ATAC/DLC.—  The air transportable communi- cation (ATAC) and down-link communication (DLC) buoys are intended for use as a means of communi- cation  between  an  aircraft  and  a  submarine.  The ATAC  buoy  is  commendable  from  the  aircraft  and provides  up-link  and  down-link  communications  by  a preselected   code. The   DLC   buoy   is   not   com- mandable and provides a down-link communications only by a preselected code. SONOBUOY  RECEIVERS Learning Objective:  Recognize  the  operating principles  and  components  of  a  typical sonobuoy  receiver. The sonobuoy receiver set that will be discussed in this chapter is the AN/ARR-75. This set is used on the  H-60  LAMPS  helicopter. The   radio   receiving   set   (RRS)   receives, demodulates, and amplifies sonobuoy transmissions in the VHF bands, It provides channels A, B, C, and D acoustic data to the data link for transmission to the ship  via  the  communications  system  control  group. Channels  E,  F,  G,  and  H  acoustic  data  is  provided direct to the data link for transmission to the ship. The  acoustic  data  is  also  routed  to  the  spectrum analyzer group for processing and display on board the  aircraft.  Simultaneous  reception  and  demodu- lation of standard sonobuoy RF channels is possible. Any one of the received channels can be selected for aural  monitoring. The  RRS  consists  of  two  radio receiver  groups. The  radio  receiver  groups  each  consist  of  four VHF radio receivers and a power supply. Each of the four  receivers  can  operate  on  a  separate  channel, independent of the others. The RF signals received by the sonobuoy antennas are applied to each of the four receiver modules, where tuned filters select the signals   for   each   module.   The   signals   then   pass through a series of amplifiers, filters, and mixers to produce the output audio signals. The output signals are supplied to the spectrum analyzer group and the data  link  system.    The spectrum analyzer processes the signals to allow monitoring by the aircrew. ACOUSTIC  SYSTEM Learning  Objective:  Recognize    components and operating principles of a typical acoustic system. The AN/UYS-1 single advanced signal processor system  (SASP)  processes  sonobuoy  acoustic  audio and displays the resulting data in a format suitable for operator evaluation in the P3-C Update III aircraft. OPERATING  PRINCIPLES The  SASP  processes  sonobuoy  audio  in  active and passive processing modes to provide long range search,  detection,  localization,  and  identification  of submarines. The sonobuoys presently in use include the  LOFAR,  DIFAR,  CASS,  DICASS,  and  BT.  The RF  signals  from  the  sonobuoys  are  received  by  the sonobuoy  receivers  and  sent  to  the  SASP.  After processing, signals are sent to the displays and the recorders for operator use. The SASP also generates command   tones   for   controlling   the   CASS   and DICASS  sonobuoys. COMPONENTS The   major   components   include   the   TS-4008/ UYS-1  spectrum  analyzer  (SA),  PP-7467/UYS-1 power   supply,   and   the   C-11104/UYS-1   control- indicator (SASP power control). TS-4008/UYS-1 Spectrum Analyzer The  TS-4008/UYS-1  spectrum  analyzer  is  a high-speed  signal  processor  designed  to  extract acoustic  target  information  from  both  active  and passive   sonobuoy   data.   The   SA   determines frequency,  amplitude,  bearing,  Doppler,  range,  and other  characteristics  for  acoustic  targets. PP-7467/UYS-1 Power Supply The PP-7467/UYS-1 power supply converts 115 volts  ac  into  120  volts  dc  operating  voltages.  The 120-volt dc power is then converted to low-level dc voltages for operation of individual circuits. A power interrupt unit protects the data against transient power interruptions  that  normally  occur  during  airborne operations. 4-27