TACAN EQUIPMENT

Figure 2-6.—TACAN modulation envelope spacing are a characteristic of that particular TACAN signal element. However, it is important to understand that proper spacing between pulses and pulse pairs is what actually provides the aircraft with the means to distinguish between the TACAN pulses and any other pulses that might be present on the received radio frequency. Check the reference data in the appropriate technical manual for specific pulse characteristics and spacing. TACAN EQUIPMENT Many different types of TACAN equipment have been used for air navigation. Today, the AN/URN-25 is taking over the task of tactical air navigation from the older AN/URN-20 on new construction ships and as ships complete overhaul. Two types of antennas are used with the AN/URN-25. They are the OE- 273(V)/URN, used primarily in shipboard installations, and the OE-258/URN, which is used primarily ashore. Because both antenna systems are similar in theory of operation, we will discuss only the OE-273/URN. In the following paragraphs, we will discuss the AN/URN-25 and the antenna group 0E-273(V)/URN, and then we will briefly discuss the AN/URN-20. TACAN SET AN/URN-25 The AN/URN-25 TACAN is used as a ground- based or shipborne beacon transponder to provide range and bearing information to aircraft equipped with TACAN equipment. It consists of two major units: the Transponder Group OX-52/URN-25, commonly referred to as unit 1, and the Control- Indicator C-10363/URN-25, commonly referred to as unit 2. These units are shown in figure 2-7. Each transponder is housed in a cabinet with two vertical drawers, one containing a coder keyer and the other containing a receiver-transmitter. The control-indicator displays the status of the transponder(s) and failure alarms, and allows limited control of the transponder(s) from a remote location. 2-5