pounds to less than 100 pounds. Benefits Because the azimuth and range units are combined in one system it provides for simpler installation. Less space is required than a VOR because a VOR requires a large counterpoise and a fairly complex phased antenna system. A TACAN system theoretically might be placed on a building, a large truck, an airplane, or a ship, and be operational in a short period of time. An airborne TACAN receiver can be used in air-to-air mode, which allows two cooperating aircraft to find their relative bearings and distance. Drawbacks For military usage a primary drawback is lack of the ability to control emissions (EMCON) and stealth. Naval TACAN operations are designed so an aircraft can find the ship and land. There is no encryption involved, an enemy can simply use the range and bearing provided to attack a ship equipped with a TACAN. Some TACANs have the ability to employ a "Demand Only" mode wherein they will only transmit when interrogated by an aircraft on-channel. It is likely that TACAN will be replaced with a differential GPS system similar to the Local Area Augmentation System called JPALS. The Joint Precision Approach and Landing System has a low probability of intercept to prevent enemy detection and an aircraft carrier version can be used for autoland operations. Some systems used in the United States modulate the transmitted signal by using a 900 RPM rotating antenna. Since this antenna is fairly large and must rotate 24 hours a day, it can cause reliability issues. Modern systems have antennas that use electronic rotation (instead of mechanical rotation) with no moving parts. See also Battle of Lima Site 85 (SAC TACAN captured March 1968) Distance measuring equipment Electronics technician Global Positioning System VHF omnidirectional range Wide Area Augmentation System References External links dB Systems, Inc. - Manufacturer of mechanically scanned, electronically scanned, shipboard, man-portable, and tactical TACAN Antennas - Complete TACAN Antenna profile with datasheets and photos Rantec Microwave Systems - Manufacturer of non-rotating TACAN antennas - Complete with antenna internal photos and specs Moog Navigation and Surveillance Systems - Fixed site, shipboard, mobile and man-portable TACAN systems Leonardo Air Traffic Management - Fixed site TACAN systems Avionics Radio navigation Aircraft instruments Air navigation