transponder transmissions may be monitored through a direct , shielded connection of an rf coupler to a transponder antenna cable . the transponder interrogated pressure altitude may quickly change and measuring accurate data including position and pressure altitude is critical . a global positioning system may be onboard a universal access transceiver and may be utilized to correct the transponder interrogated pressure altitude and position . the uat may transmit data that may include a corrected pressure altitude and a subsequent position to improve air traffic control radar beacon systems .