lowest  replaceable  unit  (LRU).  The  technical  manual lists the assemblies and components that can be replaced during  organizational  level  maintenance. Electronics  Technicians  (NEC  ET-1491  for  FFG-7 Class   ships   or   ET-1504   for   all   other   ships)   are responsible for organizational level maintenance of the AN/SPS-55.   Preventive   maintenance   (PM)   and corrective  maintenance  (CM)  include: electrical and mechanical alignments; adjustments,  and  calibration; fault  detection,  isolation,  and  module  or  major part  repair/replacement;  and all  correction  and  verification  necessary  to restore the radar set to an operating condition. Disposition  and  repair  of  failed  components  is specified   by   the   Source,   Maintenance,   and Recoverability   (SM&R)   codes   in   the   applicable Allowance  Parts  List  (APL).  Send  your  repairable modules  to  the  Designated  Overhaul  Point  (DOP)  for repair  or  condemnation. AIR SEARCH (2D) RADARS The two primary functions of air search radar are to (1)  detect  aircraft  targets  at  long  ranges  and  (2) determine  their  range  and  bearing.  Some  of  the  most widely used two-dimensional (2D) air search radars in the   Navy   are   the   AN/SPS-37A,   AN/SPS-43, AN/SPS-43A,    AN/SPS-49(V),    AN/SPS-40B/C/D/E, and AN/SPS-65(V) aboard ships and the AN/GPN-27 (ASR)  at  shore  installations. We will not discuss the AN/SPS-29, AN/SPS-37, and AN/SPS-43 radars, since the AN/SPS-49(V) radar replaces  them. AN/SPS-49(V) The AN/SPS-49(V) radar is the primary U.S. Navy early   warning   air   search   2D   radar. It  is  a very-long-range  radar,  and  provides  long-range  air surveillance   in   severe   clutter   and   jamming environments. It primarily supports the anti air warfare (AAW)  mission  on  surface  ships,  but  also  provides backup  to  the  3D  weapon  system  radar.  The AN/SPS-49(V) radar is also used for air traffic control (ATC),  air  intercept  control  (AIC),  and  antisubmarine aircraft  control  (ASAC). The AN/SPS-49(V) radar replaces the AN/SPS-29, AN/SPS-37,  AN/SPS-40,  and  AN/SPS-43  radars  in some ships, including the following ship types: CG CV DDG LHD CGN CVN FFG LSD Current  planning  calls  for  installation  of  the AN/SPS-49(V)  radar  in  160  U.S.  Navy  ships,  plus various shore installations. General  Theory  of  Operation The  AN/SPS-49(V)  is  a  narrow-fan  beam  radar developed from a Specific Operational Requirement. It provides  the  capability  to  conduct  air  search  operations on a previously unused radar frequency. This minimizes electronic  interference  between  ships  and  increases  the difficulty   for   hostile   electronic   countermeasures (ECM).  The  AN/SPS-49(V)  provides  good  bearing measurements to backup the 3D radar weapons system. Its narrow beamwidth substantially improves resistance to  jamming. The coherent side lobe canceler (CSLC) cancels jamming   and   interference   signals,   providing   the AN/SPS-49(V)  radar  further  resistance  to  jamming  and interference.  The  DMTI  capability  enhances  detection of  low-flying,  high-speed  targets. The AN/SPS-49(V)5 version, which has automatic target  detection  (ATD)  capability,  has  even  more sophisticated  antijamming  features.  This  version  offers improved clutter suppression and a digital interface to the AN/SYS-2(V) IADT system. The AN/SPS-49(V)5, does  not  cancel  non-moving  targets  as  with  MTI, instead it uses the newest development in doppler processing,  Finite  Impulse  Response  (FIR)  fibers. These filters separate radar echo returns into fixed and moving   channels   according   to   their   doppler characteristics.  The  moving  channels  contain  moving targets  only.  The  fixed  channels  contain  fixed  clutter and blind speed targets. Rejection  of  non-moving targets recurs at a later point in time in the clutter maps. The “AEGIS Tracker” modification consists of a PCB  card  set  integrated  into  the  signal  data  processor. It  adds  an  embedded  tracker,  with  direct  digital  interface with the AEGIS combat system, to the AN/SPS-49(V)7 radar  (installed  on  AEGIS  cruisers).  With  this modification   incorporated,   the   AN/SPS-49(V)7 nomenclature  changes  to  AN/SPS-49(V)8. The  digital  coherent  side  lobe  canceler  (DCSC)  is part of the Medium PRF Upgrade (MPU) modification. 2-8