Unmanned Systems Technology 003 | UAV Solutions Talon 120 | Cable harnesses | Austro Engine AE50R and AE300 | Autonomous mining | AUVSI 2015 show report | Transponders | Space systems

69 common characteristics. For example, they must have a reduced Size, Weight and Power (SWaP) burden to ensure they do not take up excessive space, which is always at a premium no matter how large the platform. Weight is also an important consideration, since heavier transponders can reduce a vehicle’s mobility. Power consumption is the third consideration. All unmanned vehicles routinely carry optronics and radar sensors, not to mention control systems and in some cases weapons, all of which place demands on power consumption, so lower consumption frees up power for other capabilities. In addition to SWaP considerations, unmanned vehicle transponders have to guarantee immunity to electromagnetic interference (EMI). This is a safeguard to ensure that communications links between the vehicle and the interrogator are not lost in the event of a release of EMI, whether it be from naturally occurring meteorological phenomena or as a result of the use of electronic warfare (EW) techniques. There is also the need to ensure that the radio emissions from the transponder, and the interrogations it receives, do not interfere with other onboard electronic subsystems. To this end, the US Department of Defense has several military standards (MIL- STD) for various aspects of unmanned vehicle transponder technology. These include MIL-STD-461, which concerns transponder immunity to EMI, and MIL- STD-464 and MIL-STD-704 that cover transponder compatibility with other onboard power systems. Transponders typically use the radio spectrum, and in the case of UAVs this can include the VHF and UHF segments, in a range that stretches from 30 MHz up to 3 GHz. Both VHF and UHF transponders have a line-of-sight range, but given that aircraft can fly at high altitudes, UAV transponders can have a range of several hundred nautical miles. Where the link between the aircraft’s transponder and the interrogator is not blocked by the Earth’s horizon, ranges of about 200 nautical miles (370 km) using a line-of-sight link are possible. That said, an over-the-horizon range of about 330 nm (just over 610 km) is possible using radio relay techniques. Here, another aircraft is positioned between the operator on the ground and the aircraft’s transponder to ‘bounce’ the signals Transponders | Focus Unmanned Systems Technology | Summer 2015 All transponders must have a reduced SWaP burden to ensure they do not take up excessive space, which is at a premium An interrogator initiates requests for data from aircraft on their identity, position and so on. This example is used by the US Navy (Courtesy of BAE Systems)