a direct digital synthesizer drives a receive sampling gate at a frequency that is offset from a transmit pulse frequency to produce an expanded time sampled echo signal . the frequency offset generates a smoothly slipping phase between realtime received echoes and the sampling gate that stroboscopically expands the apparent time of the sampled echoes with an exemplary factor of 1 - million and a range accuracy of 1 - centimeter . the flexibility and repeatability of the digitally synthesized timing system is a quantum leap over analog prior art . the rock solid stability of the dds allows further accuracy improvement via an error correction table .