TM  1-1520-240-10            4-1-1 CHAPTER  4 MISSION EQUIPMENT SECTION  I.  MISSION AVIONICS 4-1-1.  Radar Signal Detecting, AN/APR-39(V)1. The radar signal detecting set (RSDS) AN/APR-39A(V)1 is a passive electronic warfare system that provides visual and aural indications of the presence of and bearing to active radar transmitters. The RSDS detects those pulse radar  signals  usually  associated  with  hostile  fire  control radars in the H-J and MMW (millimeter wave) frequency bands. The RSDS is the heart of the helicopter threat warn- ing  suite.  It  interfaces  with  the  laser  detecting  set  AN/ AVR-2,  missile  warning  system  AN/AAR-47,  and  radar warning system AN/APR 44(V)3 to process, display, and announce threats detected by those systems. The system consists of the indicator on the center instrument panel (fig. 2-1-8), a digital processor located in the right aft avionics pod,  two  video  receivers  (one  at  station  50,  another  at station  605),  four  spiral  antennas  (hi–band)  outside  the helicopter (Two at station 26, two at station 623), and a blade  antenna  (lo-band)  mounted  on  the  bottom  of  the fuselage   at   station   99.   In   addition,   a   separate   AN/ APR-39A(V)1 volume control labeled audio on  the cen- tered console provides additional volume control capabili- ties external of the ICS (fig. 4-1-2). The RSDS is powered in the No. 2 DC bus through the ASE RADAR WARN circuit breaker on the No. 2 PDP a. The   antenna-detector   characteristics   determine the frequency range of the system. Each of the antenna- detectors contain two spiral elements, one operating in the H-J bands and operating in the MMW (millimeter wave) region. Each of the spiral elements receive radio frequency (RF) signals in their respective band and supply it to the detector circuits. The detector portion of the antenna-de- tector employs an elaborate set of filter banks that extract the video (pulses) from the RF received in each band. The resultant video outputs are then summed and provided as a composite video signal to the appropriate video receiver. b. Each video receiver has two video input chan- nels and they serve the left and right antenna-detectors for the corresponding forward or aft sector. The video receiver supplies power to the antenna-detectors and amplifies the detected video inputs from the antenna-detectors. Two vid- eo outputs are then sent to the digital processor for signal analysis. The video receiver also performs initiated built-in test on command from the digital processor c. The digital processor supplies 15 VDC operating power to the two video receivers and superimposes a self-test signal on the 15 VDC power line to the receivers during  RSDS  self-test.  The  digital  processor  receives video  inputs  from  the  video  receivers  and  processes them to determine signal parameters. These signal pa- rameters  include  pulse  repetition  interval  (PRI)  pulse with (PW), pulse spacing (PS), and signal strength. The system does not provide center frequency resolution for detected signals. It then compares these signals param- eters to the threat library stored in the emitter identification data (EID) files. If a match occurs, the digital processor send the appropriate symbol data to the indicator and a corresponding computer-synthesized voice warning mes- sage to the helicopter ICS. If the received signal parame- ters do not match a threat in the EID files, the processor generates a symbol “U” to indicate an unknown threat. It executes and evaluates the results of an IBIT routine, pro- viding an indication of results on the indicator. Also, it pro- cesses   threat   data   inputs   from   the   AN/AVR-2,   AN/ APR-44(3),  and  AN/AAR-47  systems  for  display  on  the indicator and annunciation over the ICS. d. The blade antenna senses C/D lo-band RF and routes it to the C/D band amplifier portion of the digital processor. The RF signal is filtered, limited, and detected by the C/D band amplifier with the resultant video being analyzed for the presence of a threat in the C/D band. This analysis occurs in conjunction with the hi-band sig- nal  analysis  to  determine  the  threat  type  and  current threat mode (scan. acquisition, track, launch, etc.) e. The RSDS employs a removable user data module (UDM) which is mounted in the digital processor. The UDM contains the classified portion of the system operational flight program   (OFP)   and   the   classified   emitter   identification data(EID) files. The EID files contain the threat library which includes   threat   signal   parameters,   threat   symbols,   and threat audio data. The UDM can be removed at the unit level and  reprogrammed  to  accommodate  new  and  changing threats.  It  allows  the  RSDS  to  be  tailored  to  the  specific theatre  of  operation  and/or  current  mission  requirements. Removal of the UDM from the digital processor declassifies the RSDS.