Micro-jump screening station for GPS user equipment

It has been known many years that AT quartz crystals exhibit isolated temperature induced frequency jumps on the order of 1-100 ppb and sometimes up to 1 ppm. These jumps have been found to be disruptive to the carrier and sometimes the code tracking loops used in precision GPS UE/sup 3/ equipment and may, if severe, cause temporary loss of satellite tracking. A considerable effort is in progress in time industry to isolate the causes of frequency jumps and eliminate the problem at the source. Rockwell has devised an interim solution in which each Time Compensated Clock Oscillator (TCCO) used for GPS UE is prescreened over temperature for frequency jumps and rejected if jumps larger than 5.4 m/sec (18 ppb) are found. The test set also allows statistical data collection of the MJ's so one may construct a histogram and CDF of measurable jumps which can allow SPC methods to be applied with respect to this component. The test set is fully capable of evaluating 16 oscillators simultaneously and is based on hardware and software from the Rockwell PLGR/sup 4/ GPS set being manufactured for the US Department of Defense. This paper gives a general description of the test set along with the accompanying temperature chamber and control software used to handle the huge volume of data which must be processed. Statistical data are presented from the test results that have been collected from over 2,000 production TCCO's. The data show a histogram of micro-jumps as a function of the magnitude of the jump.