stop code, and the address of the next unit. The picket reply message is comprised of the preamble, the phase reference frame, the start code, the tactical data, and the picket stop code. The Broadcast and Short Broadcast messages are the  same  format  as  a  picket  reply  message.  In  the Broadcast  mode,  one  unit  repeatedly  broadcasts  its tactical data and all other units in the net monitor this data. In the Short Broadcast mode, the operator must initiate each transmission of data. In the Net Synchronization mode, the message is a  continuously  broadcast  preamble.  The  Net  Test mode  message  consists  of  the  preamble,  the  phase reference frame, and a preset series of data words that are repeated until the test is stopped by the operator. LINK-11 DATA TERMINAL SET (DTS)— The Link-11 data terminal set is the heart of the Link-11 system. The  data  terminal  set  performs  the modulation, demodulation,  and  control  functions required for Link-11 operations. DTS ERROR DETECTION AND CORRECTION  (EDAC)—  The DTS is capable of detecting and correcting single bit errors in received data. It accomplishes this correction by decoding the six  hamming  bits  that  are  added  to  the  24-bit  data word by the transmitting DTS. When a correction is made, if there are multiple errors or the DTS is in the error detect and label mode, the error is designated by two parity bits added to the 24-bit data word before the data is sent to the CDS computer. DTS  AUDIO  TONE  GENERATION  AND CHARACTERISTICS—   The  DTS  generates  a 16-tone   composite   audio   signal. It   converts (modulates) the 24 data bits into 12 audio tones. Each tone contains two data bits. Added to these 12 tones are the three tones containing the six EDAC hamming bits. A sixteenth tone is used for Doppler correction. The audio tones are the odd harmonics of 55 Hz. The 2-20