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Myth: Changing the NCS Will Always Solve Net Problems!
MULTI-STATION  POFA

Fire Controlman Volume 06-Digital Communications
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operate properly is not generally true. It may be true only in infrequent, isolated cases. Studies have shown that in the old NTDS system (CP-642 computer and the AN/USQ-36 DTS), a dummy PU entered between a live PU and own address was required  for  NCS  data  to  be  output  at  each  NCS  report  opportunity.  Since  the CP-642 computer and the AN/USQ-36 DTS have virtually disappeared, dummy PUS should  not  be  used. Myth: Radio Silence Reduces Net Cycle Time! The effect Radio Silence has on net cycle time depends on a number of factors. As you saw in the last chapter, if a PU does not respond to a call up in 15 frames, it is interrogated again. After another 15 frames, if the PU still does not respond, the NCS polls the next PU. If the PU that goes to Radio Silence was sending reports that exceeded 38 frames, net cycle time will be reduced by the PU going to radio silence. Effective net management would be to eliminate the PU number of the unit that has to go into Radio Silence until that unit is able to reenter the net. As you can see, there are several misconceptions on the proper way to manage and troubleshoot the Link-11 system. In this chapter, we concentrate on the tools available to the technician to aid in the isolation of link problems. LINK-11  PROGRAMMED  FUNCTIONAL AND  OPERATIONAL  ANALYSIS  (POFAs) Two  types  of  POFAs  are  used  in  the  Link-11 system. These are the single station POFA, used to check components of the Link-11 on board a single station, and the multi-station POFA, used to check the connectivity of several units. SINGLE STATION POFA The single station POFA is an end-around test that transfers canned data from the computer through the crypto  device  and  the  data  terminal.  The  single station POFA can also be run through the radio set to check  out  part  of  the  audio  communications  path further. POFA Setup The POFA is a special program that is loaded into the computer. It is very important that you follow the instruction manual when attempting to run the POFA. The POFA is designed to run in full-duplex mode. Normal  link  operations  use  the  half-duplex  mode. “Full  duplex”  means  the  system  is  configured  to transmit  and  receive  data  at  the  same  time.  In  the DTS, this is accomplished by the transmit audio being fed directly into the receive input. Also, if the DTS is operating  in  full-duplex  mode,  the  rest  of  the  system, especially the crypto device, must be in fill duplex. On the KG-40, full duplex is accomplished when the front  panel  switch  is  turned  to  the  POFA  TEST position. Analyzing Single Station POFA When  a  single  station  POFA  is  completed,  a printout  of  the  results  is  produced.  To  analyze  this printout  properly,  the  technician  must  understand Figure 3-1.—Single station POFA configurations. 3-3






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