Abstract: A bi-static radar configuration measures the time-of-flight of an RF burst using differentially-configured sampling receivers. A precise differential measurement is made by simultaneously sampling a reference signal line and a free-space time-of-flight RF burst signal using separate sampling receivers having common sample timing. Two alternative sample timing systems may be used with the sampling receivers: (1) a swept delay using a delay locked loop (DLL), or (2) two precision oscillators slightly offset in frequency from each other. The receiver outputs are processed into a PWM signal to indicate antenna-to-antenna time-of-flight range or to indicate material properties. Applications include robotics, safety, material thickness measurement, material dielectric constant measurement, such as for fuel or grain moisture measurement, and through-tank fill-level measurement.