Test results and analysis of a low cost core GPS receiver for time transfer applications

Precise timing is inherent to the operation of the Global Positioning System (GPS), enabling worldwide continuous precise time transfer at a very low-cost. Motorola's GPS receivers have been used for time synchronization and frequency control for several years. Motorola has introduced the next generation of GPS receivers for precise timing, which feature improved performance and lower cost. Typically, the precise pulse from a GPS receiver is used to discipline a higher precision crystal or rubidium oscillator so that it can be synchronized to a common time stamp. The pulse stability from the GPS receiver is important in the disciplining process. The pulse is also used to synchronize the system to UTC, so the absolute accuracy of the precise pulse is of interest. Most precision timing applications are at fixed base station sites. In the case of wireless telecommunications applications, many of the sites where the GPS receiver is installed are shared with other RF antennas. The GPS signal can be jammed by various RF emitters at certain frequencies and power levels. For a GPS receiver to operate under these conditions, it must be able to track the GPS signal in the presence of in-band and out-of-band interference. The new UT Oncore/sup TM/ has been tested against UTC time standards for accuracy and atomic standards for stability. This paper outlines the tests performed and the results of these tests are compared with previous generation receivers. Other performance aspects of the GPS receiver including immunity to interference signals and startup time are also presented.