NRL/USNO two way time transfer modem design and test results

The US Naval Research Laboratory has developed a two-way time transfer modem for the United States Naval Observatory. An overview of the hardware and software design of the digital modem showing its unique features and results of satellite testing is presented. Time transfer performance is achieved in the hardware by a combination of stability, matching and calibration. Hardware stability is achieved by using synchronous digital methods in both the transmitter and receiver sections. Identical narrowband filters are used in the transmitter and the receiver section to help match temperature-dependent delays. Time transfer between sites is a master-slave technique, a master site transferring time to a network of slave sites. A personal computer is used for operator interface, modem control, data collection, and processing. With this method, both sites can be automated. Initial tests have been conducted to evaluate and verify modem performance and reduce the effects of other systematic errors