Unmanned Systems Technology 017 | AAC HAMR UAV | Autopilots | Airborne surveillance | Primoco 500 two-stroke | Faro ScanBot UGV | Transponders | Intergeo, CUAV Expo and CUAV Show reports

74 Focus | Transponders UAVs can be tracked in areas and at altitudes without secondary scan radar by using ADS-B receivers in vehicles or ground stations. SWaP The transfer of transponder technology from mainstream aviation to unmanned systems has largely been made possible through improvements in size, weight, and power (SWaP) requirements. Conventional transponders are too unwieldy in SWaP terms for UAVs below 100 lb, as they are too heavy or too large. Also, the power requirements of conventional units are too demanding for the batteries aboard smaller UAVs, and are impractical anyway. The power outputs of manned aircraft transponders enable visibility from hundreds of kilometres away, but for an 80 lb mapping UAV, for example, far less than that will be enough. That has led to the distinction between Class 1 transponders, which deliver between 18.5 dBW (125 W) and 27.0 dBW (500 W) at the antenna, and less powerful Class 2 transponders, which deliver 18.5 dBW (70 W) to 27.0 dBW (500 W). Class 2 devices are also limited by regulation to operating below 15,000 ft. The size and weight requirements of transponders have fallen over the past decade to better suit UAV SWaP constraints. Innovations such as field- programmable gate arrays, ball grid arrays and system-on-chip packages – in addition to arranging microprocessors and other components in increasingly compact ways – has led to transponder circuit boards becoming smaller and lighter, while avoiding potential collateral issues such as the heat generated by a 500 W transmitter, and any damage or malfunction that might cause in its adjacent receiver. Connectors By and large, the connectors used for Mode S transponders have not changed as smaller systems have become available. The common serial interfaces – RS-232, 422 and 485 – remain standard. The advent of ADS-B and its prime importance around the world means a UAV’s transponder is likely to be required to be able to track potentially hundreds of other craft in its vicinity that may pose a risk to it, or vice versa. However, those common interfaces are unlikely to be able to support the bandwidth necessary to transmit that much information from the ADS-B receiver to the user. For that reason, transponder systems are increasingly likely to come with Ethernet functionality to support the necessary data capacity for ADS-B, although that might make the transponders larger as Ethernet- compatible components must be integrated into the boards. The use of CAN bus in UAV transponders is also gathering support from end-users who want to connect more devices per plug. At the same time, a CAN bus may ease the burden on UAV developers struggling for space to integrate transponders into their existing vehicles, both inside the airframe and on the autopilot. Integration Manufacturers have also developed new approaches to integration – a major issue given the number of ancillary connections that a transponder needs to function effectively. For example, transponders for UAV applications in particular come December/January 2018 | Unmanned Systems Technology The ADS-B Out standard is being adopted globally by manned aviation, with UAVs likely to follow (Courtesy of Rockwell Collins) Transponders can now be scaled down to the point where Mode S devices with ADS-B Out can be installed on small UAVs with limited payload capacity (Courtesy of Sagetech)