Disciplined rubidium oscillator for harsh environments

Abstract

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.