Precise time and frequency control using the Navstar GPS and a disciplined rubidium oscillator

Shows in the first phase of testing that a rubidium oscillator's frequency can be set and maintained to within a few parts 10/sup -13/ through the oscillator's C-field. It is also demonstrated that a 1-PPS epoch can be steered into synchronism with a reference pulse by offsetting the rubidium's frequency a known amount for a predetermined amount of time to integrate out the error. This method of epoch steering is nondisruptive. It was shown in the second phase that the rubidium oscillator can be reconciled to GPS by averaging daily measurements and adjusting the C-field. Several times during this phase the 1-second epoch was adjusted while tracking, and no corruption of tracking was observed. Many people working in the precise time arena have concluded that environmental mitigation is the key to long-term stability for an atomic frequency standard whether cesium, rubidium, or whatever. The dominant sources of drift are temperature and magnetic field influences, and cesium standards are an order of magnitude better than rubidium on both counts. A major focus of the third phase is therefore on thermal mitigation in addition to developing the drift-averaging software.<
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