AbstractA precision radio ranging system that uses primarily a single carrier frequency interrogating and responding signal that is pulse amplitude modulated to provide phase shift information. A mobile interrogator finds its position by measuring ranges to each of two fixed responders. During a measurement, the interrogator has sole usage of the responder and transmits a pulse of a single frequency RF carrier. The responder measures the received carrier phase and later transmits a reply pulse on the same single frequency RF carrier which replicates this phase. The interrogator determines range to the responder from the phase difference of its own interrogation pulse and the responder reply pulse. In multiple system use, two closely spaced carrier frequencies may be time sequenced to provide multiparty two range service.