Coordinate Data Transfer Control The  coordinate  data  transfer  control  assembly enables the connection of each of the digital-to-digital converters (DDC) to one of two different computers. The  control  panel  for  the  coordinate  data  transfer control   assembly   is   shown   in   figure   4-5. The COMPUTER  SELECT  provides  switching,  such  that DDC A is connected to computer 1 and DDC B is connected to computer 2 or vice versa. Either of the two DDCs maybe connected to its monitor test panel for off-line testing. The DDC output options are the CDS (old NTDS) radio set, the CAINS system, or the test  mode. Digital-to-Digital  Converter The  digital-to-digital  converter  assembly  provides system timing, converts parallel data from the CDS computer into serial data for transmission by the UHF radio set, and converts serial data received from the radio  set  into  parallel  data  for  input  to  the  CDS computer. The DDC is the heart of the data terminal set. Monitor Test Panel The  monitor  test  panel  provides  the  technician with  a  means  to  monitor  Link-4A  operations  and  off- line testing capabilities.    There  is  one  monitor  test panel for each DDC. Pulse Amplifier The  pulse  amplifiers  provide  level  and  signal conversion functions to allow the AN/SSW- 1D/E data terminal  set  to  drive  the  serial  output  for  the  UHF radio set and the deck edge outlet boxes for CAINS. COMMUNICATIONS  SWITCHBOARD The  communications  switchboard  interconnects the   AN/SSW-1()   to   the   UHF   radio   sets. The communications switchboard is similar to the Link-11 switchboard described in chapter 2 of this manual. LINK MONITOR SYSTEM (LMS-4) The   LMS-4   provides   stand-alone   Link-4A monitor  and  readiness  check  capabilities. Its operation is similar to that of the LMS-11 covered in the previous chapter.    The  monitor  function  listens passively to the Link-4A communications between the control  station  and  the  controlled  aircraft.  Signal analysis and test message validity are performed on the  data.  The  readiness  check  function  tests  the readiness of the control station to conduct live two- way   Link-4A   operations. Control   messages transmitted by the control station are monitored and the LMS-4 generates the reply messages required to maintain two-way communications. SUMMARY—LINK-4A This   chapter   introduced   you   to   the   Link-4A communications system. The following information highlights some of the important points you should have  learned. LINK-4A CDS SYSTEM—  The Link-4A CDS system  provides  one-way  or  two-way  communication between the controlling station and up to 100 aircraft. Link-4A   messages   contain   flight   commands   and tactical information for the aircraft’s pilot. The four modes of operation for the Link-4A CDS system are intercept vectoring, air traffic control, the automatic carrier landing system, and precision course direction. Intercept  vectoring  mode  is  used  to  guide  an aircraft to an assigned target. Air traffic control mode is used to control the aircraft in a carrier’s landing traffic pattern. The automatic carrier landing system uses the carrier’s precision approach radars to land an aircraft  on  the  flight  deck  automatically.  Precision course  direction  mode  provides  very  accurate  control of an aircraft’s flight path and is used for the remote guidance  of  bombers,  reconnaissance  aircraft,  and drones. 4-6 C A R R I E R    A I R C R A F T INERTIAL NAVIGATIONAL  SYSTEMS  (CAINS)—  The CAINS   system   is   used   to   load   way-point   and alignment  data  into  the  navigation  computer  of  an