CAPABILITIES AND LIMITATIONS

TACAN SET AN/URN-20 Though not modern by any standard, the AN/URN-20 TACAN set is reliable and operates similarly to the AN/URN-25. Shown in figure 2-9, it uses the same electronically-scanned antenna and control-indicator as the AN/URN-25. The AN/URN- 20 is being replaced by the AN/URN-25. CAPABILITIES AND LIMITATIONS In the X mode of operation, the TACAN set transmits on one of 126 discrete channel frequencies (which are 1-MHz apart) from 962 to 1024 MHz and from 1151 to 1213 MHz. In the Y mode of operation, the set transmits on one of 126 discrete channel frequencies (which are 1-MHz apart) within the range of 1025 to 1150 MHz. The navigation set receiver, operating in the 1025- to 1150-MHz range for both the X and Y modes, is always displaced 63 MHz from the transmitter frequency. The TACAN set can simultaneously provide individual distance measuring service for up to 100 interrogating aircraft. Of the 3,600 pulse pairs-per-second transmitted by the TACAN, 900 pulse pairs (MAIN and AUXILIARY bursts) contain the bearing information; the remaining 2,700 pulse pairs are either random noise pulses, identity pulses, or replies to interrogating aircraft. Once every 30 seconds, the interrogation replies and random noise pulses are interrupted for the transmission of identity pulses. The navigation set has a receiver sensitivity of -92 dBm or better and a nominal peak power output of 3 kilowatts at the transponder cabinet output. (Power output may limited to less than peak by directives). Since the bearing and identification signals are delivered spontaneously and not in response to interrogations, an unlimited number of properly equipped aircraft can derive this information from the TACAN set over a line-of-sight (los) range up to 200 nautical miles. 2-9