At the 1995 Frequency ControlSymposium, performance results for the FE-5650ARb frequency standard were presented, The FE-5650A is a 2 16 cc (13 cubic inch) device capable of producing any output frequency between 1 Hz and 15 MHz, with a setting resolution of 1 x 10-l~. since then several technical improvements have been incorporated into the FE-5650A product. These improvements primarily af€ect the aging and temperature performance of manufactured devices. These improvements are of particular importance in applications such as GPS receiver clocks, where performance in relatively uncontrolled temperature environments, over a time period of -1 day are crucial.Allan variance at an averaging time of -1 day is used as a simple measure of performance to compare and rank individual devices. Measurements w i t h and without linear dnfl removal are presented, with a discussion of the practical implications of results.Statistical data from a large sample of manufactured devices are presented showing frequency aging and frequency vs. temperature performance before and after incorporation of the design improvements. Data and analysis are obtained from measurements made at FEI, as well as at NIST, in Boulder, CO.In addition, optional versions of the FE-5650A have been developed for operation over the extended military temperature range (-55 to +71"C), and also for operation in vacuum. Performance test results are presented for these devices.
A disciplined rubidium (Rb) oscillator has been developed for use in harsh environments. This oscillator operates from -40°C to +82°C, in the presence of random vibration of up to 19 g RMS; while continuously maintaining lock of both the Rb control loop and the disciplining loop. Performance under vibration is enhanced by incorporation of a quartz oscillator with active MEMS accelerometer based vibration compensation. The device warms up in less than 15 minutes, and can be disciplined to a 1 pps input, such as the signal from a GPS receiver. One of the unique features of this device is the capability to align the internally generated RF and 1 pps signals to the input 1 pps signal with a resolution of < 1 nsec. This is accomplished using a novel PLL approach for locking the internal RF signals to the disciplining 1 pps input. A number of design refinements to the Rb physics package have also been implemented which significantly improve the performance during "holdover" conditions when no disciplining signal is present. A major design goal of this device is to reduce the accumulated time error during a 24 hour holdover period to < 245 nanoseconds.The design of this device is described, and performance data is presented to demonstrate actual performance of initial production units compared to the design objectives.
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